upstream: Factor out PuTTY setup.

[thirdparty/openssh-portable.git] / mux.c

/* $OpenBSD: mux.c,v 1.101 2023/11/23 03:37:05 dtucker Exp $ */
/*
 * Copyright (c) 2002-2008 Damien Miller <djm@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/* ssh session multiplexing support */

#include "includes.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/un.h>

#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <signal.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#ifdef HAVE_PATHS_H
#include <paths.h>
#endif

#ifdef HAVE_POLL_H
#include <poll.h>
#else
# ifdef HAVE_SYS_POLL_H
#  include <sys/poll.h>
# endif
#endif

#ifdef HAVE_UTIL_H
# include <util.h>
#endif

#include "openbsd-compat/sys-queue.h"
#include "xmalloc.h"
#include "log.h"
#include "ssh.h"
#include "ssh2.h"
#include "pathnames.h"
#include "misc.h"
#include "match.h"
#include "sshbuf.h"
#include "channels.h"
#include "msg.h"
#include "packet.h"
#include "monitor_fdpass.h"
#include "sshpty.h"
#include "sshkey.h"
#include "readconf.h"
#include "clientloop.h"
#include "ssherr.h"
#include "misc.h"

/* from ssh.c */
extern int tty_flag;
extern Options options;
extern char *host;
extern struct sshbuf *command;
extern volatile sig_atomic_t quit_pending;

/* Context for session open confirmation callback */
struct mux_session_confirm_ctx {
        u_int want_tty;
        u_int want_subsys;
        u_int want_x_fwd;
        u_int want_agent_fwd;
        struct sshbuf *cmd;
        char *term;
        struct termios tio;
        char **env;
        u_int rid;
};

/* Context for stdio fwd open confirmation callback */
struct mux_stdio_confirm_ctx {
        u_int rid;
};

/* Context for global channel callback */
struct mux_channel_confirm_ctx {
        u_int cid;      /* channel id */
        u_int rid;      /* request id */
        int fid;        /* forward id */
};

/* fd to control socket */
int muxserver_sock = -1;

/* client request id */
u_int muxclient_request_id = 0;

/* Multiplexing control command */
u_int muxclient_command = 0;

/* Set when signalled. */
static volatile sig_atomic_t muxclient_terminate = 0;

/* PID of multiplex server */
static u_int muxserver_pid = 0;

static Channel *mux_listener_channel = NULL;

struct mux_master_state {
        int hello_rcvd;
};

/* mux protocol messages */
#define MUX_MSG_HELLO           0x00000001
#define MUX_C_NEW_SESSION       0x10000002
#define MUX_C_ALIVE_CHECK       0x10000004
#define MUX_C_TERMINATE         0x10000005
#define MUX_C_OPEN_FWD          0x10000006
#define MUX_C_CLOSE_FWD         0x10000007
#define MUX_C_NEW_STDIO_FWD     0x10000008
#define MUX_C_STOP_LISTENING    0x10000009
#define MUX_C_PROXY             0x1000000f
#define MUX_S_OK                0x80000001
#define MUX_S_PERMISSION_DENIED 0x80000002
#define MUX_S_FAILURE           0x80000003
#define MUX_S_EXIT_MESSAGE      0x80000004
#define MUX_S_ALIVE             0x80000005
#define MUX_S_SESSION_OPENED    0x80000006
#define MUX_S_REMOTE_PORT       0x80000007
#define MUX_S_TTY_ALLOC_FAIL    0x80000008
#define MUX_S_PROXY             0x8000000f

/* type codes for MUX_C_OPEN_FWD and MUX_C_CLOSE_FWD */
#define MUX_FWD_LOCAL   1
#define MUX_FWD_REMOTE  2
#define MUX_FWD_DYNAMIC 3

static void mux_session_confirm(struct ssh *, int, int, void *);
static void mux_stdio_confirm(struct ssh *, int, int, void *);

static int mux_master_process_hello(struct ssh *, u_int,
            Channel *, struct sshbuf *, struct sshbuf *);
static int mux_master_process_new_session(struct ssh *, u_int,
            Channel *, struct sshbuf *, struct sshbuf *);
static int mux_master_process_alive_check(struct ssh *, u_int,
            Channel *, struct sshbuf *, struct sshbuf *);
static int mux_master_process_terminate(struct ssh *, u_int,
            Channel *, struct sshbuf *, struct sshbuf *);
static int mux_master_process_open_fwd(struct ssh *, u_int,
            Channel *, struct sshbuf *, struct sshbuf *);
static int mux_master_process_close_fwd(struct ssh *, u_int,
            Channel *, struct sshbuf *, struct sshbuf *);
static int mux_master_process_stdio_fwd(struct ssh *, u_int,
            Channel *, struct sshbuf *, struct sshbuf *);
static int mux_master_process_stop_listening(struct ssh *, u_int,
            Channel *, struct sshbuf *, struct sshbuf *);
static int mux_master_process_proxy(struct ssh *, u_int,
            Channel *, struct sshbuf *, struct sshbuf *);

static const struct {
        u_int type;
        int (*handler)(struct ssh *, u_int, Channel *,
            struct sshbuf *, struct sshbuf *);
} mux_master_handlers[] = {
        { MUX_MSG_HELLO, mux_master_process_hello },
        { MUX_C_NEW_SESSION, mux_master_process_new_session },
        { MUX_C_ALIVE_CHECK, mux_master_process_alive_check },
        { MUX_C_TERMINATE, mux_master_process_terminate },
        { MUX_C_OPEN_FWD, mux_master_process_open_fwd },
        { MUX_C_CLOSE_FWD, mux_master_process_close_fwd },
        { MUX_C_NEW_STDIO_FWD, mux_master_process_stdio_fwd },
        { MUX_C_STOP_LISTENING, mux_master_process_stop_listening },
        { MUX_C_PROXY, mux_master_process_proxy },
        { 0, NULL }
};

/* Cleanup callback fired on closure of mux client _session_ channel */
static void
mux_master_session_cleanup_cb(struct ssh *ssh, int cid, int force, void *unused)
{
        Channel *cc, *c = channel_by_id(ssh, cid);

        debug3_f("entering for channel %d", cid);
        if (c == NULL)
                fatal_f("channel_by_id(%i) == NULL", cid);
        if (c->ctl_chan != -1) {
                if ((cc = channel_by_id(ssh, c->ctl_chan)) == NULL)
                        fatal_f("channel %d missing control channel %d",
                            c->self, c->ctl_chan);
                c->ctl_chan = -1;
                cc->remote_id = 0;
                cc->have_remote_id = 0;
                chan_rcvd_oclose(ssh, cc);
        }
        channel_cancel_cleanup(ssh, c->self);
}

/* Cleanup callback fired on closure of mux client _control_ channel */
static void
mux_master_control_cleanup_cb(struct ssh *ssh, int cid, int force, void *unused)
{
        Channel *sc, *c = channel_by_id(ssh, cid);

        debug3_f("entering for channel %d", cid);
        if (c == NULL)
                fatal_f("channel_by_id(%i) == NULL", cid);
        if (c->have_remote_id) {
                if ((sc = channel_by_id(ssh, c->remote_id)) == NULL)
                        fatal_f("channel %d missing session channel %u",
                            c->self, c->remote_id);
                c->remote_id = 0;
                c->have_remote_id = 0;
                sc->ctl_chan = -1;
                if (sc->type != SSH_CHANNEL_OPEN &&
                    sc->type != SSH_CHANNEL_OPENING) {
                        debug2_f("channel %d: not open", sc->self);
                        chan_mark_dead(ssh, sc);
                } else {
                        if (sc->istate == CHAN_INPUT_OPEN)
                                chan_read_failed(ssh, sc);
                        if (sc->ostate == CHAN_OUTPUT_OPEN)
                                chan_write_failed(ssh, sc);
                }
        }
        channel_cancel_cleanup(ssh, c->self);
}

/* Check mux client environment variables before passing them to mux master. */
static int
env_permitted(const char *env)
{
        u_int i;
        int ret;
        char name[1024], *cp;

        if ((cp = strchr(env, '=')) == NULL || cp == env)
                return 0;
        ret = snprintf(name, sizeof(name), "%.*s", (int)(cp - env), env);
        if (ret <= 0 || (size_t)ret >= sizeof(name)) {
                error_f("name '%.100s...' too long", env);
                return 0;
        }

        for (i = 0; i < options.num_send_env; i++)
                if (match_pattern(name, options.send_env[i]))
                        return 1;

        return 0;
}

/* Mux master protocol message handlers */

static int
mux_master_process_hello(struct ssh *ssh, u_int rid,
    Channel *c, struct sshbuf *m, struct sshbuf *reply)
{
        u_int ver;
        struct mux_master_state *state = (struct mux_master_state *)c->mux_ctx;
        int r;

        if (state == NULL)
                fatal_f("channel %d: c->mux_ctx == NULL", c->self);
        if (state->hello_rcvd) {
                error_f("HELLO received twice");
                return -1;
        }
        if ((r = sshbuf_get_u32(m, &ver)) != 0) {
                error_fr(r, "parse");
                return -1;
        }
        if (ver != SSHMUX_VER) {
                error_f("unsupported multiplexing protocol version %u "
                    "(expected %u)", ver, SSHMUX_VER);
                return -1;
        }
        debug2_f("channel %d client version %u", c->self, ver);

        /* No extensions are presently defined */
        while (sshbuf_len(m) > 0) {
                char *name = NULL;
                size_t value_len = 0;

                if ((r = sshbuf_get_cstring(m, &name, NULL)) != 0 ||
                    (r = sshbuf_get_string_direct(m, NULL, &value_len)) != 0) {
                        error_fr(r, "parse extension");
                        return -1;
                }
                debug2_f("Unrecognised extension \"%s\" length %zu",
                    name, value_len);
                free(name);
        }
        state->hello_rcvd = 1;
        return 0;
}

/* Enqueue a "ok" response to the reply buffer */
static void
reply_ok(struct sshbuf *reply, u_int rid)
{
        int r;

        if ((r = sshbuf_put_u32(reply, MUX_S_OK)) != 0 ||
            (r = sshbuf_put_u32(reply, rid)) != 0)
                fatal_fr(r, "reply");
}

/* Enqueue an error response to the reply buffer */
static void
reply_error(struct sshbuf *reply, u_int type, u_int rid, const char *msg)
{
        int r;

        if ((r = sshbuf_put_u32(reply, type)) != 0 ||
            (r = sshbuf_put_u32(reply, rid)) != 0 ||
            (r = sshbuf_put_cstring(reply, msg)) != 0)
                fatal_fr(r, "reply");
}

static int
mux_master_process_new_session(struct ssh *ssh, u_int rid,
    Channel *c, struct sshbuf *m, struct sshbuf *reply)
{
        Channel *nc;
        struct mux_session_confirm_ctx *cctx;
        char *cmd, *cp;
        u_int i, j, env_len, escape_char, window, packetmax;
        int r, new_fd[3];

        /* Reply for SSHMUX_COMMAND_OPEN */
        cctx = xcalloc(1, sizeof(*cctx));
        cctx->term = NULL;
        cctx->rid = rid;
        cmd = NULL;
        cctx->env = NULL;
        env_len = 0;
        if ((r = sshbuf_skip_string(m)) != 0 || /* reserved */
            (r = sshbuf_get_u32(m, &cctx->want_tty)) != 0 ||
            (r = sshbuf_get_u32(m, &cctx->want_x_fwd)) != 0 ||
            (r = sshbuf_get_u32(m, &cctx->want_agent_fwd)) != 0 ||
            (r = sshbuf_get_u32(m, &cctx->want_subsys)) != 0 ||
            (r = sshbuf_get_u32(m, &escape_char)) != 0 ||
            (r = sshbuf_get_cstring(m, &cctx->term, NULL)) != 0 ||
            (r = sshbuf_get_cstring(m, &cmd, NULL)) != 0) {
 malf:
                free(cmd);
                for (j = 0; j < env_len; j++)
                        free(cctx->env[j]);
                free(cctx->env);
                free(cctx->term);
                free(cctx);
                error_f("malformed message");
                return -1;
        }

#define MUX_MAX_ENV_VARS        4096
        while (sshbuf_len(m) > 0) {
                if ((r = sshbuf_get_cstring(m, &cp, NULL)) != 0)
                        goto malf;
                if (!env_permitted(cp)) {
                        free(cp);
                        continue;
                }
                cctx->env = xreallocarray(cctx->env, env_len + 2,
                    sizeof(*cctx->env));
                cctx->env[env_len++] = cp;
                cctx->env[env_len] = NULL;
                if (env_len > MUX_MAX_ENV_VARS) {
                        error_f(">%d environment variables received, "
                            "ignoring additional", MUX_MAX_ENV_VARS);
                        break;
                }
        }

        debug2_f("channel %d: request tty %d, X %d, agent %d, subsys %d, "
            "term \"%s\", cmd \"%s\", env %u", c->self,
            cctx->want_tty, cctx->want_x_fwd, cctx->want_agent_fwd,
            cctx->want_subsys, cctx->term, cmd, env_len);

        if ((cctx->cmd = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put(cctx->cmd, cmd, strlen(cmd))) != 0)
                fatal_fr(r, "sshbuf_put");
        free(cmd);
        cmd = NULL;

        /* Gather fds from client */
        for(i = 0; i < 3; i++) {
                if ((new_fd[i] = mm_receive_fd(c->sock)) == -1) {
                        error_f("failed to receive fd %d from client", i);
                        for (j = 0; j < i; j++)
                                close(new_fd[j]);
                        for (j = 0; j < env_len; j++)
                                free(cctx->env[j]);
                        free(cctx->env);
                        free(cctx->term);
                        sshbuf_free(cctx->cmd);
                        free(cctx);
                        reply_error(reply, MUX_S_FAILURE, rid,
                            "did not receive file descriptors");
                        return -1;
                }
        }

        debug3_f("got fds stdin %d, stdout %d, stderr %d",
            new_fd[0], new_fd[1], new_fd[2]);

        /* XXX support multiple child sessions in future */
        if (c->have_remote_id) {
                debug2_f("session already open");
                reply_error(reply, MUX_S_FAILURE, rid,
                    "Multiple sessions not supported");
 cleanup:
                close(new_fd[0]);
                close(new_fd[1]);
                close(new_fd[2]);
                free(cctx->term);
                if (env_len != 0) {
                        for (i = 0; i < env_len; i++)
                                free(cctx->env[i]);
                        free(cctx->env);
                }
                sshbuf_free(cctx->cmd);
                free(cctx);
                return 0;
        }

        if (options.control_master == SSHCTL_MASTER_ASK ||
            options.control_master == SSHCTL_MASTER_AUTO_ASK) {
                if (!ask_permission("Allow shared connection to %s? ", host)) {
                        debug2_f("session refused by user");
                        reply_error(reply, MUX_S_PERMISSION_DENIED, rid,
                            "Permission denied");
                        goto cleanup;
                }
        }

        /* Try to pick up ttymodes from client before it goes raw */
        if (cctx->want_tty && tcgetattr(new_fd[0], &cctx->tio) == -1)
                error_f("tcgetattr: %s", strerror(errno));

        window = CHAN_SES_WINDOW_DEFAULT;
        packetmax = CHAN_SES_PACKET_DEFAULT;
        if (cctx->want_tty) {
                window >>= 1;
                packetmax >>= 1;
        }

        nc = channel_new(ssh, "session", SSH_CHANNEL_OPENING,
            new_fd[0], new_fd[1], new_fd[2], window, packetmax,
            CHAN_EXTENDED_WRITE, "client-session", CHANNEL_NONBLOCK_STDIO);

        nc->ctl_chan = c->self;         /* link session -> control channel */
        c->remote_id = nc->self;        /* link control -> session channel */
        c->have_remote_id = 1;

        if (cctx->want_tty && escape_char != 0xffffffff) {
                channel_register_filter(ssh, nc->self,
                    client_simple_escape_filter, NULL,
                    client_filter_cleanup,
                    client_new_escape_filter_ctx((int)escape_char));
        }

        debug2_f("channel_new: %d linked to control channel %d",
            nc->self, nc->ctl_chan);

        channel_send_open(ssh, nc->self);
        channel_register_open_confirm(ssh, nc->self, mux_session_confirm, cctx);
        c->mux_pause = 1; /* stop handling messages until open_confirm done */
        channel_register_cleanup(ssh, nc->self,
            mux_master_session_cleanup_cb, 1);

        /* reply is deferred, sent by mux_session_confirm */
        return 0;
}

static int
mux_master_process_alive_check(struct ssh *ssh, u_int rid,
    Channel *c, struct sshbuf *m, struct sshbuf *reply)
{
        int r;

        debug2_f("channel %d: alive check", c->self);

        /* prepare reply */
        if ((r = sshbuf_put_u32(reply, MUX_S_ALIVE)) != 0 ||
            (r = sshbuf_put_u32(reply, rid)) != 0 ||
            (r = sshbuf_put_u32(reply, (u_int)getpid())) != 0)
                fatal_fr(r, "reply");

        return 0;
}

static int
mux_master_process_terminate(struct ssh *ssh, u_int rid,
    Channel *c, struct sshbuf *m, struct sshbuf *reply)
{
        debug2_f("channel %d: terminate request", c->self);

        if (options.control_master == SSHCTL_MASTER_ASK ||
            options.control_master == SSHCTL_MASTER_AUTO_ASK) {
                if (!ask_permission("Terminate shared connection to %s? ",
                    host)) {
                        debug2_f("termination refused by user");
                        reply_error(reply, MUX_S_PERMISSION_DENIED, rid,
                            "Permission denied");
                        return 0;
                }
        }

        quit_pending = 1;
        reply_ok(reply, rid);
        /* XXX exit happens too soon - message never makes it to client */
        return 0;
}

static char *
format_forward(u_int ftype, struct Forward *fwd)
{
        char *ret;

        switch (ftype) {
        case MUX_FWD_LOCAL:
                xasprintf(&ret, "local forward %.200s:%d -> %.200s:%d",
                    (fwd->listen_path != NULL) ? fwd->listen_path :
                    (fwd->listen_host == NULL) ?
                    (options.fwd_opts.gateway_ports ? "*" : "LOCALHOST") :
                    fwd->listen_host, fwd->listen_port,
                    (fwd->connect_path != NULL) ? fwd->connect_path :
                    fwd->connect_host, fwd->connect_port);
                break;
        case MUX_FWD_DYNAMIC:
                xasprintf(&ret, "dynamic forward %.200s:%d -> *",
                    (fwd->listen_host == NULL) ?
                    (options.fwd_opts.gateway_ports ? "*" : "LOCALHOST") :
                    fwd->listen_host, fwd->listen_port);
                break;
        case MUX_FWD_REMOTE:
                xasprintf(&ret, "remote forward %.200s:%d -> %.200s:%d",
                    (fwd->listen_path != NULL) ? fwd->listen_path :
                    (fwd->listen_host == NULL) ?
                    "LOCALHOST" : fwd->listen_host,
                    fwd->listen_port,
                    (fwd->connect_path != NULL) ? fwd->connect_path :
                    fwd->connect_host, fwd->connect_port);
                break;
        default:
                fatal_f("unknown forward type %u", ftype);
        }
        return ret;
}

static int
compare_host(const char *a, const char *b)
{
        if (a == NULL && b == NULL)
                return 1;
        if (a == NULL || b == NULL)
                return 0;
        return strcmp(a, b) == 0;
}

static int
compare_forward(struct Forward *a, struct Forward *b)
{
        if (!compare_host(a->listen_host, b->listen_host))
                return 0;
        if (!compare_host(a->listen_path, b->listen_path))
                return 0;
        if (a->listen_port != b->listen_port)
                return 0;
        if (!compare_host(a->connect_host, b->connect_host))
                return 0;
        if (!compare_host(a->connect_path, b->connect_path))
                return 0;
        if (a->connect_port != b->connect_port)
                return 0;

        return 1;
}

static void
mux_confirm_remote_forward(struct ssh *ssh, int type, u_int32_t seq, void *ctxt)
{
        struct mux_channel_confirm_ctx *fctx = ctxt;
        char *failmsg = NULL;
        struct Forward *rfwd;
        Channel *c;
        struct sshbuf *out;
        u_int port;
        int r;

        if ((c = channel_by_id(ssh, fctx->cid)) == NULL) {
                /* no channel for reply */
                error_f("unknown channel");
                return;
        }
        if ((out = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if (fctx->fid >= options.num_remote_forwards ||
            (options.remote_forwards[fctx->fid].connect_path == NULL &&
            options.remote_forwards[fctx->fid].connect_host == NULL)) {
                xasprintf(&failmsg, "unknown forwarding id %d", fctx->fid);
                goto fail;
        }
        rfwd = &options.remote_forwards[fctx->fid];
        debug_f("%s for: listen %d, connect %s:%d",
            type == SSH2_MSG_REQUEST_SUCCESS ? "success" : "failure",
            rfwd->listen_port, rfwd->connect_path ? rfwd->connect_path :
            rfwd->connect_host, rfwd->connect_port);
        if (type == SSH2_MSG_REQUEST_SUCCESS) {
                if (rfwd->listen_port == 0) {
                        if ((r = sshpkt_get_u32(ssh, &port)) != 0)
                                fatal_fr(r, "parse port");
                        if (port > 65535) {
                                fatal("Invalid allocated port %u for "
                                    "mux remote forward to %s:%d", port,
                                    rfwd->connect_host, rfwd->connect_port);
                        }
                        rfwd->allocated_port = (int)port;
                        debug("Allocated port %u for mux remote forward"
                            " to %s:%d", rfwd->allocated_port,
                            rfwd->connect_host, rfwd->connect_port);
                        if ((r = sshbuf_put_u32(out,
                            MUX_S_REMOTE_PORT)) != 0 ||
                            (r = sshbuf_put_u32(out, fctx->rid)) != 0 ||
                            (r = sshbuf_put_u32(out,
                            rfwd->allocated_port)) != 0)
                                fatal_fr(r, "reply");
                        channel_update_permission(ssh, rfwd->handle,
                            rfwd->allocated_port);
                } else {
                        reply_ok(out, fctx->rid);
                }
                goto out;
        } else {
                if (rfwd->listen_port == 0)
                        channel_update_permission(ssh, rfwd->handle, -1);
                if (rfwd->listen_path != NULL)
                        xasprintf(&failmsg, "remote port forwarding failed for "
                            "listen path %s", rfwd->listen_path);
                else
                        xasprintf(&failmsg, "remote port forwarding failed for "
                            "listen port %d", rfwd->listen_port);

                debug2_f("clearing registered forwarding for listen %d, "
                    "connect %s:%d", rfwd->listen_port,
                    rfwd->connect_path ? rfwd->connect_path :
                    rfwd->connect_host, rfwd->connect_port);

                free(rfwd->listen_host);
                free(rfwd->listen_path);
                free(rfwd->connect_host);
                free(rfwd->connect_path);
                memset(rfwd, 0, sizeof(*rfwd));
        }
 fail:
        error_f("%s", failmsg);
        reply_error(out, MUX_S_FAILURE, fctx->rid, failmsg);
        free(failmsg);
 out:
        if ((r = sshbuf_put_stringb(c->output, out)) != 0)
                fatal_fr(r, "enqueue");
        sshbuf_free(out);
        if (c->mux_pause <= 0)
                fatal_f("mux_pause %d", c->mux_pause);
        c->mux_pause = 0; /* start processing messages again */
}

static int
mux_master_process_open_fwd(struct ssh *ssh, u_int rid,
    Channel *c, struct sshbuf *m, struct sshbuf *reply)
{
        struct Forward fwd;
        char *fwd_desc = NULL;
        char *listen_addr, *connect_addr;
        u_int ftype;
        u_int lport, cport;
        int r, i, ret = 0, freefwd = 1;

        memset(&fwd, 0, sizeof(fwd));

        /* XXX - lport/cport check redundant */
        if ((r = sshbuf_get_u32(m, &ftype)) != 0 ||
            (r = sshbuf_get_cstring(m, &listen_addr, NULL)) != 0 ||
            (r = sshbuf_get_u32(m, &lport)) != 0 ||
            (r = sshbuf_get_cstring(m, &connect_addr, NULL)) != 0 ||
            (r = sshbuf_get_u32(m, &cport)) != 0 ||
            (lport != (u_int)PORT_STREAMLOCAL && lport > 65535) ||
            (cport != (u_int)PORT_STREAMLOCAL && cport > 65535)) {
                error_f("malformed message");
                ret = -1;
                goto out;
        }
        if (*listen_addr == '\0') {
                free(listen_addr);
                listen_addr = NULL;
        }
        if (*connect_addr == '\0') {
                free(connect_addr);
                connect_addr = NULL;
        }

        memset(&fwd, 0, sizeof(fwd));
        fwd.listen_port = lport;
        if (fwd.listen_port == PORT_STREAMLOCAL)
                fwd.listen_path = listen_addr;
        else
                fwd.listen_host = listen_addr;
        fwd.connect_port = cport;
        if (fwd.connect_port == PORT_STREAMLOCAL)
                fwd.connect_path = connect_addr;
        else
                fwd.connect_host = connect_addr;

        debug2_f("channel %d: request %s", c->self,
            (fwd_desc = format_forward(ftype, &fwd)));

        if (ftype != MUX_FWD_LOCAL && ftype != MUX_FWD_REMOTE &&
            ftype != MUX_FWD_DYNAMIC) {
                logit_f("invalid forwarding type %u", ftype);
 invalid:
                free(listen_addr);
                free(connect_addr);
                reply_error(reply, MUX_S_FAILURE, rid,
                    "Invalid forwarding request");
                return 0;
        }
        if (ftype == MUX_FWD_DYNAMIC && fwd.listen_path) {
                logit_f("streamlocal and dynamic forwards "
                    "are mutually exclusive");
                goto invalid;
        }
        if (fwd.listen_port != PORT_STREAMLOCAL && fwd.listen_port >= 65536) {
                logit_f("invalid listen port %u", fwd.listen_port);
                goto invalid;
        }
        if ((fwd.connect_port != PORT_STREAMLOCAL &&
            fwd.connect_port >= 65536) ||
            (ftype != MUX_FWD_DYNAMIC && ftype != MUX_FWD_REMOTE &&
            fwd.connect_port == 0)) {
                logit_f("invalid connect port %u",
                    fwd.connect_port);
                goto invalid;
        }
        if (ftype != MUX_FWD_DYNAMIC && fwd.connect_host == NULL &&
            fwd.connect_path == NULL) {
                logit_f("missing connect host");
                goto invalid;
        }

        /* Skip forwards that have already been requested */
        switch (ftype) {
        case MUX_FWD_LOCAL:
        case MUX_FWD_DYNAMIC:
                for (i = 0; i < options.num_local_forwards; i++) {
                        if (compare_forward(&fwd,
                            options.local_forwards + i)) {
 exists:
                                debug2_f("found existing forwarding");
                                reply_ok(reply, rid);
                                goto out;
                        }
                }
                break;
        case MUX_FWD_REMOTE:
                for (i = 0; i < options.num_remote_forwards; i++) {
                        if (!compare_forward(&fwd, options.remote_forwards + i))
                                continue;
                        if (fwd.listen_port != 0)
                                goto exists;
                        debug2_f("found allocated port");
                        if ((r = sshbuf_put_u32(reply,
                            MUX_S_REMOTE_PORT)) != 0 ||
                            (r = sshbuf_put_u32(reply, rid)) != 0 ||
                            (r = sshbuf_put_u32(reply,
                            options.remote_forwards[i].allocated_port)) != 0)
                                fatal_fr(r, "reply FWD_REMOTE");
                        goto out;
                }
                break;
        }

        if (options.control_master == SSHCTL_MASTER_ASK ||
            options.control_master == SSHCTL_MASTER_AUTO_ASK) {
                if (!ask_permission("Open %s on %s?", fwd_desc, host)) {
                        debug2_f("forwarding refused by user");
                        reply_error(reply, MUX_S_PERMISSION_DENIED, rid,
                            "Permission denied");
                        goto out;
                }
        }

        if (ftype == MUX_FWD_LOCAL || ftype == MUX_FWD_DYNAMIC) {
                if (!channel_setup_local_fwd_listener(ssh, &fwd,
                    &options.fwd_opts)) {
 fail:
                        logit_f("requested %s failed", fwd_desc);
                        reply_error(reply, MUX_S_FAILURE, rid,
                            "Port forwarding failed");
                        goto out;
                }
                add_local_forward(&options, &fwd);
                freefwd = 0;
        } else {
                struct mux_channel_confirm_ctx *fctx;

                fwd.handle = channel_request_remote_forwarding(ssh, &fwd);
                if (fwd.handle < 0)
                        goto fail;
                add_remote_forward(&options, &fwd);
                fctx = xcalloc(1, sizeof(*fctx));
                fctx->cid = c->self;
                fctx->rid = rid;
                fctx->fid = options.num_remote_forwards - 1;
                client_register_global_confirm(mux_confirm_remote_forward,
                    fctx);
                freefwd = 0;
                c->mux_pause = 1; /* wait for mux_confirm_remote_forward */
                /* delayed reply in mux_confirm_remote_forward */
                goto out;
        }
        reply_ok(reply, rid);
 out:
        free(fwd_desc);
        if (freefwd) {
                free(fwd.listen_host);
                free(fwd.listen_path);
                free(fwd.connect_host);
                free(fwd.connect_path);
        }
        return ret;
}

static int
mux_master_process_close_fwd(struct ssh *ssh, u_int rid,
    Channel *c, struct sshbuf *m, struct sshbuf *reply)
{
        struct Forward fwd, *found_fwd;
        char *fwd_desc = NULL;
        const char *error_reason = NULL;
        char *listen_addr = NULL, *connect_addr = NULL;
        u_int ftype;
        int r, i, ret = 0;
        u_int lport, cport;

        memset(&fwd, 0, sizeof(fwd));

        if ((r = sshbuf_get_u32(m, &ftype)) != 0 ||
            (r = sshbuf_get_cstring(m, &listen_addr, NULL)) != 0 ||
            (r = sshbuf_get_u32(m, &lport)) != 0 ||
            (r = sshbuf_get_cstring(m, &connect_addr, NULL)) != 0 ||
            (r = sshbuf_get_u32(m, &cport)) != 0 ||
            (lport != (u_int)PORT_STREAMLOCAL && lport > 65535) ||
            (cport != (u_int)PORT_STREAMLOCAL && cport > 65535)) {
                error_f("malformed message");
                ret = -1;
                goto out;
        }

        if (*listen_addr == '\0') {
                free(listen_addr);
                listen_addr = NULL;
        }
        if (*connect_addr == '\0') {
                free(connect_addr);
                connect_addr = NULL;
        }

        memset(&fwd, 0, sizeof(fwd));
        fwd.listen_port = lport;
        if (fwd.listen_port == PORT_STREAMLOCAL)
                fwd.listen_path = listen_addr;
        else
                fwd.listen_host = listen_addr;
        fwd.connect_port = cport;
        if (fwd.connect_port == PORT_STREAMLOCAL)
                fwd.connect_path = connect_addr;
        else
                fwd.connect_host = connect_addr;

        debug2_f("channel %d: request cancel %s", c->self,
            (fwd_desc = format_forward(ftype, &fwd)));

        /* make sure this has been requested */
        found_fwd = NULL;
        switch (ftype) {
        case MUX_FWD_LOCAL:
        case MUX_FWD_DYNAMIC:
                for (i = 0; i < options.num_local_forwards; i++) {
                        if (compare_forward(&fwd,
                            options.local_forwards + i)) {
                                found_fwd = options.local_forwards + i;
                                break;
                        }
                }
                break;
        case MUX_FWD_REMOTE:
                for (i = 0; i < options.num_remote_forwards; i++) {
                        if (compare_forward(&fwd,
                            options.remote_forwards + i)) {
                                found_fwd = options.remote_forwards + i;
                                break;
                        }
                }
                break;
        }

        if (found_fwd == NULL)
                error_reason = "port not forwarded";
        else if (ftype == MUX_FWD_REMOTE) {
                /*
                 * This shouldn't fail unless we confused the host/port
                 * between options.remote_forwards and permitted_opens.
                 * However, for dynamic allocated listen ports we need
                 * to use the actual listen port.
                 */
                if (channel_request_rforward_cancel(ssh, found_fwd) == -1)
                        error_reason = "port not in permitted opens";
        } else {        /* local and dynamic forwards */
                /* Ditto */
                if (channel_cancel_lport_listener(ssh, &fwd, fwd.connect_port,
                    &options.fwd_opts) == -1)
                        error_reason = "port not found";
        }

        if (error_reason != NULL)
                reply_error(reply, MUX_S_FAILURE, rid, error_reason);
        else {
                reply_ok(reply, rid);
                free(found_fwd->listen_host);
                free(found_fwd->listen_path);
                free(found_fwd->connect_host);
                free(found_fwd->connect_path);
                found_fwd->listen_host = found_fwd->connect_host = NULL;
                found_fwd->listen_path = found_fwd->connect_path = NULL;
                found_fwd->listen_port = found_fwd->connect_port = 0;
        }
 out:
        free(fwd_desc);
        free(listen_addr);
        free(connect_addr);

        return ret;
}

static int
mux_master_process_stdio_fwd(struct ssh *ssh, u_int rid,
    Channel *c, struct sshbuf *m, struct sshbuf *reply)
{
        Channel *nc;
        char *chost = NULL;
        u_int _cport, i, j;
        int ok = 0, cport, r, new_fd[2];
        struct mux_stdio_confirm_ctx *cctx;

        if ((r = sshbuf_skip_string(m)) != 0 || /* reserved */
            (r = sshbuf_get_cstring(m, &chost, NULL)) != 0 ||
            (r = sshbuf_get_u32(m, &_cport)) != 0) {
                free(chost);
                error_f("malformed message");
                return -1;
        }
        if (_cport == (u_int)PORT_STREAMLOCAL)
                cport = PORT_STREAMLOCAL;
        else if (_cport <= INT_MAX)
                cport = (int)_cport;
        else {
                free(chost);
                error_f("invalid port 0x%x", _cport);
                return -1;
        }

        debug2_f("channel %d: stdio fwd to %s:%d", c->self, chost, cport);

        /* Gather fds from client */
        for(i = 0; i < 2; i++) {
                if ((new_fd[i] = mm_receive_fd(c->sock)) == -1) {
                        error_f("failed to receive fd %d from client", i);
                        for (j = 0; j < i; j++)
                                close(new_fd[j]);
                        free(chost);

                        /* prepare reply */
                        reply_error(reply, MUX_S_FAILURE, rid,
                            "did not receive file descriptors");
                        return -1;
                }
        }

        debug3_f("got fds stdin %d, stdout %d", new_fd[0], new_fd[1]);

        /* XXX support multiple child sessions in future */
        if (c->have_remote_id) {
                debug2_f("session already open");
                reply_error(reply, MUX_S_FAILURE, rid,
                    "Multiple sessions not supported");
 cleanup:
                close(new_fd[0]);
                close(new_fd[1]);
                free(chost);
                return 0;
        }

        if (options.control_master == SSHCTL_MASTER_ASK ||
            options.control_master == SSHCTL_MASTER_AUTO_ASK) {
                if (cport == PORT_STREAMLOCAL) {
                        ok = ask_permission("Allow forward to path %s", chost);
                } else {
                        ok = ask_permission("Allow forward to [%s]:%d? ",
                            chost, cport);
                }
                if (!ok) {
                        debug2_f("stdio fwd refused by user");
                        reply_error(reply, MUX_S_PERMISSION_DENIED, rid,
                            "Permission denied");
                        goto cleanup;
                }
        }

        nc = channel_connect_stdio_fwd(ssh, chost, cport, new_fd[0], new_fd[1],
            CHANNEL_NONBLOCK_STDIO);
        free(chost);

        nc->ctl_chan = c->self;         /* link session -> control channel */
        c->remote_id = nc->self;        /* link control -> session channel */
        c->have_remote_id = 1;

        debug2_f("channel_new: %d control %d", nc->self, nc->ctl_chan);

        channel_register_cleanup(ssh, nc->self,
            mux_master_session_cleanup_cb, 1);

        cctx = xcalloc(1, sizeof(*cctx));
        cctx->rid = rid;
        channel_register_open_confirm(ssh, nc->self, mux_stdio_confirm, cctx);
        c->mux_pause = 1; /* stop handling messages until open_confirm done */

        /* reply is deferred, sent by mux_session_confirm */
        return 0;
}

/* Callback on open confirmation in mux master for a mux stdio fwd session. */
static void
mux_stdio_confirm(struct ssh *ssh, int id, int success, void *arg)
{
        struct mux_stdio_confirm_ctx *cctx = arg;
        Channel *c, *cc;
        struct sshbuf *reply;
        int r;

        if (cctx == NULL)
                fatal_f("cctx == NULL");
        if ((c = channel_by_id(ssh, id)) == NULL)
                fatal_f("no channel for id %d", id);
        if ((cc = channel_by_id(ssh, c->ctl_chan)) == NULL)
                fatal_f("channel %d lacks control channel %d",
                    id, c->ctl_chan);
        if ((reply = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");

        if (!success) {
                debug3_f("sending failure reply");
                reply_error(reply, MUX_S_FAILURE, cctx->rid,
                    "Session open refused by peer");
                /* prepare reply */
                goto done;
        }

        debug3_f("sending success reply");
        /* prepare reply */
        if ((r = sshbuf_put_u32(reply, MUX_S_SESSION_OPENED)) != 0 ||
            (r = sshbuf_put_u32(reply, cctx->rid)) != 0 ||
            (r = sshbuf_put_u32(reply, c->self)) != 0)
                fatal_fr(r, "reply");

 done:
        /* Send reply */
        if ((r = sshbuf_put_stringb(cc->output, reply)) != 0)
                fatal_fr(r, "enqueue");
        sshbuf_free(reply);

        if (cc->mux_pause <= 0)
                fatal_f("mux_pause %d", cc->mux_pause);
        cc->mux_pause = 0; /* start processing messages again */
        c->open_confirm_ctx = NULL;
        free(cctx);
}

static int
mux_master_process_stop_listening(struct ssh *ssh, u_int rid,
    Channel *c, struct sshbuf *m, struct sshbuf *reply)
{
        debug_f("channel %d: stop listening", c->self);

        if (options.control_master == SSHCTL_MASTER_ASK ||
            options.control_master == SSHCTL_MASTER_AUTO_ASK) {
                if (!ask_permission("Disable further multiplexing on shared "
                    "connection to %s? ", host)) {
                        debug2_f("stop listen refused by user");
                        reply_error(reply, MUX_S_PERMISSION_DENIED, rid,
                            "Permission denied");
                        return 0;
                }
        }

        if (mux_listener_channel != NULL) {
                channel_free(ssh, mux_listener_channel);
                client_stop_mux();
                free(options.control_path);
                options.control_path = NULL;
                mux_listener_channel = NULL;
                muxserver_sock = -1;
        }

        reply_ok(reply, rid);
        return 0;
}

static int
mux_master_process_proxy(struct ssh *ssh, u_int rid,
    Channel *c, struct sshbuf *m, struct sshbuf *reply)
{
        int r;

        debug_f("channel %d: proxy request", c->self);

        c->mux_rcb = channel_proxy_downstream;
        if ((r = sshbuf_put_u32(reply, MUX_S_PROXY)) != 0 ||
            (r = sshbuf_put_u32(reply, rid)) != 0)
                fatal_fr(r, "reply");

        return 0;
}

/* Channel callbacks fired on read/write from mux client fd */
static int
mux_master_read_cb(struct ssh *ssh, Channel *c)
{
        struct mux_master_state *state = (struct mux_master_state *)c->mux_ctx;
        struct sshbuf *in = NULL, *out = NULL;
        u_int type, rid, i;
        int r, ret = -1;

        if ((out = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");

        /* Setup ctx and  */
        if (c->mux_ctx == NULL) {
                state = xcalloc(1, sizeof(*state));
                c->mux_ctx = state;
                channel_register_cleanup(ssh, c->self,
                    mux_master_control_cleanup_cb, 0);

                /* Send hello */
                if ((r = sshbuf_put_u32(out, MUX_MSG_HELLO)) != 0 ||
                    (r = sshbuf_put_u32(out, SSHMUX_VER)) != 0)
                        fatal_fr(r, "reply");
                /* no extensions */
                if ((r = sshbuf_put_stringb(c->output, out)) != 0)
                        fatal_fr(r, "enqueue");
                debug3_f("channel %d: hello sent", c->self);
                ret = 0;
                goto out;
        }

        /* Channel code ensures that we receive whole packets */
        if ((r = sshbuf_froms(c->input, &in)) != 0) {
 malf:
                error_f("malformed message");
                goto out;
        }

        if ((r = sshbuf_get_u32(in, &type)) != 0)
                goto malf;
        debug3_f("channel %d packet type 0x%08x len %zu", c->self,
            type, sshbuf_len(in));

        if (type == MUX_MSG_HELLO)
                rid = 0;
        else {
                if (!state->hello_rcvd) {
                        error_f("expected MUX_MSG_HELLO(0x%08x), "
                            "received 0x%08x", MUX_MSG_HELLO, type);
                        goto out;
                }
                if ((r = sshbuf_get_u32(in, &rid)) != 0)
                        goto malf;
        }

        for (i = 0; mux_master_handlers[i].handler != NULL; i++) {
                if (type == mux_master_handlers[i].type) {
                        ret = mux_master_handlers[i].handler(ssh, rid,
                            c, in, out);
                        break;
                }
        }
        if (mux_master_handlers[i].handler == NULL) {
                error_f("unsupported mux message 0x%08x", type);
                reply_error(out, MUX_S_FAILURE, rid, "unsupported request");
                ret = 0;
        }
        /* Enqueue reply packet */
        if (sshbuf_len(out) != 0 &&
            (r = sshbuf_put_stringb(c->output, out)) != 0)
                fatal_fr(r, "enqueue");
 out:
        sshbuf_free(in);
        sshbuf_free(out);
        return ret;
}

void
mux_exit_message(struct ssh *ssh, Channel *c, int exitval)
{
        struct sshbuf *m;
        Channel *mux_chan;
        int r;

        debug3_f("channel %d: exit message, exitval %d", c->self, exitval);

        if ((mux_chan = channel_by_id(ssh, c->ctl_chan)) == NULL)
                fatal_f("channel %d missing mux %d", c->self, c->ctl_chan);

        /* Append exit message packet to control socket output queue */
        if ((m = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put_u32(m, MUX_S_EXIT_MESSAGE)) != 0 ||
            (r = sshbuf_put_u32(m, c->self)) != 0 ||
            (r = sshbuf_put_u32(m, exitval)) != 0 ||
            (r = sshbuf_put_stringb(mux_chan->output, m)) != 0)
                fatal_fr(r, "reply");
        sshbuf_free(m);
}

void
mux_tty_alloc_failed(struct ssh *ssh, Channel *c)
{
        struct sshbuf *m;
        Channel *mux_chan;
        int r;

        debug3_f("channel %d: TTY alloc failed", c->self);

        if ((mux_chan = channel_by_id(ssh, c->ctl_chan)) == NULL)
                fatal_f("channel %d missing mux %d", c->self, c->ctl_chan);

        /* Append exit message packet to control socket output queue */
        if ((m = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put_u32(m, MUX_S_TTY_ALLOC_FAIL)) != 0 ||
            (r = sshbuf_put_u32(m, c->self)) != 0 ||
            (r = sshbuf_put_stringb(mux_chan->output, m)) != 0)
                fatal_fr(r, "reply");
        sshbuf_free(m);
}

/* Prepare a mux master to listen on a Unix domain socket. */
void
muxserver_listen(struct ssh *ssh)
{
        mode_t old_umask;
        char *orig_control_path = options.control_path;
        char rbuf[16+1];
        u_int i, r;
        int oerrno;

        if (options.control_path == NULL ||
            options.control_master == SSHCTL_MASTER_NO)
                return;

        debug("setting up multiplex master socket");

        /*
         * Use a temporary path before listen so we can pseudo-atomically
         * establish the listening socket in its final location to avoid
         * other processes racing in between bind() and listen() and hitting
         * an unready socket.
         */
        for (i = 0; i < sizeof(rbuf) - 1; i++) {
                r = arc4random_uniform(26+26+10);
                rbuf[i] = (r < 26) ? 'a' + r :
                    (r < 26*2) ? 'A' + r - 26 :
                    '0' + r - 26 - 26;
        }
        rbuf[sizeof(rbuf) - 1] = '\0';
        options.control_path = NULL;
        xasprintf(&options.control_path, "%s.%s", orig_control_path, rbuf);
        debug3_f("temporary control path %s", options.control_path);

        old_umask = umask(0177);
        muxserver_sock = unix_listener(options.control_path, 64, 0);
        oerrno = errno;
        umask(old_umask);
        if (muxserver_sock < 0) {
                if (oerrno == EINVAL || oerrno == EADDRINUSE) {
                        error("ControlSocket %s already exists, "
                            "disabling multiplexing", options.control_path);
 disable_mux_master:
                        if (muxserver_sock != -1) {
                                close(muxserver_sock);
                                muxserver_sock = -1;
                        }
                        free(orig_control_path);
                        free(options.control_path);
                        options.control_path = NULL;
                        options.control_master = SSHCTL_MASTER_NO;
                        return;
                } else {
                        /* unix_listener() logs the error */
                        cleanup_exit(255);
                }
        }

        /* Now atomically "move" the mux socket into position */
        if (link(options.control_path, orig_control_path) != 0) {
                if (errno != EEXIST) {
                        fatal_f("link mux listener %s => %s: %s",
                            options.control_path, orig_control_path,
                            strerror(errno));
                }
                error("ControlSocket %s already exists, disabling multiplexing",
                    orig_control_path);
                unlink(options.control_path);
                goto disable_mux_master;
        }
        unlink(options.control_path);
        free(options.control_path);
        options.control_path = orig_control_path;

        set_nonblock(muxserver_sock);

        mux_listener_channel = channel_new(ssh, "mux listener",
            SSH_CHANNEL_MUX_LISTENER, muxserver_sock, muxserver_sock, -1,
            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
            0, options.control_path, 1);
        mux_listener_channel->mux_rcb = mux_master_read_cb;
        debug3_f("mux listener channel %d fd %d",
            mux_listener_channel->self, mux_listener_channel->sock);
}

/* Callback on open confirmation in mux master for a mux client session. */
static void
mux_session_confirm(struct ssh *ssh, int id, int success, void *arg)
{
        struct mux_session_confirm_ctx *cctx = arg;
        const char *display;
        Channel *c, *cc;
        int i, r;
        struct sshbuf *reply;

        if (cctx == NULL)
                fatal_f("cctx == NULL");
        if ((c = channel_by_id(ssh, id)) == NULL)
                fatal_f("no channel for id %d", id);
        if ((cc = channel_by_id(ssh, c->ctl_chan)) == NULL)
                fatal_f("channel %d lacks control channel %d",
                    id, c->ctl_chan);
        if ((reply = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");

        if (!success) {
                debug3_f("sending failure reply");
                reply_error(reply, MUX_S_FAILURE, cctx->rid,
                    "Session open refused by peer");
                goto done;
        }

        display = getenv("DISPLAY");
        if (cctx->want_x_fwd && options.forward_x11 && display != NULL) {
                char *proto, *data;

                /* Get reasonable local authentication information. */
                if (client_x11_get_proto(ssh, display, options.xauth_location,
                    options.forward_x11_trusted, options.forward_x11_timeout,
                    &proto, &data) == 0) {
                        /* Request forwarding with authentication spoofing. */
                        debug("Requesting X11 forwarding with authentication "
                            "spoofing.");
                        x11_request_forwarding_with_spoofing(ssh, id,
                            display, proto, data, 1);
                        /* XXX exit_on_forward_failure */
                        client_expect_confirm(ssh, id, "X11 forwarding",
                            CONFIRM_WARN);
                }
        }

        if (cctx->want_agent_fwd && options.forward_agent) {
                debug("Requesting authentication agent forwarding.");
                channel_request_start(ssh, id, "auth-agent-req@openssh.com", 0);
                if ((r = sshpkt_send(ssh)) != 0)
                        fatal_fr(r, "send");
        }

        client_session2_setup(ssh, id, cctx->want_tty, cctx->want_subsys,
            cctx->term, &cctx->tio, c->rfd, cctx->cmd, cctx->env);

        debug3_f("sending success reply");
        /* prepare reply */
        if ((r = sshbuf_put_u32(reply, MUX_S_SESSION_OPENED)) != 0 ||
            (r = sshbuf_put_u32(reply, cctx->rid)) != 0 ||
            (r = sshbuf_put_u32(reply, c->self)) != 0)
                fatal_fr(r, "reply");

 done:
        /* Send reply */
        if ((r = sshbuf_put_stringb(cc->output, reply)) != 0)
                fatal_fr(r, "enqueue");
        sshbuf_free(reply);

        if (cc->mux_pause <= 0)
                fatal_f("mux_pause %d", cc->mux_pause);
        cc->mux_pause = 0; /* start processing messages again */
        c->open_confirm_ctx = NULL;
        sshbuf_free(cctx->cmd);
        free(cctx->term);
        if (cctx->env != NULL) {
                for (i = 0; cctx->env[i] != NULL; i++)
                        free(cctx->env[i]);
                free(cctx->env);
        }
        free(cctx);
}

/* ** Multiplexing client support */

/* Exit signal handler */
static void
control_client_sighandler(int signo)
{
        muxclient_terminate = signo;
}

/*
 * Relay signal handler - used to pass some signals from mux client to
 * mux master.
 */
static void
control_client_sigrelay(int signo)
{
        int save_errno = errno;

        if (muxserver_pid > 1)
                kill(muxserver_pid, signo);

        errno = save_errno;
}

static int
mux_client_read(int fd, struct sshbuf *b, size_t need, int timeout_ms)
{
        size_t have;
        ssize_t len;
        u_char *p;
        int r;

        if ((r = sshbuf_reserve(b, need, &p)) != 0)
                fatal_fr(r, "reserve");
        for (have = 0; have < need; ) {
                if (muxclient_terminate) {
                        errno = EINTR;
                        return -1;
                }
                len = read(fd, p + have, need - have);
                if (len == -1) {
                        switch (errno) {
#if defined(EWOULDBLOCK) && (EWOULDBLOCK != EAGAIN)
                        case EWOULDBLOCK:
#endif
                        case EAGAIN:
                                if (waitrfd(fd, &timeout_ms,
                                    &muxclient_terminate) == -1 &&
                                    errno != EINTR)
                                        return -1;      /* timeout */
                                /* FALLTHROUGH */
                        case EINTR:
                                continue;
                        default:
                                return -1;
                        }
                }
                if (len == 0) {
                        errno = EPIPE;
                        return -1;
                }
                have += (size_t)len;
        }
        return 0;
}

static int
mux_client_write_packet(int fd, struct sshbuf *m)
{
        struct sshbuf *queue;
        u_int have, need;
        int r, oerrno, len;
        const u_char *ptr;
        struct pollfd pfd;

        pfd.fd = fd;
        pfd.events = POLLOUT;
        if ((queue = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put_stringb(queue, m)) != 0)
                fatal_fr(r, "enqueue");

        need = sshbuf_len(queue);
        ptr = sshbuf_ptr(queue);

        for (have = 0; have < need; ) {
                if (muxclient_terminate) {
                        sshbuf_free(queue);
                        errno = EINTR;
                        return -1;
                }
                len = write(fd, ptr + have, need - have);
                if (len == -1) {
                        switch (errno) {
#if defined(EWOULDBLOCK) && (EWOULDBLOCK != EAGAIN)
                        case EWOULDBLOCK:
#endif
                        case EAGAIN:
                                (void)poll(&pfd, 1, -1);
                                /* FALLTHROUGH */
                        case EINTR:
                                continue;
                        default:
                                oerrno = errno;
                                sshbuf_free(queue);
                                errno = oerrno;
                                return -1;
                        }
                }
                if (len == 0) {
                        sshbuf_free(queue);
                        errno = EPIPE;
                        return -1;
                }
                have += (u_int)len;
        }
        sshbuf_free(queue);
        return 0;
}

static int
mux_client_read_packet_timeout(int fd, struct sshbuf *m, int timeout_ms)
{
        struct sshbuf *queue;
        size_t need, have;
        const u_char *ptr;
        int r, oerrno;

        if ((queue = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if (mux_client_read(fd, queue, 4, timeout_ms) != 0) {
                if ((oerrno = errno) == EPIPE)
                        debug3_f("read header failed: %s",
                            strerror(errno));
                sshbuf_free(queue);
                errno = oerrno;
                return -1;
        }
        need = PEEK_U32(sshbuf_ptr(queue));
        if (mux_client_read(fd, queue, need, timeout_ms) != 0) {
                oerrno = errno;
                debug3_f("read body failed: %s", strerror(errno));
                sshbuf_free(queue);
                errno = oerrno;
                return -1;
        }
        if ((r = sshbuf_get_string_direct(queue, &ptr, &have)) != 0 ||
            (r = sshbuf_put(m, ptr, have)) != 0)
                fatal_fr(r, "dequeue");
        sshbuf_free(queue);
        return 0;
}

static int
mux_client_read_packet(int fd, struct sshbuf *m)
{
        return mux_client_read_packet_timeout(fd, m, -1);
}

static int
mux_client_hello_exchange(int fd, int timeout_ms)
{
        struct sshbuf *m;
        u_int type, ver;
        int r, ret = -1;

        if ((m = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put_u32(m, MUX_MSG_HELLO)) != 0 ||
            (r = sshbuf_put_u32(m, SSHMUX_VER)) != 0)
                fatal_fr(r, "assemble hello");
        /* no extensions */

        if (mux_client_write_packet(fd, m) != 0) {
                debug_f("write packet: %s", strerror(errno));
                goto out;
        }

        sshbuf_reset(m);

        /* Read their HELLO */
        if (mux_client_read_packet_timeout(fd, m, timeout_ms) != 0) {
                debug_f("read packet failed");
                goto out;
        }

        if ((r = sshbuf_get_u32(m, &type)) != 0)
                fatal_fr(r, "parse type");
        if (type != MUX_MSG_HELLO) {
                error_f("expected HELLO (%u) got %u", MUX_MSG_HELLO, type);
                goto out;
        }
        if ((r = sshbuf_get_u32(m, &ver)) != 0)
                fatal_fr(r, "parse version");
        if (ver != SSHMUX_VER) {
                error("Unsupported multiplexing protocol version %d "
                    "(expected %d)", ver, SSHMUX_VER);
                goto out;
        }
        debug2_f("master version %u", ver);
        /* No extensions are presently defined */
        while (sshbuf_len(m) > 0) {
                char *name = NULL;

                if ((r = sshbuf_get_cstring(m, &name, NULL)) != 0 ||
                    (r = sshbuf_skip_string(m)) != 0) { /* value */
                        error_fr(r, "parse extension");
                        goto out;
                }
                debug2("Unrecognised master extension \"%s\"", name);
                free(name);
        }
        /* success */
        ret = 0;
 out:
        sshbuf_free(m);
        return ret;
}

static u_int
mux_client_request_alive(int fd)
{
        struct sshbuf *m;
        char *e;
        u_int pid, type, rid;
        int r;

        debug3_f("entering");

        if ((m = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put_u32(m, MUX_C_ALIVE_CHECK)) != 0 ||
            (r = sshbuf_put_u32(m, muxclient_request_id)) != 0)
                fatal_fr(r, "assemble");

        if (mux_client_write_packet(fd, m) != 0)
                fatal_f("write packet: %s", strerror(errno));

        sshbuf_reset(m);

        /* Read their reply */
        if (mux_client_read_packet(fd, m) != 0) {
                sshbuf_free(m);
                return 0;
        }

        if ((r = sshbuf_get_u32(m, &type)) != 0)
                fatal_fr(r, "parse type");
        if (type != MUX_S_ALIVE) {
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                fatal_f("master returned error: %s", e);
        }

        if ((r = sshbuf_get_u32(m, &rid)) != 0)
                fatal_fr(r, "parse remote ID");
        if (rid != muxclient_request_id)
                fatal_f("out of sequence reply: my id %u theirs %u",
                    muxclient_request_id, rid);
        if ((r = sshbuf_get_u32(m, &pid)) != 0)
                fatal_fr(r, "parse PID");
        sshbuf_free(m);

        debug3_f("done pid = %u", pid);

        muxclient_request_id++;

        return pid;
}

static void
mux_client_request_terminate(int fd)
{
        struct sshbuf *m;
        char *e;
        u_int type, rid;
        int r;

        debug3_f("entering");

        if ((m = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put_u32(m, MUX_C_TERMINATE)) != 0 ||
            (r = sshbuf_put_u32(m, muxclient_request_id)) != 0)
                fatal_fr(r, "request");

        if (mux_client_write_packet(fd, m) != 0)
                fatal_f("write packet: %s", strerror(errno));

        sshbuf_reset(m);

        /* Read their reply */
        if (mux_client_read_packet(fd, m) != 0) {
                /* Remote end exited already */
                if (errno == EPIPE) {
                        sshbuf_free(m);
                        return;
                }
                fatal_f("read from master failed: %s", strerror(errno));
        }

        if ((r = sshbuf_get_u32(m, &type)) != 0 ||
            (r = sshbuf_get_u32(m, &rid)) != 0)
                fatal_fr(r, "parse");
        if (rid != muxclient_request_id)
                fatal_f("out of sequence reply: my id %u theirs %u",
                    muxclient_request_id, rid);
        switch (type) {
        case MUX_S_OK:
                break;
        case MUX_S_PERMISSION_DENIED:
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                fatal("Master refused termination request: %s", e);
        case MUX_S_FAILURE:
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                fatal_f("termination request failed: %s", e);
        default:
                fatal_f("unexpected response from master 0x%08x", type);
        }
        sshbuf_free(m);
        muxclient_request_id++;
}

static int
mux_client_forward(int fd, int cancel_flag, u_int ftype, struct Forward *fwd)
{
        struct sshbuf *m;
        char *e, *fwd_desc;
        const char *lhost, *chost;
        u_int type, rid;
        int r;

        fwd_desc = format_forward(ftype, fwd);
        debug("Requesting %s %s",
            cancel_flag ? "cancellation of" : "forwarding of", fwd_desc);
        free(fwd_desc);

        type = cancel_flag ? MUX_C_CLOSE_FWD : MUX_C_OPEN_FWD;
        if (fwd->listen_path != NULL)
                lhost = fwd->listen_path;
        else if (fwd->listen_host == NULL)
                lhost = "";
        else if (*fwd->listen_host == '\0')
                lhost = "*";
        else
                lhost = fwd->listen_host;

        if (fwd->connect_path != NULL)
                chost = fwd->connect_path;
        else if (fwd->connect_host == NULL)
                chost = "";
        else
                chost = fwd->connect_host;

        if ((m = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put_u32(m, type)) != 0 ||
            (r = sshbuf_put_u32(m, muxclient_request_id)) != 0 ||
            (r = sshbuf_put_u32(m, ftype)) != 0 ||
            (r = sshbuf_put_cstring(m, lhost)) != 0 ||
            (r = sshbuf_put_u32(m, fwd->listen_port)) != 0 ||
            (r = sshbuf_put_cstring(m, chost)) != 0 ||
            (r = sshbuf_put_u32(m, fwd->connect_port)) != 0)
                fatal_fr(r, "request");

        if (mux_client_write_packet(fd, m) != 0)
                fatal_f("write packet: %s", strerror(errno));

        sshbuf_reset(m);

        /* Read their reply */
        if (mux_client_read_packet(fd, m) != 0) {
                sshbuf_free(m);
                return -1;
        }

        if ((r = sshbuf_get_u32(m, &type)) != 0 ||
            (r = sshbuf_get_u32(m, &rid)) != 0)
                fatal_fr(r, "parse");
        if (rid != muxclient_request_id)
                fatal_f("out of sequence reply: my id %u theirs %u",
                    muxclient_request_id, rid);

        switch (type) {
        case MUX_S_OK:
                break;
        case MUX_S_REMOTE_PORT:
                if (cancel_flag)
                        fatal_f("got MUX_S_REMOTE_PORT for cancel");
                if ((r = sshbuf_get_u32(m, &fwd->allocated_port)) != 0)
                        fatal_fr(r, "parse port");
                verbose("Allocated port %u for remote forward to %s:%d",
                    fwd->allocated_port,
                    fwd->connect_host ? fwd->connect_host : "",
                    fwd->connect_port);
                if (muxclient_command == SSHMUX_COMMAND_FORWARD)
                        fprintf(stdout, "%i\n", fwd->allocated_port);
                break;
        case MUX_S_PERMISSION_DENIED:
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                sshbuf_free(m);
                error("Master refused forwarding request: %s", e);
                return -1;
        case MUX_S_FAILURE:
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                sshbuf_free(m);
                error_f("forwarding request failed: %s", e);
                return -1;
        default:
                fatal_f("unexpected response from master 0x%08x", type);
        }
        sshbuf_free(m);

        muxclient_request_id++;
        return 0;
}

static int
mux_client_forwards(int fd, int cancel_flag)
{
        int i, ret = 0;

        debug3_f("%s forwardings: %d local, %d remote",
            cancel_flag ? "cancel" : "request",
            options.num_local_forwards, options.num_remote_forwards);

        /* XXX ExitOnForwardingFailure */
        for (i = 0; i < options.num_local_forwards; i++) {
                if (mux_client_forward(fd, cancel_flag,
                    options.local_forwards[i].connect_port == 0 ?
                    MUX_FWD_DYNAMIC : MUX_FWD_LOCAL,
                    options.local_forwards + i) != 0)
                        ret = -1;
        }
        for (i = 0; i < options.num_remote_forwards; i++) {
                if (mux_client_forward(fd, cancel_flag, MUX_FWD_REMOTE,
                    options.remote_forwards + i) != 0)
                        ret = -1;
        }
        return ret;
}

static int
mux_client_request_session(int fd)
{
        struct sshbuf *m;
        char *e;
        const char *term = NULL;
        u_int i, echar, rid, sid, esid, exitval, type, exitval_seen;
        extern char **environ;
        int r, rawmode = 0;

        debug3_f("entering");

        if ((muxserver_pid = mux_client_request_alive(fd)) == 0) {
                error_f("master alive request failed");
                return -1;
        }

        ssh_signal(SIGPIPE, SIG_IGN);

        if (options.stdin_null && stdfd_devnull(1, 0, 0) == -1)
                fatal_f("stdfd_devnull failed");

        if ((term = lookup_env_in_list("TERM", options.setenv,
            options.num_setenv)) == NULL || *term == '\0')
                term = getenv("TERM");

        echar = 0xffffffff;
        if (options.escape_char != SSH_ESCAPECHAR_NONE)
            echar = (u_int)options.escape_char;

        if ((m = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put_u32(m, MUX_C_NEW_SESSION)) != 0 ||
            (r = sshbuf_put_u32(m, muxclient_request_id)) != 0 ||
            (r = sshbuf_put_string(m, NULL, 0)) != 0 || /* reserved */
            (r = sshbuf_put_u32(m, tty_flag)) != 0 ||
            (r = sshbuf_put_u32(m, options.forward_x11)) != 0 ||
            (r = sshbuf_put_u32(m, options.forward_agent)) != 0 ||
            (r = sshbuf_put_u32(m, options.session_type == SESSION_TYPE_SUBSYSTEM)) != 0 ||
            (r = sshbuf_put_u32(m, echar)) != 0 ||
            (r = sshbuf_put_cstring(m, term == NULL ? "" : term)) != 0 ||
            (r = sshbuf_put_stringb(m, command)) != 0)
                fatal_fr(r, "request");

        /* Pass environment */
        if (options.num_send_env > 0 && environ != NULL) {
                for (i = 0; environ[i] != NULL; i++) {
                        if (!env_permitted(environ[i]))
                                continue;
                        if ((r = sshbuf_put_cstring(m, environ[i])) != 0)
                                fatal_fr(r, "request sendenv");
                }
        }
        for (i = 0; i < options.num_setenv; i++) {
                if ((r = sshbuf_put_cstring(m, options.setenv[i])) != 0)
                        fatal_fr(r, "request setenv");
        }

        if (mux_client_write_packet(fd, m) != 0)
                fatal_f("write packet: %s", strerror(errno));

        /* Send the stdio file descriptors */
        if (mm_send_fd(fd, STDIN_FILENO) == -1 ||
            mm_send_fd(fd, STDOUT_FILENO) == -1 ||
            mm_send_fd(fd, STDERR_FILENO) == -1)
                fatal_f("send fds failed");

        debug3_f("session request sent");

        /* Read their reply */
        sshbuf_reset(m);
        if (mux_client_read_packet(fd, m) != 0) {
                error_f("read from master failed: %s", strerror(errno));
                sshbuf_free(m);
                return -1;
        }

        if ((r = sshbuf_get_u32(m, &type)) != 0 ||
            (r = sshbuf_get_u32(m, &rid)) != 0)
                fatal_fr(r, "parse");
        if (rid != muxclient_request_id)
                fatal_f("out of sequence reply: my id %u theirs %u",
                    muxclient_request_id, rid);

        switch (type) {
        case MUX_S_SESSION_OPENED:
                if ((r = sshbuf_get_u32(m, &sid)) != 0)
                        fatal_fr(r, "parse session ID");
                debug_f("master session id: %u", sid);
                break;
        case MUX_S_PERMISSION_DENIED:
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                error("Master refused session request: %s", e);
                sshbuf_free(m);
                return -1;
        case MUX_S_FAILURE:
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                error_f("session request failed: %s", e);
                sshbuf_free(m);
                return -1;
        default:
                sshbuf_free(m);
                error_f("unexpected response from master 0x%08x", type);
                return -1;
        }
        muxclient_request_id++;

        if (pledge("stdio proc tty", NULL) == -1)
                fatal_f("pledge(): %s", strerror(errno));
        platform_pledge_mux();

        ssh_signal(SIGHUP, control_client_sighandler);
        ssh_signal(SIGINT, control_client_sighandler);
        ssh_signal(SIGTERM, control_client_sighandler);
        ssh_signal(SIGWINCH, control_client_sigrelay);

        if (options.fork_after_authentication)
                daemon(1, 1);
        else {
                rawmode = tty_flag;
                if (tty_flag) {
                        enter_raw_mode(
                            options.request_tty == REQUEST_TTY_FORCE);
                }
        }

        /*
         * Stick around until the controlee closes the client_fd.
         * Before it does, it is expected to write an exit message.
         * This process must read the value and wait for the closure of
         * the client_fd; if this one closes early, the multiplex master will
         * terminate early too (possibly losing data).
         */
        for (exitval = 255, exitval_seen = 0;;) {
                sshbuf_reset(m);
                if (mux_client_read_packet(fd, m) != 0)
                        break;
                if ((r = sshbuf_get_u32(m, &type)) != 0)
                        fatal_fr(r, "parse type");
                switch (type) {
                case MUX_S_TTY_ALLOC_FAIL:
                        if ((r = sshbuf_get_u32(m, &esid)) != 0)
                                fatal_fr(r, "parse session ID");
                        if (esid != sid)
                                fatal_f("tty alloc fail on unknown session: "
                                    "my id %u theirs %u", sid, esid);
                        leave_raw_mode(options.request_tty ==
                            REQUEST_TTY_FORCE);
                        rawmode = 0;
                        continue;
                case MUX_S_EXIT_MESSAGE:
                        if ((r = sshbuf_get_u32(m, &esid)) != 0)
                                fatal_fr(r, "parse session ID");
                        if (esid != sid)
                                fatal_f("exit on unknown session: "
                                    "my id %u theirs %u", sid, esid);
                        if (exitval_seen)
                                fatal_f("exitval sent twice");
                        if ((r = sshbuf_get_u32(m, &exitval)) != 0)
                                fatal_fr(r, "parse exitval");
                        exitval_seen = 1;
                        continue;
                default:
                        if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                                fatal_fr(r, "parse error message");
                        fatal_f("master returned error: %s", e);
                }
        }

        close(fd);
        if (rawmode)
                leave_raw_mode(options.request_tty == REQUEST_TTY_FORCE);

        if (muxclient_terminate) {
                debug2("Exiting on signal: %s", strsignal(muxclient_terminate));
                exitval = 255;
        } else if (!exitval_seen) {
                debug2("Control master terminated unexpectedly");
                exitval = 255;
        } else
                debug2("Received exit status from master %d", exitval);

        if (tty_flag && options.log_level >= SYSLOG_LEVEL_INFO)
                fprintf(stderr, "Shared connection to %s closed.\r\n", host);

        exit(exitval);
}

static int
mux_client_proxy(int fd)
{
        struct sshbuf *m;
        char *e;
        u_int type, rid;
        int r;

        if ((m = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put_u32(m, MUX_C_PROXY)) != 0 ||
            (r = sshbuf_put_u32(m, muxclient_request_id)) != 0)
                fatal_fr(r, "request");
        if (mux_client_write_packet(fd, m) != 0)
                fatal_f("write packet: %s", strerror(errno));

        sshbuf_reset(m);

        /* Read their reply */
        if (mux_client_read_packet(fd, m) != 0) {
                sshbuf_free(m);
                return 0;
        }
        if ((r = sshbuf_get_u32(m, &type)) != 0 ||
            (r = sshbuf_get_u32(m, &rid)) != 0)
                fatal_fr(r, "parse");
        if (rid != muxclient_request_id)
                fatal_f("out of sequence reply: my id %u theirs %u",
                    muxclient_request_id, rid);
        if (type != MUX_S_PROXY) {
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                fatal_f("master returned error: %s", e);
        }
        sshbuf_free(m);

        debug3_f("done");
        muxclient_request_id++;
        return 0;
}

static int
mux_client_request_stdio_fwd(int fd)
{
        struct sshbuf *m;
        char *e;
        u_int type, rid, sid;
        int r;

        debug3_f("entering");

        if ((muxserver_pid = mux_client_request_alive(fd)) == 0) {
                error_f("master alive request failed");
                return -1;
        }

        ssh_signal(SIGPIPE, SIG_IGN);

        if (options.stdin_null && stdfd_devnull(1, 0, 0) == -1)
                fatal_f("stdfd_devnull failed");

        if ((m = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put_u32(m, MUX_C_NEW_STDIO_FWD)) != 0 ||
            (r = sshbuf_put_u32(m, muxclient_request_id)) != 0 ||
            (r = sshbuf_put_string(m, NULL, 0)) != 0 || /* reserved */
            (r = sshbuf_put_cstring(m, options.stdio_forward_host)) != 0 ||
            (r = sshbuf_put_u32(m, options.stdio_forward_port)) != 0)
                fatal_fr(r, "request");

        if (mux_client_write_packet(fd, m) != 0)
                fatal_f("write packet: %s", strerror(errno));

        /* Send the stdio file descriptors */
        if (mm_send_fd(fd, STDIN_FILENO) == -1 ||
            mm_send_fd(fd, STDOUT_FILENO) == -1)
                fatal_f("send fds failed");

        if (pledge("stdio proc tty", NULL) == -1)
                fatal_f("pledge(): %s", strerror(errno));
        platform_pledge_mux();

        debug3_f("stdio forward request sent");

        /* Read their reply */
        sshbuf_reset(m);

        if (mux_client_read_packet(fd, m) != 0) {
                error_f("read from master failed: %s", strerror(errno));
                sshbuf_free(m);
                return -1;
        }

        if ((r = sshbuf_get_u32(m, &type)) != 0 ||
            (r = sshbuf_get_u32(m, &rid)) != 0)
                fatal_fr(r, "parse");
        if (rid != muxclient_request_id)
                fatal_f("out of sequence reply: my id %u theirs %u",
                    muxclient_request_id, rid);
        switch (type) {
        case MUX_S_SESSION_OPENED:
                if ((r = sshbuf_get_u32(m, &sid)) != 0)
                        fatal_fr(r, "parse session ID");
                debug_f("master session id: %u", sid);
                break;
        case MUX_S_PERMISSION_DENIED:
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                sshbuf_free(m);
                fatal("Master refused stdio forwarding request: %s", e);
        case MUX_S_FAILURE:
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                sshbuf_free(m);
                fatal("Stdio forwarding request failed: %s", e);
        default:
                sshbuf_free(m);
                error_f("unexpected response from master 0x%08x", type);
                return -1;
        }
        muxclient_request_id++;

        ssh_signal(SIGHUP, control_client_sighandler);
        ssh_signal(SIGINT, control_client_sighandler);
        ssh_signal(SIGTERM, control_client_sighandler);
        ssh_signal(SIGWINCH, control_client_sigrelay);

        /*
         * Stick around until the controlee closes the client_fd.
         */
        sshbuf_reset(m);
        if (mux_client_read_packet(fd, m) != 0) {
                if (errno == EPIPE ||
                    (errno == EINTR && muxclient_terminate != 0))
                        return 0;
                fatal_f("mux_client_read_packet: %s", strerror(errno));
        }
        fatal_f("master returned unexpected message %u", type);
}

static void
mux_client_request_stop_listening(int fd)
{
        struct sshbuf *m;
        char *e;
        u_int type, rid;
        int r;

        debug3_f("entering");

        if ((m = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_put_u32(m, MUX_C_STOP_LISTENING)) != 0 ||
            (r = sshbuf_put_u32(m, muxclient_request_id)) != 0)
                fatal_fr(r, "request");

        if (mux_client_write_packet(fd, m) != 0)
                fatal_f("write packet: %s", strerror(errno));

        sshbuf_reset(m);

        /* Read their reply */
        if (mux_client_read_packet(fd, m) != 0)
                fatal_f("read from master failed: %s", strerror(errno));

        if ((r = sshbuf_get_u32(m, &type)) != 0 ||
            (r = sshbuf_get_u32(m, &rid)) != 0)
                fatal_fr(r, "parse");
        if (rid != muxclient_request_id)
                fatal_f("out of sequence reply: my id %u theirs %u",
                    muxclient_request_id, rid);

        switch (type) {
        case MUX_S_OK:
                break;
        case MUX_S_PERMISSION_DENIED:
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                fatal("Master refused stop listening request: %s", e);
        case MUX_S_FAILURE:
                if ((r = sshbuf_get_cstring(m, &e, NULL)) != 0)
                        fatal_fr(r, "parse error message");
                fatal_f("stop listening request failed: %s", e);
        default:
                fatal_f("unexpected response from master 0x%08x", type);
        }
        sshbuf_free(m);
        muxclient_request_id++;
}

/* Multiplex client main loop. */
int
muxclient(const char *path)
{
        struct sockaddr_un addr;
        int sock, timeout = options.connection_timeout, timeout_ms = -1;
        u_int pid;

        if (muxclient_command == 0) {
                if (options.stdio_forward_host != NULL)
                        muxclient_command = SSHMUX_COMMAND_STDIO_FWD;
                else
                        muxclient_command = SSHMUX_COMMAND_OPEN;
        }

        switch (options.control_master) {
        case SSHCTL_MASTER_AUTO:
        case SSHCTL_MASTER_AUTO_ASK:
                debug("auto-mux: Trying existing master at '%s'", path);
                /* FALLTHROUGH */
        case SSHCTL_MASTER_NO:
                break;
        default:
                return -1;
        }

        memset(&addr, '\0', sizeof(addr));
        addr.sun_family = AF_UNIX;

        if (strlcpy(addr.sun_path, path,
            sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
                fatal("ControlPath too long ('%s' >= %u bytes)", path,
                    (unsigned int)sizeof(addr.sun_path));

        if ((sock = socket(PF_UNIX, SOCK_STREAM, 0)) == -1)
                fatal_f("socket(): %s", strerror(errno));

        if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
                switch (muxclient_command) {
                case SSHMUX_COMMAND_OPEN:
                case SSHMUX_COMMAND_STDIO_FWD:
                        break;
                default:
                        fatal("Control socket connect(%.100s): %s", path,
                            strerror(errno));
                }
                if (errno == ECONNREFUSED &&
                    options.control_master != SSHCTL_MASTER_NO) {
                        debug("Stale control socket %.100s, unlinking", path);
                        unlink(path);
                } else if (errno == ENOENT) {
                        debug("Control socket \"%.100s\" does not exist", path);
                } else {
                        error("Control socket connect(%.100s): %s", path,
                            strerror(errno));
                }
                close(sock);
                return -1;
        }
        set_nonblock(sock);

        /* Timeout on initial connection only. */
        if (timeout > 0 && timeout < INT_MAX / 1000)
                timeout_ms = timeout * 1000;

        if (mux_client_hello_exchange(sock, timeout_ms) != 0) {
                error_f("master hello exchange failed");
                close(sock);
                return -1;
        }

        switch (muxclient_command) {
        case SSHMUX_COMMAND_ALIVE_CHECK:
                if ((pid = mux_client_request_alive(sock)) == 0)
                        fatal_f("master alive check failed");
                fprintf(stderr, "Master running (pid=%u)\r\n", pid);
                exit(0);
        case SSHMUX_COMMAND_TERMINATE:
                mux_client_request_terminate(sock);
                if (options.log_level != SYSLOG_LEVEL_QUIET)
                        fprintf(stderr, "Exit request sent.\r\n");
                exit(0);
        case SSHMUX_COMMAND_FORWARD:
                if (mux_client_forwards(sock, 0) != 0)
                        fatal_f("master forward request failed");
                exit(0);
        case SSHMUX_COMMAND_OPEN:
                if (mux_client_forwards(sock, 0) != 0) {
                        error_f("master forward request failed");
                        return -1;
                }
                mux_client_request_session(sock);
                return -1;
        case SSHMUX_COMMAND_STDIO_FWD:
                mux_client_request_stdio_fwd(sock);
                exit(0);
        case SSHMUX_COMMAND_STOP:
                mux_client_request_stop_listening(sock);
                if (options.log_level != SYSLOG_LEVEL_QUIET)
                        fprintf(stderr, "Stop listening request sent.\r\n");
                exit(0);
        case SSHMUX_COMMAND_CANCEL_FWD:
                if (mux_client_forwards(sock, 1) != 0)
                        error_f("master cancel forward request failed");
                exit(0);
        case SSHMUX_COMMAND_PROXY:
                mux_client_proxy(sock);
                return (sock);
        default:
                fatal("unrecognised muxclient_command %d", muxclient_command);
        }
}