- djm@cvs.openbsd.org 2010/01/26 01:28:35

     [channels.c channels.h clientloop.c clientloop.h mux.c nchan.c ssh.c]
     rewrite ssh(1) multiplexing code to a more sensible protocol.

     The new multiplexing code uses channels for the listener and
     accepted control sockets to make the mux master non-blocking, so
     no stalls when processing messages from a slave.

     avoid use of fatal() in mux master protocol parsing so an errant slave
     process cannot take down a running master.

     implement requesting of port-forwards over multiplexed sessions. Any
     port forwards requested by the slave are added to those the master has
     established.

     add support for stdio forwarding ("ssh -W host:port ...") in mux slaves.

     document master/slave mux protocol so that other tools can use it to
     control a running ssh(1). Note: there are no guarantees that this
     protocol won't be incompatibly changed (though it is versioned).

     feedback Salvador Fandino, dtucker@
     channel changes ok markus@

1 files changed, 1425 insertions, 415 deletions

diff --git a/mux.c b/mux.c
index 239edd5f5..dcd6dc028 100644
--- a/mux.c
+++ b/mux.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: mux.c,v 1.9 2010/01/09 05:04:24 djm Exp $ */
+/* $OpenBSD: mux.c,v 1.10 2010/01/26 01:28:35 djm Exp $ */
 /*
  * Copyright (c) 2002-2008 Damien Miller <djm@openbsd.org>
  *
@@ -17,25 +17,21 @@
 
 /* ssh session multiplexing support */
 
-#include "includes.h"
-
 /*
  * TODO:
- *   1. partial reads in muxserver_accept_control (maybe make channels
- *      from accepted connections)
- *   2. Better signalling from master to slave, especially passing of
+ *   - Better signalling from master to slave, especially passing of
  *      error messages
- *   3. Better fall-back from mux slave error to new connection.
- *   3. Add/delete forwardings via slave
- *   4. ExitOnForwardingFailure (after #3 obviously)
- *   5. Maybe extension mechanisms for multi-X11/multi-agent forwarding
- *   6. Document the mux mini-protocol somewhere.
- *   7. Support ~^Z in mux slaves.
- *   8. Inspect or control sessions in master.
- *   9. If we ever support the "signal" channel request, send signals on
- *      sessions in master.
+ *   - Better fall-back from mux slave error to new connection.
+ *   - ExitOnForwardingFailure
+ *   - Maybe extension mechanisms for multi-X11/multi-agent forwarding
+ *   - Support ~^Z in mux slaves.
+ *   - Inspect or control sessions in master.
+ *   - If we ever support the "signal" channel request, send signals on
+ *     sessions in master.
  */
 
+#include "includes.h"
+
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/stat.h>
@@ -55,6 +51,14 @@
 #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
@@ -88,13 +92,16 @@ extern int stdin_null_flag;
 extern char *host;
 extern int subsystem_flag;
 extern Buffer command;
+extern volatile sig_atomic_t quit_pending;
+extern char *stdio_forward_host;
+extern int stdio_forward_port;
 
 /* Context for session open confirmation callback */
 struct mux_session_confirm_ctx {
-        int want_tty;
-        int want_subsys;
-        int want_x_fwd;
-        int want_agent_fwd;
+        u_int want_tty;
+        u_int want_subsys;
+        u_int want_x_fwd;
+        u_int want_agent_fwd;
         Buffer cmd;
         char *term;
         struct termios tio;
@@ -104,6 +111,9 @@ struct mux_session_confirm_ctx {
 /* 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;
 
@@ -113,16 +123,823 @@ 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_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
+
+/* 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(int, void *);
+
+static int process_mux_master_hello(u_int, Channel *, Buffer *, Buffer *);
+static int process_mux_new_session(u_int, Channel *, Buffer *, Buffer *);
+static int process_mux_alive_check(u_int, Channel *, Buffer *, Buffer *);
+static int process_mux_terminate(u_int, Channel *, Buffer *, Buffer *);
+static int process_mux_open_fwd(u_int, Channel *, Buffer *, Buffer *);
+static int process_mux_close_fwd(u_int, Channel *, Buffer *, Buffer *);
+static int process_mux_stdio_fwd(u_int, Channel *, Buffer *, Buffer *);
+
+static const struct {
+        u_int type;
+        int (*handler)(u_int, Channel *, Buffer *, Buffer *);
+} mux_master_handlers[] = {
+        { MUX_MSG_HELLO, process_mux_master_hello },
+        { MUX_C_NEW_SESSION, process_mux_new_session },
+        { MUX_C_ALIVE_CHECK, process_mux_alive_check },
+        { MUX_C_TERMINATE, process_mux_terminate },
+        { MUX_C_OPEN_FWD, process_mux_open_fwd },
+        { MUX_C_CLOSE_FWD, process_mux_close_fwd },
+        { MUX_C_NEW_STDIO_FWD, process_mux_stdio_fwd },
+        { 0, NULL }
+};
+
+/* Cleanup callback fired on closure of mux slave _session_ channel */
+/* ARGSUSED */
+static void
+mux_master_session_cleanup_cb(int cid, void *unused)
+{
+        Channel *cc, *c = channel_by_id(cid);
+
+        debug3("%s: entering for channel %d", __func__, cid);
+        if (c == NULL)
+                fatal("%s: channel_by_id(%i) == NULL", __func__, cid);
+        if (c->ctl_chan != -1) {
+                if ((cc = channel_by_id(c->ctl_chan)) == NULL)
+                        fatal("%s: channel %d missing control channel %d",
+                            __func__, c->self, c->ctl_chan);
+                c->ctl_chan = -1;
+                cc->remote_id = -1;
+                chan_rcvd_oclose(cc);
+        }
+        channel_cancel_cleanup(c->self);
+}
+
+/* Cleanup callback fired on closure of mux slave _control_ channel */
+/* ARGSUSED */
+static void
+mux_master_control_cleanup_cb(int cid, void *unused)
+{
+        Channel *sc, *c = channel_by_id(cid);
+
+        debug3("%s: entering for channel %d", __func__, cid);
+        if (c == NULL)
+                fatal("%s: channel_by_id(%i) == NULL", __func__, cid);
+        if (c->remote_id != -1) {
+                if ((sc = channel_by_id(c->remote_id)) == NULL)
+                        debug2("%s: channel %d n session channel %d",
+                            __func__, c->self, c->remote_id);
+                c->remote_id = -1;
+                sc->ctl_chan = -1;
+                chan_mark_dead(sc);
+        }
+        channel_cancel_cleanup(c->self);
+}
+
+/* Check mux client environment variables before passing them to mux master. */
+static int
+env_permitted(char *env)
+{
+        int i, 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("env_permitted: 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
+process_mux_master_hello(u_int rid, Channel *c, Buffer *m, Buffer *r)
+{
+        u_int ver;
+        struct mux_master_state *state = (struct mux_master_state *)c->mux_ctx;
+
+        if (state == NULL)
+                fatal("%s: channel %d: c->mux_ctx == NULL", __func__, c->self);
+        if (state->hello_rcvd) {
+                error("%s: HELLO received twice", __func__);
+                return -1;
+        }
+        if (buffer_get_int_ret(&ver, m) != 0) {
+ malf:
+                error("%s: malformed message", __func__);
+                return -1;
+        }
+        if (ver != SSHMUX_VER) {
+                error("Unsupported multiplexing protocol version %d "
+                    "(expected %d)", ver, SSHMUX_VER);
+                return -1;
+        }
+        debug2("%s: channel %d slave version %u", __func__, c->self, ver);
+
+        /* No extensions are presently defined */
+        while (buffer_len(m) > 0) {
+                char *name = buffer_get_string_ret(m, NULL);
+                char *value = buffer_get_string_ret(m, NULL);
+
+                if (name == NULL || value == NULL) {
+                        if (name != NULL)
+                                xfree(name);
+                        goto malf;
+                }
+                debug2("Unrecognised slave extension \"%s\"", name);
+                xfree(name);
+                xfree(value);
+        }
+        state->hello_rcvd = 1;
+        return 0;
+}
+
+static int
+process_mux_new_session(u_int rid, Channel *c, Buffer *m, Buffer *r)
+{
+        Channel *nc;
+        struct mux_session_confirm_ctx *cctx;
+        char *reserved, *cmd, *cp;
+        u_int i, j, len, env_len, escape_char, window, packetmax;
+        int new_fd[3];
+
+        /* Reply for SSHMUX_COMMAND_OPEN */
+        cctx = xcalloc(1, sizeof(*cctx));
+        cctx->term = NULL;
+        cmd = reserved = NULL;
+        if ((reserved = buffer_get_string_ret(m, NULL)) == NULL ||
+            buffer_get_int_ret(&cctx->want_tty, m) != 0 ||
+            buffer_get_int_ret(&cctx->want_x_fwd, m) != 0 ||
+            buffer_get_int_ret(&cctx->want_agent_fwd, m) != 0 ||
+            buffer_get_int_ret(&cctx->want_subsys, m) != 0 ||
+            buffer_get_int_ret(&escape_char, m) != 0 ||
+            (cctx->term = buffer_get_string_ret(m, &len)) == NULL ||
+            (cmd = buffer_get_string_ret(m, &len)) == NULL) {
+ malf:
+                if (cmd != NULL)
+                        xfree(cmd);
+                if (reserved != NULL)
+                        xfree(reserved);
+                if (cctx->term != NULL)
+                        xfree(cctx->term);
+                error("%s: malformed message", __func__);
+                return -1;
+        }
+        xfree(reserved);
+        reserved = NULL;
+
+        cctx->env = NULL;
+        env_len = 0;
+        while (buffer_len(m) > 0) {
+#define MUX_MAX_ENV_VARS        4096
+                if ((cp = buffer_get_string_ret(m, &len)) == NULL) {
+                        xfree(cmd);
+                        goto malf;
+                }
+                if (!env_permitted(cp)) {
+                        xfree(cp);
+                        continue;
+                }
+                cctx->env = xrealloc(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(">%d environment variables received, ignoring "
+                            "additional", MUX_MAX_ENV_VARS);
+                        break;
+                }
+        }
+
+        debug2("%s: channel %d: request tty %d, X %d, agent %d, subsys %d, "
+            "term \"%s\", cmd \"%s\", env %u", __func__, c->self,
+            cctx->want_tty, cctx->want_x_fwd, cctx->want_agent_fwd,
+            cctx->want_subsys, cctx->term, cmd, env_len);
+
+        buffer_init(&cctx->cmd);
+        buffer_append(&cctx->cmd, cmd, strlen(cmd));
+        xfree(cmd);
+        cmd = NULL;
+
+        /* Gather fds from client */
+        for(i = 0; i < 3; i++) {
+                if ((new_fd[i] = mm_receive_fd(c->sock)) == -1) {
+                        error("%s: failed to receive fd %d from slave",
+                            __func__, i);
+                        for (j = 0; j < i; j++)
+                                close(new_fd[j]);
+                        for (j = 0; j < env_len; j++)
+                                xfree(cctx->env[j]);
+                        if (env_len > 0)
+                                xfree(cctx->env);
+                        xfree(cctx->term);
+                        buffer_free(&cctx->cmd);
+                        xfree(cctx);
+
+                        /* prepare reply */
+                        buffer_put_int(r, MUX_S_FAILURE);
+                        buffer_put_int(r, rid);
+                        buffer_put_cstring(r,
+                            "did not receive file descriptors");
+                        return -1;
+                }
+        }
+
+        debug3("%s: got fds stdin %d, stdout %d, stderr %d", __func__,
+            new_fd[0], new_fd[1], new_fd[2]);
+
+        /* XXX support multiple child sessions in future */
+        if (c->remote_id != -1) {
+                debug2("%s: session already open", __func__);
+                /* prepare reply */
+                buffer_put_int(r, MUX_S_FAILURE);
+                buffer_put_int(r, rid);
+                buffer_put_cstring(r, "Multiple sessions not supported");
+ cleanup:
+                close(new_fd[0]);
+                close(new_fd[1]);
+                close(new_fd[2]);
+                xfree(cctx->term);
+                if (env_len != 0) {
+                        for (i = 0; i < env_len; i++)
+                                xfree(cctx->env[i]);
+                        xfree(cctx->env);
+                }
+                buffer_free(&cctx->cmd);
+                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("%s: session refused by user", __func__);
+                        /* prepare reply */
+                        buffer_put_int(r, MUX_S_PERMISSION_DENIED);
+                        buffer_put_int(r, rid);
+                        buffer_put_cstring(r, "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("%s: tcgetattr: %s", __func__, strerror(errno));
+
+        /* enable nonblocking unless tty */
+        if (!isatty(new_fd[0]))
+                set_nonblock(new_fd[0]);
+        if (!isatty(new_fd[1]))
+                set_nonblock(new_fd[1]);
+        if (!isatty(new_fd[2]))
+                set_nonblock(new_fd[2]);
+
+        window = CHAN_SES_WINDOW_DEFAULT;
+        packetmax = CHAN_SES_PACKET_DEFAULT;
+        if (cctx->want_tty) {
+                window >>= 1;
+                packetmax >>= 1;
+        }
+
+        nc = channel_new("session", SSH_CHANNEL_OPENING,
+            new_fd[0], new_fd[1], new_fd[2], window, packetmax,
+            CHAN_EXTENDED_WRITE, "client-session", /*nonblock*/0);
+
+        nc->ctl_chan = c->self;         /* link session -> control channel */
+        c->remote_id = nc->self;        /* link control -> session channel */
+
+        if (cctx->want_tty && escape_char != 0xffffffff) {
+                channel_register_filter(nc->self,
+                    client_simple_escape_filter, NULL,
+                    client_filter_cleanup,
+                    client_new_escape_filter_ctx((int)escape_char));
+        }
+
+        debug2("%s: channel_new: %d linked to control channel %d",
+            __func__, nc->self, nc->ctl_chan);
+
+        channel_send_open(nc->self);
+        channel_register_open_confirm(nc->self, mux_session_confirm, cctx);
+        channel_register_cleanup(nc->self, mux_master_session_cleanup_cb, 0);
+
+        /* prepare reply */
+        /* XXX defer until mux_session_confirm() fires */
+        buffer_put_int(r, MUX_S_SESSION_OPENED);
+        buffer_put_int(r, rid);
+        buffer_put_int(r, nc->self);
+
+        return 0;
+}
+
+static int
+process_mux_alive_check(u_int rid, Channel *c, Buffer *m, Buffer *r)
+{
+        debug2("%s: channel %d: alive check", __func__, c->self);
+
+        /* prepare reply */
+        buffer_put_int(r, MUX_S_ALIVE);
+        buffer_put_int(r, rid);
+        buffer_put_int(r, (u_int)getpid());
+
+        return 0;
+}
+
+static int
+process_mux_terminate(u_int rid, Channel *c, Buffer *m, Buffer *r)
+{
+        debug2("%s: channel %d: terminate request", __func__, 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("%s: termination refused by user", __func__);
+                        buffer_put_int(r, MUX_S_PERMISSION_DENIED);
+                        buffer_put_int(r, rid);
+                        buffer_put_cstring(r, "Permission denied");
+                        return 0;
+                }
+        }
+
+        quit_pending = 1;
+        buffer_put_int(r, MUX_S_OK);
+        buffer_put_int(r, rid);
+        /* XXX exit happens too soon - message never makes it to client */
+        return 0;
+}
+
+static char *
+format_forward(u_int ftype, Forward *fwd)
+{
+        char *ret;
+
+        switch (ftype) {
+        case MUX_FWD_LOCAL:
+                xasprintf(&ret, "local forward %.200s:%d -> %.200s:%d",
+                    (fwd->listen_host == NULL) ?
+                    (options.gateway_ports ? "*" : "LOCALHOST") :
+                    fwd->listen_host, fwd->listen_port,
+                    fwd->connect_host, fwd->connect_port);
+                break;
+        case MUX_FWD_DYNAMIC:
+                xasprintf(&ret, "dynamic forward %.200s:%d -> *",
+                    (fwd->listen_host == NULL) ?
+                    (options.gateway_ports ? "*" : "LOCALHOST") :
+                     fwd->listen_host, fwd->listen_port);
+                break;
+        case MUX_FWD_REMOTE:
+                xasprintf(&ret, "remote forward %.200s:%d -> %.200s:%d",
+                    (fwd->listen_host == NULL) ?
+                    "LOCALHOST" : fwd->listen_host,
+                    fwd->listen_port,
+                    fwd->connect_host, fwd->connect_port);
+                break;
+        default:
+                fatal("%s: unknown forward type %u", __func__, 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(Forward *a, Forward *b)
+{
+        if (!compare_host(a->listen_host, b->listen_host))
+                return 0;
+        if (a->listen_port != b->listen_port)
+                return 0;
+        if (!compare_host(a->connect_host, b->connect_host))
+                return 0;
+        if (a->connect_port != b->connect_port)
+                return 0;
+
+        return 1;
+}
+
+static int
+process_mux_open_fwd(u_int rid, Channel *c, Buffer *m, Buffer *r)
+{
+        Forward fwd;
+        char *fwd_desc = NULL;
+        u_int ftype;
+        int i, ret = 0, freefwd = 1;
+
+        fwd.listen_host = fwd.connect_host = NULL;
+        if (buffer_get_int_ret(&ftype, m) != 0 ||
+            (fwd.listen_host = buffer_get_string_ret(m, NULL)) == NULL ||
+            buffer_get_int_ret(&fwd.listen_port, m) != 0 ||
+            (fwd.connect_host = buffer_get_string_ret(m, NULL)) == NULL ||
+            buffer_get_int_ret(&fwd.connect_port, m) != 0) {
+                error("%s: malformed message", __func__);
+                ret = -1;
+                goto out;
+        }
+
+        if (*fwd.listen_host == '\0') {
+                xfree(fwd.listen_host);
+                fwd.listen_host = NULL;
+        }
+        if (*fwd.connect_host == '\0') {
+                xfree(fwd.connect_host);
+                fwd.connect_host = NULL;
+        }
+
+        debug2("%s: channel %d: request %s", __func__, c->self,
+            (fwd_desc = format_forward(ftype, &fwd)));
+
+        if (ftype != MUX_FWD_LOCAL && ftype != MUX_FWD_REMOTE &&
+            ftype != MUX_FWD_DYNAMIC) {
+                logit("%s: invalid forwarding type %u", __func__, ftype);
+ invalid:
+                xfree(fwd.listen_host);
+                xfree(fwd.connect_host);
+                buffer_put_int(r, MUX_S_FAILURE);
+                buffer_put_int(r, rid);
+                buffer_put_cstring(r, "Invalid forwarding request");
+                return 0;
+        }
+        /* XXX support rport0 forwarding with reply of port assigned */
+        if (fwd.listen_port == 0 || fwd.listen_port >= 65536) {
+                logit("%s: invalid listen port %u", __func__,
+                    fwd.listen_port);
+                goto invalid;
+        }
+        if (fwd.connect_port >= 65536 || (ftype != MUX_FWD_DYNAMIC &&
+            ftype != MUX_FWD_REMOTE && fwd.connect_port == 0)) {
+                logit("%s: invalid connect port %u", __func__,
+                    fwd.connect_port);
+                goto invalid;
+        }
+        if (ftype != MUX_FWD_DYNAMIC && fwd.connect_host == NULL) {
+                logit("%s: missing connect host", __func__);
+                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("%s: found existing forwarding",
+                                    __func__);
+                                buffer_put_int(r, MUX_S_OK);
+                                buffer_put_int(r, 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))
+                                goto exists;
+                }
+                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("%s: forwarding refused by user", __func__);
+                        buffer_put_int(r, MUX_S_PERMISSION_DENIED);
+                        buffer_put_int(r, rid);
+                        buffer_put_cstring(r, "Permission denied");
+                        goto out;
+                }
+        }
+
+        if (ftype == MUX_FWD_LOCAL || ftype == MUX_FWD_DYNAMIC) {
+                if (options.num_local_forwards + 1 >=
+                    SSH_MAX_FORWARDS_PER_DIRECTION ||
+                    channel_setup_local_fwd_listener(fwd.listen_host,
+                    fwd.listen_port, fwd.connect_host, fwd.connect_port,
+                    options.gateway_ports) < 0) {
+ fail:
+                        logit("slave-requested %s failed", fwd_desc);
+                        buffer_put_int(r, MUX_S_FAILURE);
+                        buffer_put_int(r, rid);
+                        buffer_put_cstring(r, "Port forwarding failed");
+                        goto out;
+                }
+                add_local_forward(&options, &fwd);
+                freefwd = 0;
+        } else {
+                /* XXX wait for remote to confirm */
+                if (options.num_remote_forwards + 1 >=
+                    SSH_MAX_FORWARDS_PER_DIRECTION ||
+                    channel_request_remote_forwarding(fwd.listen_host,
+                    fwd.listen_port, fwd.connect_host, fwd.connect_port) < 0)
+                        goto fail;
+                add_remote_forward(&options, &fwd);
+                freefwd = 0;
+        }
+        buffer_put_int(r, MUX_S_OK);
+        buffer_put_int(r, rid);
+ out:
+        if (fwd_desc != NULL)
+                xfree(fwd_desc);
+        if (freefwd) {
+                if (fwd.listen_host != NULL)
+                        xfree(fwd.listen_host);
+                if (fwd.connect_host != NULL)
+                        xfree(fwd.connect_host);
+        }
+        return ret;
+}
+
+static int
+process_mux_close_fwd(u_int rid, Channel *c, Buffer *m, Buffer *r)
+{
+        Forward fwd;
+        char *fwd_desc = NULL;
+        u_int ftype;
+        int ret = 0;
+
+        fwd.listen_host = fwd.connect_host = NULL;
+        if (buffer_get_int_ret(&ftype, m) != 0 ||
+            (fwd.listen_host = buffer_get_string_ret(m, NULL)) == NULL ||
+            buffer_get_int_ret(&fwd.listen_port, m) != 0 ||
+            (fwd.connect_host = buffer_get_string_ret(m, NULL)) == NULL ||
+            buffer_get_int_ret(&fwd.connect_port, m) != 0) {
+                error("%s: malformed message", __func__);
+                ret = -1;
+                goto out;
+        }
+
+        if (*fwd.listen_host == '\0') {
+                xfree(fwd.listen_host);
+                fwd.listen_host = NULL;
+        }
+        if (*fwd.connect_host == '\0') {
+                xfree(fwd.connect_host);
+                fwd.connect_host = NULL;
+        }
+
+        debug2("%s: channel %d: request %s", __func__, c->self,
+            (fwd_desc = format_forward(ftype, &fwd)));
+
+        /* XXX implement this */
+        buffer_put_int(r, MUX_S_FAILURE);
+        buffer_put_int(r, rid);
+        buffer_put_cstring(r, "unimplemented");
+
+ out:
+        if (fwd_desc != NULL)
+                xfree(fwd_desc);
+        if (fwd.listen_host != NULL)
+                xfree(fwd.listen_host);
+        if (fwd.connect_host != NULL)
+                xfree(fwd.connect_host);
+
+        return ret;
+}
+
+static int
+process_mux_stdio_fwd(u_int rid, Channel *c, Buffer *m, Buffer *r)
+{
+        Channel *nc;
+        char *reserved, *chost;
+        u_int cport, i, j;
+        int new_fd[2];
+
+        chost = reserved = NULL;
+        if ((reserved = buffer_get_string_ret(m, NULL)) == NULL ||
+           (chost = buffer_get_string_ret(m, NULL)) == NULL ||
+            buffer_get_int_ret(&cport, m) != 0) {
+                if (reserved != NULL)
+                        xfree(reserved);
+                if (chost != NULL)
+                        xfree(chost);
+                error("%s: malformed message", __func__);
+                return -1;
+        }
+        xfree(reserved);
+
+        debug2("%s: channel %d: request stdio fwd to %s:%u",
+            __func__, 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("%s: failed to receive fd %d from slave",
+                            __func__, i);
+                        for (j = 0; j < i; j++)
+                                close(new_fd[j]);
+                        xfree(chost);
+
+                        /* prepare reply */
+                        buffer_put_int(r, MUX_S_FAILURE);
+                        buffer_put_int(r, rid);
+                        buffer_put_cstring(r,
+                            "did not receive file descriptors");
+                        return -1;
+                }
+        }
+
+        debug3("%s: got fds stdin %d, stdout %d", __func__,
+            new_fd[0], new_fd[1]);
+
+        /* XXX support multiple child sessions in future */
+        if (c->remote_id != -1) {
+                debug2("%s: session already open", __func__);
+                /* prepare reply */
+                buffer_put_int(r, MUX_S_FAILURE);
+                buffer_put_int(r, rid);
+                buffer_put_cstring(r, "Multiple sessions not supported");
+ cleanup:
+                close(new_fd[0]);
+                close(new_fd[1]);
+                xfree(chost);
+                return 0;
+        }
+
+        if (options.control_master == SSHCTL_MASTER_ASK ||
+            options.control_master == SSHCTL_MASTER_AUTO_ASK) {
+                if (!ask_permission("Allow forward to to %s:%u? ",
+                    chost, cport)) {
+                        debug2("%s: stdio fwd refused by user", __func__);
+                        /* prepare reply */
+                        buffer_put_int(r, MUX_S_PERMISSION_DENIED);
+                        buffer_put_int(r, rid);
+                        buffer_put_cstring(r, "Permission denied");
+                        goto cleanup;
+                }
+        }
+
+        /* enable nonblocking unless tty */
+        if (!isatty(new_fd[0]))
+                set_nonblock(new_fd[0]);
+        if (!isatty(new_fd[1]))
+                set_nonblock(new_fd[1]);
+
+        nc = channel_connect_stdio_fwd(chost, cport, new_fd[0], new_fd[1]);
+
+        nc->ctl_chan = c->self;         /* link session -> control channel */
+        c->remote_id = nc->self;        /* link control -> session channel */
+
+        debug2("%s: channel_new: %d linked to control channel %d",
+            __func__, nc->self, nc->ctl_chan);
 
-/* ** Multiplexing master support */
+        channel_register_cleanup(nc->self, mux_master_session_cleanup_cb, 0);
+
+        /* prepare reply */
+        /* XXX defer until channel confirmed */
+        buffer_put_int(r, MUX_S_SESSION_OPENED);
+        buffer_put_int(r, rid);
+        buffer_put_int(r, nc->self);
+
+        return 0;
+}
+
+/* Channel callbacks fired on read/write from mux slave fd */
+static int
+mux_master_read_cb(Channel *c)
+{
+        struct mux_master_state *state = (struct mux_master_state *)c->mux_ctx;
+        Buffer in, out;
+        void *ptr;
+        u_int type, rid, have, i;
+        int ret = -1;
+
+        /* Setup ctx and  */
+        if (c->mux_ctx == NULL) {
+                state = xcalloc(1, sizeof(state));
+                c->mux_ctx = state;
+                channel_register_cleanup(c->self,
+                    mux_master_control_cleanup_cb, 0);
+
+                /* Send hello */
+                buffer_init(&out);
+                buffer_put_int(&out, MUX_MSG_HELLO);
+                buffer_put_int(&out, SSHMUX_VER);
+                /* no extensions */
+                buffer_put_string(&c->output, buffer_ptr(&out),
+                    buffer_len(&out));
+                buffer_free(&out);
+                debug3("%s: channel %d: hello sent", __func__, c->self);
+                return 0;
+        }
+
+        buffer_init(&in);
+        buffer_init(&out);
+
+        /* Channel code ensures that we receive whole packets */
+        if ((ptr = buffer_get_string_ptr_ret(&c->input, &have)) == NULL) {
+ malf:
+                error("%s: malformed message", __func__);
+                goto out;
+        }
+        buffer_append(&in, ptr, have);
+
+        if (buffer_get_int_ret(&type, &in) != 0)
+                goto malf;
+        debug3("%s: channel %d packet type 0x%08x len %u",
+            __func__, c->self, type, buffer_len(&in));
+
+        if (type == MUX_MSG_HELLO)
+                rid = 0;
+        else {
+                if (!state->hello_rcvd) {
+                        error("%s: expected MUX_MSG_HELLO(0x%08x), "
+                            "received 0x%08x", __func__, MUX_MSG_HELLO, type);
+                        goto out;
+                }
+                if (buffer_get_int_ret(&rid, &in) != 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(rid, c, &in, &out);
+                        break;
+                }
+        }
+        if (mux_master_handlers[i].handler == NULL) {
+                error("%s: unsupported mux message 0x%08x", __func__, type);
+                buffer_put_int(&out, MUX_S_FAILURE);
+                buffer_put_int(&out, rid);
+                buffer_put_cstring(&out, "unsupported request");
+                ret = 0;
+        }
+        /* Enqueue reply packet */
+        if (buffer_len(&out) != 0) {
+                buffer_put_string(&c->output, buffer_ptr(&out),
+                    buffer_len(&out));
+        }
+ out:
+        buffer_free(&in);
+        buffer_free(&out);
+        return ret;
+}
+
+void
+mux_exit_message(Channel *c, int exitval)
+{
+        Buffer m;
+        Channel *mux_chan;
+
+        debug3("%s: channel %d: exit message, evitval %d", __func__, c->self,
+            exitval);
+
+        if ((mux_chan = channel_by_id(c->ctl_chan)) == NULL)
+                fatal("%s: channel %d missing mux channel %d",
+                    __func__, c->self, c->ctl_chan);
+
+        /* Append exit message packet to control socket output queue */
+        buffer_init(&m);
+        buffer_put_int(&m, MUX_S_EXIT_MESSAGE);
+        buffer_put_int(&m, c->self);
+        buffer_put_int(&m, exitval);
+
+        buffer_put_string(&mux_chan->output, buffer_ptr(&m), buffer_len(&m));
+        buffer_free(&m);
+}
 
 /* Prepare a mux master to listen on a Unix domain socket. */
 void
 muxserver_listen(void)
 {
         struct sockaddr_un addr;
+        socklen_t sun_len;
         mode_t old_umask;
-        int addr_len;
 
         if (options.control_path == NULL ||
             options.control_master == SSHCTL_MASTER_NO)
@@ -132,7 +949,7 @@ muxserver_listen(void)
 
         memset(&addr, '\0', sizeof(addr));
         addr.sun_family = AF_UNIX;
-        addr_len = offsetof(struct sockaddr_un, sun_path) +
+        sun_len = offsetof(struct sockaddr_un, sun_path) +
             strlen(options.control_path) + 1;
 
         if (strlcpy(addr.sun_path, options.control_path,
@@ -143,7 +960,7 @@ muxserver_listen(void)
                 fatal("%s socket(): %s", __func__, strerror(errno));
 
         old_umask = umask(0177);
-        if (bind(muxserver_sock, (struct sockaddr *)&addr, addr_len) == -1) {
+        if (bind(muxserver_sock, (struct sockaddr *)&addr, sun_len) == -1) {
                 muxserver_sock = -1;
                 if (errno == EINVAL || errno == EADDRINUSE) {
                         error("ControlSocket %s already exists, "
@@ -163,6 +980,14 @@ muxserver_listen(void)
                 fatal("%s listen(): %s", __func__, strerror(errno));
 
         set_nonblock(muxserver_sock);
+
+        mux_listener_channel = channel_new("mux listener",
+            SSH_CHANNEL_MUX_LISTENER, muxserver_sock, muxserver_sock, -1,
+            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
+            0, addr.sun_path, 1);
+        mux_listener_channel->mux_rcb = mux_master_read_cb;
+        debug3("%s: mux listener channel %d fd %d", __func__,
+            mux_listener_channel->self, mux_listener_channel->sock);
 }
 
 /* Callback on open confirmation in mux master for a mux client session. */
@@ -176,7 +1001,7 @@ mux_session_confirm(int id, void *arg)
 
         if (cctx == NULL)
                 fatal("%s: cctx == NULL", __func__);
-        if ((c = channel_lookup(id)) == NULL)
+        if ((c = channel_by_id(id)) == NULL)
                 fatal("%s: no channel for id %d", __func__, id);
 
         display = getenv("DISPLAY");
@@ -211,291 +1036,616 @@ mux_session_confirm(int id, void *arg)
         xfree(cctx);
 }
 
+/* ** Multiplexing client support */
+
+/* Exit signal handler */
+static void
+control_client_sighandler(int signo)
+{
+        muxclient_terminate = signo;
+}
+
 /*
- * Accept a connection on the mux master socket and process the
- * client's request. Returns flag indicating whether mux master should
- * begin graceful close.
+ * Relay signal handler - used to pass some signals from mux client to
+ * mux master.
  */
-int
-muxserver_accept_control(void)
+static void
+control_client_sigrelay(int signo)
 {
-        Buffer m;
-        Channel *c;
-        int client_fd, new_fd[3], ver, allowed, window, packetmax;
-        socklen_t addrlen;
-        struct sockaddr_storage addr;
-        struct mux_session_confirm_ctx *cctx;
-        char *cmd;
-        u_int i, j, len, env_len, mux_command, flags, escape_char;
-        uid_t euid;
-        gid_t egid;
-        int start_close = 0;
+        int save_errno = errno;
 
-        /*
-         * Accept connection on control socket
-         */
-        memset(&addr, 0, sizeof(addr));
-        addrlen = sizeof(addr);
-        if ((client_fd = accept(muxserver_sock,
-            (struct sockaddr*)&addr, &addrlen)) == -1) {
-                error("%s accept: %s", __func__, strerror(errno));
-                return 0;
+        if (muxserver_pid > 1)
+                kill(muxserver_pid, signo);
+
+        errno = save_errno;
+}
+
+static int
+mux_client_read(int fd, Buffer *b, u_int need)
+{
+        u_int have;
+        ssize_t len;
+        u_char *p;
+        struct pollfd pfd;
+
+        pfd.fd = fd;
+        pfd.events = POLLIN;
+        p = buffer_append_space(b, need);
+        for (have = 0; have < need; ) {
+                if (muxclient_terminate) {
+                        errno = EINTR;
+                        return -1;
+                }
+                len = read(fd, p + have, need - have);
+                if (len < 0) {
+                        switch (errno) {
+#if defined(EWOULDBLOCK) && (EWOULDBLOCK != EAGAIN)
+                        case EWOULDBLOCK:
+#endif
+                        case EAGAIN:
+                                (void)poll(&pfd, 1, -1);
+                                /* FALLTHROUGH */
+                        case EINTR:
+                                continue;
+                        default:
+                                return -1;
+                        }
+                }
+                if (len == 0) {
+                        errno = EPIPE;
+                        return -1;
+                }
+                have += (u_int)len;
         }
+        return 0;
+}
 
-        if (getpeereid(client_fd, &euid, &egid) < 0) {
-                error("%s getpeereid failed: %s", __func__, strerror(errno));
-                close(client_fd);
-                return 0;
+static int
+mux_client_write_packet(int fd, Buffer *m)
+{
+        Buffer queue;
+        u_int have, need;
+        int oerrno, len;
+        u_char *ptr;
+        struct pollfd pfd;
+
+        pfd.fd = fd;
+        pfd.events = POLLOUT;
+        buffer_init(&queue);
+        buffer_put_string(&queue, buffer_ptr(m), buffer_len(m));
+
+        need = buffer_len(&queue);
+        ptr = buffer_ptr(&queue);
+
+        for (have = 0; have < need; ) {
+                if (muxclient_terminate) {
+                        buffer_free(&queue);
+                        errno = EINTR;
+                        return -1;
+                }
+                len = write(fd, ptr + have, need - have);
+                if (len < 0) {
+                        switch (errno) {
+#if defined(EWOULDBLOCK) && (EWOULDBLOCK != EAGAIN)
+                        case EWOULDBLOCK:
+#endif
+                        case EAGAIN:
+                                (void)poll(&pfd, 1, -1);
+                                /* FALLTHROUGH */
+                        case EINTR:
+                                continue;
+                        default:
+                                oerrno = errno;
+                                buffer_free(&queue);
+                                errno = oerrno;
+                                return -1;
+                        }
+                }
+                if (len == 0) {
+                        buffer_free(&queue);
+                        errno = EPIPE;
+                        return -1;
+                }
+                have += (u_int)len;
         }
-        if ((euid != 0) && (getuid() != euid)) {
-                error("control mode uid mismatch: peer euid %u != uid %u",
-                    (u_int) euid, (u_int) getuid());
-                close(client_fd);
-                return 0;
+        buffer_free(&queue);
+        return 0;
+}
+
+static int
+mux_client_read_packet(int fd, Buffer *m)
+{
+        Buffer queue;
+        u_int need, have;
+        void *ptr;
+        int oerrno;
+
+        buffer_init(&queue);
+        if (mux_client_read(fd, &queue, 4) != 0) {
+                if ((oerrno = errno) == EPIPE)
+                debug3("%s: read header failed: %s", __func__, strerror(errno));
+                errno = oerrno;
+                return -1;
         }
+        need = get_u32(buffer_ptr(&queue));
+        if (mux_client_read(fd, &queue, need) != 0) {
+                oerrno = errno;
+                debug3("%s: read body failed: %s", __func__, strerror(errno));
+                errno = oerrno;
+                return -1;
+        }
+        ptr = buffer_get_string_ptr(&queue, &have);
+        buffer_append(m, ptr, have);
+        buffer_free(&queue);
+        return 0;
+}
 
-        /* XXX handle asynchronously */
-        unset_nonblock(client_fd);
+static int
+mux_client_hello_exchange(int fd)
+{
+        Buffer m;
+        u_int type, ver;
 
-        /* Read command */
         buffer_init(&m);
-        if (ssh_msg_recv(client_fd, &m) == -1) {
-                error("%s: client msg_recv failed", __func__);
-                close(client_fd);
+        buffer_put_int(&m, MUX_MSG_HELLO);
+        buffer_put_int(&m, SSHMUX_VER);
+        /* no extensions */
+
+        if (mux_client_write_packet(fd, &m) != 0)
+                fatal("%s: write packet: %s", __func__, strerror(errno));
+
+        buffer_clear(&m);
+
+        /* Read their HELLO */
+        if (mux_client_read_packet(fd, &m) != 0) {
                 buffer_free(&m);
-                return 0;
+                return -1;
         }
-        if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
-                error("%s: wrong client version %d", __func__, ver);
+
+        type = buffer_get_int(&m);
+        if (type != MUX_MSG_HELLO)
+                fatal("%s: expected HELLO (%u) received %u",
+                    __func__, MUX_MSG_HELLO, type);
+        ver = buffer_get_int(&m);
+        if (ver != SSHMUX_VER)
+                fatal("Unsupported multiplexing protocol version %d "
+                    "(expected %d)", ver, SSHMUX_VER);
+        debug2("%s: master version %u", __func__, ver);
+        /* No extensions are presently defined */
+        while (buffer_len(&m) > 0) {
+                char *name = buffer_get_string(&m, NULL);
+                char *value = buffer_get_string(&m, NULL);
+
+                debug2("Unrecognised master extension \"%s\"", name);
+                xfree(name);
+                xfree(value);
+        }
+        buffer_free(&m);
+        return 0;
+}
+
+static u_int
+mux_client_request_alive(int fd)
+{
+        Buffer m;
+        char *e;
+        u_int pid, type, rid;
+
+        debug3("%s: entering", __func__);
+
+        buffer_init(&m);
+        buffer_put_int(&m, MUX_C_ALIVE_CHECK);
+        buffer_put_int(&m, muxclient_request_id);
+
+        if (mux_client_write_packet(fd, &m) != 0)
+                fatal("%s: write packet: %s", __func__, strerror(errno));
+
+        buffer_clear(&m);
+
+        /* Read their reply */
+        if (mux_client_read_packet(fd, &m) != 0) {
                 buffer_free(&m);
-                close(client_fd);
                 return 0;
         }
 
-        allowed = 1;
-        mux_command = buffer_get_int(&m);
-        flags = buffer_get_int(&m);
+        type = buffer_get_int(&m);
+        if (type != MUX_S_ALIVE) {
+                e = buffer_get_string(&m, NULL);
+                fatal("%s: master returned error: %s", __func__, e);
+        }
+
+        if ((rid = buffer_get_int(&m)) != muxclient_request_id)
+                fatal("%s: out of sequence reply: my id %u theirs %u",
+                    __func__, muxclient_request_id, rid);
+        pid = buffer_get_int(&m);
+        buffer_free(&m);
+
+        debug3("%s: done pid = %u", __func__, pid);
+
+        muxclient_request_id++;
+
+        return pid;
+}
+
+static void
+mux_client_request_terminate(int fd)
+{
+        Buffer m;
+        char *e;
+        u_int type, rid;
+
+        debug3("%s: entering", __func__);
+
+        buffer_init(&m);
+        buffer_put_int(&m, MUX_C_TERMINATE);
+        buffer_put_int(&m, muxclient_request_id);
+
+        if (mux_client_write_packet(fd, &m) != 0)
+                fatal("%s: write packet: %s", __func__, strerror(errno));
 
         buffer_clear(&m);
 
-        switch (mux_command) {
-        case SSHMUX_COMMAND_OPEN:
-                if (options.control_master == SSHCTL_MASTER_ASK ||
-                    options.control_master == SSHCTL_MASTER_AUTO_ASK)
-                        allowed = ask_permission("Allow shared connection "
-                            "to %s? ", host);
-                /* continue below */
-                break;
-        case SSHMUX_COMMAND_TERMINATE:
-                if (options.control_master == SSHCTL_MASTER_ASK ||
-                    options.control_master == SSHCTL_MASTER_AUTO_ASK)
-                        allowed = ask_permission("Terminate shared connection "
-                            "to %s? ", host);
-                if (allowed)
-                        start_close = 1;
-                /* FALLTHROUGH */
-        case SSHMUX_COMMAND_ALIVE_CHECK:
-                /* Reply for SSHMUX_COMMAND_TERMINATE and ALIVE_CHECK */
-                buffer_clear(&m);
-                buffer_put_int(&m, allowed);
-                buffer_put_int(&m, getpid());
-                if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
-                        error("%s: client msg_send failed", __func__);
-                        close(client_fd);
+        /* Read their reply */
+        if (mux_client_read_packet(fd, &m) != 0) {
+                /* Remote end exited already */
+                if (errno == EPIPE) {
                         buffer_free(&m);
-                        return start_close;
+                        return;
                 }
-                buffer_free(&m);
-                close(client_fd);
-                return start_close;
+                fatal("%s: read from master failed: %s",
+                    __func__, strerror(errno));
+        }
+
+        type = buffer_get_int(&m);
+        if ((rid = buffer_get_int(&m)) != muxclient_request_id)
+                fatal("%s: out of sequence reply: my id %u theirs %u",
+                    __func__, muxclient_request_id, rid);
+        switch (type) {
+        case MUX_S_OK:
+                break;
+        case MUX_S_PERMISSION_DENIED:
+                e = buffer_get_string(&m, NULL);
+                fatal("Master refused termination request: %s", e);
+        case MUX_S_FAILURE:
+                e = buffer_get_string(&m, NULL);
+                fatal("%s: termination request failed: %s", __func__, e);
         default:
-                error("Unsupported command %d", mux_command);
-                buffer_free(&m);
-                close(client_fd);
-                return 0;
+                fatal("%s: unexpected response from master 0x%08x",
+                    __func__, type);
         }
+        buffer_free(&m);
+        muxclient_request_id++;
+}
+
+static int
+mux_client_request_forward(int fd, u_int ftype, Forward *fwd)
+{
+        Buffer m;
+        char *e, *fwd_desc;
+        u_int type, rid;
+
+        fwd_desc = format_forward(ftype, fwd);
+        debug("Requesting %s", fwd_desc);
+        xfree(fwd_desc);
+
+        buffer_init(&m);
+        buffer_put_int(&m, MUX_C_OPEN_FWD);
+        buffer_put_int(&m, muxclient_request_id);
+        buffer_put_int(&m, ftype);
+        buffer_put_cstring(&m,
+            fwd->listen_host == NULL ? "" : fwd->listen_host);
+        buffer_put_int(&m, fwd->listen_port);
+        buffer_put_cstring(&m,
+            fwd->connect_host == NULL ? "" : fwd->connect_host);
+        buffer_put_int(&m, fwd->connect_port);
+
+        if (mux_client_write_packet(fd, &m) != 0)
+                fatal("%s: write packet: %s", __func__, strerror(errno));
 
-        /* Reply for SSHMUX_COMMAND_OPEN */
         buffer_clear(&m);
-        buffer_put_int(&m, allowed);
-        buffer_put_int(&m, getpid());
-        if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
-                error("%s: client msg_send failed", __func__);
-                close(client_fd);
+
+        /* Read their reply */
+        if (mux_client_read_packet(fd, &m) != 0) {
                 buffer_free(&m);
-                return 0;
+                return -1;
         }
 
-        if (!allowed) {
-                error("Refused control connection");
-                close(client_fd);
+        type = buffer_get_int(&m);
+        if ((rid = buffer_get_int(&m)) != muxclient_request_id)
+                fatal("%s: out of sequence reply: my id %u theirs %u",
+                    __func__, muxclient_request_id, rid);
+        switch (type) {
+        case MUX_S_OK:
+                break;
+        case MUX_S_PERMISSION_DENIED:
+                e = buffer_get_string(&m, NULL);
                 buffer_free(&m);
-                return 0;
+                error("Master refused forwarding request: %s", e);
+                return -1;
+        case MUX_S_FAILURE:
+                e = buffer_get_string(&m, NULL);
+                buffer_free(&m);
+                error("%s: session request failed: %s", __func__, e);
+                return -1;
+        default:
+                fatal("%s: unexpected response from master 0x%08x",
+                    __func__, type);
         }
+        buffer_free(&m);
 
-        buffer_clear(&m);
-        if (ssh_msg_recv(client_fd, &m) == -1) {
-                error("%s: client msg_recv failed", __func__);
-                close(client_fd);
-                buffer_free(&m);
-                return 0;
+        muxclient_request_id++;
+        return 0;
+}
+
+static int
+mux_client_request_forwards(int fd)
+{
+        int i;
+
+        debug3("%s: requesting forwardings: %d local, %d remote", __func__,
+            options.num_local_forwards, options.num_remote_forwards);
+
+        /* XXX ExitOnForwardingFailure */
+        for (i = 0; i < options.num_local_forwards; i++) {
+                if (mux_client_request_forward(fd,
+                    options.local_forwards[i].connect_port == 0 ?
+                    MUX_FWD_DYNAMIC : MUX_FWD_LOCAL,
+                    options.local_forwards + i) != 0)
+                        return -1;
         }
-        if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
-                error("%s: wrong client version %d", __func__, ver);
-                buffer_free(&m);
-                close(client_fd);
-                return 0;
+        for (i = 0; i < options.num_remote_forwards; i++) {
+                if (mux_client_request_forward(fd, MUX_FWD_REMOTE,
+                    options.remote_forwards + i) != 0)
+                        return -1;
         }
+        return 0;
+}
 
-        cctx = xcalloc(1, sizeof(*cctx));
-        cctx->want_tty = (flags & SSHMUX_FLAG_TTY) != 0;
-        cctx->want_subsys = (flags & SSHMUX_FLAG_SUBSYS) != 0;
-        cctx->want_x_fwd = (flags & SSHMUX_FLAG_X11_FWD) != 0;
-        cctx->want_agent_fwd = (flags & SSHMUX_FLAG_AGENT_FWD) != 0;
-        cctx->term = buffer_get_string(&m, &len);
-        escape_char = buffer_get_int(&m);
-
-        cmd = buffer_get_string(&m, &len);
-        buffer_init(&cctx->cmd);
-        buffer_append(&cctx->cmd, cmd, strlen(cmd));
+static int
+mux_client_request_session(int fd)
+{
+        Buffer m;
+        char *e, *term;
+        u_int i, rid, sid, esid, exitval, type, exitval_seen;
+        extern char **environ;
+        int devnull;
 
-        env_len = buffer_get_int(&m);
-        env_len = MIN(env_len, 4096);
-        debug3("%s: receiving %d env vars", __func__, env_len);
-        if (env_len != 0) {
-                cctx->env = xcalloc(env_len + 1, sizeof(*cctx->env));
-                for (i = 0; i < env_len; i++)
-                        cctx->env[i] = buffer_get_string(&m, &len);
-                cctx->env[i] = NULL;
+        debug3("%s: entering", __func__);
+
+        if ((muxserver_pid = mux_client_request_alive(fd)) == 0) {
+                error("%s: master alive request failed", __func__);
+                return -1;
         }
 
-        debug2("%s: accepted tty %d, subsys %d, cmd %s", __func__,
-            cctx->want_tty, cctx->want_subsys, cmd);
-        xfree(cmd);
+        signal(SIGPIPE, SIG_IGN);
 
-        /* Gather fds from client */
-        for(i = 0; i < 3; i++) {
-                if ((new_fd[i] = mm_receive_fd(client_fd)) == -1) {
-                        error("%s: failed to receive fd %d from slave",
-                            __func__, i);
-                        for (j = 0; j < i; j++)
-                                close(new_fd[j]);
-                        for (j = 0; j < env_len; j++)
-                                xfree(cctx->env[j]);
-                        if (env_len > 0)
-                                xfree(cctx->env);
-                        xfree(cctx->term);
-                        buffer_free(&cctx->cmd);
-                        close(client_fd);
-                        xfree(cctx);
-                        return 0;
+        if (stdin_null_flag) {
+                if ((devnull = open(_PATH_DEVNULL, O_RDONLY)) == -1)
+                        fatal("open(/dev/null): %s", strerror(errno));
+                if (dup2(devnull, STDIN_FILENO) == -1)
+                        fatal("dup2: %s", strerror(errno));
+                if (devnull > STDERR_FILENO)
+                        close(devnull);
+        }
+
+        term = getenv("TERM");
+
+        buffer_init(&m);
+        buffer_put_int(&m, MUX_C_NEW_SESSION);
+        buffer_put_int(&m, muxclient_request_id);
+        buffer_put_cstring(&m, ""); /* reserved */
+        buffer_put_int(&m, tty_flag);
+        buffer_put_int(&m, options.forward_x11);
+        buffer_put_int(&m, options.forward_agent);
+        buffer_put_int(&m, subsystem_flag);
+        buffer_put_int(&m, options.escape_char == SSH_ESCAPECHAR_NONE ?
+            0xffffffff : (u_int)options.escape_char);
+        buffer_put_cstring(&m, term == NULL ? "" : term);
+        buffer_put_string(&m, buffer_ptr(&command), buffer_len(&command));
+
+        if (options.num_send_env > 0 && environ != NULL) {
+                /* Pass environment */
+                for (i = 0; environ[i] != NULL; i++) {
+                        if (env_permitted(environ[i])) {
+                                buffer_put_cstring(&m, environ[i]);
+                        }
                 }
         }
 
-        debug2("%s: got fds stdin %d, stdout %d, stderr %d", __func__,
-            new_fd[0], new_fd[1], new_fd[2]);
+        if (mux_client_write_packet(fd, &m) != 0)
+                fatal("%s: write packet: %s", __func__, strerror(errno));
 
-        /* Try to pick up ttymodes from client before it goes raw */
-        if (cctx->want_tty && tcgetattr(new_fd[0], &cctx->tio) == -1)
-                error("%s: tcgetattr: %s", __func__, 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("%s: send fds failed", __func__);
 
-        /* This roundtrip is just for synchronisation of ttymodes */
+        debug3("%s: session request sent", __func__);
+
+        /* Read their reply */
         buffer_clear(&m);
-        if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
-                error("%s: client msg_send failed", __func__);
-                close(client_fd);
-                close(new_fd[0]);
-                close(new_fd[1]);
-                close(new_fd[2]);
+        if (mux_client_read_packet(fd, &m) != 0) {
+                error("%s: read from master failed: %s",
+                    __func__, strerror(errno));
                 buffer_free(&m);
-                xfree(cctx->term);
-                if (env_len != 0) {
-                        for (i = 0; i < env_len; i++)
-                                xfree(cctx->env[i]);
-                        xfree(cctx->env);
-                }
-                return 0;
+                return -1;
         }
-        buffer_free(&m);
 
-        /* enable nonblocking unless tty */
-        if (!isatty(new_fd[0]))
-                set_nonblock(new_fd[0]);
-        if (!isatty(new_fd[1]))
-                set_nonblock(new_fd[1]);
-        if (!isatty(new_fd[2]))
-                set_nonblock(new_fd[2]);
+        type = buffer_get_int(&m);
+        if ((rid = buffer_get_int(&m)) != muxclient_request_id)
+                fatal("%s: out of sequence reply: my id %u theirs %u",
+                    __func__, muxclient_request_id, rid);
+        switch (type) {
+        case MUX_S_SESSION_OPENED:
+                sid = buffer_get_int(&m);
+                debug("%s: master session id: %u", __func__, sid);
+                break;
+        case MUX_S_PERMISSION_DENIED:
+                e = buffer_get_string(&m, NULL);
+                buffer_free(&m);
+                error("Master refused forwarding request: %s", e);
+                return -1;
+        case MUX_S_FAILURE:
+                e = buffer_get_string(&m, NULL);
+                buffer_free(&m);
+                error("%s: forwarding request failed: %s", __func__, e);
+                return -1;
+        default:
+                buffer_free(&m);
+                error("%s: unexpected response from master 0x%08x",
+                    __func__, type);
+                return -1;
+        }
+        muxclient_request_id++;
 
-        set_nonblock(client_fd);
+        signal(SIGHUP, control_client_sighandler);
+        signal(SIGINT, control_client_sighandler);
+        signal(SIGTERM, control_client_sighandler);
+        signal(SIGWINCH, control_client_sigrelay);
 
-        window = CHAN_SES_WINDOW_DEFAULT;
-        packetmax = CHAN_SES_PACKET_DEFAULT;
-        if (cctx->want_tty) {
-                window >>= 1;
-                packetmax >>= 1;
-        }
-        
-        c = channel_new("session", SSH_CHANNEL_OPENING,
-            new_fd[0], new_fd[1], new_fd[2], window, packetmax,
-            CHAN_EXTENDED_WRITE, "client-session", /*nonblock*/0);
+        if (tty_flag)
+                enter_raw_mode(force_tty_flag);
 
-        c->ctl_fd = client_fd;
-        if (cctx->want_tty && escape_char != 0xffffffff) {
-                channel_register_filter(c->self,
-                    client_simple_escape_filter, NULL,
-                    client_filter_cleanup,
-                    client_new_escape_filter_ctx((int)escape_char));
+        /*
+         * 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;;) {
+                buffer_clear(&m);
+                if (mux_client_read_packet(fd, &m) != 0)
+                        break;
+                type = buffer_get_int(&m);
+                if (type != MUX_S_EXIT_MESSAGE) {
+                        e = buffer_get_string(&m, NULL);
+                        fatal("%s: master returned error: %s", __func__, e);
+                }
+                if ((esid = buffer_get_int(&m)) != sid)
+                        fatal("%s: exit on unknown session: my id %u theirs %u",
+                            __func__, sid, esid);
+                debug("%s: master session id: %u", __func__, sid);
+                if (exitval_seen)
+                        fatal("%s: exitval sent twice", __func__);
+                exitval = buffer_get_int(&m);
+                exitval_seen = 1;
         }
 
-        debug3("%s: channel_new: %d", __func__, c->self);
+        close(fd);
+        leave_raw_mode(force_tty_flag);
 
-        channel_send_open(c->self);
-        channel_register_open_confirm(c->self, mux_session_confirm, cctx);
-        return 0;
-}
+        if (muxclient_terminate) {
+                debug2("Exiting on signal %d", muxclient_terminate);
+                exitval = 255;
+        } else if (!exitval_seen) {
+                debug2("Control master terminated unexpectedly");
+                exitval = 255;
+        } else
+                debug2("Received exit status from master %d", exitval);
 
-/* ** Multiplexing client support */
+        if (tty_flag && options.log_level != SYSLOG_LEVEL_QUIET)
+                fprintf(stderr, "Shared connection to %s closed.\r\n", host);
 
-/* Exit signal handler */
-static void
-control_client_sighandler(int signo)
-{
-        muxclient_terminate = signo;
+        exit(exitval);
 }
 
-/*
- * Relay signal handler - used to pass some signals from mux client to
- * mux master.
- */
-static void
-control_client_sigrelay(int signo)
+static int
+mux_client_request_stdio_fwd(int fd)
 {
-        int save_errno = errno;
+        Buffer m;
+        char *e;
+        u_int type, rid, sid;
+        int devnull;
 
-        if (muxserver_pid > 1)
-                kill(muxserver_pid, signo);
+        debug3("%s: entering", __func__);
 
-        errno = save_errno;
-}
+        if ((muxserver_pid = mux_client_request_alive(fd)) == 0) {
+                error("%s: master alive request failed", __func__);
+                return -1;
+        }
 
-/* Check mux client environment variables before passing them to mux master. */
-static int
-env_permitted(char *env)
-{
-        int i, ret;
-        char name[1024], *cp;
+        signal(SIGPIPE, SIG_IGN);
 
-        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))
-                fatal("env_permitted: name '%.100s...' too long", env);
+        if (stdin_null_flag) {
+                if ((devnull = open(_PATH_DEVNULL, O_RDONLY)) == -1)
+                        fatal("open(/dev/null): %s", strerror(errno));
+                if (dup2(devnull, STDIN_FILENO) == -1)
+                        fatal("dup2: %s", strerror(errno));
+                if (devnull > STDERR_FILENO)
+                        close(devnull);
+        }
 
-        for (i = 0; i < options.num_send_env; i++)
-                if (match_pattern(name, options.send_env[i]))
-                        return (1);
+        buffer_init(&m);
+        buffer_put_int(&m, MUX_C_NEW_STDIO_FWD);
+        buffer_put_int(&m, muxclient_request_id);
+        buffer_put_cstring(&m, ""); /* reserved */
+        buffer_put_cstring(&m, stdio_forward_host);
+        buffer_put_int(&m, stdio_forward_port);
+
+        if (mux_client_write_packet(fd, &m) != 0)
+                fatal("%s: write packet: %s", __func__, strerror(errno));
+
+        /* Send the stdio file descriptors */
+        if (mm_send_fd(fd, STDIN_FILENO) == -1 ||
+            mm_send_fd(fd, STDOUT_FILENO) == -1)
+                fatal("%s: send fds failed", __func__);
+
+        debug3("%s: stdio forward request sent", __func__);
+
+        /* Read their reply */
+        buffer_clear(&m);
+
+        if (mux_client_read_packet(fd, &m) != 0) {
+                error("%s: read from master failed: %s",
+                    __func__, strerror(errno));
+                buffer_free(&m);
+                return -1;
+        }
+
+        type = buffer_get_int(&m);
+        if ((rid = buffer_get_int(&m)) != muxclient_request_id)
+                fatal("%s: out of sequence reply: my id %u theirs %u",
+                    __func__, muxclient_request_id, rid);
+        switch (type) {
+        case MUX_S_SESSION_OPENED:
+                sid = buffer_get_int(&m);
+                debug("%s: master session id: %u", __func__, sid);
+                break;
+        case MUX_S_PERMISSION_DENIED:
+                e = buffer_get_string(&m, NULL);
+                buffer_free(&m);
+                fatal("Master refused forwarding request: %s", e);
+        case MUX_S_FAILURE:
+                e = buffer_get_string(&m, NULL);
+                buffer_free(&m);
+                fatal("%s: stdio forwarding request failed: %s", __func__, e);
+        default:
+                buffer_free(&m);
+                error("%s: unexpected response from master 0x%08x",
+                    __func__, type);
+                return -1;
+        }
+        muxclient_request_id++;
+
+        signal(SIGHUP, control_client_sighandler);
+        signal(SIGINT, control_client_sighandler);
+        signal(SIGTERM, control_client_sighandler);
+        signal(SIGWINCH, control_client_sigrelay);
 
-        return (0);
+        /*
+         * Stick around until the controlee closes the client_fd.
+         */
+        buffer_clear(&m);
+        if (mux_client_read_packet(fd, &m) != 0) {
+                if (errno == EPIPE ||
+                    (errno == EINTR && muxclient_terminate != 0))
+                        return 0;
+                fatal("%s: mux_client_read_packet: %s",
+                    __func__, strerror(errno));
+        }
+        fatal("%s: master returned unexpected message %u", __func__, type);
 }
 
 /* Multiplex client main loop. */
@@ -503,14 +1653,16 @@ void
 muxclient(const char *path)
 {
         struct sockaddr_un addr;
-        int i, r, fd, sock, exitval[2], num_env, addr_len;
-        Buffer m;
-        char *term;
-        extern char **environ;
-        u_int allowed, flags;
+        socklen_t sun_len;
+        int sock;
+        u_int pid;
 
-        if (muxclient_command == 0)
-                muxclient_command = SSHMUX_COMMAND_OPEN;
+        if (muxclient_command == 0) {
+                if (stdio_forward_host != NULL)
+                        muxclient_command = SSHMUX_COMMAND_STDIO_FWD;
+                else
+                        muxclient_command = SSHMUX_COMMAND_OPEN;
+        }
 
         switch (options.control_master) {
         case SSHCTL_MASTER_AUTO:
@@ -525,7 +1677,7 @@ muxclient(const char *path)
 
         memset(&addr, '\0', sizeof(addr));
         addr.sun_family = AF_UNIX;
-        addr_len = offsetof(struct sockaddr_un, sun_path) +
+        sun_len = offsetof(struct sockaddr_un, sun_path) +
             strlen(path) + 1;
 
         if (strlcpy(addr.sun_path, path,
@@ -535,8 +1687,12 @@ muxclient(const char *path)
         if ((sock = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
                 fatal("%s socket(): %s", __func__, strerror(errno));
 
-        if (connect(sock, (struct sockaddr *)&addr, addr_len) == -1) {
-                if (muxclient_command != SSHMUX_COMMAND_OPEN) {
+        if (connect(sock, (struct sockaddr *)&addr, sun_len) == -1) {
+                switch (muxclient_command) {
+                case SSHMUX_COMMAND_OPEN:
+                case SSHMUX_COMMAND_STDIO_FWD:
+                        break;
+                default:
                         fatal("Control socket connect(%.100s): %s", path,
                             strerror(errno));
                 }
@@ -549,181 +1705,35 @@ muxclient(const char *path)
                 close(sock);
                 return;
         }
+        set_nonblock(sock);
 
-        if (stdin_null_flag) {
-                if ((fd = open(_PATH_DEVNULL, O_RDONLY)) == -1)
-                        fatal("open(/dev/null): %s", strerror(errno));
-                if (dup2(fd, STDIN_FILENO) == -1)
-                        fatal("dup2: %s", strerror(errno));
-                if (fd > STDERR_FILENO)
-                        close(fd);
-        }
-
-        term = getenv("TERM");
-
-        flags = 0;
-        if (tty_flag)
-                flags |= SSHMUX_FLAG_TTY;
-        if (subsystem_flag)
-                flags |= SSHMUX_FLAG_SUBSYS;
-        if (options.forward_x11)
-                flags |= SSHMUX_FLAG_X11_FWD;
-        if (options.forward_agent)
-                flags |= SSHMUX_FLAG_AGENT_FWD;
-
-        signal(SIGPIPE, SIG_IGN);
-
-        buffer_init(&m);
-
-        /* Send our command to server */
-        buffer_put_int(&m, muxclient_command);
-        buffer_put_int(&m, flags);
-        if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1) {
-                error("%s: msg_send", __func__);
- muxerr:
+        if (mux_client_hello_exchange(sock) != 0) {
+                error("%s: master hello exchange failed", __func__);
                 close(sock);
-                buffer_free(&m);
-                if (muxclient_command != SSHMUX_COMMAND_OPEN)
-                        cleanup_exit(255);
-                logit("Falling back to non-multiplexed connection");
-                xfree(options.control_path);
-                options.control_path = NULL;
-                options.control_master = SSHCTL_MASTER_NO;
                 return;
         }
-        buffer_clear(&m);
-
-        /* Get authorisation status and PID of controlee */
-        if (ssh_msg_recv(sock, &m) == -1) {
-                error("%s: Did not receive reply from master", __func__);
-                goto muxerr;
-        }
-        if (buffer_get_char(&m) != SSHMUX_VER) {
-                error("%s: Master replied with wrong version", __func__);
-                goto muxerr;
-        }
-        if (buffer_get_int_ret(&allowed, &m) != 0) {
-                error("%s: bad server reply", __func__);
-                goto muxerr;
-        }
-        if (allowed != 1) {
-                error("Connection to master denied");
-                goto muxerr;
-        }
-        muxserver_pid = buffer_get_int(&m);
-
-        buffer_clear(&m);
 
         switch (muxclient_command) {
         case SSHMUX_COMMAND_ALIVE_CHECK:
-                fprintf(stderr, "Master running (pid=%d)\r\n",
-                    muxserver_pid);
+                if ((pid = mux_client_request_alive(sock)) == 0)
+                        fatal("%s: master alive check failed", __func__);
+                fprintf(stderr, "Master running (pid=%d)\r\n", pid);
                 exit(0);
         case SSHMUX_COMMAND_TERMINATE:
+                mux_client_request_terminate(sock);
                 fprintf(stderr, "Exit request sent.\r\n");
                 exit(0);
         case SSHMUX_COMMAND_OPEN:
-                buffer_put_cstring(&m, term ? term : "");
-                if (options.escape_char == SSH_ESCAPECHAR_NONE)
-                        buffer_put_int(&m, 0xffffffff);
-                else
-                        buffer_put_int(&m, options.escape_char);
-                buffer_append(&command, "\0", 1);
-                buffer_put_cstring(&m, buffer_ptr(&command));
-
-                if (options.num_send_env == 0 || environ == NULL) {
-                        buffer_put_int(&m, 0);
-                } else {
-                        /* Pass environment */
-                        num_env = 0;
-                        for (i = 0; environ[i] != NULL; i++) {
-                                if (env_permitted(environ[i]))
-                                        num_env++; /* Count */
-                        }
-                        buffer_put_int(&m, num_env);
-                for (i = 0; environ[i] != NULL && num_env >= 0; i++) {
-                                if (env_permitted(environ[i])) {
-                                        num_env--;
-                                        buffer_put_cstring(&m, environ[i]);
-                                }
-                        }
+                if (mux_client_request_forwards(sock) != 0) {
+                        error("%s: master forward request failed", __func__);
+                        return;
                 }
-                break;
+                mux_client_request_session(sock);
+                return;
+        case SSHMUX_COMMAND_STDIO_FWD:
+                mux_client_request_stdio_fwd(sock);
+                exit(0);
         default:
                 fatal("unrecognised muxclient_command %d", muxclient_command);
         }
-
-        if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1) {
-                error("%s: msg_send", __func__);
-                goto muxerr;
-        }
-
-        if (mm_send_fd(sock, STDIN_FILENO) == -1 ||
-            mm_send_fd(sock, STDOUT_FILENO) == -1 ||
-            mm_send_fd(sock, STDERR_FILENO) == -1) {
-                error("%s: send fds failed", __func__);
-                goto muxerr;
-        }
-
-        /*
-         * Mux errors are non-recoverable from this point as the master
-         * has ownership of the session now.
-         */
-
-        /* Wait for reply, so master has a chance to gather ttymodes */
-        buffer_clear(&m);
-        if (ssh_msg_recv(sock, &m) == -1)
-                fatal("%s: msg_recv", __func__);
-        if (buffer_get_char(&m) != SSHMUX_VER)
-                fatal("%s: wrong version", __func__);
-        buffer_free(&m);
-
-        signal(SIGHUP, control_client_sighandler);
-        signal(SIGINT, control_client_sighandler);
-        signal(SIGTERM, control_client_sighandler);
-        signal(SIGWINCH, control_client_sigrelay);
-
-        if (tty_flag)
-                enter_raw_mode(force_tty_flag);
-
-        /*
-         * Stick around until the controlee closes the client_fd.
-         * Before it does, it is expected to write this process' exit
-         * value (one int). 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).
-         */
-        exitval[0] = 0;
-        for (i = 0; !muxclient_terminate && i < (int)sizeof(exitval);) {
-                r = read(sock, (char *)exitval + i, sizeof(exitval) - i);
-                if (r == 0) {
-                        debug2("Received EOF from master");
-                        break;
-                }
-                if (r == -1) {
-                        if (errno == EINTR)
-                                continue;
-                        fatal("%s: read %s", __func__, strerror(errno));
-                }
-                i += r;
-        }
-
-        close(sock);
-        leave_raw_mode(force_tty_flag);
-        if (i > (int)sizeof(int))
-                fatal("%s: master returned too much data (%d > %lu)",
-                    __func__, i, (u_long)sizeof(int));
-        if (muxclient_terminate) {
-                debug2("Exiting on signal %d", muxclient_terminate);
-                exitval[0] = 255;
-        } else if (i < (int)sizeof(int)) {
-                debug2("Control master terminated unexpectedly");
-                exitval[0] = 255;
-        } else
-                debug2("Received exit status from master %d", exitval[0]);
-
-        if (tty_flag && options.log_level != SYSLOG_LEVEL_QUIET)
-                fprintf(stderr, "Shared connection to %s closed.\r\n", host);
-
-        exit(exitval[0]);
 }