* New upstream release (closes: #474301). Important changes not previously

  backported to 4.7p1:
  - 4.9/4.9p1 (http://www.openssh.com/txt/release-4.9):
    + Added chroot(2) support for sshd(8), controlled by a new option
      "ChrootDirectory" (closes: #139047, LP: #24777).
    + Linked sftp-server(8) into sshd(8). The internal sftp server is used
      when the command "internal-sftp" is specified in a Subsystem or
      ForceCommand declaration. When used with ChrootDirectory, the
      internal sftp server requires no special configuration of files
      inside the chroot environment.
    + Added a protocol extension method "posix-rename@openssh.com" for
      sftp-server(8) to perform POSIX atomic rename() operations; sftp(1)
      prefers this if available (closes: #308561).
    + Removed the fixed limit of 100 file handles in sftp-server(8).
    + ssh(8) will now skip generation of SSH protocol 1 ephemeral server
      keys when in inetd mode and protocol 2 connections are negotiated.
      This speeds up protocol 2 connections to inetd-mode servers that
      also allow Protocol 1.
    + Accept the PermitRootLogin directive in a sshd_config(5) Match
      block. Allows for, e.g. permitting root only from the local network.
    + Reworked sftp(1) argument splitting and escaping to be more
      internally consistent (i.e. between sftp commands) and more
      consistent with sh(1). Please note that this will change the
      interpretation of some quoted strings, especially those with
      embedded backslash escape sequences.
    + Support "Banner=none" in sshd_config(5) to disable sending of a
      pre-login banner (e.g. in a Match block).
    + ssh(1) ProxyCommands are now executed with $SHELL rather than
      /bin/sh.
    + ssh(1)'s ConnectTimeout option is now applied to both the TCP
      connection and the SSH banner exchange (previously it just covered
      the TCP connection). This allows callers of ssh(1) to better detect
      and deal with stuck servers that accept a TCP connection but don't
      progress the protocol, and also makes ConnectTimeout useful for
      connections via a ProxyCommand.
    + scp(1) incorrectly reported "stalled" on slow copies (closes:
      #140828).
    + scp(1) date underflow for timestamps before epoch.
    + ssh(1) used the obsolete SIG DNS RRtype for host keys in DNS,
      instead of the current standard RRSIG.
    + Correctly drain ACKs when a sftp(1) upload write fails midway,
      avoids a fatal() exit from what should be a recoverable condition.
    + Fixed ssh-keygen(1) selective host key hashing (i.e. "ssh-keygen -HF
      hostname") to not include any IP address in the data to be hashed.
    + Make ssh(1) skip listening on the IPv6 wildcard address when a
      binding address of 0.0.0.0 is used against an old SSH server that
      does not support the RFC4254 syntax for wildcard bind addresses.
    + Enable IPV6_V6ONLY socket option on sshd(8) listen socket, as is
      already done for X11/TCP forwarding sockets (closes: #439661).
    + Fix FD leak that could hang a ssh(1) connection multiplexing master.
    + Make ssh(1) -q option documentation consistent with reality.
    + Fixed sshd(8) PAM support not calling pam_session_close(), or
      failing to call it with root privileges (closes: #372680).
    + Fix activation of OpenSSL engine support when requested in configure
      (LP: #119295).
  - 5.1/5.1p1 (http://www.openssh.com/txt/release-5.1):
    + Introduce experimental SSH Fingerprint ASCII Visualisation to ssh(1)
      and ssh-keygen(1). Visual fingerprint display is controlled by a new
      ssh_config(5) option "VisualHostKey". The intent is to render SSH
      host keys in a visual form that is amenable to easy recall and
      rejection of changed host keys.
    + sshd_config(5) now supports CIDR address/masklen matching in "Match
      address" blocks, with a fallback to classic wildcard matching.
    + sshd(8) now supports CIDR matching in ~/.ssh/authorized_keys
      from="..." restrictions, also with a fallback to classic wildcard
      matching.
    + Added an extended test mode (-T) to sshd(8) to request that it write
      its effective configuration to stdout and exit. Extended test mode
      also supports the specification of connection parameters (username,
      source address and hostname) to test the application of
      sshd_config(5) Match rules.
    + ssh(1) now prints the number of bytes transferred and the overall
      connection throughput for SSH protocol 2 sessions when in verbose
      mode (previously these statistics were displayed for protocol 1
      connections only).
    + sftp-server(8) now supports extension methods statvfs@openssh.com
      and fstatvfs@openssh.com that implement statvfs(2)-like operations.
    + sftp(1) now has a "df" command to the sftp client that uses the
      statvfs@openssh.com to produce a df(1)-like display of filesystem
      space and inode utilisation (requires statvfs@openssh.com support on
      the server).
    + Added a MaxSessions option to sshd_config(5) to allow control of the
      number of multiplexed sessions supported over a single TCP
      connection. This allows increasing the number of allowed sessions
      above the previous default of 10, disabling connection multiplexing
      (MaxSessions=1) or disallowing login/shell/subsystem sessions
      entirely (MaxSessions=0).
    + Added a no-more-sessions@openssh.com global request extension that
      is sent from ssh(1) to sshd(8) when the client knows that it will
      never request another session (i.e. when session multiplexing is
      disabled). This allows a server to disallow further session requests
      and terminate the session in cases where the client has been
      hijacked.
    + ssh-keygen(1) now supports the use of the -l option in combination
      with -F to search for a host in ~/.ssh/known_hosts and display its
      fingerprint.
    + ssh-keyscan(1) now defaults to "rsa" (protocol 2) keys, instead of
      "rsa1".
    + Added an AllowAgentForwarding option to sshd_config(8) to control
      whether authentication agent forwarding is permitted. Note that this
      is a loose control, as a client may install their own unofficial
      forwarder.
    + ssh(1) and sshd(8): avoid unnecessary malloc/copy/free when
      receiving network data, resulting in a ~10% speedup.
    + ssh(1) and sshd(8) will now try additional addresses when connecting
      to a port forward destination whose DNS name resolves to more than
      one address. The previous behaviour was to try the only first
      address and give up if that failed.
    + ssh(1) and sshd(8) now support signalling that channels are
      half-closed for writing, through a channel protocol extension
      notification "eow@openssh.com". This allows propagation of closed
      file descriptors, so that commands such as "ssh -2 localhost od
      /bin/ls | true" do not send unnecessary data over the wire.
    + sshd(8): increased the default size of ssh protocol 1 ephemeral keys
      from 768 to 1024 bits.
    + When ssh(1) has been requested to fork after authentication ("ssh
      -f") with ExitOnForwardFailure enabled, delay the fork until after
      replies for any -R forwards have been seen. Allows for robust
      detection of -R forward failure when using -f.
    + "Match group" blocks in sshd_config(5) now support negation of
      groups. E.g. "Match group staff,!guests".
    + sftp(1) and sftp-server(8) now allow chmod-like operations to set
      set[ug]id/sticky bits.
    + The MaxAuthTries option is now permitted in sshd_config(5) match
      blocks.
    + Multiplexed ssh(1) sessions now support a subset of the ~ escapes
      that are available to a primary connection.
    + ssh(1) connection multiplexing will now fall back to creating a new
      connection in most error cases (closes: #352830).
    + Make ssh(1) deal more gracefully with channel requests that fail.
      Previously it would optimistically assume that requests would always
      succeed, which could cause hangs if they did not (e.g. when the
      server runs out of file descriptors).
    + ssh(1) now reports multiplexing errors via the multiplex slave's
      stderr where possible (subject to LogLevel in the mux master).
    + Prevent sshd(8) from erroneously applying public key restrictions
      leaned from ~/.ssh/authorized_keys to other authentication methods
      when public key authentication subsequently fails (LP: #161047).
    + Fixed an UMAC alignment problem that manifested on Itanium
      platforms.

1 files changed, 728 insertions, 0 deletions

diff --git a/mux.c b/mux.c
new file mode 100644
index 000000000..4669e5328
--- /dev/null
+++ b/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]);
+}