log: use thread-safe localtime_r()

This fixes a race in liblxc logging which can lead to deadlocks. The reproducer for this issue before this is to simply compile with --enable-tests and then run: lxc-test-concurrent -j 20 -m create,start,stop,destroy -D which should deadlock. Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

log: use thread-safe localtime_r()
5b3214ca · Christian Brauner · Stéphane Graber · dfc0b35f · 5b3214ca
Commit 5b3214ca authored Nov 25, 2016 by Christian Brauner Committed by Stéphane Graber Nov 30, 2016
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Showing with 7 additions and 5 deletions

log.c src/lxc/log.c +7 -5

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--- a/src/lxc/log.c
+++ b/src/lxc/log.c
@@ -20,6 +20,8 @@
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
+
+#define _GNU_SOURCE
 #include <assert.h>
 #include <stdio.h>
 #include <errno.h>
@@ -31,8 +33,6 @@
 #include <pthread.h>
 #include <time.h>

-#define __USE_GNU /* for *_CLOEXEC */
-
 #include <fcntl.h>
 #include <stdlib.h>

@@ -72,7 +72,7 @@ static int log_append_logfile(const struct lxc_log_appender *appender,
 {
 	char date[LXC_LOG_DATEFOMAT_SIZE] = "20150427012246";
 	char buffer[LXC_LOG_BUFFER_SIZE];
-	const struct tm *t;
+	struct tm newtime;
 	int n;
 	int ms;
 	int fd_to_use = -1;
@@ -88,8 +88,10 @@ static int log_append_logfile(const struct lxc_log_appender *appender,
 	if (fd_to_use == -1)
 		return 0;

-	t = localtime(&event->timestamp.tv_sec);
-	strftime(date, sizeof(date), "%Y%m%d%H%M%S", t);
+	if (!localtime_r(&event->timestamp.tv_sec, &newtime))
+		return 0;
+
+	strftime(date, sizeof(date), "%Y%m%d%H%M%S", &newtime);
 	ms = event->timestamp.tv_usec / 1000;
 	n = snprintf(buffer, sizeof(buffer),
 		     "%15s %10s.%03d %-8s %s - %s:%s:%d - ",