dropbear: update to 2013.62

[tomato.git] / release / src / router / dropbear / common-channel.c

/*
 * Dropbear SSH
 * 
 * Copyright (c) 2002-2004 Matt Johnston
 * All rights reserved.
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE. */

/* Handle the multiplexed channels, such as sessions, x11, agent connections */

#include "includes.h"
#include "session.h"
#include "packet.h"
#include "ssh.h"
#include "buffer.h"
#include "circbuffer.h"
#include "dbutil.h"
#include "channel.h"
#include "ssh.h"
#include "listener.h"
#include "runopts.h"

static void send_msg_channel_open_failure(unsigned int remotechan, int reason,
                const unsigned char *text, const unsigned char *lang);
static void send_msg_channel_open_confirmation(struct Channel* channel,
                unsigned int recvwindow, 
                unsigned int recvmaxpacket);
static void writechannel(struct Channel* channel, int fd, circbuffer *cbuf);
static void send_msg_channel_window_adjust(struct Channel *channel, 
                unsigned int incr);
static void send_msg_channel_data(struct Channel *channel, int isextended);
static void send_msg_channel_eof(struct Channel *channel);
static void send_msg_channel_close(struct Channel *channel);
static void remove_channel(struct Channel *channel);
static void check_in_progress(struct Channel *channel);
static unsigned int write_pending(struct Channel * channel);
static void check_close(struct Channel *channel);
static void close_chan_fd(struct Channel *channel, int fd, int how);

#define FD_UNINIT (-2)
#define FD_CLOSED (-1)

#define ERRFD_IS_READ(channel) ((channel)->extrabuf == NULL)
#define ERRFD_IS_WRITE(channel) (!ERRFD_IS_READ(channel))

/* Initialise all the channels */
void chaninitialise(const struct ChanType *chantypes[]) {

        /* may as well create space for a single channel */
        ses.channels = (struct Channel**)m_malloc(sizeof(struct Channel*));
        ses.chansize = 1;
        ses.channels[0] = NULL;
        ses.chancount = 0;

        ses.chantypes = chantypes;

#ifdef USING_LISTENERS
        listeners_initialise();
#endif

}

/* Clean up channels, freeing allocated memory */
void chancleanup() {

        unsigned int i;

        TRACE(("enter chancleanup"))
        for (i = 0; i < ses.chansize; i++) {
                if (ses.channels[i] != NULL) {
                        TRACE(("channel %d closing", i))
                        remove_channel(ses.channels[i]);
                }
        }
        m_free(ses.channels);
        TRACE(("leave chancleanup"))
}

static void
chan_initwritebuf(struct Channel *channel)
{
        dropbear_assert(channel->writebuf->size == 0 && channel->recvwindow == 0);
        cbuf_free(channel->writebuf);
        channel->writebuf = cbuf_new(opts.recv_window);
        channel->recvwindow = opts.recv_window;
}

/* Create a new channel entry, send a reply confirm or failure */
/* If remotechan, transwindow and transmaxpacket are not know (for a new
 * outgoing connection, with them to be filled on confirmation), they should
 * all be set to 0 */
static struct Channel* newchannel(unsigned int remotechan, 
                const struct ChanType *type, 
                unsigned int transwindow, unsigned int transmaxpacket) {

        struct Channel * newchan;
        unsigned int i, j;

        TRACE(("enter newchannel"))
        
        /* first see if we can use existing channels */
        for (i = 0; i < ses.chansize; i++) {
                if (ses.channels[i] == NULL) {
                        break;
                }
        }

        /* otherwise extend the list */
        if (i == ses.chansize) {
                if (ses.chansize >= MAX_CHANNELS) {
                        TRACE(("leave newchannel: max chans reached"))
                        return NULL;
                }

                /* extend the channels */
                ses.channels = (struct Channel**)m_realloc(ses.channels,
                                (ses.chansize+CHAN_EXTEND_SIZE)*sizeof(struct Channel*));

                ses.chansize += CHAN_EXTEND_SIZE;

                /* set the new channels to null */
                for (j = i; j < ses.chansize; j++) {
                        ses.channels[j] = NULL;
                }

        }
        
        newchan = (struct Channel*)m_malloc(sizeof(struct Channel));
        newchan->type = type;
        newchan->index = i;
        newchan->sent_close = newchan->recv_close = 0;
        newchan->sent_eof = newchan->recv_eof = 0;
        newchan->close_handler_done = 0;

        newchan->remotechan = remotechan;
        newchan->transwindow = transwindow;
        newchan->transmaxpacket = transmaxpacket;
        
        newchan->typedata = NULL;
        newchan->writefd = FD_UNINIT;
        newchan->readfd = FD_UNINIT;
        newchan->errfd = FD_CLOSED; /* this isn't always set to start with */
        newchan->initconn = 0;
        newchan->await_open = 0;
        newchan->flushing = 0;

        newchan->writebuf = cbuf_new(0); /* resized later by chan_initwritebuf */
        newchan->recvwindow = 0;

        newchan->extrabuf = NULL; /* The user code can set it up */
        newchan->recvdonelen = 0;
        newchan->recvmaxpacket = RECV_MAX_PAYLOAD_LEN;

        ses.channels[i] = newchan;
        ses.chancount++;

        TRACE(("leave newchannel"))

        return newchan;
}

/* Returns the channel structure corresponding to the channel in the current
 * data packet (ses.payload must be positioned appropriately).
 * A valid channel is always returns, it will fail fatally with an unknown
 * channel */
static struct Channel* getchannel_msg(const char* kind) {

        unsigned int chan;

        chan = buf_getint(ses.payload);
        if (chan >= ses.chansize || ses.channels[chan] == NULL) {
                if (kind) {
                        dropbear_exit("%s for unknown channel %d", kind, chan);
                } else {
                        dropbear_exit("Unknown channel %d", chan);
                }
        }
        return ses.channels[chan];
}

struct Channel* getchannel() {
        return getchannel_msg(NULL);
}

/* Iterate through the channels, performing IO if available */
void channelio(fd_set *readfds, fd_set *writefds) {

        struct Channel *channel;
        unsigned int i;

        /* foreach channel */
        for (i = 0; i < ses.chansize; i++) {

                channel = ses.channels[i];
                if (channel == NULL) {
                        /* only process in-use channels */
                        continue;
                }

                /* read data and send it over the wire */
                if (channel->readfd >= 0 && FD_ISSET(channel->readfd, readfds)) {
                        TRACE(("send normal readfd"))
                        send_msg_channel_data(channel, 0);
                }

                /* read stderr data and send it over the wire */
                if (ERRFD_IS_READ(channel) && channel->errfd >= 0 
                        && FD_ISSET(channel->errfd, readfds)) {
                                TRACE(("send normal errfd"))
                                send_msg_channel_data(channel, 1);
                }

                /* write to program/pipe stdin */
                if (channel->writefd >= 0 && FD_ISSET(channel->writefd, writefds)) {
                        if (channel->initconn) {
                                /* XXX should this go somewhere cleaner? */
                                check_in_progress(channel);
                                continue; /* Important not to use the channel after
                                                         check_in_progress(), as it may be NULL */
                        }
                        writechannel(channel, channel->writefd, channel->writebuf);
                }
                
                /* stderr for client mode */
                if (ERRFD_IS_WRITE(channel)
                                && channel->errfd >= 0 && FD_ISSET(channel->errfd, writefds)) {
                        writechannel(channel, channel->errfd, channel->extrabuf);
                }
        
                /* handle any channel closing etc */
                check_close(channel);

        }

        /* Listeners such as TCP, X11, agent-auth */
#ifdef USING_LISTENERS
        handle_listeners(readfds);
#endif
}


/* Returns true if there is data remaining to be written to stdin or
 * stderr of a channel's endpoint. */
static unsigned int write_pending(struct Channel * channel) {

        if (channel->writefd >= 0 && cbuf_getused(channel->writebuf) > 0) {
                return 1;
        } else if (channel->errfd >= 0 && channel->extrabuf && 
                        cbuf_getused(channel->extrabuf) > 0) {
                return 1;
        }
        return 0;
}


/* EOF/close handling */
static void check_close(struct Channel *channel) {
        int close_allowed = 0;

        TRACE2(("check_close: writefd %d, readfd %d, errfd %d, sent_close %d, recv_close %d",
                                channel->writefd, channel->readfd,
                                channel->errfd, channel->sent_close, channel->recv_close))
        TRACE2(("writebuf size %d extrabuf size %d",
                                channel->writebuf ? cbuf_getused(channel->writebuf) : 0,
                                channel->extrabuf ? cbuf_getused(channel->extrabuf) : 0))

        if (!channel->flushing 
                && !channel->close_handler_done
                && channel->type->check_close
                && channel->type->check_close(channel))
        {
                channel->flushing = 1;
        }
        
        /* if a type-specific check_close is defined we will only exit
           once that has been triggered. this is only used for a server "session"
           channel, to ensure that the shell has exited (and the exit status 
           retrieved) before we close things up. */
        if (!channel->type->check_close 
                || channel->close_handler_done
                || channel->type->check_close(channel)) {
                close_allowed = 1;
        }

        if (channel->recv_close && !write_pending(channel) && close_allowed) {
                if (!channel->sent_close) {
                        TRACE(("Sending MSG_CHANNEL_CLOSE in response to same."))
                        send_msg_channel_close(channel);
                }
                remove_channel(channel);
                return;
        }

        if ((channel->recv_eof && !write_pending(channel))
                /* have a server "session" and child has exited */
                || (channel->type->check_close && close_allowed)) {
                close_chan_fd(channel, channel->writefd, SHUT_WR);
        }

        /* Special handling for flushing read data after an exit. We
           read regardless of whether the select FD was set,
           and if there isn't data available, the channel will get closed. */
        if (channel->flushing) {
                TRACE(("might send data, flushing"))
                if (channel->readfd >= 0 && channel->transwindow > 0) {
                        TRACE(("send data readfd"))
                        send_msg_channel_data(channel, 0);
                }
                if (ERRFD_IS_READ(channel) && channel->errfd >= 0 
                        && channel->transwindow > 0) {
                        TRACE(("send data errfd"))
                        send_msg_channel_data(channel, 1);
                }
        }

        /* If we're not going to send any more data, send EOF */
        if (!channel->sent_eof
                        && channel->readfd == FD_CLOSED 
                        && (ERRFD_IS_WRITE(channel) || channel->errfd == FD_CLOSED)) {
                send_msg_channel_eof(channel);
        }

        /* And if we can't receive any more data from them either, close up */
        if (channel->readfd == FD_CLOSED
                        && channel->writefd == FD_CLOSED
                        && (ERRFD_IS_WRITE(channel) || channel->errfd == FD_CLOSED)
                        && !channel->sent_close
                        && close_allowed
                        && !write_pending(channel)) {
                TRACE(("sending close, readfd is closed"))
                send_msg_channel_close(channel);
        }
}

/* Check whether a deferred (EINPROGRESS) connect() was successful, and
 * if so, set up the channel properly. Otherwise, the channel is cleaned up, so
 * it is important that the channel reference isn't used after a call to this
 * function */
static void check_in_progress(struct Channel *channel) {

        int val;
        socklen_t vallen = sizeof(val);

        TRACE(("enter check_in_progress"))

        if (getsockopt(channel->writefd, SOL_SOCKET, SO_ERROR, &val, &vallen)
                        || val != 0) {
                send_msg_channel_open_failure(channel->remotechan,
                                SSH_OPEN_CONNECT_FAILED, "", "");
                close(channel->writefd);
                remove_channel(channel);
                TRACE(("leave check_in_progress: fail"))
        } else {
                chan_initwritebuf(channel);
                send_msg_channel_open_confirmation(channel, channel->recvwindow,
                                channel->recvmaxpacket);
                channel->readfd = channel->writefd;
                channel->initconn = 0;
                TRACE(("leave check_in_progress: success"))
        }
}


/* Send the close message and set the channel as closed */
static void send_msg_channel_close(struct Channel *channel) {

        TRACE(("enter send_msg_channel_close %p", channel))
        if (channel->type->closehandler 
                        && !channel->close_handler_done) {
                channel->type->closehandler(channel);
                channel->close_handler_done = 1;
        }
        
        CHECKCLEARTOWRITE();

        buf_putbyte(ses.writepayload, SSH_MSG_CHANNEL_CLOSE);
        buf_putint(ses.writepayload, channel->remotechan);

        encrypt_packet();

        channel->sent_eof = 1;
        channel->sent_close = 1;
        close_chan_fd(channel, channel->readfd, SHUT_RD);
        close_chan_fd(channel, channel->errfd, SHUT_RDWR);
        close_chan_fd(channel, channel->writefd, SHUT_WR);
        TRACE(("leave send_msg_channel_close"))
}

/* call this when trans/eof channels are closed */
static void send_msg_channel_eof(struct Channel *channel) {

        TRACE(("enter send_msg_channel_eof"))
        CHECKCLEARTOWRITE();

        buf_putbyte(ses.writepayload, SSH_MSG_CHANNEL_EOF);
        buf_putint(ses.writepayload, channel->remotechan);

        encrypt_packet();

        channel->sent_eof = 1;

        TRACE(("leave send_msg_channel_eof"))
}

/* Called to write data out to the local side of the channel. 
 * Only called when we know we can write to a channel, writes as much as
 * possible */
static void writechannel(struct Channel* channel, int fd, circbuffer *cbuf) {

        int len, maxlen;

        TRACE(("enter writechannel fd %d", fd))

        maxlen = cbuf_readlen(cbuf);

        /* Write the data out */
        len = write(fd, cbuf_readptr(cbuf, maxlen), maxlen);
        if (len <= 0) {
                TRACE(("errno %d len %d", errno, len))
                if (len < 0 && errno != EINTR) {
                        close_chan_fd(channel, fd, SHUT_WR);
                }
                TRACE(("leave writechannel: len <= 0"))
                return;
        }
        TRACE(("writechannel wrote %d", len))

        cbuf_incrread(cbuf, len);
        channel->recvdonelen += len;

        /* Window adjust handling */
        if (channel->recvdonelen >= RECV_WINDOWEXTEND) {
                /* Set it back to max window */
                send_msg_channel_window_adjust(channel, channel->recvdonelen);
                channel->recvwindow += channel->recvdonelen;
                channel->recvdonelen = 0;
        }

        dropbear_assert(channel->recvwindow <= opts.recv_window);
        dropbear_assert(channel->recvwindow <= cbuf_getavail(channel->writebuf));
        dropbear_assert(channel->extrabuf == NULL ||
                        channel->recvwindow <= cbuf_getavail(channel->extrabuf));
        
        TRACE(("leave writechannel"))
}

/* Set the file descriptors for the main select in session.c
 * This avoid channels which don't have any window available, are closed, etc*/
void setchannelfds(fd_set *readfds, fd_set *writefds) {
        
        unsigned int i;
        struct Channel * channel;
        
        for (i = 0; i < ses.chansize; i++) {

                channel = ses.channels[i];
                if (channel == NULL) {
                        continue;
                }

                /* Stuff to put over the wire */
                if (channel->transwindow > 0) {

                        if (channel->readfd >= 0) {
                                FD_SET(channel->readfd, readfds);
                        }
                        
                        if (ERRFD_IS_READ(channel) && channel->errfd >= 0) {
                                        FD_SET(channel->errfd, readfds);
                        }
                }

                /* Stuff from the wire */
                if (channel->initconn
                        ||(channel->writefd >= 0 && cbuf_getused(channel->writebuf) > 0)) {
                                FD_SET(channel->writefd, writefds);
                }

                if (ERRFD_IS_WRITE(channel) && channel->errfd >= 0 
                                && cbuf_getused(channel->extrabuf) > 0) {
                                FD_SET(channel->errfd, writefds);
                }

        } /* foreach channel */

#ifdef USING_LISTENERS
        set_listener_fds(readfds);
#endif

}

/* handle the channel EOF event, by closing the channel filedescriptor. The
 * channel isn't closed yet, it is left until the incoming (from the program
 * etc) FD is also EOF */
void recv_msg_channel_eof() {

        struct Channel * channel;

        TRACE(("enter recv_msg_channel_eof"))

        channel = getchannel_msg("EOF");

        channel->recv_eof = 1;

        check_close(channel);
        TRACE(("leave recv_msg_channel_eof"))
}


/* Handle channel closure(), respond in kind and close the channels */
void recv_msg_channel_close() {

        struct Channel * channel;

        TRACE(("enter recv_msg_channel_close"))

        channel = getchannel_msg("Close");

        channel->recv_eof = 1;
        channel->recv_close = 1;

        check_close(channel);
        TRACE(("leave recv_msg_channel_close"))
}

/* Remove a channel entry, this is only executed after both sides have sent
 * channel close */
static void remove_channel(struct Channel * channel) {

        TRACE(("enter remove_channel"))
        TRACE(("channel index is %d", channel->index))

        cbuf_free(channel->writebuf);
        channel->writebuf = NULL;

        if (channel->extrabuf) {
                cbuf_free(channel->extrabuf);
                channel->extrabuf = NULL;
        }


        /* close the FDs in case they haven't been done
         * yet (they might have been shutdown etc) */
        TRACE(("CLOSE writefd %d", channel->writefd))
        close(channel->writefd);
        TRACE(("CLOSE readfd %d", channel->readfd))
        close(channel->readfd);
        TRACE(("CLOSE errfd %d", channel->errfd))
        close(channel->errfd);

        if (!channel->close_handler_done
                && channel->type->closehandler) {
                channel->type->closehandler(channel);
                channel->close_handler_done = 1;
        }

        ses.channels[channel->index] = NULL;
        m_free(channel);
        ses.chancount--;

        TRACE(("leave remove_channel"))
}

/* Handle channel specific requests, passing off to corresponding handlers
 * such as chansession or x11fwd */
void recv_msg_channel_request() {

        struct Channel *channel;

        channel = getchannel();

        TRACE(("enter recv_msg_channel_request %p", channel))

        if (channel->sent_close) {
                TRACE(("leave recv_msg_channel_request: already closed channel"))
                return;
        }

        if (channel->type->reqhandler 
                        && !channel->close_handler_done) {
                channel->type->reqhandler(channel);
        } else {
                send_msg_channel_failure(channel);
        }

        TRACE(("leave recv_msg_channel_request"))

}

/* Reads data from the server's program/shell/etc, and puts it in a
 * channel_data packet to send.
 * chan is the remote channel, isextended is 0 if it is normal data, 1
 * if it is extended data. if it is extended, then the type is in
 * exttype */
static void send_msg_channel_data(struct Channel *channel, int isextended) {

        int len;
        size_t maxlen, size_pos;
        int fd;

        CHECKCLEARTOWRITE();

        TRACE(("enter send_msg_channel_data"))
        dropbear_assert(!channel->sent_close);

        if (isextended) {
                fd = channel->errfd;
        } else {
                fd = channel->readfd;
        }
        TRACE(("enter send_msg_channel_data isextended %d fd %d", isextended, fd))
        dropbear_assert(fd >= 0);

        maxlen = MIN(channel->transwindow, channel->transmaxpacket);
        /* -(1+4+4) is SSH_MSG_CHANNEL_DATA, channel number, string length, and 
         * exttype if is extended */
        maxlen = MIN(maxlen, 
                        ses.writepayload->size - 1 - 4 - 4 - (isextended ? 4 : 0));
        TRACE(("maxlen %zd", maxlen))
        if (maxlen == 0) {
                TRACE(("leave send_msg_channel_data: no window"))
                return;
        }

        buf_putbyte(ses.writepayload, 
                        isextended ? SSH_MSG_CHANNEL_EXTENDED_DATA : SSH_MSG_CHANNEL_DATA);
        buf_putint(ses.writepayload, channel->remotechan);
        if (isextended) {
                buf_putint(ses.writepayload, SSH_EXTENDED_DATA_STDERR);
        }
        /* a dummy size first ...*/
        size_pos = ses.writepayload->pos;
        buf_putint(ses.writepayload, 0);

        /* read the data */
        len = read(fd, buf_getwriteptr(ses.writepayload, maxlen), maxlen);

        if (len <= 0) {
                if (len == 0 || errno != EINTR) {
                        /* This will also get hit in the case of EAGAIN. The only
                        time we expect to receive EAGAIN is when we're flushing a FD,
                        in which case it can be treated the same as EOF */
                        close_chan_fd(channel, fd, SHUT_RD);
                }
                buf_setpos(ses.writepayload, 0);
                buf_setlen(ses.writepayload, 0);
                TRACE(("leave send_msg_channel_data: len %d read err %d or EOF for fd %d", 
                                        len, errno, fd))
                return;
        }

        if (channel->read_mangler) {
                channel->read_mangler(channel, buf_getwriteptr(ses.writepayload, len), &len);
                if (len == 0) {
                        buf_setpos(ses.writepayload, 0);
                        buf_setlen(ses.writepayload, 0);
                        return;
                }
        }

        TRACE(("send_msg_channel_data: len %d fd %d", len, fd))
        buf_incrwritepos(ses.writepayload, len);
        /* ... real size here */
        buf_setpos(ses.writepayload, size_pos);
        buf_putint(ses.writepayload, len);

        channel->transwindow -= len;

        encrypt_packet();
        
        /* If we receive less data than we requested when flushing, we've
           reached the equivalent of EOF */
        if (channel->flushing && len < (ssize_t)maxlen)
        {
                TRACE(("closing from channel, flushing out."))
                close_chan_fd(channel, fd, SHUT_RD);
        }
        TRACE(("leave send_msg_channel_data"))
}

/* We receive channel data */
void recv_msg_channel_data() {

        struct Channel *channel;

        channel = getchannel();

        common_recv_msg_channel_data(channel, channel->writefd, channel->writebuf);
}

/* Shared for data and stderr data - when we receive data, put it in a buffer
 * for writing to the local file descriptor */
void common_recv_msg_channel_data(struct Channel *channel, int fd, 
                circbuffer * cbuf) {

        unsigned int datalen;
        unsigned int maxdata;
        unsigned int buflen;
        unsigned int len;

        TRACE(("enter recv_msg_channel_data"))

        if (channel->recv_eof) {
                dropbear_exit("Received data after eof");
        }

        if (fd < 0 || !cbuf) {
                /* If we have encountered failed write, the far side might still
                 * be sending data without having yet received our close notification.
                 * We just drop the data. */
                return;
        }

        datalen = buf_getint(ses.payload);
        TRACE(("length %d", datalen))

        maxdata = cbuf_getavail(cbuf);

        /* Whilst the spec says we "MAY ignore data past the end" this could
         * lead to corrupted file transfers etc (chunks missed etc). It's better to
         * just die horribly */
        if (datalen > maxdata) {
                dropbear_exit("Oversized packet");
        }

        /* We may have to run throught twice, if the buffer wraps around. Can't
         * just "leave it for next time" like with writechannel, since this
         * is payload data */
        len = datalen;
        while (len > 0) {
                buflen = cbuf_writelen(cbuf);
                buflen = MIN(buflen, len);

                memcpy(cbuf_writeptr(cbuf, buflen), 
                                buf_getptr(ses.payload, buflen), buflen);
                cbuf_incrwrite(cbuf, buflen);
                buf_incrpos(ses.payload, buflen);
                len -= buflen;
        }

        dropbear_assert(channel->recvwindow >= datalen);
        channel->recvwindow -= datalen;
        dropbear_assert(channel->recvwindow <= opts.recv_window);

        TRACE(("leave recv_msg_channel_data"))
}

/* Increment the outgoing data window for a channel - the remote end limits
 * the amount of data which may be transmitted, this window is decremented
 * as data is sent, and incremented upon receiving window-adjust messages */
void recv_msg_channel_window_adjust() {

        struct Channel * channel;
        unsigned int incr;
        
        channel = getchannel();
        
        incr = buf_getint(ses.payload);
        TRACE(("received window increment %d", incr))
        incr = MIN(incr, TRANS_MAX_WIN_INCR);
        
        channel->transwindow += incr;
        channel->transwindow = MIN(channel->transwindow, TRANS_MAX_WINDOW);

}

/* Increment the incoming data window for a channel, and let the remote
 * end know */
static void send_msg_channel_window_adjust(struct Channel* channel, 
                unsigned int incr) {

        TRACE(("sending window adjust %d", incr))
        CHECKCLEARTOWRITE();

        buf_putbyte(ses.writepayload, SSH_MSG_CHANNEL_WINDOW_ADJUST);
        buf_putint(ses.writepayload, channel->remotechan);
        buf_putint(ses.writepayload, incr);

        encrypt_packet();
}
        
/* Handle a new channel request, performing any channel-type-specific setup */
void recv_msg_channel_open() {

        unsigned char *type;
        unsigned int typelen;
        unsigned int remotechan, transwindow, transmaxpacket;
        struct Channel *channel;
        const struct ChanType **cp;
        const struct ChanType *chantype;
        unsigned int errtype = SSH_OPEN_UNKNOWN_CHANNEL_TYPE;
        int ret;


        TRACE(("enter recv_msg_channel_open"))

        /* get the packet contents */
        type = buf_getstring(ses.payload, &typelen);

        remotechan = buf_getint(ses.payload);
        transwindow = buf_getint(ses.payload);
        transwindow = MIN(transwindow, TRANS_MAX_WINDOW);
        transmaxpacket = buf_getint(ses.payload);
        transmaxpacket = MIN(transmaxpacket, TRANS_MAX_PAYLOAD_LEN);

        /* figure what type of packet it is */
        if (typelen > MAX_NAME_LEN) {
                goto failure;
        }

        /* Get the channel type. Client and server style invokation will set up a
         * different list for ses.chantypes at startup. We just iterate through
         * this list and find the matching name */
        for (cp = &ses.chantypes[0], chantype = (*cp); 
                        chantype != NULL;
                        cp++, chantype = (*cp)) {
                if (strcmp(type, chantype->name) == 0) {
                        break;
                }
        }

        if (chantype == NULL) {
                TRACE(("No matching type for '%s'", type))
                goto failure;
        }

        TRACE(("matched type '%s'", type))

        /* create the channel */
        channel = newchannel(remotechan, chantype, transwindow, transmaxpacket);

        if (channel == NULL) {
                TRACE(("newchannel returned NULL"))
                goto failure;
        }

        if (channel->type->inithandler) {
                ret = channel->type->inithandler(channel);
                if (ret == SSH_OPEN_IN_PROGRESS) {
                        /* We'll send the confirmation later */
                        goto cleanup;
                }
                if (ret > 0) {
                        errtype = ret;
                        remove_channel(channel);
                        TRACE(("inithandler returned failure %d", ret))
                        goto failure;
                }
        }

        chan_initwritebuf(channel);

        /* success */
        send_msg_channel_open_confirmation(channel, channel->recvwindow,
                        channel->recvmaxpacket);
        goto cleanup;

failure:
        TRACE(("recv_msg_channel_open failure"))
        send_msg_channel_open_failure(remotechan, errtype, "", "");

cleanup:
        m_free(type);

        TRACE(("leave recv_msg_channel_open"))
}

/* Send a failure message */
void send_msg_channel_failure(struct Channel *channel) {

        TRACE(("enter send_msg_channel_failure"))
        CHECKCLEARTOWRITE();

        buf_putbyte(ses.writepayload, SSH_MSG_CHANNEL_FAILURE);
        buf_putint(ses.writepayload, channel->remotechan);

        encrypt_packet();
        TRACE(("leave send_msg_channel_failure"))
}

/* Send a success message */
void send_msg_channel_success(struct Channel *channel) {

        TRACE(("enter send_msg_channel_success"))
        CHECKCLEARTOWRITE();

        buf_putbyte(ses.writepayload, SSH_MSG_CHANNEL_SUCCESS);
        buf_putint(ses.writepayload, channel->remotechan);

        encrypt_packet();
        TRACE(("leave send_msg_channel_success"))
}

/* Send a channel open failure message, with a corresponding reason
 * code (usually resource shortage or unknown chan type) */
static void send_msg_channel_open_failure(unsigned int remotechan, 
                int reason, const unsigned char *text, const unsigned char *lang) {

        TRACE(("enter send_msg_channel_open_failure"))
        CHECKCLEARTOWRITE();
        
        buf_putbyte(ses.writepayload, SSH_MSG_CHANNEL_OPEN_FAILURE);
        buf_putint(ses.writepayload, remotechan);
        buf_putint(ses.writepayload, reason);
        buf_putstring(ses.writepayload, text, strlen((char*)text));
        buf_putstring(ses.writepayload, lang, strlen((char*)lang));

        encrypt_packet();
        TRACE(("leave send_msg_channel_open_failure"))
}

/* Confirm a channel open, and let the remote end know what number we've
 * allocated and the receive parameters */
static void send_msg_channel_open_confirmation(struct Channel* channel,
                unsigned int recvwindow, 
                unsigned int recvmaxpacket) {

        TRACE(("enter send_msg_channel_open_confirmation"))
        CHECKCLEARTOWRITE();

        buf_putbyte(ses.writepayload, SSH_MSG_CHANNEL_OPEN_CONFIRMATION);
        buf_putint(ses.writepayload, channel->remotechan);
        buf_putint(ses.writepayload, channel->index);
        buf_putint(ses.writepayload, recvwindow);
        buf_putint(ses.writepayload, recvmaxpacket);

        encrypt_packet();
        TRACE(("leave send_msg_channel_open_confirmation"))
}

/* close a fd, how is SHUT_RD or SHUT_WR */
static void close_chan_fd(struct Channel *channel, int fd, int how) {

        int closein = 0, closeout = 0;

        if (channel->type->sepfds) {
                TRACE(("SHUTDOWN(%d, %d)", fd, how))
                shutdown(fd, how);
                if (how == 0) {
                        closeout = 1;
                } else {
                        closein = 1;
                }
        } else {
                TRACE(("CLOSE some fd %d", fd))
                close(fd);
                closein = closeout = 1;
        }

        if (closeout && (fd == channel->readfd)) {
                channel->readfd = FD_CLOSED;
        }
        if (closeout && ERRFD_IS_READ(channel) && (fd == channel->errfd)) {
                channel->errfd = FD_CLOSED;
        }

        if (closein && fd == channel->writefd) {
                channel->writefd = FD_CLOSED;
        }
        if (closein && ERRFD_IS_WRITE(channel) && (fd == channel->errfd)) {
                channel->errfd = FD_CLOSED;
        }

        /* if we called shutdown on it and all references are gone, then we 
         * need to close() it to stop it lingering */
        if (channel->type->sepfds && channel->readfd == FD_CLOSED 
                && channel->writefd == FD_CLOSED && channel->errfd == FD_CLOSED) {
                TRACE(("CLOSE (finally) of %d", fd))
                close(fd);
        }
}


#if defined(USING_LISTENERS) || defined(DROPBEAR_CLIENT)
/* Create a new channel, and start the open request. This is intended
 * for X11, agent, tcp forwarding, and should be filled with channel-specific
 * options, with the calling function calling encrypt_packet() after
 * completion. It is mandatory for the caller to encrypt_packet() if
 * DROPBEAR_SUCCESS is returned */
int send_msg_channel_open_init(int fd, const struct ChanType *type) {

        struct Channel* chan;

        TRACE(("enter send_msg_channel_open_init()"))
        chan = newchannel(0, type, 0, 0);
        if (!chan) {
                TRACE(("leave send_msg_channel_open_init() - FAILED in newchannel()"))
                return DROPBEAR_FAILURE;
        }

        /* Outbound opened channels don't make use of in-progress connections,
         * we can set it up straight away */
        chan_initwritebuf(chan);

        /* set fd non-blocking */
        setnonblocking(fd);

        chan->writefd = chan->readfd = fd;
        ses.maxfd = MAX(ses.maxfd, fd);

        chan->await_open = 1;

        /* now open the channel connection */
        CHECKCLEARTOWRITE();

        buf_putbyte(ses.writepayload, SSH_MSG_CHANNEL_OPEN);
        buf_putstring(ses.writepayload, type->name, strlen(type->name));
        buf_putint(ses.writepayload, chan->index);
        buf_putint(ses.writepayload, opts.recv_window);
        buf_putint(ses.writepayload, RECV_MAX_PAYLOAD_LEN);

        TRACE(("leave send_msg_channel_open_init()"))
        return DROPBEAR_SUCCESS;
}

/* Confirmation that our channel open request (for forwardings) was 
 * successful*/
void recv_msg_channel_open_confirmation() {

        struct Channel * channel;
        int ret;

        TRACE(("enter recv_msg_channel_open_confirmation"))

        channel = getchannel();

        if (!channel->await_open) {
                dropbear_exit("Unexpected channel reply");
        }
        channel->await_open = 0;

        channel->remotechan =  buf_getint(ses.payload);
        channel->transwindow = buf_getint(ses.payload);
        channel->transmaxpacket = buf_getint(ses.payload);
        
        TRACE(("new chan remote %d local %d", 
                                channel->remotechan, channel->index))

        /* Run the inithandler callback */
        if (channel->type->inithandler) {
                ret = channel->type->inithandler(channel);
                if (ret > 0) {
                        remove_channel(channel);
                        TRACE(("inithandler returned failure %d", ret))
                }
        }

        
        TRACE(("leave recv_msg_channel_open_confirmation"))
}

/* Notification that our channel open request failed */
void recv_msg_channel_open_failure() {

        struct Channel * channel;

        channel = getchannel();

        if (!channel->await_open) {
                dropbear_exit("Unexpected channel reply");
        }
        channel->await_open = 0;

        remove_channel(channel);
}
#endif /* USING_LISTENERS */