Adding upstream version 1:9.2p1.upstream/1%9.2p1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2344 insertions, 0 deletions

diff --git a/mux.c b/mux.c
new file mode 100644
index 0000000..e7580ac
--- /dev/null
+++ b/mux.c
@@ -0,0 +1,2344 @@
+/* $OpenBSD: mux.c,v 1.95 2023/01/06 02:39:59 djm 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 <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"
+
+/* 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 */
+/* ARGSUSED */
+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 */
+/* ARGSUSED */
+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 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;
+	}
+
+	debug2_f("channel %d: stdio fwd to %s:%u", 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 (!ask_permission("Allow forward to %s:%u? ",
+		    chost, cport)) {
+			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)
+{
+	size_t have;
+	ssize_t len;
+	u_char *p;
+	struct pollfd pfd;
+	int r;
+
+	pfd.fd = fd;
+	pfd.events = POLLIN;
+	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:
+				(void)poll(&pfd, 1, -1);
+				/* 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(int fd, struct sshbuf *m)
+{
+	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) != 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) != 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_hello_exchange(int fd)
+{
+	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(fd, m) != 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;
+
+	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);
+
+	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;
+	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");
+		/* 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);
+
+	if (mux_client_hello_exchange(sock) != 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);
+	}
+}