1 files changed, 46 insertions, 4 deletions

diff --git a/mux.c b/mux.c
index 5c3857ee8..c010b614e 100644
--- a/mux.c
+++ b/mux.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: mux.c,v 1.21 2010/06/25 23:15:36 djm Exp $ */
+/* $OpenBSD: mux.c,v 1.22 2010/09/20 07:19:27 djm Exp $ */
 /*
  * Copyright (c) 2002-2008 Damien Miller <djm@openbsd.org>
  *
@@ -1026,6 +1026,9 @@ muxserver_listen(void)
         struct sockaddr_un addr;
         socklen_t sun_len;
         mode_t old_umask;
+        char *orig_control_path = options.control_path;
+        char rbuf[16+1];
+        u_int i, r;
 
         if (options.control_path == NULL ||
             options.control_master == SSHCTL_MASTER_NO)
@@ -1033,6 +1036,23 @@ muxserver_listen(void)
 
         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("%s: temporary control path %s", __func__, options.control_path);
+
         memset(&addr, '\0', sizeof(addr));
         addr.sun_family = AF_UNIX;
         sun_len = offsetof(struct sockaddr_un, sun_path) +
@@ -1051,6 +1071,7 @@ muxserver_listen(void)
                 if (errno == EINVAL || errno == EADDRINUSE) {
                         error("ControlSocket %s already exists, "
                             "disabling multiplexing", options.control_path);
+ disable_mux_master:
                         close(muxserver_sock);
                         muxserver_sock = -1;
                         xfree(options.control_path);
@@ -1065,12 +1086,29 @@ muxserver_listen(void)
         if (listen(muxserver_sock, 64) == -1)
                 fatal("%s listen(): %s", __func__, strerror(errno));
 
+        /* Now atomically "move" the mux socket into position */
+        if (link(options.control_path, orig_control_path) != 0) {
+                if (errno != EEXIST) {
+                        fatal("%s: link mux listener %s => %s: %s", __func__, 
+                            options.control_path, orig_control_path,
+                            strerror(errno));
+                }
+                error("ControlSocket %s already exists, disabling multiplexing",
+                    orig_control_path);
+                xfree(orig_control_path);
+                unlink(options.control_path);
+                goto disable_mux_master;
+        }
+        unlink(options.control_path);
+        xfree(options.control_path);
+        options.control_path = orig_control_path;
+
         set_nonblock(muxserver_sock);
 
         mux_listener_channel = channel_new("mux listener",
             SSH_CHANNEL_MUX_LISTENER, muxserver_sock, muxserver_sock, -1,
             CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
-            0, addr.sun_path, 1);
+            0, options.control_path, 1);
         mux_listener_channel->mux_rcb = mux_master_read_cb;
         debug3("%s: mux listener channel %d fd %d", __func__,
             mux_listener_channel->self, mux_listener_channel->sock);
@@ -1823,9 +1861,13 @@ muxclient(const char *path)
                         fatal("Control socket connect(%.100s): %s", path,
                             strerror(errno));
                 }
-                if (errno == ENOENT)
+                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 {
+                } else {
                         error("Control socket connect(%.100s): %s", path,
                             strerror(errno));
                 }