#

# Implements watchdog process, which backs up login_grace_time alarm.

#

# If the main process is hung in a syscall, SIGALRM is queued but not

# delivered and the connection stays unauthenticated for too long.

#

# Function start_grace_watchdog forks of a watchdog process, that sends the

# main process a SIGTERM, if it does neither authenticate nor exit before

# (login_grace_time + GRACE_WATCHDOG_THRESHOLD).

# If the main process does not react to SIGTERM, SIGKILL is sent after

# additional GRACE_WATCHDOG_THRESHOLD seconds.

#

# Patch source: in-house

# Reported to [email protected] as security issue.

#

# Per agreement with upstream developers, filed:

#    https://bugzilla.mindrot.org/show_bug.cgi?id=2615

#

diff -pur old/sshd.c new/sshd.c

--- old/sshd.c

+++ new/sshd.c

 /* Unprivileged user */

 struct passwd *privsep_pw = NULL;

+/* Pid of process backing up login_grace_time alarm. */

+pid_t grace_watchdog_pid = -1;

+

+/* Time in seconds */

+#define	GRACE_WATCHDOG_THRESHOLD 10

+

 /* Prototypes for various functions defined later in this file. */

 void destroy_sensitive_data(void);

 void demote_sensitive_data(void);

 		signal(SIGTERM, SIG_IGN);

 		kill(0, SIGTERM);

 	}

+	stop_grace_watchdog();

 	/* Log error and exit. */

 	sigdie("Timeout before authentication for %s port %d",

 	    ssh_remote_ipaddr(active_state), ssh_remote_port(active_state));

 }

+static inline void

+sleep_reliably(unsigned int seconds)

+{

+	while (seconds > 0)

+		seconds = sleep(seconds);

+}

+

+/*

+ * Implements watchdog process, which backs up login_grace_time alarm.

+ *

+ * If the main process is hung in a syscall, SIGALRM is queued but not

+ * delivered and the connection stays unauthenticated for too long.

+ *

+ * This function forks off a watchdog process, which sends the main process

+ * a SIGTERM, if it does neither authenticate nor exit before

+ * (login_grace_time + GRACE_WATCHDOG_THRESHOLD).

+ * If the main process does not react to SIGTERM, SIGKILL is sent after

+ * additional GRACE_WATCHDOG_THRESHOLD seconds.

+ */

+static void

+start_grace_watchdog(int login_grace_time)

+{

+	pid_t ppid = getpid();

+

+	if (login_grace_time == 0)

+		return;

+

+	if (grace_watchdog_pid != -1) {

+		error("login_grace_time watchdog process already running");

+		return;

+	}

+

+	grace_watchdog_pid = fork();

+	if (grace_watchdog_pid == -1)

+		fatal("fork of login_grace_time watchdog process failed");

+	else if (grace_watchdog_pid > 0)

+		return;

+

+	/* child */

+

+	/* close open fds, including client socket and startup_pipe */

+	closefrom(3);

+

+	/* kill the monitor with SIGTERM after timeout + threshold */

+	sleep_reliably(login_grace_time + GRACE_WATCHDOG_THRESHOLD);

+	if (getppid() != ppid) {

+		debug("login_grace_time watchdog still active, "

+		    "but watched process %d already exited.", (int)ppid);

+		exit(0);

+	}

+	error("Timeout before authentication for %s. Killing process %d "

+	    "with SIGTERM.", ssh_remote_ipaddr(active_state), (int)ppid);

+	kill(ppid, SIGTERM);

+

+	/* if neccessary, kill it with SIGKILL */

+	sleep_reliably(GRACE_WATCHDOG_THRESHOLD);

+	if (getppid() != ppid)

+		exit(0);

+	error("Watched process %d did not respond to SIGTERM. "

+	    "Killing it with SIGKILL.", (int)ppid);

+	kill(ppid, SIGKILL);

+

+	/* give up */

+	sleep_reliably(GRACE_WATCHDOG_THRESHOLD);

+	if (getppid() == ppid) {

+		error("login_grace_time watchdog failed to kill %d", (int)ppid);

+		exit(255);

+	}

+	exit(0);

+}

+

+/* kill grace watchdog process */

+static void

+stop_grace_watchdog()

+{

+	if (grace_watchdog_pid == -1) {

+		debug3("login_grace_time watchdog process not running");

+		return;

+	}

+

+	kill(grace_watchdog_pid, SIGTERM);

+	while (waitpid(grace_watchdog_pid, NULL, 0) < 0) {

+		if (errno == EINTR)

+			continue;

+	}

+	grace_watchdog_pid = -1;

+}

+

 		/* child */

 		close(pmonitor->m_sendfd);

 		close(pmonitor->m_log_recvfd);

+		grace_watchdog_pid = -1;

 		/* Arrange for logging to be sent to the monitor */

 		set_log_handler(mm_log_handler, pmonitor);

 	 * are about to discover the bug.

 	 */

 	signal(SIGALRM, grace_alarm_handler);

-	if (!debug_flag)

+	if (!debug_flag) {

 		alarm(options.login_grace_time);

+		start_grace_watchdog(options.login_grace_time);

+	}

 	sshd_exchange_identification(ssh, sock_in, sock_out);

 	 */

 	alarm(0);

 	signal(SIGALRM, SIG_DFL);

+	stop_grace_watchdog();

 	authctxt->authenticated = 1;

 	if (startup_pipe != -1) {

 		close(startup_pipe);