Download raw body.
ssh multiplexing: handle stale sockets better
Hi,
This makes ssh create it multiplexing socket earlier when in master
mode and more gracefully handle the case where it already exists.
This is https://bugzilla.mindrot.org/show_bug.cgi?id=3971
ok?
Index: usr.bin/ssh/clientloop.h
===================================================================
RCS file: /cvs/src/usr.bin/ssh/clientloop.h,v
diff -u -p -r1.41 clientloop.h
--- usr.bin/ssh/clientloop.h 3 Mar 2026 09:57:25 -0000 1.41
+++ usr.bin/ssh/clientloop.h 15 Sep 2026 07:42:48 -0000
@@ -78,6 +78,7 @@ void client_expect_confirm(struct ssh *,
#define SSHMUX_COMMAND_CONNINFO 9 /* Show connection information */
#define SSHMUX_COMMAND_CHANINFO 10 /* Show channels information */
+int muxserver(const char *);
void muxserver_listen(struct ssh *);
int muxclient(const char *);
void mux_exit_message(struct ssh *, Channel *, int);
Index: usr.bin/ssh/mux.c
===================================================================
RCS file: /cvs/src/usr.bin/ssh/mux.c,v
diff -u -p -r1.113 mux.c
--- usr.bin/ssh/mux.c 2 Apr 2026 07:39:57 -0000 1.113
+++ usr.bin/ssh/mux.c 15 Sep 2026 07:42:49 -0000
@@ -1313,21 +1313,20 @@ mux_tty_alloc_failed(struct ssh *ssh, Ch
sshbuf_free(m);
}
-/* Prepare a mux master to listen on a Unix domain socket. */
-void
-muxserver_listen(struct ssh *ssh)
+/*
+ * Create a listening Unix domain socket for mux master or find out that
+ * one exists already.
+ */
+int
+muxserver(const char *path)
{
mode_t old_umask;
- char *orig_control_path = options.control_path;
+ char *tmp_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");
+ debug("trying to set-up a multiplex master socket");
/*
* Use a temporary path before listen so we can pseudo-atomically
@@ -1342,51 +1341,53 @@ muxserver_listen(struct ssh *ssh)
'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);
+ xasprintf(&tmp_path, "%s.%s", path, rbuf);
+ debug3_f("temporary control path %s", tmp_path);
old_umask = umask(0177);
- muxserver_sock = unix_listener(options.control_path, 64, 0);
+ muxserver_sock = unix_listener(tmp_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;
+ error("Temporary ControlSocket %s already exists", tmp_path);
+ free(tmp_path);
+ return -1;
} else {
/* unix_listener() logs the error */
cleanup_exit(255);
}
}
+ set_nonblock(muxserver_sock);
/* Now atomically "move" the mux socket into position */
- if (link(options.control_path, orig_control_path) != 0) {
+ if (link(tmp_path, path) != 0) {
if (errno != EEXIST) {
fatal_f("link mux listener %s => %s: %s",
- options.control_path, orig_control_path,
+ tmp_path, path,
strerror(errno));
}
- error("ControlSocket %s already exists, disabling multiplexing",
- orig_control_path);
- unlink(options.control_path);
- goto disable_mux_master;
+ debug("ControlSocket %s already exists", path);
+ close(muxserver_sock);
+ muxserver_sock = -1;
}
- unlink(options.control_path);
- free(options.control_path);
- options.control_path = orig_control_path;
+ unlink(tmp_path);
+ free(tmp_path);
+ return muxserver_sock;
+}
- set_nonblock(muxserver_sock);
+/* Prepare a mux master to listen on the previously created Unix domain socket. */
+void
+muxserver_listen(struct ssh *ssh)
+{
+ if (options.control_path == NULL ||
+ options.control_master == SSHCTL_MASTER_NO)
+ return;
+
+ debug("setting up multiplex master socket");
+ if (muxserver_sock < 0) {
+ muxserver_sock = muxserver(options.control_path);
+ }
mux_listener_channel = channel_new(ssh, "mux listener",
SSH_CHANNEL_MUX_LISTENER, muxserver_sock, muxserver_sock, -1,
Index: usr.bin/ssh/ssh-keygen.1
===================================================================
RCS file: /cvs/src/usr.bin/ssh/ssh-keygen.1,v
diff -u -p -r1.241 ssh-keygen.1
--- usr.bin/ssh/ssh-keygen.1 15 Sep 2026 07:40:58 -0000 1.241
+++ usr.bin/ssh/ssh-keygen.1 15 Sep 2026 07:42:49 -0000
@@ -1,4 +1,4 @@
-.\" $OpenBSD: ssh-keygen.1,v 1.241 2026/09/15 07:40:58 djm Exp $
+.\" $OpenBSD: ssh-keygen.1,v 1.240 2026/08/07 05:49:53 djm Exp $
.\"
.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -35,7 +35,7 @@
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
-.Dd $Mdocdate: September 15 2026 $
+.Dd $Mdocdate: August 7 2026 $
.Dt SSH-KEYGEN 1
.Os
.Sh NAME
@@ -289,7 +289,7 @@ When saving a private key, this option s
rounds used.
Higher numbers result in slower passphrase verification and increased
resistance to brute-force password cracking (should the keys be stolen).
-The default is 24 rounds.
+The default is 16 rounds.
.It Fl B
Show the bubblebabble digest of specified private or public key file.
.It Fl b Ar bits
Index: usr.bin/ssh/ssh.c
===================================================================
RCS file: /cvs/src/usr.bin/ssh/ssh.c,v
diff -u -p -r1.637 ssh.c
--- usr.bin/ssh/ssh.c 7 Aug 2026 05:03:56 -0000 1.637
+++ usr.bin/ssh/ssh.c 15 Sep 2026 07:42:49 -0000
@@ -1612,7 +1612,11 @@ main(int ac, char **av)
fatal("No ControlPath specified for \"-O\" command");
if (options.control_path != NULL) {
int sock;
- if ((sock = muxclient(options.control_path)) >= 0) {
+
+ if (muxclient_command == 0 &&
+ (sock = muxserver(options.control_path)) >= 0) {
+ debug("We will be multiplex master, not client.");
+ } else if ((sock = muxclient(options.control_path)) >= 0) {
if (ssh_packet_set_connection(ssh, sock, sock) == NULL)
fatal("ssh_packet_set_connection failed");
ssh_packet_set_mux(ssh);
Index: regress/usr.bin/ssh/multiplex.sh
===================================================================
RCS file: /cvs/src/regress/usr.bin/ssh/multiplex.sh,v
diff -u -p -r1.41 multiplex.sh
--- regress/usr.bin/ssh/multiplex.sh 7 Dec 2025 02:59:53 -0000 1.41
+++ regress/usr.bin/ssh/multiplex.sh 15 Sep 2026 07:42:49 -0000
@@ -42,6 +42,24 @@ if [ $? -ne 0 ]; then
fail "environment not found"
fi
+start_auto_mux_master()
+{
+ trace "start master (with ControlMaster=auto), fork to background"
+ ${SSH} -Nn2 -o ControlMaster=auto -S$CTL -F $OBJ/ssh_config -oSendEnv="_XXX_TEST" somehost \
+ -E $TEST_REGRESS_LOGFILE 2>&1 &
+ # NB. $SSH_PID will be killed by test-exec.sh:cleanup on fatal errors.
+ SSH_PID=$!
+ sleep 2
+ wait_for_mux_master_ready
+}
+
+verbose "test $tid: stale control socket"
+trace "correctly handle stale control socket"
+kill -9 ${SSH_PID} 2>/dev/null
+wait ${SSH_PID}
+test -e "$CTL" || fail "control socket did not remain (after killing ssh command)"
+start_auto_mux_master
+
verbose "test $tid: envpass"
trace "env passing over multiplexed connection"
${SSH} -F $OBJ/ssh_config -oSetEnv="_XXX_TEST=foo" -S$CTL otherhost sh << 'EOF'
@@ -189,6 +207,7 @@ ${SSH} -F $OBJ/ssh_config -S $CTL -Oexit
# Wait for master to exit
wait $SSH_PID
kill -0 $SSH_PID >/dev/null 2>&1 && fail "exit command failed"
+test ! -e "$CTL" || fail "control socket still exists after exit command"
# Enable compression and alternative kex for next conninfo test.
if $SSH -Q compression | grep zlib@openssh.com >/dev/null; then
ssh multiplexing: handle stale sockets better