mld6query(8): Rename mld6.c -> mld6query.c

[dragonfly.git] / crypto / openssh / channels.c

/* $OpenBSD: channels.c,v 1.375 2017/09/24 13:45:34 djm Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * This file contains functions for generic socket connection forwarding.
 * There is also code for initiating connection forwarding for X11 connections,
 * arbitrary tcp/ip connections, and the authentication agent connection.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 *
 * SSH2 support added by Markus Friedl.
 * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
 * Copyright (c) 1999 Dug Song.  All rights reserved.
 * Copyright (c) 1999 Theo de Raadt.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#include <sys/socket.h>
#ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
#endif

#include <netinet/in.h>
#include <arpa/inet.h>

#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <netdb.h>
#include <stdarg.h>
#ifdef HAVE_STDINT_H
 #include <stdint.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>

#include "openbsd-compat/sys-queue.h"
#include "xmalloc.h"
#include "ssh.h"
#include "ssh2.h"
#include "ssherr.h"
#include "sshbuf.h"
#include "packet.h"
#include "log.h"
#include "misc.h"
#include "channels.h"
#include "compat.h"
#include "canohost.h"
#include "key.h"
#include "authfd.h"
#include "pathnames.h"

/* -- agent forwarding */
#define NUM_SOCKS       10

/* -- tcp forwarding */
/* special-case port number meaning allow any port */
#define FWD_PERMIT_ANY_PORT     0

/* special-case wildcard meaning allow any host */
#define FWD_PERMIT_ANY_HOST     "*"

/* -- X11 forwarding */
/* Maximum number of fake X11 displays to try. */
#define MAX_DISPLAYS  1000

/*
 * Data structure for storing which hosts are permitted for forward requests.
 * The local sides of any remote forwards are stored in this array to prevent
 * a corrupt remote server from accessing arbitrary TCP/IP ports on our local
 * network (which might be behind a firewall).
 */
/* XXX: streamlocal wants a path instead of host:port */
/*      Overload host_to_connect; we could just make this match Forward */
/*      XXX - can we use listen_host instead of listen_path? */
typedef struct {
        char *host_to_connect;          /* Connect to 'host'. */
        int port_to_connect;            /* Connect to 'port'. */
        char *listen_host;              /* Remote side should listen address. */
        char *listen_path;              /* Remote side should listen path. */
        int listen_port;                /* Remote side should listen port. */
        Channel *downstream;            /* Downstream mux*/
} ForwardPermission;

typedef void chan_fn(struct ssh *, Channel *c,
    fd_set *readset, fd_set *writeset);

/* Master structure for channels state */
struct ssh_channels {
        /*
         * Pointer to an array containing all allocated channels.  The array
         * is dynamically extended as needed.
         */
        Channel **channels;

        /*
         * Size of the channel array.  All slots of the array must always be
         * initialized (at least the type field); unused slots set to NULL
         */
        u_int channels_alloc;

        /*
         * Maximum file descriptor value used in any of the channels.  This is
         * updated in channel_new.
         */
        int channel_max_fd;

        /*
         * 'channel_pre*' are called just before select() to add any bits
         * relevant to channels in the select bitmasks.
         *
         * 'channel_post*': perform any appropriate operations for
         * channels which have events pending.
         */
        chan_fn **channel_pre;
        chan_fn **channel_post;

        /* -- tcp forwarding */

        /* List of all permitted host/port pairs to connect by the user. */
        ForwardPermission *permitted_opens;

        /* List of all permitted host/port pairs to connect by the admin. */
        ForwardPermission *permitted_adm_opens;

        /*
         * Number of permitted host/port pairs in the array permitted by
         * the user.
         */
        u_int num_permitted_opens;

        /*
         * Number of permitted host/port pair in the array permitted by
         * the admin.
         */
        u_int num_adm_permitted_opens;

        /*
         * If this is true, all opens are permitted.  This is the case on
         * the server on which we have to trust the client anyway, and the
         * user could do anything after logging in anyway.
         */
        int all_opens_permitted;

        /* -- X11 forwarding */

        /* Saved X11 local (client) display. */
        char *x11_saved_display;

        /* Saved X11 authentication protocol name. */
        char *x11_saved_proto;

        /* Saved X11 authentication data.  This is the real data. */
        char *x11_saved_data;
        u_int x11_saved_data_len;

        /* Deadline after which all X11 connections are refused */
        u_int x11_refuse_time;

        /*
         * Fake X11 authentication data.  This is what the server will be
         * sending us; we should replace any occurrences of this by the
         * real data.
         */
        u_char *x11_fake_data;
        u_int x11_fake_data_len;

        /* AF_UNSPEC or AF_INET or AF_INET6 */
        int IPv4or6;
};

/* helper */
static void port_open_helper(struct ssh *ssh, Channel *c, char *rtype);
static const char *channel_rfwd_bind_host(const char *listen_host);

/* non-blocking connect helpers */
static int connect_next(struct channel_connect *);
static void channel_connect_ctx_free(struct channel_connect *);
static Channel *rdynamic_connect_prepare(struct ssh *, char *, char *);
static int rdynamic_connect_finish(struct ssh *, Channel *);

/* Setup helper */
static void channel_handler_init(struct ssh_channels *sc);

/* -- channel core */

void
channel_init_channels(struct ssh *ssh)
{
        struct ssh_channels *sc;

        if ((sc = calloc(1, sizeof(*sc))) == NULL ||
            (sc->channel_pre = calloc(SSH_CHANNEL_MAX_TYPE,
            sizeof(*sc->channel_pre))) == NULL ||
            (sc->channel_post = calloc(SSH_CHANNEL_MAX_TYPE,
            sizeof(*sc->channel_post))) == NULL)
                fatal("%s: allocation failed", __func__);
        sc->channels_alloc = 10;
        sc->channels = xcalloc(sc->channels_alloc, sizeof(*sc->channels));
        sc->IPv4or6 = AF_UNSPEC;
        channel_handler_init(sc);

        ssh->chanctxt = sc;
}

Channel *
channel_by_id(struct ssh *ssh, int id)
{
        Channel *c;

        if (id < 0 || (u_int)id >= ssh->chanctxt->channels_alloc) {
                logit("%s: %d: bad id", __func__, id);
                return NULL;
        }
        c = ssh->chanctxt->channels[id];
        if (c == NULL) {
                logit("%s: %d: bad id: channel free", __func__, id);
                return NULL;
        }
        return c;
}

Channel *
channel_by_remote_id(struct ssh *ssh, u_int remote_id)
{
        Channel *c;
        u_int i;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c != NULL && c->have_remote_id && c->remote_id == remote_id)
                        return c;
        }
        return NULL;
}

/*
 * Returns the channel if it is allowed to receive protocol messages.
 * Private channels, like listening sockets, may not receive messages.
 */
Channel *
channel_lookup(struct ssh *ssh, int id)
{
        Channel *c;

        if ((c = channel_by_id(ssh, id)) == NULL)
                return NULL;

        switch (c->type) {
        case SSH_CHANNEL_X11_OPEN:
        case SSH_CHANNEL_LARVAL:
        case SSH_CHANNEL_CONNECTING:
        case SSH_CHANNEL_DYNAMIC:
        case SSH_CHANNEL_RDYNAMIC_OPEN:
        case SSH_CHANNEL_RDYNAMIC_FINISH:
        case SSH_CHANNEL_OPENING:
        case SSH_CHANNEL_OPEN:
        case SSH_CHANNEL_ABANDONED:
        case SSH_CHANNEL_MUX_PROXY:
                return c;
        }
        logit("Non-public channel %d, type %d.", id, c->type);
        return NULL;
}

/*
 * Register filedescriptors for a channel, used when allocating a channel or
 * when the channel consumer/producer is ready, e.g. shell exec'd
 */
static void
channel_register_fds(struct ssh *ssh, Channel *c, int rfd, int wfd, int efd,
    int extusage, int nonblock, int is_tty)
{
        struct ssh_channels *sc = ssh->chanctxt;

        /* Update the maximum file descriptor value. */
        sc->channel_max_fd = MAXIMUM(sc->channel_max_fd, rfd);
        sc->channel_max_fd = MAXIMUM(sc->channel_max_fd, wfd);
        sc->channel_max_fd = MAXIMUM(sc->channel_max_fd, efd);

        if (rfd != -1)
                fcntl(rfd, F_SETFD, FD_CLOEXEC);
        if (wfd != -1 && wfd != rfd)
                fcntl(wfd, F_SETFD, FD_CLOEXEC);
        if (efd != -1 && efd != rfd && efd != wfd)
                fcntl(efd, F_SETFD, FD_CLOEXEC);

        c->rfd = rfd;
        c->wfd = wfd;
        c->sock = (rfd == wfd) ? rfd : -1;
        c->efd = efd;
        c->extended_usage = extusage;

        if ((c->isatty = is_tty) != 0)
                debug2("channel %d: rfd %d isatty", c->self, c->rfd);
#ifdef _AIX
        /* XXX: Later AIX versions can't push as much data to tty */
        c->wfd_isatty = is_tty || isatty(c->wfd);
#endif

        /* enable nonblocking mode */
        if (nonblock) {
                if (rfd != -1)
                        set_nonblock(rfd);
                if (wfd != -1)
                        set_nonblock(wfd);
                if (efd != -1)
                        set_nonblock(efd);
        }
}

/*
 * Allocate a new channel object and set its type and socket. This will cause
 * remote_name to be freed.
 */
Channel *
channel_new(struct ssh *ssh, char *ctype, int type, int rfd, int wfd, int efd,
    u_int window, u_int maxpack, int extusage, char *remote_name, int nonblock)
{
        struct ssh_channels *sc = ssh->chanctxt;
        u_int i, found;
        Channel *c;

        /* Try to find a free slot where to put the new channel. */
        for (i = 0; i < sc->channels_alloc; i++) {
                if (sc->channels[i] == NULL) {
                        /* Found a free slot. */
                        found = i;
                        break;
                }
        }
        if (i >= sc->channels_alloc) {
                /*
                 * There are no free slots. Take last+1 slot and expand
                 * the array.
                 */
                found = sc->channels_alloc;
                if (sc->channels_alloc > CHANNELS_MAX_CHANNELS)
                        fatal("%s: internal error: channels_alloc %d too big",
                            __func__, sc->channels_alloc);
                sc->channels = xrecallocarray(sc->channels, sc->channels_alloc,
                    sc->channels_alloc + 10, sizeof(*sc->channels));
                sc->channels_alloc += 10;
                debug2("channel: expanding %d", sc->channels_alloc);
        }
        /* Initialize and return new channel. */
        c = sc->channels[found] = xcalloc(1, sizeof(Channel));
        if ((c->input = sshbuf_new()) == NULL ||
            (c->output = sshbuf_new()) == NULL ||
            (c->extended = sshbuf_new()) == NULL)
                fatal("%s: sshbuf_new failed", __func__);
        c->ostate = CHAN_OUTPUT_OPEN;
        c->istate = CHAN_INPUT_OPEN;
        channel_register_fds(ssh, c, rfd, wfd, efd, extusage, nonblock, 0);
        c->self = found;
        c->type = type;
        c->ctype = ctype;
        c->local_window = window;
        c->local_window_max = window;
        c->local_maxpacket = maxpack;
        c->remote_name = xstrdup(remote_name);
        c->ctl_chan = -1;
        c->delayed = 1;         /* prevent call to channel_post handler */
        TAILQ_INIT(&c->status_confirms);
        debug("channel %d: new [%s]", found, remote_name);
        return c;
}

static void
channel_find_maxfd(struct ssh_channels *sc)
{
        u_int i;
        int max = 0;
        Channel *c;

        for (i = 0; i < sc->channels_alloc; i++) {
                c = sc->channels[i];
                if (c != NULL) {
                        max = MAXIMUM(max, c->rfd);
                        max = MAXIMUM(max, c->wfd);
                        max = MAXIMUM(max, c->efd);
                }
        }
        sc->channel_max_fd = max;
}

int
channel_close_fd(struct ssh *ssh, int *fdp)
{
        struct ssh_channels *sc = ssh->chanctxt;
        int ret = 0, fd = *fdp;

        if (fd != -1) {
                ret = close(fd);
                *fdp = -1;
                if (fd == sc->channel_max_fd)
                        channel_find_maxfd(sc);
        }
        return ret;
}

/* Close all channel fd/socket. */
static void
channel_close_fds(struct ssh *ssh, Channel *c)
{
        channel_close_fd(ssh, &c->sock);
        channel_close_fd(ssh, &c->rfd);
        channel_close_fd(ssh, &c->wfd);
        channel_close_fd(ssh, &c->efd);
}

static void
fwd_perm_clear(ForwardPermission *fp)
{
        free(fp->host_to_connect);
        free(fp->listen_host);
        free(fp->listen_path);
        bzero(fp, sizeof(*fp));
}

enum { FWDPERM_USER, FWDPERM_ADMIN };

static int
fwd_perm_list_add(struct ssh *ssh, int which,
    const char *host_to_connect, int port_to_connect,
    const char *listen_host, const char *listen_path, int listen_port,
    Channel *downstream)
{
        ForwardPermission **fpl;
        u_int n, *nfpl;

        switch (which) {
        case FWDPERM_USER:
                fpl = &ssh->chanctxt->permitted_opens;
                nfpl = &ssh->chanctxt->num_permitted_opens;
                break;
        case FWDPERM_ADMIN:
                fpl = &ssh->chanctxt->permitted_adm_opens;
                nfpl = &ssh->chanctxt->num_adm_permitted_opens;
                break;
        default:
                fatal("%s: invalid list %d", __func__, which);
        }

        if (*nfpl >= INT_MAX)
                fatal("%s: overflow", __func__);

        *fpl = xrecallocarray(*fpl, *nfpl, *nfpl + 1, sizeof(**fpl));
        n = (*nfpl)++;
#define MAYBE_DUP(s) ((s == NULL) ? NULL : xstrdup(s))
        (*fpl)[n].host_to_connect = MAYBE_DUP(host_to_connect);
        (*fpl)[n].port_to_connect = port_to_connect;
        (*fpl)[n].listen_host = MAYBE_DUP(listen_host);
        (*fpl)[n].listen_path = MAYBE_DUP(listen_path);
        (*fpl)[n].listen_port = listen_port;
        (*fpl)[n].downstream = downstream;
#undef MAYBE_DUP
        return (int)n;
}

static void
mux_remove_remote_forwardings(struct ssh *ssh, Channel *c)
{
        struct ssh_channels *sc = ssh->chanctxt;
        ForwardPermission *fp;
        int r;
        u_int i;

        for (i = 0; i < sc->num_permitted_opens; i++) {
                fp = &sc->permitted_opens[i];
                if (fp->downstream != c)
                        continue;

                /* cancel on the server, since mux client is gone */
                debug("channel %d: cleanup remote forward for %s:%u",
                    c->self, fp->listen_host, fp->listen_port);
                if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
                    (r = sshpkt_put_cstring(ssh,
                    "cancel-tcpip-forward")) != 0 ||
                    (r = sshpkt_put_u8(ssh, 0)) != 0 ||
                    (r = sshpkt_put_cstring(ssh,
                    channel_rfwd_bind_host(fp->listen_host))) != 0 ||
                    (r = sshpkt_put_u32(ssh, fp->listen_port)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0) {
                        fatal("%s: channel %i: %s", __func__,
                            c->self, ssh_err(r));
                }
                fwd_perm_clear(fp); /* unregister */
        }
}

/* Free the channel and close its fd/socket. */
void
channel_free(struct ssh *ssh, Channel *c)
{
        struct ssh_channels *sc = ssh->chanctxt;
        char *s;
        u_int i, n;
        Channel *other;
        struct channel_confirm *cc;

        for (n = 0, i = 0; i < sc->channels_alloc; i++) {
                if ((other = sc->channels[i]) == NULL)
                        continue;
                n++;
                /* detach from mux client and prepare for closing */
                if (c->type == SSH_CHANNEL_MUX_CLIENT &&
                    other->type == SSH_CHANNEL_MUX_PROXY &&
                    other->mux_ctx == c) {
                        other->mux_ctx = NULL;
                        other->type = SSH_CHANNEL_OPEN;
                        other->istate = CHAN_INPUT_CLOSED;
                        other->ostate = CHAN_OUTPUT_CLOSED;
                }
        }
        debug("channel %d: free: %s, nchannels %u", c->self,
            c->remote_name ? c->remote_name : "???", n);

        if (c->type == SSH_CHANNEL_MUX_CLIENT)
                mux_remove_remote_forwardings(ssh, c);

        s = channel_open_message(ssh);
        debug3("channel %d: status: %s", c->self, s);
        free(s);

        channel_close_fds(ssh, c);
        sshbuf_free(c->input);
        sshbuf_free(c->output);
        sshbuf_free(c->extended);
        c->input = c->output = c->extended = NULL;
        free(c->remote_name);
        c->remote_name = NULL;
        free(c->path);
        c->path = NULL;
        free(c->listening_addr);
        c->listening_addr = NULL;
        while ((cc = TAILQ_FIRST(&c->status_confirms)) != NULL) {
                if (cc->abandon_cb != NULL)
                        cc->abandon_cb(ssh, c, cc->ctx);
                TAILQ_REMOVE(&c->status_confirms, cc, entry);
                explicit_bzero(cc, sizeof(*cc));
                free(cc);
        }
        if (c->filter_cleanup != NULL && c->filter_ctx != NULL)
                c->filter_cleanup(ssh, c->self, c->filter_ctx);
        sc->channels[c->self] = NULL;
        explicit_bzero(c, sizeof(*c));
        free(c);
}

void
channel_free_all(struct ssh *ssh)
{
        u_int i;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++)
                if (ssh->chanctxt->channels[i] != NULL)
                        channel_free(ssh, ssh->chanctxt->channels[i]);
}

/*
 * Closes the sockets/fds of all channels.  This is used to close extra file
 * descriptors after a fork.
 */
void
channel_close_all(struct ssh *ssh)
{
        u_int i;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++)
                if (ssh->chanctxt->channels[i] != NULL)
                        channel_close_fds(ssh, ssh->chanctxt->channels[i]);
}

/*
 * Stop listening to channels.
 */
void
channel_stop_listening(struct ssh *ssh)
{
        u_int i;
        Channel *c;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c != NULL) {
                        switch (c->type) {
                        case SSH_CHANNEL_AUTH_SOCKET:
                        case SSH_CHANNEL_PORT_LISTENER:
                        case SSH_CHANNEL_RPORT_LISTENER:
                        case SSH_CHANNEL_X11_LISTENER:
                        case SSH_CHANNEL_UNIX_LISTENER:
                        case SSH_CHANNEL_RUNIX_LISTENER:
                                channel_close_fd(ssh, &c->sock);
                                channel_free(ssh, c);
                                break;
                        }
                }
        }
}

/*
 * Returns true if no channel has too much buffered data, and false if one or
 * more channel is overfull.
 */
int
channel_not_very_much_buffered_data(struct ssh *ssh)
{
        u_int i;
        u_int maxsize = ssh_packet_get_maxsize(ssh);
        Channel *c;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c == NULL || c->type != SSH_CHANNEL_OPEN)
                        continue;
                if (sshbuf_len(c->output) > maxsize) {
                        debug2("channel %d: big output buffer %zu > %u",
                            c->self, sshbuf_len(c->output), maxsize);
                        return 0;
                }
        }
        return 1;
}

/* Returns true if any channel is still open. */
int
channel_still_open(struct ssh *ssh)
{
        u_int i;
        Channel *c;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c == NULL)
                        continue;
                switch (c->type) {
                case SSH_CHANNEL_X11_LISTENER:
                case SSH_CHANNEL_PORT_LISTENER:
                case SSH_CHANNEL_RPORT_LISTENER:
                case SSH_CHANNEL_MUX_LISTENER:
                case SSH_CHANNEL_CLOSED:
                case SSH_CHANNEL_AUTH_SOCKET:
                case SSH_CHANNEL_DYNAMIC:
                case SSH_CHANNEL_RDYNAMIC_OPEN:
                case SSH_CHANNEL_CONNECTING:
                case SSH_CHANNEL_ZOMBIE:
                case SSH_CHANNEL_ABANDONED:
                case SSH_CHANNEL_UNIX_LISTENER:
                case SSH_CHANNEL_RUNIX_LISTENER:
                        continue;
                case SSH_CHANNEL_LARVAL:
                        continue;
                case SSH_CHANNEL_OPENING:
                case SSH_CHANNEL_OPEN:
                case SSH_CHANNEL_RDYNAMIC_FINISH:
                case SSH_CHANNEL_X11_OPEN:
                case SSH_CHANNEL_MUX_CLIENT:
                case SSH_CHANNEL_MUX_PROXY:
                        return 1;
                default:
                        fatal("%s: bad channel type %d", __func__, c->type);
                        /* NOTREACHED */
                }
        }
        return 0;
}

/* Returns the id of an open channel suitable for keepaliving */
int
channel_find_open(struct ssh *ssh)
{
        u_int i;
        Channel *c;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c == NULL || !c->have_remote_id)
                        continue;
                switch (c->type) {
                case SSH_CHANNEL_CLOSED:
                case SSH_CHANNEL_DYNAMIC:
                case SSH_CHANNEL_RDYNAMIC_OPEN:
                case SSH_CHANNEL_RDYNAMIC_FINISH:
                case SSH_CHANNEL_X11_LISTENER:
                case SSH_CHANNEL_PORT_LISTENER:
                case SSH_CHANNEL_RPORT_LISTENER:
                case SSH_CHANNEL_MUX_LISTENER:
                case SSH_CHANNEL_MUX_CLIENT:
                case SSH_CHANNEL_MUX_PROXY:
                case SSH_CHANNEL_OPENING:
                case SSH_CHANNEL_CONNECTING:
                case SSH_CHANNEL_ZOMBIE:
                case SSH_CHANNEL_ABANDONED:
                case SSH_CHANNEL_UNIX_LISTENER:
                case SSH_CHANNEL_RUNIX_LISTENER:
                        continue;
                case SSH_CHANNEL_LARVAL:
                case SSH_CHANNEL_AUTH_SOCKET:
                case SSH_CHANNEL_OPEN:
                case SSH_CHANNEL_X11_OPEN:
                        return i;
                default:
                        fatal("%s: bad channel type %d", __func__, c->type);
                        /* NOTREACHED */
                }
        }
        return -1;
}

/*
 * Returns a message describing the currently open forwarded connections,
 * suitable for sending to the client.  The message contains crlf pairs for
 * newlines.
 */
char *
channel_open_message(struct ssh *ssh)
{
        struct sshbuf *buf;
        Channel *c;
        u_int i;
        int r;
        char *ret;

        if ((buf = sshbuf_new()) == NULL)
                fatal("%s: sshbuf_new", __func__);
        if ((r = sshbuf_putf(buf,
            "The following connections are open:\r\n")) != 0)
                fatal("%s: sshbuf_putf: %s", __func__, ssh_err(r));
        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c == NULL)
                        continue;
                switch (c->type) {
                case SSH_CHANNEL_X11_LISTENER:
                case SSH_CHANNEL_PORT_LISTENER:
                case SSH_CHANNEL_RPORT_LISTENER:
                case SSH_CHANNEL_CLOSED:
                case SSH_CHANNEL_AUTH_SOCKET:
                case SSH_CHANNEL_ZOMBIE:
                case SSH_CHANNEL_ABANDONED:
                case SSH_CHANNEL_MUX_LISTENER:
                case SSH_CHANNEL_UNIX_LISTENER:
                case SSH_CHANNEL_RUNIX_LISTENER:
                        continue;
                case SSH_CHANNEL_LARVAL:
                case SSH_CHANNEL_OPENING:
                case SSH_CHANNEL_CONNECTING:
                case SSH_CHANNEL_DYNAMIC:
                case SSH_CHANNEL_RDYNAMIC_OPEN:
                case SSH_CHANNEL_RDYNAMIC_FINISH:
                case SSH_CHANNEL_OPEN:
                case SSH_CHANNEL_X11_OPEN:
                case SSH_CHANNEL_MUX_PROXY:
                case SSH_CHANNEL_MUX_CLIENT:
                        if ((r = sshbuf_putf(buf, "  #%d %.300s "
                            "(t%d %s%u i%u/%zu o%u/%zu fd %d/%d cc %d)\r\n",
                            c->self, c->remote_name,
                            c->type,
                            c->have_remote_id ? "r" : "nr", c->remote_id,
                            c->istate, sshbuf_len(c->input),
                            c->ostate, sshbuf_len(c->output),
                            c->rfd, c->wfd, c->ctl_chan)) != 0)
                                fatal("%s: sshbuf_putf: %s",
                                    __func__, ssh_err(r));
                        continue;
                default:
                        fatal("%s: bad channel type %d", __func__, c->type);
                        /* NOTREACHED */
                }
        }
        if ((ret = sshbuf_dup_string(buf)) == NULL)
                fatal("%s: sshbuf_dup_string", __func__);
        sshbuf_free(buf);
        return ret;
}

static void
open_preamble(struct ssh *ssh, const char *where, Channel *c, const char *type)
{
        int r;

        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_OPEN)) != 0 ||
            (r = sshpkt_put_cstring(ssh, type)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0) {
                fatal("%s: channel %i: open: %s", where, c->self, ssh_err(r));
        }
}

void
channel_send_open(struct ssh *ssh, int id)
{
        Channel *c = channel_lookup(ssh, id);
        int r;

        if (c == NULL) {
                logit("channel_send_open: %d: bad id", id);
                return;
        }
        debug2("channel %d: send open", id);
        open_preamble(ssh, __func__, c, c->ctype);
        if ((r = sshpkt_send(ssh)) != 0)
                fatal("%s: channel %i: %s", __func__, c->self, ssh_err(r));
}

void
channel_request_start(struct ssh *ssh, int id, char *service, int wantconfirm)
{
        Channel *c = channel_lookup(ssh, id);
        int r;

        if (c == NULL) {
                logit("%s: %d: unknown channel id", __func__, id);
                return;
        }
        if (!c->have_remote_id)
                fatal(":%s: channel %d: no remote id", __func__, c->self);

        debug2("channel %d: request %s confirm %d", id, service, wantconfirm);
        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_REQUEST)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
            (r = sshpkt_put_cstring(ssh, service)) != 0 ||
            (r = sshpkt_put_u8(ssh, wantconfirm)) != 0) {
                fatal("%s: channel %i: %s", __func__, c->self, ssh_err(r));
        }
}

void
channel_register_status_confirm(struct ssh *ssh, int id,
    channel_confirm_cb *cb, channel_confirm_abandon_cb *abandon_cb, void *ctx)
{
        struct channel_confirm *cc;
        Channel *c;

        if ((c = channel_lookup(ssh, id)) == NULL)
                fatal("%s: %d: bad id", __func__, id);

        cc = xcalloc(1, sizeof(*cc));
        cc->cb = cb;
        cc->abandon_cb = abandon_cb;
        cc->ctx = ctx;
        TAILQ_INSERT_TAIL(&c->status_confirms, cc, entry);
}

void
channel_register_open_confirm(struct ssh *ssh, int id,
    channel_open_fn *fn, void *ctx)
{
        Channel *c = channel_lookup(ssh, id);

        if (c == NULL) {
                logit("%s: %d: bad id", __func__, id);
                return;
        }
        c->open_confirm = fn;
        c->open_confirm_ctx = ctx;
}

void
channel_register_cleanup(struct ssh *ssh, int id,
    channel_callback_fn *fn, int do_close)
{
        Channel *c = channel_by_id(ssh, id);

        if (c == NULL) {
                logit("%s: %d: bad id", __func__, id);
                return;
        }
        c->detach_user = fn;
        c->detach_close = do_close;
}

void
channel_cancel_cleanup(struct ssh *ssh, int id)
{
        Channel *c = channel_by_id(ssh, id);

        if (c == NULL) {
                logit("%s: %d: bad id", __func__, id);
                return;
        }
        c->detach_user = NULL;
        c->detach_close = 0;
}

void
channel_register_filter(struct ssh *ssh, int id, channel_infilter_fn *ifn,
    channel_outfilter_fn *ofn, channel_filter_cleanup_fn *cfn, void *ctx)
{
        Channel *c = channel_lookup(ssh, id);

        if (c == NULL) {
                logit("%s: %d: bad id", __func__, id);
                return;
        }
        c->input_filter = ifn;
        c->output_filter = ofn;
        c->filter_ctx = ctx;
        c->filter_cleanup = cfn;
}

void
channel_set_fds(struct ssh *ssh, int id, int rfd, int wfd, int efd,
    int extusage, int nonblock, int is_tty, u_int window_max)
{
        Channel *c = channel_lookup(ssh, id);
        int r;

        if (c == NULL || c->type != SSH_CHANNEL_LARVAL)
                fatal("channel_activate for non-larval channel %d.", id);
        if (!c->have_remote_id)
                fatal(":%s: channel %d: no remote id", __func__, c->self);

        channel_register_fds(ssh, c, rfd, wfd, efd, extusage, nonblock, is_tty);
        c->type = SSH_CHANNEL_OPEN;
        c->local_window = c->local_window_max = window_max;

        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_WINDOW_ADJUST)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
            (r = sshpkt_send(ssh)) != 0)
                fatal("%s: channel %i: %s", __func__, c->self, ssh_err(r));
}

static void
channel_pre_listener(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        FD_SET(c->sock, readset);
}

static void
channel_pre_connecting(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        debug3("channel %d: waiting for connection", c->self);
        FD_SET(c->sock, writeset);
}

static void
channel_pre_open(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        if (c->istate == CHAN_INPUT_OPEN &&
            c->remote_window > 0 &&
            sshbuf_len(c->input) < c->remote_window &&
            sshbuf_check_reserve(c->input, CHAN_RBUF) == 0)
                FD_SET(c->rfd, readset);
        if (c->ostate == CHAN_OUTPUT_OPEN ||
            c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
                if (sshbuf_len(c->output) > 0) {
                        FD_SET(c->wfd, writeset);
                } else if (c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
                        if (CHANNEL_EFD_OUTPUT_ACTIVE(c))
                                debug2("channel %d: "
                                    "obuf_empty delayed efd %d/(%zu)", c->self,
                                    c->efd, sshbuf_len(c->extended));
                        else
                                chan_obuf_empty(ssh, c);
                }
        }
        /** XXX check close conditions, too */
        if (c->efd != -1 && !(c->istate == CHAN_INPUT_CLOSED &&
            c->ostate == CHAN_OUTPUT_CLOSED)) {
                if (c->extended_usage == CHAN_EXTENDED_WRITE &&
                    sshbuf_len(c->extended) > 0)
                        FD_SET(c->efd, writeset);
                else if (c->efd != -1 && !(c->flags & CHAN_EOF_SENT) &&
                    (c->extended_usage == CHAN_EXTENDED_READ ||
                    c->extended_usage == CHAN_EXTENDED_IGNORE) &&
                    sshbuf_len(c->extended) < c->remote_window)
                        FD_SET(c->efd, readset);
        }
        /* XXX: What about efd? races? */
}

/*
 * This is a special state for X11 authentication spoofing.  An opened X11
 * connection (when authentication spoofing is being done) remains in this
 * state until the first packet has been completely read.  The authentication
 * data in that packet is then substituted by the real data if it matches the
 * fake data, and the channel is put into normal mode.
 * XXX All this happens at the client side.
 * Returns: 0 = need more data, -1 = wrong cookie, 1 = ok
 */
static int
x11_open_helper(struct ssh *ssh, struct sshbuf *b)
{
        struct ssh_channels *sc = ssh->chanctxt;
        u_char *ucp;
        u_int proto_len, data_len;

        /* Is this being called after the refusal deadline? */
        if (sc->x11_refuse_time != 0 &&
            (u_int)monotime() >= sc->x11_refuse_time) {
                verbose("Rejected X11 connection after ForwardX11Timeout "
                    "expired");
                return -1;
        }

        /* Check if the fixed size part of the packet is in buffer. */
        if (sshbuf_len(b) < 12)
                return 0;

        /* Parse the lengths of variable-length fields. */
        ucp = sshbuf_mutable_ptr(b);
        if (ucp[0] == 0x42) {   /* Byte order MSB first. */
                proto_len = 256 * ucp[6] + ucp[7];
                data_len = 256 * ucp[8] + ucp[9];
        } else if (ucp[0] == 0x6c) {    /* Byte order LSB first. */
                proto_len = ucp[6] + 256 * ucp[7];
                data_len = ucp[8] + 256 * ucp[9];
        } else {
                debug2("Initial X11 packet contains bad byte order byte: 0x%x",
                    ucp[0]);
                return -1;
        }

        /* Check if the whole packet is in buffer. */
        if (sshbuf_len(b) <
            12 + ((proto_len + 3) & ~3) + ((data_len + 3) & ~3))
                return 0;

        /* Check if authentication protocol matches. */
        if (proto_len != strlen(sc->x11_saved_proto) ||
            memcmp(ucp + 12, sc->x11_saved_proto, proto_len) != 0) {
                debug2("X11 connection uses different authentication protocol.");
                return -1;
        }
        /* Check if authentication data matches our fake data. */
        if (data_len != sc->x11_fake_data_len ||
            timingsafe_bcmp(ucp + 12 + ((proto_len + 3) & ~3),
                sc->x11_fake_data, sc->x11_fake_data_len) != 0) {
                debug2("X11 auth data does not match fake data.");
                return -1;
        }
        /* Check fake data length */
        if (sc->x11_fake_data_len != sc->x11_saved_data_len) {
                error("X11 fake_data_len %d != saved_data_len %d",
                    sc->x11_fake_data_len, sc->x11_saved_data_len);
                return -1;
        }
        /*
         * Received authentication protocol and data match
         * our fake data. Substitute the fake data with real
         * data.
         */
        memcpy(ucp + 12 + ((proto_len + 3) & ~3),
            sc->x11_saved_data, sc->x11_saved_data_len);
        return 1;
}

static void
channel_pre_x11_open(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        int ret = x11_open_helper(ssh, c->output);

        /* c->force_drain = 1; */

        if (ret == 1) {
                c->type = SSH_CHANNEL_OPEN;
                channel_pre_open(ssh, c, readset, writeset);
        } else if (ret == -1) {
                logit("X11 connection rejected because of wrong authentication.");
                debug2("X11 rejected %d i%d/o%d",
                    c->self, c->istate, c->ostate);
                chan_read_failed(ssh, c);
                sshbuf_reset(c->input);
                chan_ibuf_empty(ssh, c);
                sshbuf_reset(c->output);
                chan_write_failed(ssh, c);
                debug2("X11 closed %d i%d/o%d", c->self, c->istate, c->ostate);
        }
}

static void
channel_pre_mux_client(struct ssh *ssh,
    Channel *c, fd_set *readset, fd_set *writeset)
{
        if (c->istate == CHAN_INPUT_OPEN && !c->mux_pause &&
            sshbuf_check_reserve(c->input, CHAN_RBUF) == 0)
                FD_SET(c->rfd, readset);
        if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
                /* clear buffer immediately (discard any partial packet) */
                sshbuf_reset(c->input);
                chan_ibuf_empty(ssh, c);
                /* Start output drain. XXX just kill chan? */
                chan_rcvd_oclose(ssh, c);
        }
        if (c->ostate == CHAN_OUTPUT_OPEN ||
            c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
                if (sshbuf_len(c->output) > 0)
                        FD_SET(c->wfd, writeset);
                else if (c->ostate == CHAN_OUTPUT_WAIT_DRAIN)
                        chan_obuf_empty(ssh, c);
        }
}

/* try to decode a socks4 header */
static int
channel_decode_socks4(Channel *c, struct sshbuf *input, struct sshbuf *output)
{
        const u_char *p;
        char *host;
        u_int len, have, i, found, need;
        char username[256];
        struct {
                u_int8_t version;
                u_int8_t command;
                u_int16_t dest_port;
                struct in_addr dest_addr;
        } s4_req, s4_rsp;
        int r;

        debug2("channel %d: decode socks4", c->self);

        have = sshbuf_len(input);
        len = sizeof(s4_req);
        if (have < len)
                return 0;
        p = sshbuf_ptr(input);

        need = 1;
        /* SOCKS4A uses an invalid IP address 0.0.0.x */
        if (p[4] == 0 && p[5] == 0 && p[6] == 0 && p[7] != 0) {
                debug2("channel %d: socks4a request", c->self);
                /* ... and needs an extra string (the hostname) */
                need = 2;
        }
        /* Check for terminating NUL on the string(s) */
        for (found = 0, i = len; i < have; i++) {
                if (p[i] == '\0') {
                        found++;
                        if (found == need)
                                break;
                }
                if (i > 1024) {
                        /* the peer is probably sending garbage */
                        debug("channel %d: decode socks4: too long",
                            c->self);
                        return -1;
                }
        }
        if (found < need)
                return 0;
        if ((r = sshbuf_get(input, &s4_req.version, 1)) != 0 ||
            (r = sshbuf_get(input, &s4_req.command, 1)) != 0 ||
            (r = sshbuf_get(input, &s4_req.dest_port, 2)) != 0 ||
            (r = sshbuf_get(input, &s4_req.dest_addr, 4)) != 0) {
                debug("channels %d: decode socks4: %s", c->self, ssh_err(r));
                return -1;
        }
        have = sshbuf_len(input);
        p = sshbuf_ptr(input);
        if (memchr(p, '\0', have) == NULL) {
                error("channel %d: decode socks4: user not nul terminated",
                    c->self);
                return -1;
        }
        len = strlen(p);
        debug2("channel %d: decode socks4: user %s/%d", c->self, p, len);
        len++; /* trailing '\0' */
        strlcpy(username, p, sizeof(username));
        if ((r = sshbuf_consume(input, len)) != 0) {
                fatal("%s: channel %d: consume: %s", __func__,
                    c->self, ssh_err(r));
        }
        free(c->path);
        c->path = NULL;
        if (need == 1) {                        /* SOCKS4: one string */
                host = inet_ntoa(s4_req.dest_addr);
                c->path = xstrdup(host);
        } else {                                /* SOCKS4A: two strings */
                have = sshbuf_len(input);
                p = sshbuf_ptr(input);
                if (memchr(p, '\0', have) == NULL) {
                        error("channel %d: decode socks4a: host not nul "
                            "terminated", c->self);
                        return -1;
                }
                len = strlen(p);
                debug2("channel %d: decode socks4a: host %s/%d",
                    c->self, p, len);
                len++;                          /* trailing '\0' */
                if (len > NI_MAXHOST) {
                        error("channel %d: hostname \"%.100s\" too long",
                            c->self, p);
                        return -1;
                }
                c->path = xstrdup(p);
                if ((r = sshbuf_consume(input, len)) != 0) {
                        fatal("%s: channel %d: consume: %s", __func__,
                            c->self, ssh_err(r));
                }
        }
        c->host_port = ntohs(s4_req.dest_port);

        debug2("channel %d: dynamic request: socks4 host %s port %u command %u",
            c->self, c->path, c->host_port, s4_req.command);

        if (s4_req.command != 1) {
                debug("channel %d: cannot handle: %s cn %d",
                    c->self, need == 1 ? "SOCKS4" : "SOCKS4A", s4_req.command);
                return -1;
        }
        s4_rsp.version = 0;                     /* vn: 0 for reply */
        s4_rsp.command = 90;                    /* cd: req granted */
        s4_rsp.dest_port = 0;                   /* ignored */
        s4_rsp.dest_addr.s_addr = INADDR_ANY;   /* ignored */
        if ((r = sshbuf_put(output, &s4_rsp, sizeof(s4_rsp))) != 0) {
                fatal("%s: channel %d: append reply: %s", __func__,
                    c->self, ssh_err(r));
        }
        return 1;
}

/* try to decode a socks5 header */
#define SSH_SOCKS5_AUTHDONE     0x1000
#define SSH_SOCKS5_NOAUTH       0x00
#define SSH_SOCKS5_IPV4         0x01
#define SSH_SOCKS5_DOMAIN       0x03
#define SSH_SOCKS5_IPV6         0x04
#define SSH_SOCKS5_CONNECT      0x01
#define SSH_SOCKS5_SUCCESS      0x00

static int
channel_decode_socks5(Channel *c, struct sshbuf *input, struct sshbuf *output)
{
        /* XXX use get/put_u8 instead of trusting struct padding */
        struct {
                u_int8_t version;
                u_int8_t command;
                u_int8_t reserved;
                u_int8_t atyp;
        } s5_req, s5_rsp;
        u_int16_t dest_port;
        char dest_addr[255+1], ntop[INET6_ADDRSTRLEN];
        const u_char *p;
        u_int have, need, i, found, nmethods, addrlen, af;
        int r;

        debug2("channel %d: decode socks5", c->self);
        p = sshbuf_ptr(input);
        if (p[0] != 0x05)
                return -1;
        have = sshbuf_len(input);
        if (!(c->flags & SSH_SOCKS5_AUTHDONE)) {
                /* format: ver | nmethods | methods */
                if (have < 2)
                        return 0;
                nmethods = p[1];
                if (have < nmethods + 2)
                        return 0;
                /* look for method: "NO AUTHENTICATION REQUIRED" */
                for (found = 0, i = 2; i < nmethods + 2; i++) {
                        if (p[i] == SSH_SOCKS5_NOAUTH) {
                                found = 1;
                                break;
                        }
                }
                if (!found) {
                        debug("channel %d: method SSH_SOCKS5_NOAUTH not found",
                            c->self);
                        return -1;
                }
                if ((r = sshbuf_consume(input, nmethods + 2)) != 0) {
                        fatal("%s: channel %d: consume: %s", __func__,
                            c->self, ssh_err(r));
                }
                /* version, method */
                if ((r = sshbuf_put_u8(output, 0x05)) != 0 ||
                    (r = sshbuf_put_u8(output, SSH_SOCKS5_NOAUTH)) != 0) {
                        fatal("%s: channel %d: append reply: %s", __func__,
                            c->self, ssh_err(r));
                }
                c->flags |= SSH_SOCKS5_AUTHDONE;
                debug2("channel %d: socks5 auth done", c->self);
                return 0;                               /* need more */
        }
        debug2("channel %d: socks5 post auth", c->self);
        if (have < sizeof(s5_req)+1)
                return 0;                       /* need more */
        memcpy(&s5_req, p, sizeof(s5_req));
        if (s5_req.version != 0x05 ||
            s5_req.command != SSH_SOCKS5_CONNECT ||
            s5_req.reserved != 0x00) {
                debug2("channel %d: only socks5 connect supported", c->self);
                return -1;
        }
        switch (s5_req.atyp){
        case SSH_SOCKS5_IPV4:
                addrlen = 4;
                af = AF_INET;
                break;
        case SSH_SOCKS5_DOMAIN:
                addrlen = p[sizeof(s5_req)];
                af = -1;
                break;
        case SSH_SOCKS5_IPV6:
                addrlen = 16;
                af = AF_INET6;
                break;
        default:
                debug2("channel %d: bad socks5 atyp %d", c->self, s5_req.atyp);
                return -1;
        }
        need = sizeof(s5_req) + addrlen + 2;
        if (s5_req.atyp == SSH_SOCKS5_DOMAIN)
                need++;
        if (have < need)
                return 0;
        if ((r = sshbuf_consume(input, sizeof(s5_req))) != 0) {
                fatal("%s: channel %d: consume: %s", __func__,
                    c->self, ssh_err(r));
        }
        if (s5_req.atyp == SSH_SOCKS5_DOMAIN) {
                /* host string length */
                if ((r = sshbuf_consume(input, 1)) != 0) {
                        fatal("%s: channel %d: consume: %s", __func__,
                            c->self, ssh_err(r));
                }
        }
        if ((r = sshbuf_get(input, &dest_addr, addrlen)) != 0 ||
            (r = sshbuf_get(input, &dest_port, 2)) != 0) {
                debug("channel %d: parse addr/port: %s", c->self, ssh_err(r));
                return -1;
        }
        dest_addr[addrlen] = '\0';
        free(c->path);
        c->path = NULL;
        if (s5_req.atyp == SSH_SOCKS5_DOMAIN) {
                if (addrlen >= NI_MAXHOST) {
                        error("channel %d: dynamic request: socks5 hostname "
                            "\"%.100s\" too long", c->self, dest_addr);
                        return -1;
                }
                c->path = xstrdup(dest_addr);
        } else {
                if (inet_ntop(af, dest_addr, ntop, sizeof(ntop)) == NULL)
                        return -1;
                c->path = xstrdup(ntop);
        }
        c->host_port = ntohs(dest_port);

        debug2("channel %d: dynamic request: socks5 host %s port %u command %u",
            c->self, c->path, c->host_port, s5_req.command);

        s5_rsp.version = 0x05;
        s5_rsp.command = SSH_SOCKS5_SUCCESS;
        s5_rsp.reserved = 0;                    /* ignored */
        s5_rsp.atyp = SSH_SOCKS5_IPV4;
        dest_port = 0;                          /* ignored */

        if ((r = sshbuf_put(output, &s5_rsp, sizeof(s5_rsp))) != 0 ||
            (r = sshbuf_put_u32(output, ntohl(INADDR_ANY))) != 0 ||
            (r = sshbuf_put(output, &dest_port, sizeof(dest_port))) != 0)
                fatal("%s: channel %d: append reply: %s", __func__,
                    c->self, ssh_err(r));
        return 1;
}

Channel *
channel_connect_stdio_fwd(struct ssh *ssh,
    const char *host_to_connect, u_short port_to_connect, int in, int out)
{
        Channel *c;

        debug("%s %s:%d", __func__, host_to_connect, port_to_connect);

        c = channel_new(ssh, "stdio-forward", SSH_CHANNEL_OPENING, in, out,
            -1, CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
            0, "stdio-forward", /*nonblock*/0);

        c->path = xstrdup(host_to_connect);
        c->host_port = port_to_connect;
        c->listening_port = 0;
        c->force_drain = 1;

        channel_register_fds(ssh, c, in, out, -1, 0, 1, 0);
        port_open_helper(ssh, c, "direct-tcpip");

        return c;
}

/* dynamic port forwarding */
static void
channel_pre_dynamic(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        const u_char *p;
        u_int have;
        int ret;

        have = sshbuf_len(c->input);
        debug2("channel %d: pre_dynamic: have %d", c->self, have);
        /* sshbuf_dump(c->input, stderr); */
        /* check if the fixed size part of the packet is in buffer. */
        if (have < 3) {
                /* need more */
                FD_SET(c->sock, readset);
                return;
        }
        /* try to guess the protocol */
        p = sshbuf_ptr(c->input);
        /* XXX sshbuf_peek_u8? */
        switch (p[0]) {
        case 0x04:
                ret = channel_decode_socks4(c, c->input, c->output);
                break;
        case 0x05:
                ret = channel_decode_socks5(c, c->input, c->output);
                break;
        default:
                ret = -1;
                break;
        }
        if (ret < 0) {
                chan_mark_dead(ssh, c);
        } else if (ret == 0) {
                debug2("channel %d: pre_dynamic: need more", c->self);
                /* need more */
                FD_SET(c->sock, readset);
                if (sshbuf_len(c->output))
                        FD_SET(c->sock, writeset);
        } else {
                /* switch to the next state */
                c->type = SSH_CHANNEL_OPENING;
                port_open_helper(ssh, c, "direct-tcpip");
        }
}

/* simulate read-error */
static void
rdynamic_close(struct ssh *ssh, Channel *c)
{
        c->type = SSH_CHANNEL_OPEN;
        chan_read_failed(ssh, c);
        sshbuf_reset(c->input);
        chan_ibuf_empty(ssh, c);
        sshbuf_reset(c->output);
        chan_write_failed(ssh, c);
}

/* reverse dynamic port forwarding */
static void
channel_before_prepare_select_rdynamic(struct ssh *ssh, Channel *c)
{
        const u_char *p;
        u_int have, len;
        int r, ret;

        have = sshbuf_len(c->output);
        debug2("channel %d: pre_rdynamic: have %d", c->self, have);
        /* sshbuf_dump(c->output, stderr); */
        /* EOF received */
        if (c->flags & CHAN_EOF_RCVD) {
                if ((r = sshbuf_consume(c->output, have)) != 0) {
                        fatal("%s: channel %d: consume: %s",
                            __func__, c->self, ssh_err(r));
                }
                rdynamic_close(ssh, c);
                return;
        }
        /* check if the fixed size part of the packet is in buffer. */
        if (have < 3)
                return;
        /* try to guess the protocol */
        p = sshbuf_ptr(c->output);
        switch (p[0]) {
        case 0x04:
                /* switch input/output for reverse forwarding */
                ret = channel_decode_socks4(c, c->output, c->input);
                break;
        case 0x05:
                ret = channel_decode_socks5(c, c->output, c->input);
                break;
        default:
                ret = -1;
                break;
        }
        if (ret < 0) {
                rdynamic_close(ssh, c);
        } else if (ret == 0) {
                debug2("channel %d: pre_rdynamic: need more", c->self);
                /* send socks request to peer */
                len = sshbuf_len(c->input);
                if (len > 0 && len < c->remote_window) {
                        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
                            (r = sshpkt_put_stringb(ssh, c->input)) != 0 ||
                            (r = sshpkt_send(ssh)) != 0) {
                                fatal("%s: channel %i: rdynamic: %s", __func__,
                                    c->self, ssh_err(r));
                        }
                        if ((r = sshbuf_consume(c->input, len)) != 0) {
                                fatal("%s: channel %d: consume: %s",
                                    __func__, c->self, ssh_err(r));
                        }
                        c->remote_window -= len;
                }
        } else if (rdynamic_connect_finish(ssh, c) < 0) {
                /* the connect failed */
                rdynamic_close(ssh, c);
        }
}

/* This is our fake X11 server socket. */
static void
channel_post_x11_listener(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        Channel *nc;
        struct sockaddr_storage addr;
        int r, newsock, oerrno, remote_port;
        socklen_t addrlen;
        char buf[16384], *remote_ipaddr;

        if (!FD_ISSET(c->sock, readset))
                return;

        debug("X11 connection requested.");
        addrlen = sizeof(addr);
        newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
        if (c->single_connection) {
                oerrno = errno;
                debug2("single_connection: closing X11 listener.");
                channel_close_fd(ssh, &c->sock);
                chan_mark_dead(ssh, c);
                errno = oerrno;
        }
        if (newsock < 0) {
                if (errno != EINTR && errno != EWOULDBLOCK &&
                    errno != ECONNABORTED)
                        error("accept: %.100s", strerror(errno));
                if (errno == EMFILE || errno == ENFILE)
                        c->notbefore = monotime() + 1;
                return;
        }
        set_nodelay(newsock);
        remote_ipaddr = get_peer_ipaddr(newsock);
        remote_port = get_peer_port(newsock);
        snprintf(buf, sizeof buf, "X11 connection from %.200s port %d",
            remote_ipaddr, remote_port);

        nc = channel_new(ssh, "accepted x11 socket",
            SSH_CHANNEL_OPENING, newsock, newsock, -1,
            c->local_window_max, c->local_maxpacket, 0, buf, 1);
        open_preamble(ssh, __func__, nc, "x11");
        if ((r = sshpkt_put_cstring(ssh, remote_ipaddr)) != 0) {
                fatal("%s: channel %i: reply %s", __func__,
                    c->self, ssh_err(r));
        }
        if ((datafellows & SSH_BUG_X11FWD) != 0)
                debug2("channel %d: ssh2 x11 bug compat mode", nc->self);
        else if ((r = sshpkt_put_u32(ssh, remote_port)) != 0) {
                fatal("%s: channel %i: reply %s", __func__,
                    c->self, ssh_err(r));
        }
        if ((r = sshpkt_send(ssh)) != 0)
                fatal("%s: channel %i: send %s", __func__, c->self, ssh_err(r));
        free(remote_ipaddr);
}

static void
port_open_helper(struct ssh *ssh, Channel *c, char *rtype)
{
        char *local_ipaddr = get_local_ipaddr(c->sock);
        int local_port = c->sock == -1 ? 65536 : get_local_port(c->sock);
        char *remote_ipaddr = get_peer_ipaddr(c->sock);
        int remote_port = get_peer_port(c->sock);
        int r;

        if (remote_port == -1) {
                /* Fake addr/port to appease peers that validate it (Tectia) */
                free(remote_ipaddr);
                remote_ipaddr = xstrdup("127.0.0.1");
                remote_port = 65535;
        }

        free(c->remote_name);
        xasprintf(&c->remote_name,
            "%s: listening port %d for %.100s port %d, "
            "connect from %.200s port %d to %.100s port %d",
            rtype, c->listening_port, c->path, c->host_port,
            remote_ipaddr, remote_port, local_ipaddr, local_port);

        open_preamble(ssh, __func__, c, rtype);
        if (strcmp(rtype, "direct-tcpip") == 0) {
                /* target host, port */
                if ((r = sshpkt_put_cstring(ssh, c->path)) != 0 ||
                    (r = sshpkt_put_u32(ssh, c->host_port)) != 0) {
                        fatal("%s: channel %i: reply %s", __func__,
                            c->self, ssh_err(r));
                }
        } else if (strcmp(rtype, "direct-streamlocal@openssh.com") == 0) {
                /* target path */
                if ((r = sshpkt_put_cstring(ssh, c->path)) != 0) {
                        fatal("%s: channel %i: reply %s", __func__,
                            c->self, ssh_err(r));
                }
        } else if (strcmp(rtype, "forwarded-streamlocal@openssh.com") == 0) {
                /* listen path */
                if ((r = sshpkt_put_cstring(ssh, c->path)) != 0) {
                        fatal("%s: channel %i: reply %s", __func__,
                            c->self, ssh_err(r));
                }
        } else {
                /* listen address, port */
                if ((r = sshpkt_put_cstring(ssh, c->path)) != 0 ||
                    (r = sshpkt_put_u32(ssh, local_port)) != 0) {
                        fatal("%s: channel %i: reply %s", __func__,
                            c->self, ssh_err(r));
                }
        }
        if (strcmp(rtype, "forwarded-streamlocal@openssh.com") == 0) {
                /* reserved for future owner/mode info */
                if ((r = sshpkt_put_cstring(ssh, "")) != 0) {
                        fatal("%s: channel %i: reply %s", __func__,
                            c->self, ssh_err(r));
                }
        } else {
                /* originator host and port */
                if ((r = sshpkt_put_cstring(ssh, remote_ipaddr)) != 0 ||
                    (r = sshpkt_put_u32(ssh, (u_int)remote_port)) != 0) {
                        fatal("%s: channel %i: reply %s", __func__,
                            c->self, ssh_err(r));
                }
        }
        if ((r = sshpkt_send(ssh)) != 0)
                fatal("%s: channel %i: send %s", __func__, c->self, ssh_err(r));
        free(remote_ipaddr);
        free(local_ipaddr);
}

static void
channel_set_reuseaddr(int fd)
{
        int on = 1;

        /*
         * Set socket options.
         * Allow local port reuse in TIME_WAIT.
         */
        if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) == -1)
                error("setsockopt SO_REUSEADDR fd %d: %s", fd, strerror(errno));
}

void
channel_set_x11_refuse_time(struct ssh *ssh, u_int refuse_time)
{
        ssh->chanctxt->x11_refuse_time = refuse_time;
}

/*
 * This socket is listening for connections to a forwarded TCP/IP port.
 */
static void
channel_post_port_listener(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        Channel *nc;
        struct sockaddr_storage addr;
        int newsock, nextstate;
        socklen_t addrlen;
        char *rtype;

        if (!FD_ISSET(c->sock, readset))
                return;

        debug("Connection to port %d forwarding to %.100s port %d requested.",
            c->listening_port, c->path, c->host_port);

        if (c->type == SSH_CHANNEL_RPORT_LISTENER) {
                nextstate = SSH_CHANNEL_OPENING;
                rtype = "forwarded-tcpip";
        } else if (c->type == SSH_CHANNEL_RUNIX_LISTENER) {
                nextstate = SSH_CHANNEL_OPENING;
                rtype = "forwarded-streamlocal@openssh.com";
        } else if (c->host_port == PORT_STREAMLOCAL) {
                nextstate = SSH_CHANNEL_OPENING;
                rtype = "direct-streamlocal@openssh.com";
        } else if (c->host_port == 0) {
                nextstate = SSH_CHANNEL_DYNAMIC;
                rtype = "dynamic-tcpip";
        } else {
                nextstate = SSH_CHANNEL_OPENING;
                rtype = "direct-tcpip";
        }

        addrlen = sizeof(addr);
        newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
        if (newsock < 0) {
                if (errno != EINTR && errno != EWOULDBLOCK &&
                    errno != ECONNABORTED)
                        error("accept: %.100s", strerror(errno));
                if (errno == EMFILE || errno == ENFILE)
                        c->notbefore = monotime() + 1;
                return;
        }
        if (c->host_port != PORT_STREAMLOCAL)
                set_nodelay(newsock);
        nc = channel_new(ssh, rtype, nextstate, newsock, newsock, -1,
            c->local_window_max, c->local_maxpacket, 0, rtype, 1);
        nc->listening_port = c->listening_port;
        nc->host_port = c->host_port;
        if (c->path != NULL)
                nc->path = xstrdup(c->path);

        if (nextstate != SSH_CHANNEL_DYNAMIC)
                port_open_helper(ssh, nc, rtype);
}

/*
 * This is the authentication agent socket listening for connections from
 * clients.
 */
static void
channel_post_auth_listener(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        Channel *nc;
        int r, newsock;
        struct sockaddr_storage addr;
        socklen_t addrlen;

        if (!FD_ISSET(c->sock, readset))
                return;

        addrlen = sizeof(addr);
        newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
        if (newsock < 0) {
                error("accept from auth socket: %.100s", strerror(errno));
                if (errno == EMFILE || errno == ENFILE)
                        c->notbefore = monotime() + 1;
                return;
        }
        nc = channel_new(ssh, "accepted auth socket",
            SSH_CHANNEL_OPENING, newsock, newsock, -1,
            c->local_window_max, c->local_maxpacket,
            0, "accepted auth socket", 1);
        open_preamble(ssh, __func__, nc, "auth-agent@openssh.com");
        if ((r = sshpkt_send(ssh)) != 0)
                fatal("%s: channel %i: %s", __func__, c->self, ssh_err(r));
}

static void
channel_post_connecting(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        int err = 0, sock, isopen, r;
        socklen_t sz = sizeof(err);

        if (!FD_ISSET(c->sock, writeset))
                return;
        if (!c->have_remote_id)
                fatal(":%s: channel %d: no remote id", __func__, c->self);
        /* for rdynamic the OPEN_CONFIRMATION has been sent already */
        isopen = (c->type == SSH_CHANNEL_RDYNAMIC_FINISH);
        if (getsockopt(c->sock, SOL_SOCKET, SO_ERROR, &err, &sz) < 0) {
                err = errno;
                error("getsockopt SO_ERROR failed");
        }
        if (err == 0) {
                debug("channel %d: connected to %s port %d",
                    c->self, c->connect_ctx.host, c->connect_ctx.port);
                channel_connect_ctx_free(&c->connect_ctx);
                c->type = SSH_CHANNEL_OPEN;
                if (isopen) {
                        /* no message necessary */
                } else {
                        if ((r = sshpkt_start(ssh,
                            SSH2_MSG_CHANNEL_OPEN_CONFIRMATION)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->local_maxpacket))
                            != 0)
                                fatal("%s: channel %i: confirm: %s", __func__,
                                    c->self, ssh_err(r));
                        if ((r = sshpkt_send(ssh)) != 0)
                                fatal("%s: channel %i: %s", __func__, c->self,
                                    ssh_err(r));
                }
        } else {
                debug("channel %d: connection failed: %s",
                    c->self, strerror(err));
                /* Try next address, if any */
                if ((sock = connect_next(&c->connect_ctx)) > 0) {
                        close(c->sock);
                        c->sock = c->rfd = c->wfd = sock;
                        channel_find_maxfd(ssh->chanctxt);
                        return;
                }
                /* Exhausted all addresses */
                error("connect_to %.100s port %d: failed.",
                    c->connect_ctx.host, c->connect_ctx.port);
                channel_connect_ctx_free(&c->connect_ctx);
                if (isopen) {
                        rdynamic_close(ssh, c);
                } else {
                        if ((r = sshpkt_start(ssh,
                            SSH2_MSG_CHANNEL_OPEN_FAILURE)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
                            (r = sshpkt_put_u32(ssh, SSH2_OPEN_CONNECT_FAILED))
                            != 0)
                                fatal("%s: channel %i: failure: %s", __func__,
                                    c->self, ssh_err(r));
                        if ((datafellows & SSH_BUG_OPENFAILURE) == 0 &&
                            ((r = sshpkt_put_cstring(ssh, strerror(err))) != 0 ||
                            (r = sshpkt_put_cstring(ssh, "")) != 0))
                                fatal("%s: channel %i: failure: %s", __func__,
                                    c->self, ssh_err(r));
                        if ((r = sshpkt_send(ssh)) != 0)
                                fatal("%s: channel %i: %s", __func__, c->self,
                                    ssh_err(r));
                        chan_mark_dead(ssh, c);
                }
        }
}

static int
channel_handle_rfd(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        char buf[CHAN_RBUF];
        ssize_t len;
        int r, force;

        force = c->isatty && c->detach_close && c->istate != CHAN_INPUT_CLOSED;

        if (c->rfd == -1 || (!force && !FD_ISSET(c->rfd, readset)))
                return 1;

        errno = 0;
        len = read(c->rfd, buf, sizeof(buf));
        if (len < 0 && (errno == EINTR ||
            ((errno == EAGAIN || errno == EWOULDBLOCK) && !force)))
                return 1;
#ifndef PTY_ZEROREAD
        if (len <= 0) {
#else
        if ((!c->isatty && len <= 0) ||
            (c->isatty && (len < 0 || (len == 0 && errno != 0)))) {
#endif
                debug2("channel %d: read<=0 rfd %d len %zd",
                    c->self, c->rfd, len);
                if (c->type != SSH_CHANNEL_OPEN) {
                        debug2("channel %d: not open", c->self);
                        chan_mark_dead(ssh, c);
                        return -1;
                } else {
                        chan_read_failed(ssh, c);
                }
                return -1;
        }
        if (c->input_filter != NULL) {
                if (c->input_filter(ssh, c, buf, len) == -1) {
                        debug2("channel %d: filter stops", c->self);
                        chan_read_failed(ssh, c);
                }
        } else if (c->datagram) {
                if ((r = sshbuf_put_string(c->input, buf, len)) != 0)
                        fatal("%s: channel %d: put datagram: %s", __func__,
                            c->self, ssh_err(r));
        } else if ((r = sshbuf_put(c->input, buf, len)) != 0) {
                fatal("%s: channel %d: put data: %s", __func__,
                    c->self, ssh_err(r));
        }
        return 1;
}

static int
channel_handle_wfd(struct ssh *ssh, Channel *c,
   fd_set *readset, fd_set *writeset)
{
        struct termios tio;
        u_char *data = NULL, *buf; /* XXX const; need filter API change */
        size_t dlen, olen = 0;
        int r, len;

        if (c->wfd == -1 || !FD_ISSET(c->wfd, writeset) ||
            sshbuf_len(c->output) == 0)
                return 1;

        /* Send buffered output data to the socket. */
        olen = sshbuf_len(c->output);
        if (c->output_filter != NULL) {
                if ((buf = c->output_filter(ssh, c, &data, &dlen)) == NULL) {
                        debug2("channel %d: filter stops", c->self);
                        if (c->type != SSH_CHANNEL_OPEN)
                                chan_mark_dead(ssh, c);
                        else
                                chan_write_failed(ssh, c);
                        return -1;
                }
        } else if (c->datagram) {
                if ((r = sshbuf_get_string(c->output, &data, &dlen)) != 0)
                        fatal("%s: channel %d: get datagram: %s", __func__,
                            c->self, ssh_err(r));
                buf = data;
        } else {
                buf = data = sshbuf_mutable_ptr(c->output);
                dlen = sshbuf_len(c->output);
        }

        if (c->datagram) {
                /* ignore truncated writes, datagrams might get lost */
                len = write(c->wfd, buf, dlen);
                free(data);
                if (len < 0 && (errno == EINTR || errno == EAGAIN ||
                    errno == EWOULDBLOCK))
                        return 1;
                if (len <= 0)
                        goto write_fail;
                goto out;
        }

#ifdef _AIX
        /* XXX: Later AIX versions can't push as much data to tty */
        if (c->wfd_isatty)
                dlen = MIN(dlen, 8*1024);
#endif

        len = write(c->wfd, buf, dlen);
        if (len < 0 &&
            (errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK))
                return 1;
        if (len <= 0) {
 write_fail:
                if (c->type != SSH_CHANNEL_OPEN) {
                        debug2("channel %d: not open", c->self);
                        chan_mark_dead(ssh, c);
                        return -1;
                } else {
                        chan_write_failed(ssh, c);
                }
                return -1;
        }
#ifndef BROKEN_TCGETATTR_ICANON
        if (c->isatty && dlen >= 1 && buf[0] != '\r') {
                if (tcgetattr(c->wfd, &tio) == 0 &&
                    !(tio.c_lflag & ECHO) && (tio.c_lflag & ICANON)) {
                        /*
                         * Simulate echo to reduce the impact of
                         * traffic analysis. We need to match the
                         * size of a SSH2_MSG_CHANNEL_DATA message
                         * (4 byte channel id + buf)
                         */
                        if ((r = sshpkt_msg_ignore(ssh, 4+len)) != 0 ||
                            (r = sshpkt_send(ssh)) != 0)
                                fatal("%s: channel %d: ignore: %s",
                                    __func__, c->self, ssh_err(r));
                }
        }
#endif /* BROKEN_TCGETATTR_ICANON */
        if ((r = sshbuf_consume(c->output, len)) != 0) {
                fatal("%s: channel %d: consume: %s",
                    __func__, c->self, ssh_err(r));
        }
 out:
        c->local_consumed += olen - sshbuf_len(c->output);

        return 1;
}

static int
channel_handle_efd_write(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        int r;
        ssize_t len;

        if (!FD_ISSET(c->efd, writeset) || sshbuf_len(c->extended) == 0)
                return 1;

        len = write(c->efd, sshbuf_ptr(c->extended),
            sshbuf_len(c->extended));
        debug2("channel %d: written %zd to efd %d", c->self, len, c->efd);
        if (len < 0 && (errno == EINTR || errno == EAGAIN ||
            errno == EWOULDBLOCK))
                return 1;
        if (len <= 0) {
                debug2("channel %d: closing write-efd %d", c->self, c->efd);
                channel_close_fd(ssh, &c->efd);
        } else {
                if ((r = sshbuf_consume(c->extended, len)) != 0) {
                        fatal("%s: channel %d: consume: %s",
                            __func__, c->self, ssh_err(r));
                }
                c->local_consumed += len;
        }
        return 1;
}

static int
channel_handle_efd_read(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        char buf[CHAN_RBUF];
        int r;
        ssize_t len;

        if (!c->detach_close && !FD_ISSET(c->efd, readset))
                return 1;

        len = read(c->efd, buf, sizeof(buf));
        debug2("channel %d: read %zd from efd %d", c->self, len, c->efd);
        if (len < 0 && (errno == EINTR || ((errno == EAGAIN ||
            errno == EWOULDBLOCK) && !c->detach_close)))
                return 1;
        if (len <= 0) {
                debug2("channel %d: closing read-efd %d",
                    c->self, c->efd);
                channel_close_fd(ssh, &c->efd);
        } else {
                if (c->extended_usage == CHAN_EXTENDED_IGNORE) {
                        debug3("channel %d: discard efd",
                            c->self);
                } else if ((r = sshbuf_put(c->extended, buf, len)) != 0) {
                        fatal("%s: channel %d: append: %s",
                            __func__, c->self, ssh_err(r));
                }
        }
        return 1;
}

static int
channel_handle_efd(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        if (c->efd == -1)
                return 1;

        /** XXX handle drain efd, too */

        if (c->extended_usage == CHAN_EXTENDED_WRITE)
                return channel_handle_efd_write(ssh, c, readset, writeset);
        else if (c->extended_usage == CHAN_EXTENDED_READ ||
            c->extended_usage == CHAN_EXTENDED_IGNORE)
                return channel_handle_efd_read(ssh, c, readset, writeset);

        return 1;
}

static int
channel_check_window(struct ssh *ssh, Channel *c)
{
        int r;

        if (c->type == SSH_CHANNEL_OPEN &&
            !(c->flags & (CHAN_CLOSE_SENT|CHAN_CLOSE_RCVD)) &&
            ((c->local_window_max - c->local_window >
            c->local_maxpacket*3) ||
            c->local_window < c->local_window_max/2) &&
            c->local_consumed > 0) {
                if (!c->have_remote_id)
                        fatal(":%s: channel %d: no remote id",
                            __func__, c->self);
                if ((r = sshpkt_start(ssh,
                    SSH2_MSG_CHANNEL_WINDOW_ADJUST)) != 0 ||
                    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
                    (r = sshpkt_put_u32(ssh, c->local_consumed)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0) {
                        fatal("%s: channel %i: %s", __func__,
                            c->self, ssh_err(r));
                }
                debug2("channel %d: window %d sent adjust %d",
                    c->self, c->local_window,
                    c->local_consumed);
                c->local_window += c->local_consumed;
                c->local_consumed = 0;
        }
        return 1;
}

static void
channel_post_open(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        channel_handle_rfd(ssh, c, readset, writeset);
        channel_handle_wfd(ssh, c, readset, writeset);
        channel_handle_efd(ssh, c, readset, writeset);
        channel_check_window(ssh, c);
}

static u_int
read_mux(struct ssh *ssh, Channel *c, u_int need)
{
        char buf[CHAN_RBUF];
        ssize_t len;
        u_int rlen;
        int r;

        if (sshbuf_len(c->input) < need) {
                rlen = need - sshbuf_len(c->input);
                len = read(c->rfd, buf, MINIMUM(rlen, CHAN_RBUF));
                if (len < 0 && (errno == EINTR || errno == EAGAIN))
                        return sshbuf_len(c->input);
                if (len <= 0) {
                        debug2("channel %d: ctl read<=0 rfd %d len %zd",
                            c->self, c->rfd, len);
                        chan_read_failed(ssh, c);
                        return 0;
                } else if ((r = sshbuf_put(c->input, buf, len)) != 0) {
                        fatal("%s: channel %d: append: %s",
                            __func__, c->self, ssh_err(r));
                }
        }
        return sshbuf_len(c->input);
}

static void
channel_post_mux_client_read(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        u_int need;

        if (c->rfd == -1 || !FD_ISSET(c->rfd, readset))
                return;
        if (c->istate != CHAN_INPUT_OPEN && c->istate != CHAN_INPUT_WAIT_DRAIN)
                return;
        if (c->mux_pause)
                return;

        /*
         * Don't not read past the precise end of packets to
         * avoid disrupting fd passing.
         */
        if (read_mux(ssh, c, 4) < 4) /* read header */
                return;
        /* XXX sshbuf_peek_u32 */
        need = PEEK_U32(sshbuf_ptr(c->input));
#define CHANNEL_MUX_MAX_PACKET  (256 * 1024)
        if (need > CHANNEL_MUX_MAX_PACKET) {
                debug2("channel %d: packet too big %u > %u",
                    c->self, CHANNEL_MUX_MAX_PACKET, need);
                chan_rcvd_oclose(ssh, c);
                return;
        }
        if (read_mux(ssh, c, need + 4) < need + 4) /* read body */
                return;
        if (c->mux_rcb(ssh, c) != 0) {
                debug("channel %d: mux_rcb failed", c->self);
                chan_mark_dead(ssh, c);
                return;
        }
}

static void
channel_post_mux_client_write(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        ssize_t len;
        int r;

        if (c->wfd == -1 || !FD_ISSET(c->wfd, writeset) ||
            sshbuf_len(c->output) == 0)
                return;

        len = write(c->wfd, sshbuf_ptr(c->output), sshbuf_len(c->output));
        if (len < 0 && (errno == EINTR || errno == EAGAIN))
                return;
        if (len <= 0) {
                chan_mark_dead(ssh, c);
                return;
        }
        if ((r = sshbuf_consume(c->output, len)) != 0)
                fatal("%s: channel %d: consume: %s", __func__,
                    c->self, ssh_err(r));
}

static void
channel_post_mux_client(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        channel_post_mux_client_read(ssh, c, readset, writeset);
        channel_post_mux_client_write(ssh, c, readset, writeset);
}

static void
channel_post_mux_listener(struct ssh *ssh, Channel *c,
    fd_set *readset, fd_set *writeset)
{
        Channel *nc;
        struct sockaddr_storage addr;
        socklen_t addrlen;
        int newsock;
        uid_t euid;
        gid_t egid;

        if (!FD_ISSET(c->sock, readset))
                return;

        debug("multiplexing control connection");

        /*
         * Accept connection on control socket
         */
        memset(&addr, 0, sizeof(addr));
        addrlen = sizeof(addr);
        if ((newsock = accept(c->sock, (struct sockaddr*)&addr,
            &addrlen)) == -1) {
                error("%s accept: %s", __func__, strerror(errno));
                if (errno == EMFILE || errno == ENFILE)
                        c->notbefore = monotime() + 1;
                return;
        }

        if (getpeereid(newsock, &euid, &egid) < 0) {
                error("%s getpeereid failed: %s", __func__,
                    strerror(errno));
                close(newsock);
                return;
        }
        if ((euid != 0) && (getuid() != euid)) {
                error("multiplex uid mismatch: peer euid %u != uid %u",
                    (u_int)euid, (u_int)getuid());
                close(newsock);
                return;
        }
        nc = channel_new(ssh, "multiplex client", SSH_CHANNEL_MUX_CLIENT,
            newsock, newsock, -1, c->local_window_max,
            c->local_maxpacket, 0, "mux-control", 1);
        nc->mux_rcb = c->mux_rcb;
        debug3("%s: new mux channel %d fd %d", __func__, nc->self, nc->sock);
        /* establish state */
        nc->mux_rcb(ssh, nc);
        /* mux state transitions must not elicit protocol messages */
        nc->flags |= CHAN_LOCAL;
}

static void
channel_handler_init(struct ssh_channels *sc)
{
        chan_fn **pre, **post;

        if ((pre = calloc(SSH_CHANNEL_MAX_TYPE, sizeof(*pre))) == NULL ||
           (post = calloc(SSH_CHANNEL_MAX_TYPE, sizeof(*post))) == NULL)
                fatal("%s: allocation failed", __func__);

        pre[SSH_CHANNEL_OPEN] =                 &channel_pre_open;
        pre[SSH_CHANNEL_X11_OPEN] =             &channel_pre_x11_open;
        pre[SSH_CHANNEL_PORT_LISTENER] =        &channel_pre_listener;
        pre[SSH_CHANNEL_RPORT_LISTENER] =       &channel_pre_listener;
        pre[SSH_CHANNEL_UNIX_LISTENER] =        &channel_pre_listener;
        pre[SSH_CHANNEL_RUNIX_LISTENER] =       &channel_pre_listener;
        pre[SSH_CHANNEL_X11_LISTENER] =         &channel_pre_listener;
        pre[SSH_CHANNEL_AUTH_SOCKET] =          &channel_pre_listener;
        pre[SSH_CHANNEL_CONNECTING] =           &channel_pre_connecting;
        pre[SSH_CHANNEL_DYNAMIC] =              &channel_pre_dynamic;
        pre[SSH_CHANNEL_RDYNAMIC_FINISH] =      &channel_pre_connecting;
        pre[SSH_CHANNEL_MUX_LISTENER] =         &channel_pre_listener;
        pre[SSH_CHANNEL_MUX_CLIENT] =           &channel_pre_mux_client;

        post[SSH_CHANNEL_OPEN] =                &channel_post_open;
        post[SSH_CHANNEL_PORT_LISTENER] =       &channel_post_port_listener;
        post[SSH_CHANNEL_RPORT_LISTENER] =      &channel_post_port_listener;
        post[SSH_CHANNEL_UNIX_LISTENER] =       &channel_post_port_listener;
        post[SSH_CHANNEL_RUNIX_LISTENER] =      &channel_post_port_listener;
        post[SSH_CHANNEL_X11_LISTENER] =        &channel_post_x11_listener;
        post[SSH_CHANNEL_AUTH_SOCKET] =         &channel_post_auth_listener;
        post[SSH_CHANNEL_CONNECTING] =          &channel_post_connecting;
        post[SSH_CHANNEL_DYNAMIC] =             &channel_post_open;
        post[SSH_CHANNEL_RDYNAMIC_FINISH] =     &channel_post_connecting;
        post[SSH_CHANNEL_MUX_LISTENER] =        &channel_post_mux_listener;
        post[SSH_CHANNEL_MUX_CLIENT] =          &channel_post_mux_client;

        sc->channel_pre = pre;
        sc->channel_post = post;
}

/* gc dead channels */
static void
channel_garbage_collect(struct ssh *ssh, Channel *c)
{
        if (c == NULL)
                return;
        if (c->detach_user != NULL) {
                if (!chan_is_dead(ssh, c, c->detach_close))
                        return;
                debug2("channel %d: gc: notify user", c->self);
                c->detach_user(ssh, c->self, NULL);
                /* if we still have a callback */
                if (c->detach_user != NULL)
                        return;
                debug2("channel %d: gc: user detached", c->self);
        }
        if (!chan_is_dead(ssh, c, 1))
                return;
        debug2("channel %d: garbage collecting", c->self);
        channel_free(ssh, c);
}

enum channel_table { CHAN_PRE, CHAN_POST };

static void
channel_handler(struct ssh *ssh, int table,
    fd_set *readset, fd_set *writeset, time_t *unpause_secs)
{
        struct ssh_channels *sc = ssh->chanctxt;
        chan_fn **ftab = table == CHAN_PRE ? sc->channel_pre : sc->channel_post;
        u_int i, oalloc;
        Channel *c;
        time_t now;

        now = monotime();
        if (unpause_secs != NULL)
                *unpause_secs = 0;
        for (i = 0, oalloc = sc->channels_alloc; i < oalloc; i++) {
                c = sc->channels[i];
                if (c == NULL)
                        continue;
                if (c->delayed) {
                        if (table == CHAN_PRE)
                                c->delayed = 0;
                        else
                                continue;
                }
                if (ftab[c->type] != NULL) {
                        /*
                         * Run handlers that are not paused.
                         */
                        if (c->notbefore <= now)
                                (*ftab[c->type])(ssh, c, readset, writeset);
                        else if (unpause_secs != NULL) {
                                /*
                                 * Collect the time that the earliest
                                 * channel comes off pause.
                                 */
                                debug3("%s: chan %d: skip for %d more seconds",
                                    __func__, c->self,
                                    (int)(c->notbefore - now));
                                if (*unpause_secs == 0 ||
                                    (c->notbefore - now) < *unpause_secs)
                                        *unpause_secs = c->notbefore - now;
                        }
                }
                channel_garbage_collect(ssh, c);
        }
        if (unpause_secs != NULL && *unpause_secs != 0)
                debug3("%s: first channel unpauses in %d seconds",
                    __func__, (int)*unpause_secs);
}

/*
 * Create sockets before allocating the select bitmasks.
 * This is necessary for things that need to happen after reading
 * the network-input but before channel_prepare_select().
 */
static void
channel_before_prepare_select(struct ssh *ssh)
{
        struct ssh_channels *sc = ssh->chanctxt;
        Channel *c;
        u_int i, oalloc;

        for (i = 0, oalloc = sc->channels_alloc; i < oalloc; i++) {
                c = sc->channels[i];
                if (c == NULL)
                        continue;
                if (c->type == SSH_CHANNEL_RDYNAMIC_OPEN)
                        channel_before_prepare_select_rdynamic(ssh, c);
        }
}

/*
 * Allocate/update select bitmasks and add any bits relevant to channels in
 * select bitmasks.
 */
void
channel_prepare_select(struct ssh *ssh, fd_set **readsetp, fd_set **writesetp,
    int *maxfdp, u_int *nallocp, time_t *minwait_secs)
{
        u_int n, sz, nfdset;

        channel_before_prepare_select(ssh); /* might update channel_max_fd */

        n = MAXIMUM(*maxfdp, ssh->chanctxt->channel_max_fd);

        nfdset = howmany(n+1, NFDBITS);
        /* Explicitly test here, because xrealloc isn't always called */
        if (nfdset && SIZE_MAX / nfdset < sizeof(fd_mask))
                fatal("channel_prepare_select: max_fd (%d) is too large", n);
        sz = nfdset * sizeof(fd_mask);

        /* perhaps check sz < nalloc/2 and shrink? */
        if (*readsetp == NULL || sz > *nallocp) {
                *readsetp = xreallocarray(*readsetp, nfdset, sizeof(fd_mask));
                *writesetp = xreallocarray(*writesetp, nfdset, sizeof(fd_mask));
                *nallocp = sz;
        }
        *maxfdp = n;
        memset(*readsetp, 0, sz);
        memset(*writesetp, 0, sz);

        if (!ssh_packet_is_rekeying(ssh))
                channel_handler(ssh, CHAN_PRE, *readsetp, *writesetp,
                    minwait_secs);
}

/*
 * After select, perform any appropriate operations for channels which have
 * events pending.
 */
void
channel_after_select(struct ssh *ssh, fd_set *readset, fd_set *writeset)
{
        channel_handler(ssh, CHAN_POST, readset, writeset, NULL);
}

/*
 * Enqueue data for channels with open or draining c->input.
 */
static void
channel_output_poll_input_open(struct ssh *ssh, Channel *c)
{
        size_t len, plen;
        const u_char *pkt;
        int r;

        if ((len = sshbuf_len(c->input)) == 0) {
                if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
                        /*
                         * input-buffer is empty and read-socket shutdown:
                         * tell peer, that we will not send more data:
                         * send IEOF.
                         * hack for extended data: delay EOF if EFD still
                         * in use.
                         */
                        if (CHANNEL_EFD_INPUT_ACTIVE(c))
                                debug2("channel %d: "
                                    "ibuf_empty delayed efd %d/(%zu)",
                                    c->self, c->efd, sshbuf_len(c->extended));
                        else
                                chan_ibuf_empty(ssh, c);
                }
                return;
        }

        if (!c->have_remote_id)
                fatal(":%s: channel %d: no remote id", __func__, c->self);

        if (c->datagram) {
                /* Check datagram will fit; drop if not */
                if ((r = sshbuf_get_string_direct(c->input, &pkt, &plen)) != 0)
                        fatal("%s: channel %d: get datagram: %s", __func__,
                            c->self, ssh_err(r));
                /*
                 * XXX this does tail-drop on the datagram queue which is
                 * usually suboptimal compared to head-drop. Better to have
                 * backpressure at read time? (i.e. read + discard)
                 */
                if (plen > c->remote_window || plen > c->remote_maxpacket) {
                        debug("channel %d: datagram too big", c->self);
                        return;
                }
                /* Enqueue it */
                if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
                    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
                    (r = sshpkt_put_string(ssh, pkt, plen)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0) {
                        fatal("%s: channel %i: datagram: %s", __func__,
                            c->self, ssh_err(r));
                }
                c->remote_window -= plen;
                return;
        }

        /* Enqueue packet for buffered data. */
        if (len > c->remote_window)
                len = c->remote_window;
        if (len > c->remote_maxpacket)
                len = c->remote_maxpacket;
        if (len == 0)
                return;
        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
            (r = sshpkt_put_string(ssh, sshbuf_ptr(c->input), len)) != 0 ||
            (r = sshpkt_send(ssh)) != 0) {
                fatal("%s: channel %i: data: %s", __func__,
                    c->self, ssh_err(r));
        }
        if ((r = sshbuf_consume(c->input, len)) != 0)
                fatal("%s: channel %i: consume: %s", __func__,
                    c->self, ssh_err(r));
        c->remote_window -= len;
}

/*
 * Enqueue data for channels with open c->extended in read mode.
 */
static void
channel_output_poll_extended_read(struct ssh *ssh, Channel *c)
{
        size_t len;
        int r;

        if ((len = sshbuf_len(c->extended)) == 0)
                return;

        debug2("channel %d: rwin %u elen %zu euse %d", c->self,
            c->remote_window, sshbuf_len(c->extended), c->extended_usage);
        if (len > c->remote_window)
                len = c->remote_window;
        if (len > c->remote_maxpacket)
                len = c->remote_maxpacket;
        if (len == 0)
                return;
        if (!c->have_remote_id)
                fatal(":%s: channel %d: no remote id", __func__, c->self);
        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_EXTENDED_DATA)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
            (r = sshpkt_put_u32(ssh, SSH2_EXTENDED_DATA_STDERR)) != 0 ||
            (r = sshpkt_put_string(ssh, sshbuf_ptr(c->extended), len)) != 0 ||
            (r = sshpkt_send(ssh)) != 0) {
                fatal("%s: channel %i: data: %s", __func__,
                    c->self, ssh_err(r));
        }
        if ((r = sshbuf_consume(c->extended, len)) != 0)
                fatal("%s: channel %i: consume: %s", __func__,
                    c->self, ssh_err(r));
        c->remote_window -= len;
        debug2("channel %d: sent ext data %zu", c->self, len);
}

/* If there is data to send to the connection, enqueue some of it now. */
void
channel_output_poll(struct ssh *ssh)
{
        struct ssh_channels *sc = ssh->chanctxt;
        Channel *c;
        u_int i;

        for (i = 0; i < sc->channels_alloc; i++) {
                c = sc->channels[i];
                if (c == NULL)
                        continue;

                /*
                 * We are only interested in channels that can have buffered
                 * incoming data.
                 */
                if (c->type != SSH_CHANNEL_OPEN)
                        continue;
                if ((c->flags & (CHAN_CLOSE_SENT|CHAN_CLOSE_RCVD))) {
                        /* XXX is this true? */
                        debug3("channel %d: will not send data after close",
                            c->self);
                        continue;
                }

                /* Get the amount of buffered data for this channel. */
                if (c->istate == CHAN_INPUT_OPEN ||
                    c->istate == CHAN_INPUT_WAIT_DRAIN)
                        channel_output_poll_input_open(ssh, c);
                /* Send extended data, i.e. stderr */
                if (!(c->flags & CHAN_EOF_SENT) &&
                    c->extended_usage == CHAN_EXTENDED_READ)
                        channel_output_poll_extended_read(ssh, c);
        }
}

/* -- mux proxy support  */

/*
 * When multiplexing channel messages for mux clients we have to deal
 * with downstream messages from the mux client and upstream messages
 * from the ssh server:
 * 1) Handling downstream messages is straightforward and happens
 *    in channel_proxy_downstream():
 *    - We forward all messages (mostly) unmodified to the server.
 *    - However, in order to route messages from upstream to the correct
 *      downstream client, we have to replace the channel IDs used by the
 *      mux clients with a unique channel ID because the mux clients might
 *      use conflicting channel IDs.
 *    - so we inspect and change both SSH2_MSG_CHANNEL_OPEN and
 *      SSH2_MSG_CHANNEL_OPEN_CONFIRMATION messages, create a local
 *      SSH_CHANNEL_MUX_PROXY channel and replace the mux clients ID
 *      with the newly allocated channel ID.
 * 2) Upstream messages are received by matching SSH_CHANNEL_MUX_PROXY
 *    channels and procesed by channel_proxy_upstream(). The local channel ID
 *    is then translated back to the original mux client ID.
 * 3) In both cases we need to keep track of matching SSH2_MSG_CHANNEL_CLOSE
 *    messages so we can clean up SSH_CHANNEL_MUX_PROXY channels.
 * 4) The SSH_CHANNEL_MUX_PROXY channels also need to closed when the
 *    downstream mux client are removed.
 * 5) Handling SSH2_MSG_CHANNEL_OPEN messages from the upstream server
 *    requires more work, because they are not addressed to a specific
 *    channel. E.g. client_request_forwarded_tcpip() needs to figure
 *    out whether the request is addressed to the local client or a
 *    specific downstream client based on the listen-address/port.
 * 6) Agent and X11-Forwarding have a similar problem and are currenly
 *    not supported as the matching session/channel cannot be identified
 *    easily.
 */

/*
 * receive packets from downstream mux clients:
 * channel callback fired on read from mux client, creates
 * SSH_CHANNEL_MUX_PROXY channels and translates channel IDs
 * on channel creation.
 */
int
channel_proxy_downstream(struct ssh *ssh, Channel *downstream)
{
        Channel *c = NULL;
        struct sshbuf *original = NULL, *modified = NULL;
        const u_char *cp;
        char *ctype = NULL, *listen_host = NULL;
        u_char type;
        size_t have;
        int ret = -1, r;
        u_int id, remote_id, listen_port;

        /* sshbuf_dump(downstream->input, stderr); */
        if ((r = sshbuf_get_string_direct(downstream->input, &cp, &have))
            != 0) {
                error("%s: malformed message: %s", __func__, ssh_err(r));
                return -1;
        }
        if (have < 2) {
                error("%s: short message", __func__);
                return -1;
        }
        type = cp[1];
        /* skip padlen + type */
        cp += 2;
        have -= 2;
        if (ssh_packet_log_type(type))
                debug3("%s: channel %u: down->up: type %u", __func__,
                    downstream->self, type);

        switch (type) {
        case SSH2_MSG_CHANNEL_OPEN:
                if ((original = sshbuf_from(cp, have)) == NULL ||
                    (modified = sshbuf_new()) == NULL) {
                        error("%s: alloc", __func__);
                        goto out;
                }
                if ((r = sshbuf_get_cstring(original, &ctype, NULL)) != 0 ||
                    (r = sshbuf_get_u32(original, &id)) != 0) {
                        error("%s: parse error %s", __func__, ssh_err(r));
                        goto out;
                }
                c = channel_new(ssh, "mux proxy", SSH_CHANNEL_MUX_PROXY,
                   -1, -1, -1, 0, 0, 0, ctype, 1);
                c->mux_ctx = downstream;        /* point to mux client */
                c->mux_downstream_id = id;      /* original downstream id */
                if ((r = sshbuf_put_cstring(modified, ctype)) != 0 ||
                    (r = sshbuf_put_u32(modified, c->self)) != 0 ||
                    (r = sshbuf_putb(modified, original)) != 0) {
                        error("%s: compose error %s", __func__, ssh_err(r));
                        channel_free(ssh, c);
                        goto out;
                }
                break;
        case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
                /*
                 * Almost the same as SSH2_MSG_CHANNEL_OPEN, except then we
                 * need to parse 'remote_id' instead of 'ctype'.
                 */
                if ((original = sshbuf_from(cp, have)) == NULL ||
                    (modified = sshbuf_new()) == NULL) {
                        error("%s: alloc", __func__);
                        goto out;
                }
                if ((r = sshbuf_get_u32(original, &remote_id)) != 0 ||
                    (r = sshbuf_get_u32(original, &id)) != 0) {
                        error("%s: parse error %s", __func__, ssh_err(r));
                        goto out;
                }
                c = channel_new(ssh, "mux proxy", SSH_CHANNEL_MUX_PROXY,
                   -1, -1, -1, 0, 0, 0, "mux-down-connect", 1);
                c->mux_ctx = downstream;        /* point to mux client */
                c->mux_downstream_id = id;
                c->remote_id = remote_id;
                c->have_remote_id = 1;
                if ((r = sshbuf_put_u32(modified, remote_id)) != 0 ||
                    (r = sshbuf_put_u32(modified, c->self)) != 0 ||
                    (r = sshbuf_putb(modified, original)) != 0) {
                        error("%s: compose error %s", __func__, ssh_err(r));
                        channel_free(ssh, c);
                        goto out;
                }
                break;
        case SSH2_MSG_GLOBAL_REQUEST:
                if ((original = sshbuf_from(cp, have)) == NULL) {
                        error("%s: alloc", __func__);
                        goto out;
                }
                if ((r = sshbuf_get_cstring(original, &ctype, NULL)) != 0) {
                        error("%s: parse error %s", __func__, ssh_err(r));
                        goto out;
                }
                if (strcmp(ctype, "tcpip-forward") != 0) {
                        error("%s: unsupported request %s", __func__, ctype);
                        goto out;
                }
                if ((r = sshbuf_get_u8(original, NULL)) != 0 ||
                    (r = sshbuf_get_cstring(original, &listen_host, NULL)) != 0 ||
                    (r = sshbuf_get_u32(original, &listen_port)) != 0) {
                        error("%s: parse error %s", __func__, ssh_err(r));
                        goto out;
                }
                if (listen_port > 65535) {
                        error("%s: tcpip-forward for %s: bad port %u",
                            __func__, listen_host, listen_port);
                        goto out;
                }
                /* Record that connection to this host/port is permitted. */
                fwd_perm_list_add(ssh, FWDPERM_USER, "<mux>", -1,
                    listen_host, NULL, (int)listen_port, downstream);
                listen_host = NULL;
                break;
        case SSH2_MSG_CHANNEL_CLOSE:
                if (have < 4)
                        break;
                remote_id = PEEK_U32(cp);
                if ((c = channel_by_remote_id(ssh, remote_id)) != NULL) {
                        if (c->flags & CHAN_CLOSE_RCVD)
                                channel_free(ssh, c);
                        else
                                c->flags |= CHAN_CLOSE_SENT;
                }
                break;
        }
        if (modified) {
                if ((r = sshpkt_start(ssh, type)) != 0 ||
                    (r = sshpkt_putb(ssh, modified)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0) {
                        error("%s: send %s", __func__, ssh_err(r));
                        goto out;
                }
        } else {
                if ((r = sshpkt_start(ssh, type)) != 0 ||
                    (r = sshpkt_put(ssh, cp, have)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0) {
                        error("%s: send %s", __func__, ssh_err(r));
                        goto out;
                }
        }
        ret = 0;
 out:
        free(ctype);
        free(listen_host);
        sshbuf_free(original);
        sshbuf_free(modified);
        return ret;
}

/*
 * receive packets from upstream server and de-multiplex packets
 * to correct downstream:
 * implemented as a helper for channel input handlers,
 * replaces local (proxy) channel ID with downstream channel ID.
 */
int
channel_proxy_upstream(Channel *c, int type, u_int32_t seq, struct ssh *ssh)
{
        struct sshbuf *b = NULL;
        Channel *downstream;
        const u_char *cp = NULL;
        size_t len;
        int r;

        /*
         * When receiving packets from the peer we need to check whether we
         * need to forward the packets to the mux client. In this case we
         * restore the orignal channel id and keep track of CLOSE messages,
         * so we can cleanup the channel.
         */
        if (c == NULL || c->type != SSH_CHANNEL_MUX_PROXY)
                return 0;
        if ((downstream = c->mux_ctx) == NULL)
                return 0;
        switch (type) {
        case SSH2_MSG_CHANNEL_CLOSE:
        case SSH2_MSG_CHANNEL_DATA:
        case SSH2_MSG_CHANNEL_EOF:
        case SSH2_MSG_CHANNEL_EXTENDED_DATA:
        case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
        case SSH2_MSG_CHANNEL_OPEN_FAILURE:
        case SSH2_MSG_CHANNEL_WINDOW_ADJUST:
        case SSH2_MSG_CHANNEL_SUCCESS:
        case SSH2_MSG_CHANNEL_FAILURE:
        case SSH2_MSG_CHANNEL_REQUEST:
                break;
        default:
                debug2("%s: channel %u: unsupported type %u", __func__,
                    c->self, type);
                return 0;
        }
        if ((b = sshbuf_new()) == NULL) {
                error("%s: alloc reply", __func__);
                goto out;
        }
        /* get remaining payload (after id) */
        cp = sshpkt_ptr(ssh, &len);
        if (cp == NULL) {
                error("%s: no packet", __func__);
                goto out;
        }
        /* translate id and send to muxclient */
        if ((r = sshbuf_put_u8(b, 0)) != 0 ||   /* padlen */
            (r = sshbuf_put_u8(b, type)) != 0 ||
            (r = sshbuf_put_u32(b, c->mux_downstream_id)) != 0 ||
            (r = sshbuf_put(b, cp, len)) != 0 ||
            (r = sshbuf_put_stringb(downstream->output, b)) != 0) {
                error("%s: compose for muxclient %s", __func__, ssh_err(r));
                goto out;
        }
        /* sshbuf_dump(b, stderr); */
        if (ssh_packet_log_type(type))
                debug3("%s: channel %u: up->down: type %u", __func__, c->self,
                    type);
 out:
        /* update state */
        switch (type) {
        case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
                /* record remote_id for SSH2_MSG_CHANNEL_CLOSE */
                if (cp && len > 4) {
                        c->remote_id = PEEK_U32(cp);
                        c->have_remote_id = 1;
                }
                break;
        case SSH2_MSG_CHANNEL_CLOSE:
                if (c->flags & CHAN_CLOSE_SENT)
                        channel_free(ssh, c);
                else
                        c->flags |= CHAN_CLOSE_RCVD;
                break;
        }
        sshbuf_free(b);
        return 1;
}

/* -- protocol input */

/* Parse a channel ID from the current packet */
static int
channel_parse_id(struct ssh *ssh, const char *where, const char *what)
{
        u_int32_t id;
        int r;

        if ((r = sshpkt_get_u32(ssh, &id)) != 0) {
                error("%s: parse id: %s", where, ssh_err(r));
                ssh_packet_disconnect(ssh, "Invalid %s message", what);
        }
        if (id > INT_MAX) {
                error("%s: bad channel id %u: %s", where, id, ssh_err(r));
                ssh_packet_disconnect(ssh, "Invalid %s channel id", what);
        }
        return (int)id;
}

/* Lookup a channel from an ID in the current packet */
static Channel *
channel_from_packet_id(struct ssh *ssh, const char *where, const char *what)
{
        int id = channel_parse_id(ssh, where, what);
        Channel *c;

        if ((c = channel_lookup(ssh, id)) == NULL) {
                ssh_packet_disconnect(ssh,
                    "%s packet referred to nonexistent channel %d", what, id);
        }
        return c;
}

int
channel_input_data(int type, u_int32_t seq, struct ssh *ssh)
{
        const u_char *data;
        size_t data_len, win_len;
        Channel *c = channel_from_packet_id(ssh, __func__, "data");
        int r;

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;

        /* Ignore any data for non-open channels (might happen on close) */
        if (c->type != SSH_CHANNEL_OPEN &&
            c->type != SSH_CHANNEL_RDYNAMIC_OPEN &&
            c->type != SSH_CHANNEL_RDYNAMIC_FINISH &&
            c->type != SSH_CHANNEL_X11_OPEN)
                return 0;

        /* Get the data. */
        if ((r = sshpkt_get_string_direct(ssh, &data, &data_len)) != 0)
                fatal("%s: channel %d: get data: %s", __func__,
                    c->self, ssh_err(r));
        ssh_packet_check_eom(ssh);

        win_len = data_len;
        if (c->datagram)
                win_len += 4;  /* string length header */

        /*
         * The sending side reduces its window as it sends data, so we
         * must 'fake' consumption of the data in order to ensure that window
         * updates are sent back. Otherwise the connection might deadlock.
         */
        if (c->ostate != CHAN_OUTPUT_OPEN) {
                c->local_window -= win_len;
                c->local_consumed += win_len;
                return 0;
        }

        if (win_len > c->local_maxpacket) {
                logit("channel %d: rcvd big packet %zu, maxpack %u",
                    c->self, win_len, c->local_maxpacket);
                return 0;
        }
        if (win_len > c->local_window) {
                logit("channel %d: rcvd too much data %zu, win %u",
                    c->self, win_len, c->local_window);
                return 0;
        }
        c->local_window -= win_len;

        if (c->datagram) {
                if ((r = sshbuf_put_string(c->output, data, data_len)) != 0)
                        fatal("%s: channel %d: append datagram: %s",
                            __func__, c->self, ssh_err(r));
        } else if ((r = sshbuf_put(c->output, data, data_len)) != 0)
                fatal("%s: channel %d: append data: %s",
                    __func__, c->self, ssh_err(r));

        return 0;
}

int
channel_input_extended_data(int type, u_int32_t seq, struct ssh *ssh)
{
        const u_char *data;
        size_t data_len;
        u_int32_t tcode;
        Channel *c = channel_from_packet_id(ssh, __func__, "extended data");
        int r;

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        if (c->type != SSH_CHANNEL_OPEN) {
                logit("channel %d: ext data for non open", c->self);
                return 0;
        }
        if (c->flags & CHAN_EOF_RCVD) {
                if (datafellows & SSH_BUG_EXTEOF)
                        debug("channel %d: accepting ext data after eof",
                            c->self);
                else
                        ssh_packet_disconnect(ssh, "Received extended_data "
                            "after EOF on channel %d.", c->self);
        }

        if ((r = sshpkt_get_u32(ssh, &tcode)) != 0) {
                error("%s: parse tcode: %s", __func__, ssh_err(r));
                ssh_packet_disconnect(ssh, "Invalid extended_data message");
        }
        if (c->efd == -1 ||
            c->extended_usage != CHAN_EXTENDED_WRITE ||
            tcode != SSH2_EXTENDED_DATA_STDERR) {
                logit("channel %d: bad ext data", c->self);
                return 0;
        }
        if ((r = sshpkt_get_string_direct(ssh, &data, &data_len)) != 0) {
                error("%s: parse data: %s", __func__, ssh_err(r));
                ssh_packet_disconnect(ssh, "Invalid extended_data message");
        }
        ssh_packet_check_eom(ssh);

        if (data_len > c->local_window) {
                logit("channel %d: rcvd too much extended_data %zu, win %u",
                    c->self, data_len, c->local_window);
                return 0;
        }
        debug2("channel %d: rcvd ext data %zu", c->self, data_len);
        /* XXX sshpkt_getb? */
        if ((r = sshbuf_put(c->extended, data, data_len)) != 0)
                error("%s: append: %s", __func__, ssh_err(r));
        c->local_window -= data_len;
        return 0;
}

int
channel_input_ieof(int type, u_int32_t seq, struct ssh *ssh)
{
        Channel *c = channel_from_packet_id(ssh, __func__, "ieof");

        ssh_packet_check_eom(ssh);

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        chan_rcvd_ieof(ssh, c);

        /* XXX force input close */
        if (c->force_drain && c->istate == CHAN_INPUT_OPEN) {
                debug("channel %d: FORCE input drain", c->self);
                c->istate = CHAN_INPUT_WAIT_DRAIN;
                if (sshbuf_len(c->input) == 0)
                        chan_ibuf_empty(ssh, c);
        }
        return 0;
}

int
channel_input_oclose(int type, u_int32_t seq, struct ssh *ssh)
{
        Channel *c = channel_from_packet_id(ssh, __func__, "oclose");

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        ssh_packet_check_eom(ssh);
        chan_rcvd_oclose(ssh, c);
        return 0;
}

int
channel_input_open_confirmation(int type, u_int32_t seq, struct ssh *ssh)
{
        Channel *c = channel_from_packet_id(ssh, __func__, "open confirmation");
        u_int32_t remote_window, remote_maxpacket;
        int r;

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        if (c->type != SSH_CHANNEL_OPENING)
                packet_disconnect("Received open confirmation for "
                    "non-opening channel %d.", c->self);
        /*
         * Record the remote channel number and mark that the channel
         * is now open.
         */
        if ((r = sshpkt_get_u32(ssh, &c->remote_id)) != 0 ||
            (r = sshpkt_get_u32(ssh, &remote_window)) != 0 ||
            (r = sshpkt_get_u32(ssh, &remote_maxpacket)) != 0) {
                error("%s: window/maxpacket: %s", __func__, ssh_err(r));
                packet_disconnect("Invalid open confirmation message");
        }
        ssh_packet_check_eom(ssh);

        c->have_remote_id = 1;
        c->remote_window = remote_window;
        c->remote_maxpacket = remote_maxpacket;
        c->type = SSH_CHANNEL_OPEN;
        if (c->open_confirm) {
                debug2("%s: channel %d: callback start", __func__, c->self);
                c->open_confirm(ssh, c->self, 1, c->open_confirm_ctx);
                debug2("%s: channel %d: callback done", __func__, c->self);
        }
        debug2("channel %d: open confirm rwindow %u rmax %u", c->self,
            c->remote_window, c->remote_maxpacket);
        return 0;
}

static char *
reason2txt(int reason)
{
        switch (reason) {
        case SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED:
                return "administratively prohibited";
        case SSH2_OPEN_CONNECT_FAILED:
                return "connect failed";
        case SSH2_OPEN_UNKNOWN_CHANNEL_TYPE:
                return "unknown channel type";
        case SSH2_OPEN_RESOURCE_SHORTAGE:
                return "resource shortage";
        }
        return "unknown reason";
}

int
channel_input_open_failure(int type, u_int32_t seq, struct ssh *ssh)
{
        Channel *c = channel_from_packet_id(ssh, __func__, "open failure");
        u_int32_t reason;
        char *msg = NULL;
        int r;

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        if (c->type != SSH_CHANNEL_OPENING)
                packet_disconnect("Received open failure for "
                    "non-opening channel %d.", c->self);
        if ((r = sshpkt_get_u32(ssh, &reason)) != 0) {
                error("%s: reason: %s", __func__, ssh_err(r));
                packet_disconnect("Invalid open failure message");
        }
        if ((datafellows & SSH_BUG_OPENFAILURE) == 0) {
                /* skip language */
                if ((r = sshpkt_get_cstring(ssh, &msg, NULL)) != 0 ||
                    (r = sshpkt_get_string_direct(ssh, NULL, NULL)) != 0) {
                        error("%s: message/lang: %s", __func__, ssh_err(r));
                        packet_disconnect("Invalid open failure message");
                }
        }
        ssh_packet_check_eom(ssh);
        logit("channel %d: open failed: %s%s%s", c->self,
            reason2txt(reason), msg ? ": ": "", msg ? msg : "");
        free(msg);
        if (c->open_confirm) {
                debug2("%s: channel %d: callback start", __func__, c->self);
                c->open_confirm(ssh, c->self, 0, c->open_confirm_ctx);
                debug2("%s: channel %d: callback done", __func__, c->self);
        }
        /* Schedule the channel for cleanup/deletion. */
        chan_mark_dead(ssh, c);
        return 0;
}

int
channel_input_window_adjust(int type, u_int32_t seq, struct ssh *ssh)
{
        int id = channel_parse_id(ssh, __func__, "window adjust");
        Channel *c;
        u_int32_t adjust;
        u_int new_rwin;
        int r;

        if ((c = channel_lookup(ssh, id)) == NULL) {
                logit("Received window adjust for non-open channel %d.", id);
                return 0;
        }

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        if ((r = sshpkt_get_u32(ssh, &adjust)) != 0) {
                error("%s: adjust: %s", __func__, ssh_err(r));
                packet_disconnect("Invalid window adjust message");
        }
        ssh_packet_check_eom(ssh);
        debug2("channel %d: rcvd adjust %u", c->self, adjust);
        if ((new_rwin = c->remote_window + adjust) < c->remote_window) {
                fatal("channel %d: adjust %u overflows remote window %u",
                    c->self, adjust, c->remote_window);
        }
        c->remote_window = new_rwin;
        return 0;
}

int
channel_input_status_confirm(int type, u_int32_t seq, struct ssh *ssh)
{
        int id = channel_parse_id(ssh, __func__, "status confirm");
        Channel *c;
        struct channel_confirm *cc;

        /* Reset keepalive timeout */
        packet_set_alive_timeouts(0);

        debug2("%s: type %d id %d", __func__, type, id);

        if ((c = channel_lookup(ssh, id)) == NULL) {
                logit("%s: %d: unknown", __func__, id);
                return 0;
        }
        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        ssh_packet_check_eom(ssh);
        if ((cc = TAILQ_FIRST(&c->status_confirms)) == NULL)
                return 0;
        cc->cb(ssh, type, c, cc->ctx);
        TAILQ_REMOVE(&c->status_confirms, cc, entry);
        explicit_bzero(cc, sizeof(*cc));
        free(cc);
        return 0;
}

/* -- tcp forwarding */

void
channel_set_af(struct ssh *ssh, int af)
{
        ssh->chanctxt->IPv4or6 = af;
}


/*
 * Determine whether or not a port forward listens to loopback, the
 * specified address or wildcard. On the client, a specified bind
 * address will always override gateway_ports. On the server, a
 * gateway_ports of 1 (``yes'') will override the client's specification
 * and force a wildcard bind, whereas a value of 2 (``clientspecified'')
 * will bind to whatever address the client asked for.
 *
 * Special-case listen_addrs are:
 *
 * "0.0.0.0"               -> wildcard v4/v6 if SSH_OLD_FORWARD_ADDR
 * "" (empty string), "*"  -> wildcard v4/v6
 * "localhost"             -> loopback v4/v6
 * "127.0.0.1" / "::1"     -> accepted even if gateway_ports isn't set
 */
static const char *
channel_fwd_bind_addr(const char *listen_addr, int *wildcardp,
    int is_client, struct ForwardOptions *fwd_opts)
{
        const char *addr = NULL;
        int wildcard = 0;

        if (listen_addr == NULL) {
                /* No address specified: default to gateway_ports setting */
                if (fwd_opts->gateway_ports)
                        wildcard = 1;
        } else if (fwd_opts->gateway_ports || is_client) {
                if (((datafellows & SSH_OLD_FORWARD_ADDR) &&
                    strcmp(listen_addr, "0.0.0.0") == 0 && is_client == 0) ||
                    *listen_addr == '\0' || strcmp(listen_addr, "*") == 0 ||
                    (!is_client && fwd_opts->gateway_ports == 1)) {
                        wildcard = 1;
                        /*
                         * Notify client if they requested a specific listen
                         * address and it was overridden.
                         */
                        if (*listen_addr != '\0' &&
                            strcmp(listen_addr, "0.0.0.0") != 0 &&
                            strcmp(listen_addr, "*") != 0) {
                                packet_send_debug("Forwarding listen address "
                                    "\"%s\" overridden by server "
                                    "GatewayPorts", listen_addr);
                        }
                } else if (strcmp(listen_addr, "localhost") != 0 ||
                    strcmp(listen_addr, "127.0.0.1") == 0 ||
                    strcmp(listen_addr, "::1") == 0) {
                        /* Accept localhost address when GatewayPorts=yes */
                        addr = listen_addr;
                }
        } else if (strcmp(listen_addr, "127.0.0.1") == 0 ||
            strcmp(listen_addr, "::1") == 0) {
                /*
                 * If a specific IPv4/IPv6 localhost address has been
                 * requested then accept it even if gateway_ports is in
                 * effect. This allows the client to prefer IPv4 or IPv6.
                 */
                addr = listen_addr;
        }
        if (wildcardp != NULL)
                *wildcardp = wildcard;
        return addr;
}

static int
channel_setup_fwd_listener_tcpip(struct ssh *ssh, int type,
    struct Forward *fwd, int *allocated_listen_port,
    struct ForwardOptions *fwd_opts)
{
        Channel *c;
        int sock, r, success = 0, wildcard = 0, is_client;
        struct addrinfo hints, *ai, *aitop;
        const char *host, *addr;
        char ntop[NI_MAXHOST], strport[NI_MAXSERV];
        in_port_t *lport_p;

        is_client = (type == SSH_CHANNEL_PORT_LISTENER);

        if (is_client && fwd->connect_path != NULL) {
                host = fwd->connect_path;
        } else {
                host = (type == SSH_CHANNEL_RPORT_LISTENER) ?
                    fwd->listen_host : fwd->connect_host;
                if (host == NULL) {
                        error("No forward host name.");
                        return 0;
                }
                if (strlen(host) >= NI_MAXHOST) {
                        error("Forward host name too long.");
                        return 0;
                }
        }

        /* Determine the bind address, cf. channel_fwd_bind_addr() comment */
        addr = channel_fwd_bind_addr(fwd->listen_host, &wildcard,
            is_client, fwd_opts);
        debug3("%s: type %d wildcard %d addr %s", __func__,
            type, wildcard, (addr == NULL) ? "NULL" : addr);

        /*
         * getaddrinfo returns a loopback address if the hostname is
         * set to NULL and hints.ai_flags is not AI_PASSIVE
         */
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = ssh->chanctxt->IPv4or6;
        hints.ai_flags = wildcard ? AI_PASSIVE : 0;
        hints.ai_socktype = SOCK_STREAM;
        snprintf(strport, sizeof strport, "%d", fwd->listen_port);
        if ((r = getaddrinfo(addr, strport, &hints, &aitop)) != 0) {
                if (addr == NULL) {
                        /* This really shouldn't happen */
                        packet_disconnect("getaddrinfo: fatal error: %s",
                            ssh_gai_strerror(r));
                } else {
                        error("%s: getaddrinfo(%.64s): %s", __func__, addr,
                            ssh_gai_strerror(r));
                }
                return 0;
        }
        if (allocated_listen_port != NULL)
                *allocated_listen_port = 0;
        for (ai = aitop; ai; ai = ai->ai_next) {
                switch (ai->ai_family) {
                case AF_INET:
                        lport_p = &((struct sockaddr_in *)ai->ai_addr)->
                            sin_port;
                        break;
                case AF_INET6:
                        lport_p = &((struct sockaddr_in6 *)ai->ai_addr)->
                            sin6_port;
                        break;
                default:
                        continue;
                }
                /*
                 * If allocating a port for -R forwards, then use the
                 * same port for all address families.
                 */
                if (type == SSH_CHANNEL_RPORT_LISTENER &&
                    fwd->listen_port == 0 && allocated_listen_port != NULL &&
                    *allocated_listen_port > 0)
                        *lport_p = htons(*allocated_listen_port);

                if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop, sizeof(ntop),
                    strport, sizeof(strport),
                    NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
                        error("%s: getnameinfo failed", __func__);
                        continue;
                }
                /* Create a port to listen for the host. */
                sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
                if (sock < 0) {
                        /* this is no error since kernel may not support ipv6 */
                        verbose("socket: %.100s", strerror(errno));
                        continue;
                }

                channel_set_reuseaddr(sock);
                if (ai->ai_family == AF_INET6)
                        sock_set_v6only(sock);

                debug("Local forwarding listening on %s port %s.",
                    ntop, strport);

                /* Bind the socket to the address. */
                if (bind(sock, ai->ai_addr, ai->ai_addrlen) < 0) {
                        /*
                         * address can be in if use ipv6 address is
                         * already bound
                         */
                        if (!ai->ai_next)
                                error("bind: %.100s", strerror(errno));
                        else
                                verbose("bind: %.100s", strerror(errno));

                        close(sock);
                        continue;
                }
                /* Start listening for connections on the socket. */
                if (listen(sock, SSH_LISTEN_BACKLOG) < 0) {
                        error("listen: %.100s", strerror(errno));
                        close(sock);
                        continue;
                }

                /*
                 * fwd->listen_port == 0 requests a dynamically allocated port -
                 * record what we got.
                 */
                if (type == SSH_CHANNEL_RPORT_LISTENER &&
                    fwd->listen_port == 0 &&
                    allocated_listen_port != NULL &&
                    *allocated_listen_port == 0) {
                        *allocated_listen_port = get_local_port(sock);
                        debug("Allocated listen port %d",
                            *allocated_listen_port);
                }

                /* Allocate a channel number for the socket. */
                c = channel_new(ssh, "port listener", type, sock, sock, -1,
                    CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
                    0, "port listener", 1);
                c->path = xstrdup(host);
                c->host_port = fwd->connect_port;
                c->listening_addr = addr == NULL ? NULL : xstrdup(addr);
                if (fwd->listen_port == 0 && allocated_listen_port != NULL &&
                    !(datafellows & SSH_BUG_DYNAMIC_RPORT))
                        c->listening_port = *allocated_listen_port;
                else
                        c->listening_port = fwd->listen_port;
                success = 1;
        }
        if (success == 0)
                error("%s: cannot listen to port: %d", __func__,
                    fwd->listen_port);
        freeaddrinfo(aitop);
        return success;
}

static int
channel_setup_fwd_listener_streamlocal(struct ssh *ssh, int type,
    struct Forward *fwd, struct ForwardOptions *fwd_opts)
{
        struct sockaddr_un sunaddr;
        const char *path;
        Channel *c;
        int port, sock;
        mode_t omask;

        switch (type) {
        case SSH_CHANNEL_UNIX_LISTENER:
                if (fwd->connect_path != NULL) {
                        if (strlen(fwd->connect_path) > sizeof(sunaddr.sun_path)) {
                                error("Local connecting path too long: %s",
                                    fwd->connect_path);
                                return 0;
                        }
                        path = fwd->connect_path;
                        port = PORT_STREAMLOCAL;
                } else {
                        if (fwd->connect_host == NULL) {
                                error("No forward host name.");
                                return 0;
                        }
                        if (strlen(fwd->connect_host) >= NI_MAXHOST) {
                                error("Forward host name too long.");
                                return 0;
                        }
                        path = fwd->connect_host;
                        port = fwd->connect_port;
                }
                break;
        case SSH_CHANNEL_RUNIX_LISTENER:
                path = fwd->listen_path;
                port = PORT_STREAMLOCAL;
                break;
        default:
                error("%s: unexpected channel type %d", __func__, type);
                return 0;
        }

        if (fwd->listen_path == NULL) {
                error("No forward path name.");
                return 0;
        }
        if (strlen(fwd->listen_path) > sizeof(sunaddr.sun_path)) {
                error("Local listening path too long: %s", fwd->listen_path);
                return 0;
        }

        debug3("%s: type %d path %s", __func__, type, fwd->listen_path);

        /* Start a Unix domain listener. */
        omask = umask(fwd_opts->streamlocal_bind_mask);
        sock = unix_listener(fwd->listen_path, SSH_LISTEN_BACKLOG,
            fwd_opts->streamlocal_bind_unlink);
        umask(omask);
        if (sock < 0)
                return 0;

        debug("Local forwarding listening on path %s.", fwd->listen_path);

        /* Allocate a channel number for the socket. */
        c = channel_new(ssh, "unix listener", type, sock, sock, -1,
            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
            0, "unix listener", 1);
        c->path = xstrdup(path);
        c->host_port = port;
        c->listening_port = PORT_STREAMLOCAL;
        c->listening_addr = xstrdup(fwd->listen_path);
        return 1;
}

static int
channel_cancel_rport_listener_tcpip(struct ssh *ssh,
    const char *host, u_short port)
{
        u_int i;
        int found = 0;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                Channel *c = ssh->chanctxt->channels[i];
                if (c == NULL || c->type != SSH_CHANNEL_RPORT_LISTENER)
                        continue;
                if (strcmp(c->path, host) == 0 && c->listening_port == port) {
                        debug2("%s: close channel %d", __func__, i);
                        channel_free(ssh, c);
                        found = 1;
                }
        }

        return found;
}

static int
channel_cancel_rport_listener_streamlocal(struct ssh *ssh, const char *path)
{
        u_int i;
        int found = 0;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                Channel *c = ssh->chanctxt->channels[i];
                if (c == NULL || c->type != SSH_CHANNEL_RUNIX_LISTENER)
                        continue;
                if (c->path == NULL)
                        continue;
                if (strcmp(c->path, path) == 0) {
                        debug2("%s: close channel %d", __func__, i);
                        channel_free(ssh, c);
                        found = 1;
                }
        }

        return found;
}

int
channel_cancel_rport_listener(struct ssh *ssh, struct Forward *fwd)
{
        if (fwd->listen_path != NULL) {
                return channel_cancel_rport_listener_streamlocal(ssh,
                    fwd->listen_path);
        } else {
                return channel_cancel_rport_listener_tcpip(ssh,
                    fwd->listen_host, fwd->listen_port);
        }
}

static int
channel_cancel_lport_listener_tcpip(struct ssh *ssh,
    const char *lhost, u_short lport, int cport,
    struct ForwardOptions *fwd_opts)
{
        u_int i;
        int found = 0;
        const char *addr = channel_fwd_bind_addr(lhost, NULL, 1, fwd_opts);

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                Channel *c = ssh->chanctxt->channels[i];
                if (c == NULL || c->type != SSH_CHANNEL_PORT_LISTENER)
                        continue;
                if (c->listening_port != lport)
                        continue;
                if (cport == CHANNEL_CANCEL_PORT_STATIC) {
                        /* skip dynamic forwardings */
                        if (c->host_port == 0)
                                continue;
                } else {
                        if (c->host_port != cport)
                                continue;
                }
                if ((c->listening_addr == NULL && addr != NULL) ||
                    (c->listening_addr != NULL && addr == NULL))
                        continue;
                if (addr == NULL || strcmp(c->listening_addr, addr) == 0) {
                        debug2("%s: close channel %d", __func__, i);
                        channel_free(ssh, c);
                        found = 1;
                }
        }

        return found;
}

static int
channel_cancel_lport_listener_streamlocal(struct ssh *ssh, const char *path)
{
        u_int i;
        int found = 0;

        if (path == NULL) {
                error("%s: no path specified.", __func__);
                return 0;
        }

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                Channel *c = ssh->chanctxt->channels[i];
                if (c == NULL || c->type != SSH_CHANNEL_UNIX_LISTENER)
                        continue;
                if (c->listening_addr == NULL)
                        continue;
                if (strcmp(c->listening_addr, path) == 0) {
                        debug2("%s: close channel %d", __func__, i);
                        channel_free(ssh, c);
                        found = 1;
                }
        }

        return found;
}

int
channel_cancel_lport_listener(struct ssh *ssh,
    struct Forward *fwd, int cport, struct ForwardOptions *fwd_opts)
{
        if (fwd->listen_path != NULL) {
                return channel_cancel_lport_listener_streamlocal(ssh,
                    fwd->listen_path);
        } else {
                return channel_cancel_lport_listener_tcpip(ssh,
                    fwd->listen_host, fwd->listen_port, cport, fwd_opts);
        }
}

/* protocol local port fwd, used by ssh */
int
channel_setup_local_fwd_listener(struct ssh *ssh,
    struct Forward *fwd, struct ForwardOptions *fwd_opts)
{
        if (fwd->listen_path != NULL) {
                return channel_setup_fwd_listener_streamlocal(ssh,
                    SSH_CHANNEL_UNIX_LISTENER, fwd, fwd_opts);
        } else {
                return channel_setup_fwd_listener_tcpip(ssh,
                    SSH_CHANNEL_PORT_LISTENER, fwd, NULL, fwd_opts);
        }
}

/* protocol v2 remote port fwd, used by sshd */
int
channel_setup_remote_fwd_listener(struct ssh *ssh, struct Forward *fwd,
    int *allocated_listen_port, struct ForwardOptions *fwd_opts)
{
        if (fwd->listen_path != NULL) {
                return channel_setup_fwd_listener_streamlocal(ssh,
                    SSH_CHANNEL_RUNIX_LISTENER, fwd, fwd_opts);
        } else {
                return channel_setup_fwd_listener_tcpip(ssh,
                    SSH_CHANNEL_RPORT_LISTENER, fwd, allocated_listen_port,
                    fwd_opts);
        }
}

/*
 * Translate the requested rfwd listen host to something usable for
 * this server.
 */
static const char *
channel_rfwd_bind_host(const char *listen_host)
{
        if (listen_host == NULL) {
                if (datafellows & SSH_BUG_RFWD_ADDR)
                        return "127.0.0.1";
                else
                        return "localhost";
        } else if (*listen_host == '\0' || strcmp(listen_host, "*") == 0) {
                if (datafellows & SSH_BUG_RFWD_ADDR)
                        return "0.0.0.0";
                else
                        return "";
        } else
                return listen_host;
}

/*
 * Initiate forwarding of connections to port "port" on remote host through
 * the secure channel to host:port from local side.
 * Returns handle (index) for updating the dynamic listen port with
 * channel_update_permitted_opens().
 */
int
channel_request_remote_forwarding(struct ssh *ssh, struct Forward *fwd)
{
        int r, success = 0, idx = -1;
        char *host_to_connect, *listen_host, *listen_path;
        int port_to_connect, listen_port;

        /* Send the forward request to the remote side. */
        if (fwd->listen_path != NULL) {
                if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
                    (r = sshpkt_put_cstring(ssh,
                    "streamlocal-forward@openssh.com")) != 0 ||
                    (r = sshpkt_put_u8(ssh, 1)) != 0 || /* want reply */
                    (r = sshpkt_put_cstring(ssh, fwd->listen_path)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0 ||
                    (r = ssh_packet_write_wait(ssh)) != 0)
                        fatal("%s: request streamlocal: %s",
                            __func__, ssh_err(r));
        } else {
                if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
                    (r = sshpkt_put_cstring(ssh, "tcpip-forward")) != 0 ||
                    (r = sshpkt_put_u8(ssh, 1)) != 0 || /* want reply */
                    (r = sshpkt_put_cstring(ssh,
                    channel_rfwd_bind_host(fwd->listen_host))) != 0 ||
                    (r = sshpkt_put_u32(ssh, fwd->listen_port)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0 ||
                    (r = ssh_packet_write_wait(ssh)) != 0)
                        fatal("%s: request tcpip-forward: %s",
                            __func__, ssh_err(r));
        }
        /* Assume that server accepts the request */
        success = 1;
        if (success) {
                /* Record that connection to this host/port is permitted. */
                host_to_connect = listen_host = listen_path = NULL;
                port_to_connect = listen_port = 0;
                if (fwd->connect_path != NULL) {
                        host_to_connect = xstrdup(fwd->connect_path);
                        port_to_connect = PORT_STREAMLOCAL;
                } else {
                        host_to_connect = xstrdup(fwd->connect_host);
                        port_to_connect = fwd->connect_port;
                }
                if (fwd->listen_path != NULL) {
                        listen_path = xstrdup(fwd->listen_path);
                        listen_port = PORT_STREAMLOCAL;
                } else {
                        if (fwd->listen_host != NULL)
                                listen_host = xstrdup(fwd->listen_host);
                        listen_port = fwd->listen_port;
                }
                idx = fwd_perm_list_add(ssh, FWDPERM_USER,
                    host_to_connect, port_to_connect,
                    listen_host, listen_path, listen_port, NULL);
        }
        return idx;
}

static int
open_match(ForwardPermission *allowed_open, const char *requestedhost,
    int requestedport)
{
        if (allowed_open->host_to_connect == NULL)
                return 0;
        if (allowed_open->port_to_connect != FWD_PERMIT_ANY_PORT &&
            allowed_open->port_to_connect != requestedport)
                return 0;
        if (strcmp(allowed_open->host_to_connect, FWD_PERMIT_ANY_HOST) != 0 &&
            strcmp(allowed_open->host_to_connect, requestedhost) != 0)
                return 0;
        return 1;
}

/*
 * Note that in the listen host/port case
 * we don't support FWD_PERMIT_ANY_PORT and
 * need to translate between the configured-host (listen_host)
 * and what we've sent to the remote server (channel_rfwd_bind_host)
 */
static int
open_listen_match_tcpip(ForwardPermission *allowed_open,
    const char *requestedhost, u_short requestedport, int translate)
{
        const char *allowed_host;

        if (allowed_open->host_to_connect == NULL)
                return 0;
        if (allowed_open->listen_port != requestedport)
                return 0;
        if (!translate && allowed_open->listen_host == NULL &&
            requestedhost == NULL)
                return 1;
        allowed_host = translate ?
            channel_rfwd_bind_host(allowed_open->listen_host) :
            allowed_open->listen_host;
        if (allowed_host == NULL ||
            strcmp(allowed_host, requestedhost) != 0)
                return 0;
        return 1;
}

static int
open_listen_match_streamlocal(ForwardPermission *allowed_open,
    const char *requestedpath)
{
        if (allowed_open->host_to_connect == NULL)
                return 0;
        if (allowed_open->listen_port != PORT_STREAMLOCAL)
                return 0;
        if (allowed_open->listen_path == NULL ||
            strcmp(allowed_open->listen_path, requestedpath) != 0)
                return 0;
        return 1;
}

/*
 * Request cancellation of remote forwarding of connection host:port from
 * local side.
 */
static int
channel_request_rforward_cancel_tcpip(struct ssh *ssh,
    const char *host, u_short port)
{
        struct ssh_channels *sc = ssh->chanctxt;
        int r;
        u_int i;
        ForwardPermission *fp;

        for (i = 0; i < sc->num_permitted_opens; i++) {
                fp = &sc->permitted_opens[i];
                if (open_listen_match_tcpip(fp, host, port, 0))
                        break;
                fp = NULL;
        }
        if (fp == NULL) {
                debug("%s: requested forward not found", __func__);
                return -1;
        }
        if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
            (r = sshpkt_put_cstring(ssh, "cancel-tcpip-forward")) != 0 ||
            (r = sshpkt_put_u8(ssh, 0)) != 0 || /* want reply */
            (r = sshpkt_put_cstring(ssh, channel_rfwd_bind_host(host))) != 0 ||
            (r = sshpkt_put_u32(ssh, port)) != 0 ||
            (r = sshpkt_send(ssh)) != 0)
                fatal("%s: send cancel: %s", __func__, ssh_err(r));

        fwd_perm_clear(fp); /* unregister */

        return 0;
}

/*
 * Request cancellation of remote forwarding of Unix domain socket
 * path from local side.
 */
static int
channel_request_rforward_cancel_streamlocal(struct ssh *ssh, const char *path)
{
        struct ssh_channels *sc = ssh->chanctxt;
        int r;
        u_int i;
        ForwardPermission *fp;

        for (i = 0; i < sc->num_permitted_opens; i++) {
                fp = &sc->permitted_opens[i];
                if (open_listen_match_streamlocal(fp, path))
                        break;
                fp = NULL;
        }
        if (fp == NULL) {
                debug("%s: requested forward not found", __func__);
                return -1;
        }
        if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
            (r = sshpkt_put_cstring(ssh,
            "cancel-streamlocal-forward@openssh.com")) != 0 ||
            (r = sshpkt_put_u8(ssh, 0)) != 0 || /* want reply */
            (r = sshpkt_put_cstring(ssh, path)) != 0 ||
            (r = sshpkt_send(ssh)) != 0)
                fatal("%s: send cancel: %s", __func__, ssh_err(r));

        fwd_perm_clear(fp); /* unregister */

        return 0;
}
 
/*
 * Request cancellation of remote forwarding of a connection from local side.
 */
int
channel_request_rforward_cancel(struct ssh *ssh, struct Forward *fwd)
{
        if (fwd->listen_path != NULL) {
                return channel_request_rforward_cancel_streamlocal(ssh,
                    fwd->listen_path);
        } else {
                return channel_request_rforward_cancel_tcpip(ssh,
                    fwd->listen_host,
                    fwd->listen_port ? fwd->listen_port : fwd->allocated_port);
        }
}

/*
 * Permits opening to any host/port if permitted_opens[] is empty.  This is
 * usually called by the server, because the user could connect to any port
 * anyway, and the server has no way to know but to trust the client anyway.
 */
void
channel_permit_all_opens(struct ssh *ssh)
{
        if (ssh->chanctxt->num_permitted_opens == 0)
                ssh->chanctxt->all_opens_permitted = 1;
}

void
channel_add_permitted_opens(struct ssh *ssh, char *host, int port)
{
        struct ssh_channels *sc = ssh->chanctxt;

        debug("allow port forwarding to host %s port %d", host, port);
        fwd_perm_list_add(ssh, FWDPERM_USER, host, port, NULL, NULL, 0, NULL);
        sc->all_opens_permitted = 0;
}

/*
 * Update the listen port for a dynamic remote forward, after
 * the actual 'newport' has been allocated. If 'newport' < 0 is
 * passed then they entry will be invalidated.
 */
void
channel_update_permitted_opens(struct ssh *ssh, int idx, int newport)
{
        struct ssh_channels *sc = ssh->chanctxt;

        if (idx < 0 || (u_int)idx >= sc->num_permitted_opens) {
                debug("%s: index out of range: %d num_permitted_opens %d",
                    __func__, idx, sc->num_permitted_opens);
                return;
        }
        debug("%s allowed port %d for forwarding to host %s port %d",
            newport > 0 ? "Updating" : "Removing",
            newport,
            sc->permitted_opens[idx].host_to_connect,
            sc->permitted_opens[idx].port_to_connect);
        if (newport <= 0)
                fwd_perm_clear(&sc->permitted_opens[idx]);
        else {
                sc->permitted_opens[idx].listen_port =
                    (datafellows & SSH_BUG_DYNAMIC_RPORT) ? 0 : newport;
        }
}

int
channel_add_adm_permitted_opens(struct ssh *ssh, char *host, int port)
{
        debug("config allows port forwarding to host %s port %d", host, port);
        return fwd_perm_list_add(ssh, FWDPERM_ADMIN, host, port,
            NULL, NULL, 0, NULL);
}

void
channel_disable_adm_local_opens(struct ssh *ssh)
{
        channel_clear_adm_permitted_opens(ssh);
        fwd_perm_list_add(ssh, FWDPERM_ADMIN, NULL, 0, NULL, NULL, 0, NULL);
}

void
channel_clear_permitted_opens(struct ssh *ssh)
{
        struct ssh_channels *sc = ssh->chanctxt;

        sc->permitted_opens = xrecallocarray(sc->permitted_opens,
            sc->num_permitted_opens, 0, sizeof(*sc->permitted_opens));
        sc->num_permitted_opens = 0;
}

void
channel_clear_adm_permitted_opens(struct ssh *ssh)
{
        struct ssh_channels *sc = ssh->chanctxt;

        sc->permitted_adm_opens = xrecallocarray(sc->permitted_adm_opens,
            sc->num_adm_permitted_opens, 0, sizeof(*sc->permitted_adm_opens));
        sc->num_adm_permitted_opens = 0;
}

/* returns port number, FWD_PERMIT_ANY_PORT or -1 on error */
int
permitopen_port(const char *p)
{
        int port;

        if (strcmp(p, "*") == 0)
                return FWD_PERMIT_ANY_PORT;
        if ((port = a2port(p)) > 0)
                return port;
        return -1;
}

/* Try to start non-blocking connect to next host in cctx list */
static int
connect_next(struct channel_connect *cctx)
{
        int sock, saved_errno;
        struct sockaddr_un *sunaddr;
        char ntop[NI_MAXHOST];
        char strport[MAXIMUM(NI_MAXSERV, sizeof(sunaddr->sun_path))];

        for (; cctx->ai; cctx->ai = cctx->ai->ai_next) {
                switch (cctx->ai->ai_family) {
                case AF_UNIX:
                        /* unix:pathname instead of host:port */
                        sunaddr = (struct sockaddr_un *)cctx->ai->ai_addr;
                        strlcpy(ntop, "unix", sizeof(ntop));
                        strlcpy(strport, sunaddr->sun_path, sizeof(strport));
                        break;
                case AF_INET:
                case AF_INET6:
                        if (getnameinfo(cctx->ai->ai_addr, cctx->ai->ai_addrlen,
                            ntop, sizeof(ntop), strport, sizeof(strport),
                            NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
                                error("connect_next: getnameinfo failed");
                                continue;
                        }
                        break;
                default:
                        continue;
                }
                if ((sock = socket(cctx->ai->ai_family, cctx->ai->ai_socktype,
                    cctx->ai->ai_protocol)) == -1) {
                        if (cctx->ai->ai_next == NULL)
                                error("socket: %.100s", strerror(errno));
                        else
                                verbose("socket: %.100s", strerror(errno));
                        continue;
                }
                if (set_nonblock(sock) == -1)
                        fatal("%s: set_nonblock(%d)", __func__, sock);
                if (connect(sock, cctx->ai->ai_addr,
                    cctx->ai->ai_addrlen) == -1 && errno != EINPROGRESS) {
                        debug("connect_next: host %.100s ([%.100s]:%s): "
                            "%.100s", cctx->host, ntop, strport,
                            strerror(errno));
                        saved_errno = errno;
                        close(sock);
                        errno = saved_errno;
                        continue;       /* fail -- try next */
                }
                if (cctx->ai->ai_family != AF_UNIX)
                        set_nodelay(sock);
                debug("connect_next: host %.100s ([%.100s]:%s) "
                    "in progress, fd=%d", cctx->host, ntop, strport, sock);
                cctx->ai = cctx->ai->ai_next;
                return sock;
        }
        return -1;
}

static void
channel_connect_ctx_free(struct channel_connect *cctx)
{
        free(cctx->host);
        if (cctx->aitop) {
                if (cctx->aitop->ai_family == AF_UNIX)
                        free(cctx->aitop);
                else
                        freeaddrinfo(cctx->aitop);
        }
        memset(cctx, 0, sizeof(*cctx));
}

/*
 * Return connecting socket to remote host:port or local socket path,
 * passing back the failure reason if appropriate.
 */
static int
connect_to_helper(struct ssh *ssh, const char *name, int port, int socktype,
    char *ctype, char *rname, struct channel_connect *cctx,
    int *reason, const char **errmsg)
{
        struct addrinfo hints;
        int gaierr;
        int sock = -1;
        char strport[NI_MAXSERV];

        if (port == PORT_STREAMLOCAL) {
                struct sockaddr_un *sunaddr;
                struct addrinfo *ai;

                if (strlen(name) > sizeof(sunaddr->sun_path)) {
                        error("%.100s: %.100s", name, strerror(ENAMETOOLONG));
                        return -1;
                }

                /*
                 * Fake up a struct addrinfo for AF_UNIX connections.
                 * channel_connect_ctx_free() must check ai_family
                 * and use free() not freeaddirinfo() for AF_UNIX.
                 */
                ai = xmalloc(sizeof(*ai) + sizeof(*sunaddr));
                memset(ai, 0, sizeof(*ai) + sizeof(*sunaddr));
                ai->ai_addr = (struct sockaddr *)(ai + 1);
                ai->ai_addrlen = sizeof(*sunaddr);
                ai->ai_family = AF_UNIX;
                ai->ai_socktype = socktype;
                ai->ai_protocol = PF_UNSPEC;
                sunaddr = (struct sockaddr_un *)ai->ai_addr;
                sunaddr->sun_family = AF_UNIX;
                strlcpy(sunaddr->sun_path, name, sizeof(sunaddr->sun_path));
                cctx->aitop = ai;
        } else {
                memset(&hints, 0, sizeof(hints));
                hints.ai_family = ssh->chanctxt->IPv4or6;
                hints.ai_socktype = socktype;
                snprintf(strport, sizeof strport, "%d", port);
                if ((gaierr = getaddrinfo(name, strport, &hints, &cctx->aitop))
                    != 0) {
                        if (errmsg != NULL)
                                *errmsg = ssh_gai_strerror(gaierr);
                        if (reason != NULL)
                                *reason = SSH2_OPEN_CONNECT_FAILED;
                        error("connect_to %.100s: unknown host (%s)", name,
                            ssh_gai_strerror(gaierr));
                        return -1;
                }
        }

        cctx->host = xstrdup(name);
        cctx->port = port;
        cctx->ai = cctx->aitop;

        if ((sock = connect_next(cctx)) == -1) {
                error("connect to %.100s port %d failed: %s",
                    name, port, strerror(errno));
                return -1;
        }

        return sock;
}

/* Return CONNECTING channel to remote host:port or local socket path */
static Channel *
connect_to(struct ssh *ssh, const char *host, int port,
    char *ctype, char *rname)
{
        struct channel_connect cctx;
        Channel *c;
        int sock;

        memset(&cctx, 0, sizeof(cctx));
        sock = connect_to_helper(ssh, host, port, SOCK_STREAM, ctype, rname,
            &cctx, NULL, NULL);
        if (sock == -1) {
                channel_connect_ctx_free(&cctx);
                return NULL;
        }
        c = channel_new(ssh, ctype, SSH_CHANNEL_CONNECTING, sock, sock, -1,
            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
        c->host_port = port;
        c->path = xstrdup(host);
        c->connect_ctx = cctx;

        return c;
}

/*
 * returns either the newly connected channel or the downstream channel
 * that needs to deal with this connection.
 */
Channel *
channel_connect_by_listen_address(struct ssh *ssh, const char *listen_host,
    u_short listen_port, char *ctype, char *rname)
{
        struct ssh_channels *sc = ssh->chanctxt;
        u_int i;
        ForwardPermission *fp;

        for (i = 0; i < sc->num_permitted_opens; i++) {
                fp = &sc->permitted_opens[i];
                if (open_listen_match_tcpip(fp, listen_host, listen_port, 1)) {
                        if (fp->downstream)
                                return fp->downstream;
                        if (fp->port_to_connect == 0)
                                return rdynamic_connect_prepare(ssh,
                                    ctype, rname);
                        return connect_to(ssh,
                            fp->host_to_connect, fp->port_to_connect,
                            ctype, rname);
                }
        }
        error("WARNING: Server requests forwarding for unknown listen_port %d",
            listen_port);
        return NULL;
}

Channel *
channel_connect_by_listen_path(struct ssh *ssh, const char *path,
    char *ctype, char *rname)
{
        struct ssh_channels *sc = ssh->chanctxt;
        u_int i;
        ForwardPermission *fp;

        for (i = 0; i < sc->num_permitted_opens; i++) {
                fp = &sc->permitted_opens[i];
                if (open_listen_match_streamlocal(fp, path)) {
                        return connect_to(ssh,
                            fp->host_to_connect, fp->port_to_connect,
                            ctype, rname);
                }
        }
        error("WARNING: Server requests forwarding for unknown path %.100s",
            path);
        return NULL;
}

/* Check if connecting to that port is permitted and connect. */
Channel *
channel_connect_to_port(struct ssh *ssh, const char *host, u_short port,
    char *ctype, char *rname, int *reason, const char **errmsg)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct channel_connect cctx;
        Channel *c;
        u_int i, permit, permit_adm = 1;
        int sock;
        ForwardPermission *fp;

        permit = sc->all_opens_permitted;
        if (!permit) {
                for (i = 0; i < sc->num_permitted_opens; i++) {
                        fp = &sc->permitted_opens[i];
                        if (open_match(fp, host, port)) {
                                permit = 1;
                                break;
                        }
                }
        }

        if (sc->num_adm_permitted_opens > 0) {
                permit_adm = 0;
                for (i = 0; i < sc->num_adm_permitted_opens; i++) {
                        fp = &sc->permitted_adm_opens[i];
                        if (open_match(fp, host, port)) {
                                permit_adm = 1;
                                break;
                        }
                }
        }

        if (!permit || !permit_adm) {
                logit("Received request to connect to host %.100s port %d, "
                    "but the request was denied.", host, port);
                if (reason != NULL)
                        *reason = SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED;
                return NULL;
        }

        memset(&cctx, 0, sizeof(cctx));
        sock = connect_to_helper(ssh, host, port, SOCK_STREAM, ctype, rname,
            &cctx, reason, errmsg);
        if (sock == -1) {
                channel_connect_ctx_free(&cctx);
                return NULL;
        }

        c = channel_new(ssh, ctype, SSH_CHANNEL_CONNECTING, sock, sock, -1,
            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
        c->host_port = port;
        c->path = xstrdup(host);
        c->connect_ctx = cctx;

        return c;
}

/* Check if connecting to that path is permitted and connect. */
Channel *
channel_connect_to_path(struct ssh *ssh, const char *path,
    char *ctype, char *rname)
{
        struct ssh_channels *sc = ssh->chanctxt;
        u_int i, permit, permit_adm = 1;
        ForwardPermission *fp;

        permit = sc->all_opens_permitted;
        if (!permit) {
                for (i = 0; i < sc->num_permitted_opens; i++) {
                        fp = &sc->permitted_opens[i];
                        if (open_match(fp, path, PORT_STREAMLOCAL)) {
                                permit = 1;
                                break;
                        }
                }
        }

        if (sc->num_adm_permitted_opens > 0) {
                permit_adm = 0;
                for (i = 0; i < sc->num_adm_permitted_opens; i++) {
                        fp = &sc->permitted_adm_opens[i];
                        if (open_match(fp, path, PORT_STREAMLOCAL)) {
                                permit_adm = 1;
                                break;
                        }
                }
        }

        if (!permit || !permit_adm) {
                logit("Received request to connect to path %.100s, "
                    "but the request was denied.", path);
                return NULL;
        }
        return connect_to(ssh, path, PORT_STREAMLOCAL, ctype, rname);
}

void
channel_send_window_changes(struct ssh *ssh)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct winsize ws;
        int r;
        u_int i;

        for (i = 0; i < sc->channels_alloc; i++) {
                if (sc->channels[i] == NULL || !sc->channels[i]->client_tty ||
                    sc->channels[i]->type != SSH_CHANNEL_OPEN)
                        continue;
                if (ioctl(sc->channels[i]->rfd, TIOCGWINSZ, &ws) < 0)
                        continue;
                channel_request_start(ssh, i, "window-change", 0);
                if ((r = sshpkt_put_u32(ssh, (u_int)ws.ws_col)) != 0 ||
                    (r = sshpkt_put_u32(ssh, (u_int)ws.ws_row)) != 0 ||
                    (r = sshpkt_put_u32(ssh, (u_int)ws.ws_xpixel)) != 0 ||
                    (r = sshpkt_put_u32(ssh, (u_int)ws.ws_ypixel)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0)
                        fatal("%s: channel %u: send window-change: %s",
                            __func__, i, ssh_err(r));
        }
}

/* Return RDYNAMIC_OPEN channel: channel allows SOCKS, but is not connected */
static Channel *
rdynamic_connect_prepare(struct ssh *ssh, char *ctype, char *rname)
{
        Channel *c;
        int r;

        c = channel_new(ssh, ctype, SSH_CHANNEL_RDYNAMIC_OPEN, -1, -1, -1,
            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
        c->host_port = 0;
        c->path = NULL;

        /*
         * We need to open the channel before we have a FD,
         * so that we can get SOCKS header from peer.
         */
        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_OPEN_CONFIRMATION)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0) {
                fatal("%s: channel %i: confirm: %s", __func__,
                    c->self, ssh_err(r));
        }
        return c;
}

/* Return CONNECTING socket to remote host:port or local socket path */
static int
rdynamic_connect_finish(struct ssh *ssh, Channel *c)
{
        struct channel_connect cctx;
        int sock;

        memset(&cctx, 0, sizeof(cctx));
        sock = connect_to_helper(ssh, c->path, c->host_port, SOCK_STREAM, NULL,
            NULL, &cctx, NULL, NULL);
        if (sock == -1)
                channel_connect_ctx_free(&cctx);
        else {
                /* similar to SSH_CHANNEL_CONNECTING but we've already sent the open */
                c->type = SSH_CHANNEL_RDYNAMIC_FINISH;
                c->connect_ctx = cctx;
                channel_register_fds(ssh, c, sock, sock, -1, 0, 1, 0);
        }
        return sock;
}

/* -- X11 forwarding */

/*
 * Creates an internet domain socket for listening for X11 connections.
 * Returns 0 and a suitable display number for the DISPLAY variable
 * stored in display_numberp , or -1 if an error occurs.
 */
int
x11_create_display_inet(struct ssh *ssh, int x11_display_offset,
    int x11_use_localhost, int single_connection,
    u_int *display_numberp, int **chanids)
{
        Channel *nc = NULL;
        int display_number, sock;
        u_short port;
        struct addrinfo hints, *ai, *aitop;
        char strport[NI_MAXSERV];
        int gaierr, n, num_socks = 0, socks[NUM_SOCKS];

        if (chanids == NULL)
                return -1;

        for (display_number = x11_display_offset;
            display_number < MAX_DISPLAYS;
            display_number++) {
                port = 6000 + display_number;
                memset(&hints, 0, sizeof(hints));
                hints.ai_family = ssh->chanctxt->IPv4or6;
                hints.ai_flags = x11_use_localhost ? 0: AI_PASSIVE;
                hints.ai_socktype = SOCK_STREAM;
                snprintf(strport, sizeof strport, "%d", port);
                if ((gaierr = getaddrinfo(NULL, strport,
                    &hints, &aitop)) != 0) {
                        error("getaddrinfo: %.100s", ssh_gai_strerror(gaierr));
                        return -1;
                }
                for (ai = aitop; ai; ai = ai->ai_next) {
                        if (ai->ai_family != AF_INET &&
                            ai->ai_family != AF_INET6)
                                continue;
                        sock = socket(ai->ai_family, ai->ai_socktype,
                            ai->ai_protocol);
                        if (sock < 0) {
                                if ((errno != EINVAL) && (errno != EAFNOSUPPORT)
#ifdef EPFNOSUPPORT
                                    && (errno != EPFNOSUPPORT)
#endif 
                                    ) {
                                        error("socket: %.100s", strerror(errno));
                                        freeaddrinfo(aitop);
                                        return -1;
                                } else {
                                        debug("x11_create_display_inet: Socket family %d not supported",
                                                 ai->ai_family);
                                        continue;
                                }
                        }
                        if (ai->ai_family == AF_INET6)
                                sock_set_v6only(sock);
                        if (x11_use_localhost)
                                channel_set_reuseaddr(sock);
                        if (bind(sock, ai->ai_addr, ai->ai_addrlen) < 0) {
                                debug2("%s: bind port %d: %.100s", __func__,
                                    port, strerror(errno));
                                close(sock);
                                for (n = 0; n < num_socks; n++)
                                        close(socks[n]);
                                num_socks = 0;
                                break;
                        }
                        socks[num_socks++] = sock;
                        if (num_socks == NUM_SOCKS)
                                break;
                }
                freeaddrinfo(aitop);
                if (num_socks > 0)
                        break;
        }
        if (display_number >= MAX_DISPLAYS) {
                error("Failed to allocate internet-domain X11 display socket.");
                return -1;
        }
        /* Start listening for connections on the socket. */
        for (n = 0; n < num_socks; n++) {
                sock = socks[n];
                if (listen(sock, SSH_LISTEN_BACKLOG) < 0) {
                        error("listen: %.100s", strerror(errno));
                        close(sock);
                        return -1;
                }
        }

        /* Allocate a channel for each socket. */
        *chanids = xcalloc(num_socks + 1, sizeof(**chanids));
        for (n = 0; n < num_socks; n++) {
                sock = socks[n];
                nc = channel_new(ssh, "x11 listener",
                    SSH_CHANNEL_X11_LISTENER, sock, sock, -1,
                    CHAN_X11_WINDOW_DEFAULT, CHAN_X11_PACKET_DEFAULT,
                    0, "X11 inet listener", 1);
                nc->single_connection = single_connection;
                (*chanids)[n] = nc->self;
        }
        (*chanids)[n] = -1;

        /* Return the display number for the DISPLAY environment variable. */
        *display_numberp = display_number;
        return 0;
}

static int
connect_local_xsocket_path(const char *pathname)
{
        int sock;
        struct sockaddr_un addr;

        sock = socket(AF_UNIX, SOCK_STREAM, 0);
        if (sock < 0)
                error("socket: %.100s", strerror(errno));
        memset(&addr, 0, sizeof(addr));
        addr.sun_family = AF_UNIX;
        strlcpy(addr.sun_path, pathname, sizeof addr.sun_path);
        if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) == 0)
                return sock;
        close(sock);
        error("connect %.100s: %.100s", addr.sun_path, strerror(errno));
        return -1;
}

static int
connect_local_xsocket(u_int dnr)
{
        char buf[1024];
        snprintf(buf, sizeof buf, _PATH_UNIX_X, dnr);
        return connect_local_xsocket_path(buf);
}

#ifdef __APPLE__
static int
is_path_to_xsocket(const char *display, char *path, size_t pathlen)
{
        struct stat sbuf;

        if (strlcpy(path, display, pathlen) >= pathlen) {
                error("%s: display path too long", __func__);
                return 0;
        }
        if (display[0] != '/')
                return 0;
        if (stat(path, &sbuf) == 0) {
                return 1;
        } else {
                char *dot = strrchr(path, '.');
                if (dot != NULL) {
                        *dot = '\0';
                        if (stat(path, &sbuf) == 0) {
                                return 1;
                        }
                }
        }
        return 0;
}
#endif

int
x11_connect_display(struct ssh *ssh)
{
        u_int display_number;
        const char *display;
        char buf[1024], *cp;
        struct addrinfo hints, *ai, *aitop;
        char strport[NI_MAXSERV];
        int gaierr, sock = 0;

        /* Try to open a socket for the local X server. */
        display = getenv("DISPLAY");
        if (!display) {
                error("DISPLAY not set.");
                return -1;
        }
        /*
         * Now we decode the value of the DISPLAY variable and make a
         * connection to the real X server.
         */

#ifdef __APPLE__
        /* Check if display is a path to a socket (as set by launchd). */
        {
                char path[PATH_MAX];

                if (is_path_to_xsocket(display, path, sizeof(path))) {
                        debug("x11_connect_display: $DISPLAY is launchd");

                        /* Create a socket. */
                        sock = connect_local_xsocket_path(path);
                        if (sock < 0)
                                return -1;

                        /* OK, we now have a connection to the display. */
                        return sock;
                }
        }
#endif
        /*
         * Check if it is a unix domain socket.  Unix domain displays are in
         * one of the following formats: unix:d[.s], :d[.s], ::d[.s]
         */
        if (strncmp(display, "unix:", 5) == 0 ||
            display[0] == ':') {
                /* Connect to the unix domain socket. */
                if (sscanf(strrchr(display, ':') + 1, "%u",
                    &display_number) != 1) {
                        error("Could not parse display number from DISPLAY: "
                            "%.100s", display);
                        return -1;
                }
                /* Create a socket. */
                sock = connect_local_xsocket(display_number);
                if (sock < 0)
                        return -1;

                /* OK, we now have a connection to the display. */
                return sock;
        }
        /*
         * Connect to an inet socket.  The DISPLAY value is supposedly
         * hostname:d[.s], where hostname may also be numeric IP address.
         */
        strlcpy(buf, display, sizeof(buf));
        cp = strchr(buf, ':');
        if (!cp) {
                error("Could not find ':' in DISPLAY: %.100s", display);
                return -1;
        }
        *cp = 0;
        /*
         * buf now contains the host name.  But first we parse the
         * display number.
         */
        if (sscanf(cp + 1, "%u", &display_number) != 1) {
                error("Could not parse display number from DISPLAY: %.100s",
                    display);
                return -1;
        }

        /* Look up the host address */
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = ssh->chanctxt->IPv4or6;
        hints.ai_socktype = SOCK_STREAM;
        snprintf(strport, sizeof strport, "%u", 6000 + display_number);
        if ((gaierr = getaddrinfo(buf, strport, &hints, &aitop)) != 0) {
                error("%.100s: unknown host. (%s)", buf,
                ssh_gai_strerror(gaierr));
                return -1;
        }
        for (ai = aitop; ai; ai = ai->ai_next) {
                /* Create a socket. */
                sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
                if (sock < 0) {
                        debug2("socket: %.100s", strerror(errno));
                        continue;
                }
                /* Connect it to the display. */
                if (connect(sock, ai->ai_addr, ai->ai_addrlen) < 0) {
                        debug2("connect %.100s port %u: %.100s", buf,
                            6000 + display_number, strerror(errno));
                        close(sock);
                        continue;
                }
                /* Success */
                break;
        }
        freeaddrinfo(aitop);
        if (!ai) {
                error("connect %.100s port %u: %.100s", buf,
                    6000 + display_number, strerror(errno));
                return -1;
        }
        set_nodelay(sock);
        return sock;
}

/*
 * Requests forwarding of X11 connections, generates fake authentication
 * data, and enables authentication spoofing.
 * This should be called in the client only.
 */
void
x11_request_forwarding_with_spoofing(struct ssh *ssh, int client_session_id,
    const char *disp, const char *proto, const char *data, int want_reply)
{
        struct ssh_channels *sc = ssh->chanctxt;
        u_int data_len = (u_int) strlen(data) / 2;
        u_int i, value;
        const char *cp;
        char *new_data;
        int r, screen_number;

        if (sc->x11_saved_display == NULL)
                sc->x11_saved_display = xstrdup(disp);
        else if (strcmp(disp, sc->x11_saved_display) != 0) {
                error("x11_request_forwarding_with_spoofing: different "
                    "$DISPLAY already forwarded");
                return;
        }

        cp = strchr(disp, ':');
        if (cp)
                cp = strchr(cp, '.');
        if (cp)
                screen_number = (u_int)strtonum(cp + 1, 0, 400, NULL);
        else
                screen_number = 0;

        if (sc->x11_saved_proto == NULL) {
                /* Save protocol name. */
                sc->x11_saved_proto = xstrdup(proto);

                /* Extract real authentication data. */
                sc->x11_saved_data = xmalloc(data_len);
                for (i = 0; i < data_len; i++) {
                        if (sscanf(data + 2 * i, "%2x", &value) != 1)
                                fatal("x11_request_forwarding: bad "
                                    "authentication data: %.100s", data);
                        sc->x11_saved_data[i] = value;
                }
                sc->x11_saved_data_len = data_len;

                /* Generate fake data of the same length. */
                sc->x11_fake_data = xmalloc(data_len);
                arc4random_buf(sc->x11_fake_data, data_len);
                sc->x11_fake_data_len = data_len;
        }

        /* Convert the fake data into hex. */
        new_data = tohex(sc->x11_fake_data, data_len);

        /* Send the request packet. */
        channel_request_start(ssh, client_session_id, "x11-req", want_reply);
        if ((r = sshpkt_put_u8(ssh, 0)) != 0 || /* bool: single connection */
            (r = sshpkt_put_cstring(ssh, proto)) != 0 ||
            (r = sshpkt_put_cstring(ssh, new_data)) != 0 ||
            (r = sshpkt_put_u32(ssh, screen_number)) != 0 ||
            (r = sshpkt_send(ssh)) != 0 ||
            (r = ssh_packet_write_wait(ssh)) != 0)
                fatal("%s: send x11-req: %s", __func__, ssh_err(r));
        free(new_data);
}