Upgrade to OpenSSH 5.1p1.

I have worked hard to reduce diffs against the vendor branch.  One
notable change in that respect is that we no longer prefer DSA over
RSA - the reasons for doing so went away years ago.  This may cause
some surprises, as ssh will warn about unknown host keys even for
hosts whose keys haven't changed.

MFC after:	6 weeks

1 files changed, 728 insertions, 0 deletions

diff --git a/crypto/openssh/mux.c b/crypto/openssh/mux.c
new file mode 100644
index 0000000..79f8376
--- /dev/null
+++ b/crypto/openssh/mux.c
@@ -0,0 +1,728 @@
+/* $OpenBSD: mux.c,v 1.7 2008/06/13 17:21:20 dtucker Exp $ */
+/*
+ * Copyright (c) 2002-2008 Damien Miller <djm@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/* ssh session multiplexing support */
+
+#include "includes.h"
+
+/*
+ * TODO:
+ *   1. partial reads in muxserver_accept_control (maybe make channels
+ *      from accepted connections)
+ *   2. 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.
+ */
+
+#include <sys/types.h>
+#include <sys/param.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_UTIL_H
+# include <util.h>
+#endif
+
+#ifdef HAVE_LIBUTIL_H
+# include <libutil.h>
+#endif
+
+#include "openbsd-compat/sys-queue.h"
+#include "xmalloc.h"
+#include "log.h"
+#include "ssh.h"
+#include "pathnames.h"
+#include "misc.h"
+#include "match.h"
+#include "buffer.h"
+#include "channels.h"
+#include "msg.h"
+#include "packet.h"
+#include "monitor_fdpass.h"
+#include "sshpty.h"
+#include "key.h"
+#include "readconf.h"
+#include "clientloop.h"
+
+/* from ssh.c */
+extern int tty_flag;
+extern Options options;
+extern int stdin_null_flag;
+extern char *host;
+int subsystem_flag;
+extern Buffer command;
+
+/* 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;
+	Buffer cmd;
+	char *term;
+	struct termios tio;
+	char **env;
+};
+
+/* fd to control socket */
+int muxserver_sock = -1;
+
+/* 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;
+
+
+/* ** Multiplexing master support */
+
+/* Prepare a mux master to listen on a Unix domain socket. */
+void
+muxserver_listen(void)
+{
+	struct sockaddr_un addr;
+	mode_t old_umask;
+	int addr_len;
+
+	if (options.control_path == NULL ||
+	    options.control_master == SSHCTL_MASTER_NO)
+		return;
+
+	debug("setting up multiplex master socket");
+
+	memset(&addr, '\0', sizeof(addr));
+	addr.sun_family = AF_UNIX;
+	addr_len = offsetof(struct sockaddr_un, sun_path) +
+	    strlen(options.control_path) + 1;
+
+	if (strlcpy(addr.sun_path, options.control_path,
+	    sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
+		fatal("ControlPath too long");
+
+	if ((muxserver_sock = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
+		fatal("%s socket(): %s", __func__, strerror(errno));
+
+	old_umask = umask(0177);
+	if (bind(muxserver_sock, (struct sockaddr *)&addr, addr_len) == -1) {
+		muxserver_sock = -1;
+		if (errno == EINVAL || errno == EADDRINUSE) {
+			error("ControlSocket %s already exists, "
+			    "disabling multiplexing", options.control_path);
+			close(muxserver_sock);
+			muxserver_sock = -1;
+			xfree(options.control_path);
+			options.control_path = NULL;
+			options.control_master = SSHCTL_MASTER_NO;
+			return;
+		} else
+			fatal("%s bind(): %s", __func__, strerror(errno));
+	}
+	umask(old_umask);
+
+	if (listen(muxserver_sock, 64) == -1)
+		fatal("%s listen(): %s", __func__, strerror(errno));
+
+	set_nonblock(muxserver_sock);
+}
+
+/* Callback on open confirmation in mux master for a mux client session. */
+static void
+mux_session_confirm(int id, void *arg)
+{
+	struct mux_session_confirm_ctx *cctx = arg;
+	const char *display;
+	Channel *c;
+	int i;
+
+	if (cctx == NULL)
+		fatal("%s: cctx == NULL", __func__);
+	if ((c = channel_lookup(id)) == NULL)
+		fatal("%s: no channel for id %d", __func__, id);
+
+	display = getenv("DISPLAY");
+	if (cctx->want_x_fwd && options.forward_x11 && display != NULL) {
+		char *proto, *data;
+		/* Get reasonable local authentication information. */
+		client_x11_get_proto(display, options.xauth_location,
+		    options.forward_x11_trusted, &proto, &data);
+		/* Request forwarding with authentication spoofing. */
+		debug("Requesting X11 forwarding with authentication spoofing.");
+		x11_request_forwarding_with_spoofing(id, display, proto, data);
+		/* XXX wait for reply */
+	}
+
+	if (cctx->want_agent_fwd && options.forward_agent) {
+		debug("Requesting authentication agent forwarding.");
+		channel_request_start(id, "auth-agent-req@openssh.com", 0);
+		packet_send();
+	}
+
+	client_session2_setup(id, cctx->want_tty, cctx->want_subsys,
+	    cctx->term, &cctx->tio, c->rfd, &cctx->cmd, cctx->env);
+
+	c->open_confirm_ctx = NULL;
+	buffer_free(&cctx->cmd);
+	xfree(cctx->term);
+	if (cctx->env != NULL) {
+		for (i = 0; cctx->env[i] != NULL; i++)
+			xfree(cctx->env[i]);
+		xfree(cctx->env);
+	}
+	xfree(cctx);
+}
+
+/*
+ * Accept a connection on the mux master socket and process the
+ * client's request. Returns flag indicating whether mux master should
+ * begin graceful close.
+ */
+int
+muxserver_accept_control(void)
+{
+	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;
+
+	/*
+	 * 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 (getpeereid(client_fd, &euid, &egid) < 0) {
+		error("%s getpeereid failed: %s", __func__, strerror(errno));
+		close(client_fd);
+		return 0;
+	}
+	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;
+	}
+
+	/* XXX handle asynchronously */
+	unset_nonblock(client_fd);
+
+	/* Read command */
+	buffer_init(&m);
+	if (ssh_msg_recv(client_fd, &m) == -1) {
+		error("%s: client msg_recv failed", __func__);
+		close(client_fd);
+		buffer_free(&m);
+		return 0;
+	}
+	if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
+		error("%s: wrong client version %d", __func__, ver);
+		buffer_free(&m);
+		close(client_fd);
+		return 0;
+	}
+
+	allowed = 1;
+	mux_command = buffer_get_int(&m);
+	flags = buffer_get_int(&m);
+
+	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);
+			buffer_free(&m);
+			return start_close;
+		}
+		buffer_free(&m);
+		close(client_fd);
+		return start_close;
+	default:
+		error("Unsupported command %d", mux_command);
+		buffer_free(&m);
+		close(client_fd);
+		return 0;
+	}
+
+	/* 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);
+		buffer_free(&m);
+		return 0;
+	}
+
+	if (!allowed) {
+		error("Refused control connection");
+		close(client_fd);
+		buffer_free(&m);
+		return 0;
+	}
+
+	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;
+	}
+	if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
+		error("%s: wrong client version %d", __func__, ver);
+		buffer_free(&m);
+		close(client_fd);
+		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));
+
+	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;
+	}
+
+	debug2("%s: accepted tty %d, subsys %d, cmd %s", __func__,
+	    cctx->want_tty, cctx->want_subsys, cmd);
+	xfree(cmd);
+
+	/* 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;
+		}
+	}
+
+	debug2("%s: got fds stdin %d, stdout %d, stderr %d", __func__,
+	    new_fd[0], new_fd[1], new_fd[2]);
+
+	/* 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));
+
+	/* This roundtrip is just for synchronisation of ttymodes */
+	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]);
+		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;
+	}
+	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]);
+
+	set_nonblock(client_fd);
+
+	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);
+
+	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));
+	}
+
+	debug3("%s: channel_new: %d", __func__, c->self);
+
+	channel_send_open(c->self);
+	channel_register_open_confirm(c->self, mux_session_confirm, cctx);
+	return 0;
+}
+
+/* ** 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;
+}
+
+/* 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))
+		fatal("env_permitted: name '%.100s...' too long", env);
+
+	for (i = 0; i < options.num_send_env; i++)
+		if (match_pattern(name, options.send_env[i]))
+			return (1);
+
+	return (0);
+}
+
+/* Multiplex client main loop. */
+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;
+
+	if (muxclient_command == 0)
+		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;
+	}
+
+	memset(&addr, '\0', sizeof(addr));
+	addr.sun_family = AF_UNIX;
+	addr_len = offsetof(struct sockaddr_un, sun_path) +
+	    strlen(path) + 1;
+
+	if (strlcpy(addr.sun_path, path,
+	    sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
+		fatal("ControlPath too long");
+
+	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) {
+			fatal("Control socket connect(%.100s): %s", path,
+			    strerror(errno));
+		}
+		if (errno == ENOENT)
+			debug("Control socket \"%.100s\" does not exist", path);
+		else {
+			error("Control socket connect(%.100s): %s", path,
+			    strerror(errno));
+		}
+		close(sock);
+		return;
+	}
+
+	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:
+		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);
+		exit(0);
+	case SSHMUX_COMMAND_TERMINATE:
+		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]);
+				}
+			}
+		}
+		break;
+	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();
+
+	/*
+	 * 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();
+	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]);
+}