# HG changeset patch
# Parent  724c9ea86fe2c4a1f0e0d3aba168357ab1b2c3aa
block SIGALRM while logging through syslog to prevent deadlocks
(through grace_alarm_handler())

bnc#57354

diff --git a/openssh-7.6p1/log.c b/openssh-7.6p1/log.c
--- a/openssh-7.6p1/log.c
+++ b/openssh-7.6p1/log.c
@@ -46,16 +46,17 @@
 #include <syslog.h>
 #include <unistd.h>
 #include <errno.h>
 #if defined(HAVE_STRNVIS) && defined(HAVE_VIS_H) && !defined(BROKEN_STRNVIS)
 # include <vis.h>
 #endif
 
 #include "log.h"
+#include <signal.h>
 
 static LogLevel log_level = SYSLOG_LEVEL_INFO;
 static int log_on_stderr = 1;
 static int log_stderr_fd = STDERR_FILENO;
 static int log_facility = LOG_AUTH;
 static char *argv0;
 static log_handler_fn *log_handler;
 static void *log_handler_ctx;
@@ -396,16 +397,17 @@ do_log(LogLevel level, const char *fmt, 
 {
 #if defined(HAVE_OPENLOG_R) && defined(SYSLOG_DATA_INIT)
 	struct syslog_data sdata = SYSLOG_DATA_INIT;
 #endif
 	char msgbuf[MSGBUFSIZ];
 	char fmtbuf[MSGBUFSIZ];
 	char *txt = NULL;
 	int pri = LOG_INFO;
+	sigset_t nset, oset;
 	int saved_errno = errno;
 	log_handler_fn *tmp_handler;
 
 	if (level > log_level)
 		return;
 
 	switch (level) {
 	case SYSLOG_LEVEL_FATAL:
@@ -455,20 +457,28 @@ do_log(LogLevel level, const char *fmt, 
 		log_handler = NULL;
 		tmp_handler(level, fmtbuf, log_handler_ctx);
 		log_handler = tmp_handler;
 	} else if (log_on_stderr) {
 		snprintf(msgbuf, sizeof msgbuf, "%.*s\r\n",
 		    (int)sizeof msgbuf - 3, fmtbuf);
 		(void)write(log_stderr_fd, msgbuf, strlen(msgbuf));
 	} else {
+		/* Prevent a race between the grace_alarm which writes a
+		 * log message and terminates and main sshd code that leads
+		 * to deadlock as syslog is not async safe.
+		 */ 
+		sigemptyset(&nset);
+		sigaddset(&nset, SIGALRM);
+		sigprocmask(SIG_BLOCK, &nset, &oset);
 #if defined(HAVE_OPENLOG_R) && defined(SYSLOG_DATA_INIT)
 		openlog_r(argv0 ? argv0 : __progname, LOG_PID, log_facility, &sdata);
 		syslog_r(pri, &sdata, "%.500s", fmtbuf);
 		closelog_r(&sdata);
 #else
 		openlog(argv0 ? argv0 : __progname, LOG_PID, log_facility);
 		syslog(pri, "%.500s", fmtbuf);
 		closelog();
 #endif
+		sigprocmask(SIG_SETMASK, &oset, NULL);
 	}
 	errno = saved_errno;
 }