bridge: Reduce dependency on ifnet threads.

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

/* $OpenBSD: sshconnect.c,v 1.271 2016/01/14 22:56:56 markus Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Code to connect to a remote host, and to perform the client side of the
 * login (authentication) dialog.
 *
 * 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".
 */

#include "includes.h"

#include <sys/param.h>  /* roundup */
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/socket.h>
#ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
#endif

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

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#ifdef HAVE_PATHS_H
#include <paths.h>
#endif
#include <pwd.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "xmalloc.h"
#include "key.h"
#include "hostfile.h"
#include "ssh.h"
#include "rsa.h"
#include "buffer.h"
#include "packet.h"
#include "uidswap.h"
#include "compat.h"
#include "key.h"
#include "sshconnect.h"
#include "hostfile.h"
#include "log.h"
#include "misc.h"
#include "readconf.h"
#include "atomicio.h"
#include "dns.h"
#include "monitor_fdpass.h"
#include "ssh2.h"
#include "version.h"
#include "authfile.h"
#include "ssherr.h"
#include "authfd.h"

char *client_version_string = NULL;
char *server_version_string = NULL;
Key *previous_host_key = NULL;

static int matching_host_key_dns = 0;

static pid_t proxy_command_pid = 0;

/* import */
extern Options options;
extern char *__progname;
extern uid_t original_real_uid;
extern uid_t original_effective_uid;

static int show_other_keys(struct hostkeys *, Key *);
static void warn_changed_key(Key *);

/* Expand a proxy command */
static char *
expand_proxy_command(const char *proxy_command, const char *user,
    const char *host, int port)
{
        char *tmp, *ret, strport[NI_MAXSERV];

        snprintf(strport, sizeof strport, "%d", port);
        xasprintf(&tmp, "exec %s", proxy_command);
        ret = percent_expand(tmp, "h", host, "p", strport,
            "r", options.user, (char *)NULL);
        free(tmp);
        return ret;
}

/*
 * Connect to the given ssh server using a proxy command that passes a
 * a connected fd back to us.
 */
static int
ssh_proxy_fdpass_connect(const char *host, u_short port,
    const char *proxy_command)
{
        char *command_string;
        int sp[2], sock;
        pid_t pid;
        char *shell;

        if ((shell = getenv("SHELL")) == NULL)
                shell = _PATH_BSHELL;

        if (socketpair(AF_UNIX, SOCK_STREAM, 0, sp) < 0)
                fatal("Could not create socketpair to communicate with "
                    "proxy dialer: %.100s", strerror(errno));

        command_string = expand_proxy_command(proxy_command, options.user,
            host, port);
        debug("Executing proxy dialer command: %.500s", command_string);

        /* Fork and execute the proxy command. */
        if ((pid = fork()) == 0) {
                char *argv[10];

                /* Child.  Permanently give up superuser privileges. */
                permanently_drop_suid(original_real_uid);

                close(sp[1]);
                /* Redirect stdin and stdout. */
                if (sp[0] != 0) {
                        if (dup2(sp[0], 0) < 0)
                                perror("dup2 stdin");
                }
                if (sp[0] != 1) {
                        if (dup2(sp[0], 1) < 0)
                                perror("dup2 stdout");
                }
                if (sp[0] >= 2)
                        close(sp[0]);

                /*
                 * Stderr is left as it is so that error messages get
                 * printed on the user's terminal.
                 */
                argv[0] = shell;
                argv[1] = "-c";
                argv[2] = command_string;
                argv[3] = NULL;

                /*
                 * Execute the proxy command.
                 * Note that we gave up any extra privileges above.
                 */
                execv(argv[0], argv);
                perror(argv[0]);
                exit(1);
        }
        /* Parent. */
        if (pid < 0)
                fatal("fork failed: %.100s", strerror(errno));
        close(sp[0]);
        free(command_string);

        if ((sock = mm_receive_fd(sp[1])) == -1)
                fatal("proxy dialer did not pass back a connection");
        close(sp[1]);

        while (waitpid(pid, NULL, 0) == -1)
                if (errno != EINTR)
                        fatal("Couldn't wait for child: %s", strerror(errno));

        /* Set the connection file descriptors. */
        packet_set_connection(sock, sock);

        return 0;
}

/*
 * Connect to the given ssh server using a proxy command.
 */
static int
ssh_proxy_connect(const char *host, u_short port, const char *proxy_command)
{
        char *command_string;
        int pin[2], pout[2];
        pid_t pid;
        char *shell;

        if ((shell = getenv("SHELL")) == NULL || *shell == '\0')
                shell = _PATH_BSHELL;

        /* Create pipes for communicating with the proxy. */
        if (pipe(pin) < 0 || pipe(pout) < 0)
                fatal("Could not create pipes to communicate with the proxy: %.100s",
                    strerror(errno));

        command_string = expand_proxy_command(proxy_command, options.user,
            host, port);
        debug("Executing proxy command: %.500s", command_string);

        /* Fork and execute the proxy command. */
        if ((pid = fork()) == 0) {
                char *argv[10];

                /* Child.  Permanently give up superuser privileges. */
                permanently_drop_suid(original_real_uid);

                /* Redirect stdin and stdout. */
                close(pin[1]);
                if (pin[0] != 0) {
                        if (dup2(pin[0], 0) < 0)
                                perror("dup2 stdin");
                        close(pin[0]);
                }
                close(pout[0]);
                if (dup2(pout[1], 1) < 0)
                        perror("dup2 stdout");
                /* Cannot be 1 because pin allocated two descriptors. */
                close(pout[1]);

                /* Stderr is left as it is so that error messages get
                   printed on the user's terminal. */
                argv[0] = shell;
                argv[1] = "-c";
                argv[2] = command_string;
                argv[3] = NULL;

                /* Execute the proxy command.  Note that we gave up any
                   extra privileges above. */
                signal(SIGPIPE, SIG_DFL);
                execv(argv[0], argv);
                perror(argv[0]);
                exit(1);
        }
        /* Parent. */
        if (pid < 0)
                fatal("fork failed: %.100s", strerror(errno));
        else
                proxy_command_pid = pid; /* save pid to clean up later */

        /* Close child side of the descriptors. */
        close(pin[0]);
        close(pout[1]);

        /* Free the command name. */
        free(command_string);

        /* Set the connection file descriptors. */
        packet_set_connection(pout[0], pin[1]);

        /* Indicate OK return */
        return 0;
}

void
ssh_kill_proxy_command(void)
{
        /*
         * Send SIGHUP to proxy command if used. We don't wait() in
         * case it hangs and instead rely on init to reap the child
         */
        if (proxy_command_pid > 1)
                kill(proxy_command_pid, SIGHUP);
}

/*
 * Creates a (possibly privileged) socket for use as the ssh connection.
 */
static int
ssh_create_socket(int privileged, struct addrinfo *ai)
{
        int sock, r, gaierr;
        struct addrinfo hints, *res = NULL;

        sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
        if (sock < 0) {
                error("socket: %s", strerror(errno));
                return -1;
        }
        fcntl(sock, F_SETFD, FD_CLOEXEC);

        /* Bind the socket to an alternative local IP address */
        if (options.bind_address == NULL && !privileged)
                return sock;

        if (options.bind_address) {
                memset(&hints, 0, sizeof(hints));
                hints.ai_family = ai->ai_family;
                hints.ai_socktype = ai->ai_socktype;
                hints.ai_protocol = ai->ai_protocol;
                hints.ai_flags = AI_PASSIVE;
                gaierr = getaddrinfo(options.bind_address, NULL, &hints, &res);
                if (gaierr) {
                        error("getaddrinfo: %s: %s", options.bind_address,
                            ssh_gai_strerror(gaierr));
                        close(sock);
                        return -1;
                }
        }
        /*
         * If we are running as root and want to connect to a privileged
         * port, bind our own socket to a privileged port.
         */
        if (privileged) {
                PRIV_START;
                r = bindresvport_sa(sock, res ? res->ai_addr : NULL);
                PRIV_END;
                if (r < 0) {
                        error("bindresvport_sa: af=%d %s", ai->ai_family,
                            strerror(errno));
                        goto fail;
                }
        } else {
                if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
                        error("bind: %s: %s", options.bind_address,
                            strerror(errno));
 fail:
                        close(sock);
                        freeaddrinfo(res);
                        return -1;
                }
        }
        if (res != NULL)
                freeaddrinfo(res);
        return sock;
}

static int
timeout_connect(int sockfd, const struct sockaddr *serv_addr,
    socklen_t addrlen, int *timeoutp)
{
        fd_set *fdset;
        struct timeval tv, t_start;
        socklen_t optlen;
        int optval, rc, result = -1;

        gettimeofday(&t_start, NULL);

        if (*timeoutp <= 0) {
                result = connect(sockfd, serv_addr, addrlen);
                goto done;
        }

        set_nonblock(sockfd);
        rc = connect(sockfd, serv_addr, addrlen);
        if (rc == 0) {
                unset_nonblock(sockfd);
                result = 0;
                goto done;
        }
        if (errno != EINPROGRESS) {
                result = -1;
                goto done;
        }

        fdset = xcalloc(howmany(sockfd + 1, NFDBITS),
            sizeof(fd_mask));
        FD_SET(sockfd, fdset);
        ms_to_timeval(&tv, *timeoutp);

        for (;;) {
                rc = select(sockfd + 1, NULL, fdset, NULL, &tv);
                if (rc != -1 || errno != EINTR)
                        break;
        }

        switch (rc) {
        case 0:
                /* Timed out */
                errno = ETIMEDOUT;
                break;
        case -1:
                /* Select error */
                debug("select: %s", strerror(errno));
                break;
        case 1:
                /* Completed or failed */
                optval = 0;
                optlen = sizeof(optval);
                if (getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &optval,
                    &optlen) == -1) {
                        debug("getsockopt: %s", strerror(errno));
                        break;
                }
                if (optval != 0) {
                        errno = optval;
                        break;
                }
                result = 0;
                unset_nonblock(sockfd);
                break;
        default:
                /* Should not occur */
                fatal("Bogus return (%d) from select()", rc);
        }

        free(fdset);

 done:
        if (result == 0 && *timeoutp > 0) {
                ms_subtract_diff(&t_start, timeoutp);
                if (*timeoutp <= 0) {
                        errno = ETIMEDOUT;
                        result = -1;
                }
        }

        return (result);
}

/*
 * Opens a TCP/IP connection to the remote server on the given host.
 * The address of the remote host will be returned in hostaddr.
 * If port is 0, the default port will be used.  If needpriv is true,
 * a privileged port will be allocated to make the connection.
 * This requires super-user privileges if needpriv is true.
 * Connection_attempts specifies the maximum number of tries (one per
 * second).  If proxy_command is non-NULL, it specifies the command (with %h
 * and %p substituted for host and port, respectively) to use to contact
 * the daemon.
 */
static int
ssh_connect_direct(const char *host, struct addrinfo *aitop,
    struct sockaddr_storage *hostaddr, u_short port, int family,
    int connection_attempts, int *timeout_ms, int want_keepalive, int needpriv)
{
        int on = 1;
        int sock = -1, attempt;
        char ntop[NI_MAXHOST], strport[NI_MAXSERV];
        struct addrinfo *ai;

        debug2("%s: needpriv %d", __func__, needpriv);
        memset(ntop, 0, sizeof(ntop));
        memset(strport, 0, sizeof(strport));

        for (attempt = 0; attempt < connection_attempts; attempt++) {
                if (attempt > 0) {
                        /* Sleep a moment before retrying. */
                        sleep(1);
                        debug("Trying again...");
                }
                /*
                 * Loop through addresses for this host, and try each one in
                 * sequence until the connection succeeds.
                 */
                for (ai = aitop; ai; ai = ai->ai_next) {
                        if (ai->ai_family != AF_INET &&
                            ai->ai_family != AF_INET6)
                                continue;
                        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;
                        }
                        debug("Connecting to %.200s [%.100s] port %s.",
                                host, ntop, strport);

                        /* Create a socket for connecting. */
                        sock = ssh_create_socket(needpriv, ai);
                        if (sock < 0)
                                /* Any error is already output */
                                continue;

                        if (timeout_connect(sock, ai->ai_addr, ai->ai_addrlen,
                            timeout_ms) >= 0) {
                                /* Successful connection. */
                                memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
                                break;
                        } else {
                                debug("connect to address %s port %s: %s",
                                    ntop, strport, strerror(errno));
                                close(sock);
                                sock = -1;
                        }
                }
                if (sock != -1)
                        break;  /* Successful connection. */
        }

        /* Return failure if we didn't get a successful connection. */
        if (sock == -1) {
                error("ssh: connect to host %s port %s: %s",
                    host, strport, strerror(errno));
                return (-1);
        }

        debug("Connection established.");

        /* Set SO_KEEPALIVE if requested. */
        if (want_keepalive &&
            setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
            sizeof(on)) < 0)
                error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));

        /* Set the connection. */
        packet_set_connection(sock, sock);

        return 0;
}

int
ssh_connect(const char *host, struct addrinfo *addrs,
    struct sockaddr_storage *hostaddr, u_short port, int family,
    int connection_attempts, int *timeout_ms, int want_keepalive, int needpriv)
{
        if (options.proxy_command == NULL) {
                return ssh_connect_direct(host, addrs, hostaddr, port, family,
                    connection_attempts, timeout_ms, want_keepalive, needpriv);
        } else if (strcmp(options.proxy_command, "-") == 0) {
                packet_set_connection(STDIN_FILENO, STDOUT_FILENO);
                return 0; /* Always succeeds */
        } else if (options.proxy_use_fdpass) {
                return ssh_proxy_fdpass_connect(host, port,
                    options.proxy_command);
        }
        return ssh_proxy_connect(host, port, options.proxy_command);
}

static void
send_client_banner(int connection_out, int minor1)
{
        /* Send our own protocol version identification. */
        if (compat20) {
                xasprintf(&client_version_string, "SSH-%d.%d-%.100s\r\n",
                    PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2, SSH_VERSION);
        } else {
                xasprintf(&client_version_string, "SSH-%d.%d-%.100s\n",
                    PROTOCOL_MAJOR_1, minor1, SSH_VERSION);
        }
        if (atomicio(vwrite, connection_out, client_version_string,
            strlen(client_version_string)) != strlen(client_version_string))
                fatal("write: %.100s", strerror(errno));
        chop(client_version_string);
        debug("Local version string %.100s", client_version_string);
}

/*
 * Waits for the server identification string, and sends our own
 * identification string.
 */
void
ssh_exchange_identification(int timeout_ms)
{
        char buf[256], remote_version[256];     /* must be same size! */
        int remote_major, remote_minor, mismatch;
        int connection_in = packet_get_connection_in();
        int connection_out = packet_get_connection_out();
        int minor1 = PROTOCOL_MINOR_1, client_banner_sent = 0;
        u_int i, n;
        size_t len;
        int fdsetsz, remaining, rc;
        struct timeval t_start, t_remaining;
        fd_set *fdset;

        fdsetsz = howmany(connection_in + 1, NFDBITS) * sizeof(fd_mask);
        fdset = xcalloc(1, fdsetsz);

        /*
         * If we are SSH2-only then we can send the banner immediately and
         * save a round-trip.
         */
        if (options.protocol == SSH_PROTO_2) {
                enable_compat20();
                send_client_banner(connection_out, 0);
                client_banner_sent = 1;
        }

        /* Read other side's version identification. */
        remaining = timeout_ms;
        for (n = 0;;) {
                for (i = 0; i < sizeof(buf) - 1; i++) {
                        if (timeout_ms > 0) {
                                gettimeofday(&t_start, NULL);
                                ms_to_timeval(&t_remaining, remaining);
                                FD_SET(connection_in, fdset);
                                rc = select(connection_in + 1, fdset, NULL,
                                    fdset, &t_remaining);
                                ms_subtract_diff(&t_start, &remaining);
                                if (rc == 0 || remaining <= 0)
                                        fatal("Connection timed out during "
                                            "banner exchange");
                                if (rc == -1) {
                                        if (errno == EINTR)
                                                continue;
                                        fatal("ssh_exchange_identification: "
                                            "select: %s", strerror(errno));
                                }
                        }

                        len = atomicio(read, connection_in, &buf[i], 1);

                        if (len != 1 && errno == EPIPE)
                                fatal("ssh_exchange_identification: "
                                    "Connection closed by remote host");
                        else if (len != 1)
                                fatal("ssh_exchange_identification: "
                                    "read: %.100s", strerror(errno));
                        if (buf[i] == '\r') {
                                buf[i] = '\n';
                                buf[i + 1] = 0;
                                continue;               /**XXX wait for \n */
                        }
                        if (buf[i] == '\n') {
                                buf[i + 1] = 0;
                                break;
                        }
                        if (++n > 65536)
                                fatal("ssh_exchange_identification: "
                                    "No banner received");
                }
                buf[sizeof(buf) - 1] = 0;
                if (strncmp(buf, "SSH-", 4) == 0)
                        break;
                debug("ssh_exchange_identification: %s", buf);
        }
        server_version_string = xstrdup(buf);
        free(fdset);

        /*
         * Check that the versions match.  In future this might accept
         * several versions and set appropriate flags to handle them.
         */
        if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
            &remote_major, &remote_minor, remote_version) != 3)
                fatal("Bad remote protocol version identification: '%.100s'", buf);
        debug("Remote protocol version %d.%d, remote software version %.100s",
            remote_major, remote_minor, remote_version);

        active_state->compat = compat_datafellows(remote_version);
        mismatch = 0;

        switch (remote_major) {
        case 1:
                if (remote_minor == 99 &&
                    (options.protocol & SSH_PROTO_2) &&
                    !(options.protocol & SSH_PROTO_1_PREFERRED)) {
                        enable_compat20();
                        break;
                }
                if (!(options.protocol & SSH_PROTO_1)) {
                        mismatch = 1;
                        break;
                }
                if (remote_minor < 3) {
                        fatal("Remote machine has too old SSH software version.");
                } else if (remote_minor == 3 || remote_minor == 4) {
                        /* We speak 1.3, too. */
                        enable_compat13();
                        minor1 = 3;
                        if (options.forward_agent) {
                                logit("Agent forwarding disabled for protocol 1.3");
                                options.forward_agent = 0;
                        }
                }
                break;
        case 2:
                if (options.protocol & SSH_PROTO_2) {
                        enable_compat20();
                        break;
                }
                /* FALLTHROUGH */
        default:
                mismatch = 1;
                break;
        }
        if (mismatch)
                fatal("Protocol major versions differ: %d vs. %d",
                    (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
                    remote_major);
        if ((datafellows & SSH_BUG_DERIVEKEY) != 0)
                fatal("Server version \"%.100s\" uses unsafe key agreement; "
                    "refusing connection", remote_version);
        if ((datafellows & SSH_BUG_RSASIGMD5) != 0)
                logit("Server version \"%.100s\" uses unsafe RSA signature "
                    "scheme; disabling use of RSA keys", remote_version);
        if (!client_banner_sent)
                send_client_banner(connection_out, minor1);
        chop(server_version_string);
}

/* defaults to 'no' */
static int
confirm(const char *prompt)
{
        const char *msg, *again = "Please type 'yes' or 'no': ";
        char *p;
        int ret = -1;

        if (options.batch_mode)
                return 0;
        for (msg = prompt;;msg = again) {
                p = read_passphrase(msg, RP_ECHO);
                if (p == NULL ||
                    (p[0] == '\0') || (p[0] == '\n') ||
                    strncasecmp(p, "no", 2) == 0)
                        ret = 0;
                if (p && strncasecmp(p, "yes", 3) == 0)
                        ret = 1;
                free(p);
                if (ret != -1)
                        return ret;
        }
}

static int
check_host_cert(const char *host, const Key *host_key)
{
        const char *reason;

        if (key_cert_check_authority(host_key, 1, 0, host, &reason) != 0) {
                error("%s", reason);
                return 0;
        }
        if (buffer_len(host_key->cert->critical) != 0) {
                error("Certificate for %s contains unsupported "
                    "critical options(s)", host);
                return 0;
        }
        return 1;
}

static int
sockaddr_is_local(struct sockaddr *hostaddr)
{
        switch (hostaddr->sa_family) {
        case AF_INET:
                return (ntohl(((struct sockaddr_in *)hostaddr)->
                    sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
        case AF_INET6:
                return IN6_IS_ADDR_LOOPBACK(
                    &(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
        default:
                return 0;
        }
}

/*
 * Prepare the hostname and ip address strings that are used to lookup
 * host keys in known_hosts files. These may have a port number appended.
 */
void
get_hostfile_hostname_ipaddr(char *hostname, struct sockaddr *hostaddr,
    u_short port, char **hostfile_hostname, char **hostfile_ipaddr)
{
        char ntop[NI_MAXHOST];
        socklen_t addrlen;

        switch (hostaddr == NULL ? -1 : hostaddr->sa_family) {
        case -1:
                addrlen = 0;
                break;
        case AF_INET:
                addrlen = sizeof(struct sockaddr_in);
                break;
        case AF_INET6:
                addrlen = sizeof(struct sockaddr_in6);
                break;
        default:
                addrlen = sizeof(struct sockaddr);
                break;
        }

        /*
         * We don't have the remote ip-address for connections
         * using a proxy command
         */
        if (hostfile_ipaddr != NULL) {
                if (options.proxy_command == NULL) {
                        if (getnameinfo(hostaddr, addrlen,
                            ntop, sizeof(ntop), NULL, 0, NI_NUMERICHOST) != 0)
                        fatal("%s: getnameinfo failed", __func__);
                        *hostfile_ipaddr = put_host_port(ntop, port);
                } else {
                        *hostfile_ipaddr = xstrdup("<no hostip for proxy "
                            "command>");
                }
        }

        /*
         * Allow the user to record the key under a different name or
         * differentiate a non-standard port.  This is useful for ssh
         * tunneling over forwarded connections or if you run multiple
         * sshd's on different ports on the same machine.
         */
        if (hostfile_hostname != NULL) {
                if (options.host_key_alias != NULL) {
                        *hostfile_hostname = xstrdup(options.host_key_alias);
                        debug("using hostkeyalias: %s", *hostfile_hostname);
                } else {
                        *hostfile_hostname = put_host_port(hostname, port);
                }
        }
}

/*
 * check whether the supplied host key is valid, return -1 if the key
 * is not valid. user_hostfile[0] will not be updated if 'readonly' is true.
 */
#define RDRW    0
#define RDONLY  1
#define ROQUIET 2
static int
check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
    Key *host_key, int readonly,
    char **user_hostfiles, u_int num_user_hostfiles,
    char **system_hostfiles, u_int num_system_hostfiles)
{
        HostStatus host_status;
        HostStatus ip_status;
        Key *raw_key = NULL;
        char *ip = NULL, *host = NULL;
        char hostline[1000], *hostp, *fp, *ra;
        char msg[1024];
        const char *type;
        const struct hostkey_entry *host_found, *ip_found;
        int len, cancelled_forwarding = 0;
        int local = sockaddr_is_local(hostaddr);
        int r, want_cert = key_is_cert(host_key), host_ip_differ = 0;
        int hostkey_trusted = 0; /* Known or explicitly accepted by user */
        struct hostkeys *host_hostkeys, *ip_hostkeys;
        u_int i;

        /*
         * Force accepting of the host key for loopback/localhost. The
         * problem is that if the home directory is NFS-mounted to multiple
         * machines, localhost will refer to a different machine in each of
         * them, and the user will get bogus HOST_CHANGED warnings.  This
         * essentially disables host authentication for localhost; however,
         * this is probably not a real problem.
         */
        if (options.no_host_authentication_for_localhost == 1 && local &&
            options.host_key_alias == NULL) {
                debug("Forcing accepting of host key for "
                    "loopback/localhost.");
                return 0;
        }

        /*
         * Prepare the hostname and address strings used for hostkey lookup.
         * In some cases, these will have a port number appended.
         */
        get_hostfile_hostname_ipaddr(hostname, hostaddr, port, &host, &ip);

        /*
         * Turn off check_host_ip if the connection is to localhost, via proxy
         * command or if we don't have a hostname to compare with
         */
        if (options.check_host_ip && (local ||
            strcmp(hostname, ip) == 0 || options.proxy_command != NULL))
                options.check_host_ip = 0;

        host_hostkeys = init_hostkeys();
        for (i = 0; i < num_user_hostfiles; i++)
                load_hostkeys(host_hostkeys, host, user_hostfiles[i]);
        for (i = 0; i < num_system_hostfiles; i++)
                load_hostkeys(host_hostkeys, host, system_hostfiles[i]);

        ip_hostkeys = NULL;
        if (!want_cert && options.check_host_ip) {
                ip_hostkeys = init_hostkeys();
                for (i = 0; i < num_user_hostfiles; i++)
                        load_hostkeys(ip_hostkeys, ip, user_hostfiles[i]);
                for (i = 0; i < num_system_hostfiles; i++)
                        load_hostkeys(ip_hostkeys, ip, system_hostfiles[i]);
        }

 retry:
        /* Reload these as they may have changed on cert->key downgrade */
        want_cert = key_is_cert(host_key);
        type = key_type(host_key);

        /*
         * Check if the host key is present in the user's list of known
         * hosts or in the systemwide list.
         */
        host_status = check_key_in_hostkeys(host_hostkeys, host_key,
            &host_found);

        /*
         * Also perform check for the ip address, skip the check if we are
         * localhost, looking for a certificate, or the hostname was an ip
         * address to begin with.
         */
        if (!want_cert && ip_hostkeys != NULL) {
                ip_status = check_key_in_hostkeys(ip_hostkeys, host_key,
                    &ip_found);
                if (host_status == HOST_CHANGED &&
                    (ip_status != HOST_CHANGED || 
                    (ip_found != NULL &&
                    !key_equal(ip_found->key, host_found->key))))
                        host_ip_differ = 1;
        } else
                ip_status = host_status;

        switch (host_status) {
        case HOST_OK:
                /* The host is known and the key matches. */
                debug("Host '%.200s' is known and matches the %s host %s.",
                    host, type, want_cert ? "certificate" : "key");
                debug("Found %s in %s:%lu", want_cert ? "CA key" : "key",
                    host_found->file, host_found->line);
                if (want_cert && !check_host_cert(hostname, host_key))
                        goto fail;
                if (options.check_host_ip && ip_status == HOST_NEW) {
                        if (readonly || want_cert)
                                logit("%s host key for IP address "
                                    "'%.128s' not in list of known hosts.",
                                    type, ip);
                        else if (!add_host_to_hostfile(user_hostfiles[0], ip,
                            host_key, options.hash_known_hosts))
                                logit("Failed to add the %s host key for IP "
                                    "address '%.128s' to the list of known "
                                    "hosts (%.500s).", type, ip,
                                    user_hostfiles[0]);
                        else
                                logit("Warning: Permanently added the %s host "
                                    "key for IP address '%.128s' to the list "
                                    "of known hosts.", type, ip);
                } else if (options.visual_host_key) {
                        fp = sshkey_fingerprint(host_key,
                            options.fingerprint_hash, SSH_FP_DEFAULT);
                        ra = sshkey_fingerprint(host_key,
                            options.fingerprint_hash, SSH_FP_RANDOMART);
                        if (fp == NULL || ra == NULL)
                                fatal("%s: sshkey_fingerprint fail", __func__);
                        logit("Host key fingerprint is %s\n%s", fp, ra);
                        free(ra);
                        free(fp);
                }
                hostkey_trusted = 1;
                break;
        case HOST_NEW:
                if (options.host_key_alias == NULL && port != 0 &&
                    port != SSH_DEFAULT_PORT) {
                        debug("checking without port identifier");
                        if (check_host_key(hostname, hostaddr, 0, host_key,
                            ROQUIET, user_hostfiles, num_user_hostfiles,
                            system_hostfiles, num_system_hostfiles) == 0) {
                                debug("found matching key w/out port");
                                break;
                        }
                }
                if (readonly || want_cert)
                        goto fail;
                /* The host is new. */
                if (options.strict_host_key_checking == 1) {
                        /*
                         * User has requested strict host key checking.  We
                         * will not add the host key automatically.  The only
                         * alternative left is to abort.
                         */
                        error("No %s host key is known for %.200s and you "
                            "have requested strict checking.", type, host);
                        goto fail;
                } else if (options.strict_host_key_checking == 2) {
                        char msg1[1024], msg2[1024];

                        if (show_other_keys(host_hostkeys, host_key))
                                snprintf(msg1, sizeof(msg1),
                                    "\nbut keys of different type are already"
                                    " known for this host.");
                        else
                                snprintf(msg1, sizeof(msg1), ".");
                        /* The default */
                        fp = sshkey_fingerprint(host_key,
                            options.fingerprint_hash, SSH_FP_DEFAULT);
                        ra = sshkey_fingerprint(host_key,
                            options.fingerprint_hash, SSH_FP_RANDOMART);
                        if (fp == NULL || ra == NULL)
                                fatal("%s: sshkey_fingerprint fail", __func__);
                        msg2[0] = '\0';
                        if (options.verify_host_key_dns) {
                                if (matching_host_key_dns)
                                        snprintf(msg2, sizeof(msg2),
                                            "Matching host key fingerprint"
                                            " found in DNS.\n");
                                else
                                        snprintf(msg2, sizeof(msg2),
                                            "No matching host key fingerprint"
                                            " found in DNS.\n");
                        }
                        snprintf(msg, sizeof(msg),
                            "The authenticity of host '%.200s (%s)' can't be "
                            "established%s\n"
                            "%s key fingerprint is %s.%s%s\n%s"
                            "Are you sure you want to continue connecting "
                            "(yes/no)? ",
                            host, ip, msg1, type, fp,
                            options.visual_host_key ? "\n" : "",
                            options.visual_host_key ? ra : "",
                            msg2);
                        free(ra);
                        free(fp);
                        if (!confirm(msg))
                                goto fail;
                        hostkey_trusted = 1; /* user explicitly confirmed */
                }
                /*
                 * If not in strict mode, add the key automatically to the
                 * local known_hosts file.
                 */
                if (options.check_host_ip && ip_status == HOST_NEW) {
                        snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
                        hostp = hostline;
                        if (options.hash_known_hosts) {
                                /* Add hash of host and IP separately */
                                r = add_host_to_hostfile(user_hostfiles[0],
                                    host, host_key, options.hash_known_hosts) &&
                                    add_host_to_hostfile(user_hostfiles[0], ip,
                                    host_key, options.hash_known_hosts);
                        } else {
                                /* Add unhashed "host,ip" */
                                r = add_host_to_hostfile(user_hostfiles[0],
                                    hostline, host_key,
                                    options.hash_known_hosts);
                        }
                } else {
                        r = add_host_to_hostfile(user_hostfiles[0], host,
                            host_key, options.hash_known_hosts);
                        hostp = host;
                }

                if (!r)
                        logit("Failed to add the host to the list of known "
                            "hosts (%.500s).", user_hostfiles[0]);
                else
                        logit("Warning: Permanently added '%.200s' (%s) to the "
                            "list of known hosts.", hostp, type);
                break;
        case HOST_REVOKED:
                error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
                error("@       WARNING: REVOKED HOST KEY DETECTED!               @");
                error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
                error("The %s host key for %s is marked as revoked.", type, host);
                error("This could mean that a stolen key is being used to");
                error("impersonate this host.");

                /*
                 * If strict host key checking is in use, the user will have
                 * to edit the key manually and we can only abort.
                 */
                if (options.strict_host_key_checking) {
                        error("%s host key for %.200s was revoked and you have "
                            "requested strict checking.", type, host);
                        goto fail;
                }
                goto continue_unsafe;

        case HOST_CHANGED:
                if (want_cert) {
                        /*
                         * This is only a debug() since it is valid to have
                         * CAs with wildcard DNS matches that don't match
                         * all hosts that one might visit.
                         */
                        debug("Host certificate authority does not "
                            "match %s in %s:%lu", CA_MARKER,
                            host_found->file, host_found->line);
                        goto fail;
                }
                if (readonly == ROQUIET)
                        goto fail;
                if (options.check_host_ip && host_ip_differ) {
                        char *key_msg;
                        if (ip_status == HOST_NEW)
                                key_msg = "is unknown";
                        else if (ip_status == HOST_OK)
                                key_msg = "is unchanged";
                        else
                                key_msg = "has a different value";
                        error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
                        error("@       WARNING: POSSIBLE DNS SPOOFING DETECTED!          @");
                        error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
                        error("The %s host key for %s has changed,", type, host);
                        error("and the key for the corresponding IP address %s", ip);
                        error("%s. This could either mean that", key_msg);
                        error("DNS SPOOFING is happening or the IP address for the host");
                        error("and its host key have changed at the same time.");
                        if (ip_status != HOST_NEW)
                                error("Offending key for IP in %s:%lu",
                                    ip_found->file, ip_found->line);
                }
                /* The host key has changed. */
                warn_changed_key(host_key);
                error("Add correct host key in %.100s to get rid of this message.",
                    user_hostfiles[0]);
                error("Offending %s key in %s:%lu", key_type(host_found->key),
                    host_found->file, host_found->line);

                /*
                 * If strict host key checking is in use, the user will have
                 * to edit the key manually and we can only abort.
                 */
                if (options.strict_host_key_checking) {
                        error("%s host key for %.200s has changed and you have "
                            "requested strict checking.", type, host);
                        goto fail;
                }

 continue_unsafe:
                /*
                 * If strict host key checking has not been requested, allow
                 * the connection but without MITM-able authentication or
                 * forwarding.
                 */
                if (options.password_authentication) {
                        error("Password authentication is disabled to avoid "
                            "man-in-the-middle attacks.");
                        options.password_authentication = 0;
                        cancelled_forwarding = 1;
                }
                if (options.kbd_interactive_authentication) {
                        error("Keyboard-interactive authentication is disabled"
                            " to avoid man-in-the-middle attacks.");
                        options.kbd_interactive_authentication = 0;
                        options.challenge_response_authentication = 0;
                        cancelled_forwarding = 1;
                }
                if (options.challenge_response_authentication) {
                        error("Challenge/response authentication is disabled"
                            " to avoid man-in-the-middle attacks.");
                        options.challenge_response_authentication = 0;
                        cancelled_forwarding = 1;
                }
                if (options.forward_agent) {
                        error("Agent forwarding is disabled to avoid "
                            "man-in-the-middle attacks.");
                        options.forward_agent = 0;
                        cancelled_forwarding = 1;
                }
                if (options.forward_x11) {
                        error("X11 forwarding is disabled to avoid "
                            "man-in-the-middle attacks.");
                        options.forward_x11 = 0;
                        cancelled_forwarding = 1;
                }
                if (options.num_local_forwards > 0 ||
                    options.num_remote_forwards > 0) {
                        error("Port forwarding is disabled to avoid "
                            "man-in-the-middle attacks.");
                        options.num_local_forwards =
                            options.num_remote_forwards = 0;
                        cancelled_forwarding = 1;
                }
                if (options.tun_open != SSH_TUNMODE_NO) {
                        error("Tunnel forwarding is disabled to avoid "
                            "man-in-the-middle attacks.");
                        options.tun_open = SSH_TUNMODE_NO;
                        cancelled_forwarding = 1;
                }
                if (options.exit_on_forward_failure && cancelled_forwarding)
                        fatal("Error: forwarding disabled due to host key "
                            "check failure");
                
                /*
                 * XXX Should permit the user to change to use the new id.
                 * This could be done by converting the host key to an
                 * identifying sentence, tell that the host identifies itself
                 * by that sentence, and ask the user if he/she wishes to
                 * accept the authentication.
                 */
                break;
        case HOST_FOUND:
                fatal("internal error");
                break;
        }

        if (options.check_host_ip && host_status != HOST_CHANGED &&
            ip_status == HOST_CHANGED) {
                snprintf(msg, sizeof(msg),
                    "Warning: the %s host key for '%.200s' "
                    "differs from the key for the IP address '%.128s'"
                    "\nOffending key for IP in %s:%lu",
                    type, host, ip, ip_found->file, ip_found->line);
                if (host_status == HOST_OK) {
                        len = strlen(msg);
                        snprintf(msg + len, sizeof(msg) - len,
                            "\nMatching host key in %s:%lu",
                            host_found->file, host_found->line);
                }
                if (options.strict_host_key_checking == 1) {
                        logit("%s", msg);
                        error("Exiting, you have requested strict checking.");
                        goto fail;
                } else if (options.strict_host_key_checking == 2) {
                        strlcat(msg, "\nAre you sure you want "
                            "to continue connecting (yes/no)? ", sizeof(msg));
                        if (!confirm(msg))
                                goto fail;
                } else {
                        logit("%s", msg);
                }
        }

        if (!hostkey_trusted && options.update_hostkeys) {
                debug("%s: hostkey not known or explicitly trusted: "
                    "disabling UpdateHostkeys", __func__);
                options.update_hostkeys = 0;
        }

        free(ip);
        free(host);
        if (host_hostkeys != NULL)
                free_hostkeys(host_hostkeys);
        if (ip_hostkeys != NULL)
                free_hostkeys(ip_hostkeys);
        return 0;

fail:
        if (want_cert && host_status != HOST_REVOKED) {
                /*
                 * No matching certificate. Downgrade cert to raw key and
                 * search normally.
                 */
                debug("No matching CA found. Retry with plain key");
                raw_key = key_from_private(host_key);
                if (key_drop_cert(raw_key) != 0)
                        fatal("Couldn't drop certificate");
                host_key = raw_key;
                goto retry;
        }
        if (raw_key != NULL)
                key_free(raw_key);
        free(ip);
        free(host);
        if (host_hostkeys != NULL)
                free_hostkeys(host_hostkeys);
        if (ip_hostkeys != NULL)
                free_hostkeys(ip_hostkeys);
        return -1;
}

/* returns 0 if key verifies or -1 if key does NOT verify */
int
verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
{
        u_int i;
        int r = -1, flags = 0;
        char valid[64], *fp = NULL, *cafp = NULL;
        struct sshkey *plain = NULL;

        if ((fp = sshkey_fingerprint(host_key,
            options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
                error("%s: fingerprint host key: %s", __func__, ssh_err(r));
                r = -1;
                goto out;
        }

        if (sshkey_is_cert(host_key)) {
                if ((cafp = sshkey_fingerprint(host_key->cert->signature_key,
                    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
                        error("%s: fingerprint CA key: %s",
                            __func__, ssh_err(r));
                        r = -1;
                        goto out;
                }
                sshkey_format_cert_validity(host_key->cert,
                    valid, sizeof(valid));
                debug("Server host certificate: %s %s, serial %llu "
                    "ID \"%s\" CA %s %s valid %s",
                    sshkey_ssh_name(host_key), fp,
                    (unsigned long long)host_key->cert->serial,
                    host_key->cert->key_id,
                    sshkey_ssh_name(host_key->cert->signature_key), cafp,
                    valid);
                for (i = 0; i < host_key->cert->nprincipals; i++) {
                        debug2("Server host certificate hostname: %s",
                            host_key->cert->principals[i]);
                }
        } else {
                debug("Server host key: %s %s", compat20 ?
                    sshkey_ssh_name(host_key) : sshkey_type(host_key), fp);
        }

        if (sshkey_equal(previous_host_key, host_key)) {
                debug2("%s: server host key %s %s matches cached key",
                    __func__, sshkey_type(host_key), fp);
                r = 0;
                goto out;
        }

        /* Check in RevokedHostKeys file if specified */
        if (options.revoked_host_keys != NULL) {
                r = sshkey_check_revoked(host_key, options.revoked_host_keys);
                switch (r) {
                case 0:
                        break; /* not revoked */
                case SSH_ERR_KEY_REVOKED:
                        error("Host key %s %s revoked by file %s",
                            sshkey_type(host_key), fp,
                            options.revoked_host_keys);
                        r = -1;
                        goto out;
                default:
                        error("Error checking host key %s %s in "
                            "revoked keys file %s: %s", sshkey_type(host_key),
                            fp, options.revoked_host_keys, ssh_err(r));
                        r = -1;
                        goto out;
                }
        }

        if (options.verify_host_key_dns) {
                /*
                 * XXX certs are not yet supported for DNS, so downgrade
                 * them and try the plain key.
                 */
                if ((r = sshkey_from_private(host_key, &plain)) != 0)
                        goto out;
                if (sshkey_is_cert(plain))
                        sshkey_drop_cert(plain);
                if (verify_host_key_dns(host, hostaddr, plain, &flags) == 0) {
                        if (flags & DNS_VERIFY_FOUND) {
                                if (options.verify_host_key_dns == 1 &&
                                    flags & DNS_VERIFY_MATCH &&
                                    flags & DNS_VERIFY_SECURE) {
                                        r = 0;
                                        goto out;
                                }
                                if (flags & DNS_VERIFY_MATCH) {
                                        matching_host_key_dns = 1;
                                } else {
                                        warn_changed_key(plain);
                                        error("Update the SSHFP RR in DNS "
                                            "with the new host key to get rid "
                                            "of this message.");
                                }
                        }
                }
        }
        r = check_host_key(host, hostaddr, options.port, host_key, RDRW,
            options.user_hostfiles, options.num_user_hostfiles,
            options.system_hostfiles, options.num_system_hostfiles);

out:
        sshkey_free(plain);
        free(fp);
        free(cafp);
        if (r == 0 && host_key != NULL) {
                key_free(previous_host_key);
                previous_host_key = key_from_private(host_key);
        }

        return r;
}

/*
 * Starts a dialog with the server, and authenticates the current user on the
 * server.  This does not need any extra privileges.  The basic connection
 * to the server must already have been established before this is called.
 * If login fails, this function prints an error and never returns.
 * This function does not require super-user privileges.
 */
void
ssh_login(Sensitive *sensitive, const char *orighost,
    struct sockaddr *hostaddr, u_short port, struct passwd *pw, int timeout_ms)
{
        char *host;
        char *server_user, *local_user;

        local_user = xstrdup(pw->pw_name);
        server_user = options.user ? options.user : local_user;

        /* Convert the user-supplied hostname into all lowercase. */
        host = xstrdup(orighost);
        lowercase(host);

        /* Exchange protocol version identification strings with the server. */
        ssh_exchange_identification(timeout_ms);

        /* Put the connection into non-blocking mode. */
        packet_set_nonblocking();

        /* key exchange */
        /* authenticate user */
        debug("Authenticating to %s:%d as '%s'", host, port, server_user);
        if (compat20) {
                ssh_kex2(host, hostaddr, port);
                ssh_userauth2(local_user, server_user, host, sensitive);
        } else {
#ifdef WITH_SSH1
                ssh_kex(host, hostaddr);
                ssh_userauth1(local_user, server_user, host, sensitive);
#else
                fatal("ssh1 is not supported");
#endif
        }
        free(local_user);
}

void
ssh_put_password(char *password)
{
        int size;
        char *padded;

        if (datafellows & SSH_BUG_PASSWORDPAD) {
                packet_put_cstring(password);
                return;
        }
        size = roundup(strlen(password) + 1, 32);
        padded = xcalloc(1, size);
        strlcpy(padded, password, size);
        packet_put_string(padded, size);
        explicit_bzero(padded, size);
        free(padded);
}

/* print all known host keys for a given host, but skip keys of given type */
static int
show_other_keys(struct hostkeys *hostkeys, Key *key)
{
        int type[] = {
                KEY_RSA1,
                KEY_RSA,
                KEY_DSA,
                KEY_ECDSA,
                KEY_ED25519,
                -1
        };
        int i, ret = 0;
        char *fp, *ra;
        const struct hostkey_entry *found;

        for (i = 0; type[i] != -1; i++) {
                if (type[i] == key->type)
                        continue;
                if (!lookup_key_in_hostkeys_by_type(hostkeys, type[i], &found))
                        continue;
                fp = sshkey_fingerprint(found->key,
                    options.fingerprint_hash, SSH_FP_DEFAULT);
                ra = sshkey_fingerprint(found->key,
                    options.fingerprint_hash, SSH_FP_RANDOMART);
                if (fp == NULL || ra == NULL)
                        fatal("%s: sshkey_fingerprint fail", __func__);
                logit("WARNING: %s key found for host %s\n"
                    "in %s:%lu\n"
                    "%s key fingerprint %s.",
                    key_type(found->key),
                    found->host, found->file, found->line,
                    key_type(found->key), fp);
                if (options.visual_host_key)
                        logit("%s", ra);
                free(ra);
                free(fp);
                ret = 1;
        }
        return ret;
}

static void
warn_changed_key(Key *host_key)
{
        char *fp;

        fp = sshkey_fingerprint(host_key, options.fingerprint_hash,
            SSH_FP_DEFAULT);
        if (fp == NULL)
                fatal("%s: sshkey_fingerprint fail", __func__);

        error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
        error("@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @");
        error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
        error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
        error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
        error("It is also possible that a host key has just been changed.");
        error("The fingerprint for the %s key sent by the remote host is\n%s.",
            key_type(host_key), fp);
        error("Please contact your system administrator.");

        free(fp);
}

/*
 * Execute a local command
 */
int
ssh_local_cmd(const char *args)
{
        char *shell;
        pid_t pid;
        int status;
        void (*osighand)(int);

        if (!options.permit_local_command ||
            args == NULL || !*args)
                return (1);

        if ((shell = getenv("SHELL")) == NULL || *shell == '\0')
                shell = _PATH_BSHELL;

        osighand = signal(SIGCHLD, SIG_DFL);
        pid = fork();
        if (pid == 0) {
                signal(SIGPIPE, SIG_DFL);
                debug3("Executing %s -c \"%s\"", shell, args);
                execl(shell, shell, "-c", args, (char *)NULL);
                error("Couldn't execute %s -c \"%s\": %s",
                    shell, args, strerror(errno));
                _exit(1);
        } else if (pid == -1)
                fatal("fork failed: %.100s", strerror(errno));
        while (waitpid(pid, &status, 0) == -1)
                if (errno != EINTR)
                        fatal("Couldn't wait for child: %s", strerror(errno));
        signal(SIGCHLD, osighand);

        if (!WIFEXITED(status))
                return (1);

        return (WEXITSTATUS(status));
}

void
maybe_add_key_to_agent(char *authfile, Key *private, char *comment,
    char *passphrase)
{
        int auth_sock = -1, r;

        if (options.add_keys_to_agent == 0)
                return;

        if ((r = ssh_get_authentication_socket(&auth_sock)) != 0) {
                debug3("no authentication agent, not adding key");
                return;
        }

        if (options.add_keys_to_agent == 2 &&
            !ask_permission("Add key %s (%s) to agent?", authfile, comment)) {
                debug3("user denied adding this key");
                return;
        }

        if ((r = ssh_add_identity_constrained(auth_sock, private, comment, 0,
            (options.add_keys_to_agent == 3))) == 0)
                debug("identity added to agent: %s", authfile);
        else
                debug("could not add identity to agent: %s (%d)", authfile, r);
}