From: Umer Saleem <usaleem@ixsystems.com>
Date: Thu, 20 Jan 2022 14:29:36 +0000 (+0500)
Subject: Fix for a race condition in journal_write
X-Git-Tag: v1.8.0~11^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F1153%2Fhead;p=thirdparty%2Frrdtool-1.x.git

Fix for a race condition in journal_write

There is a race condition in journal_write() where journal_lock is
being acquired after checking whether journal_fh is NULL or not.
journal_fh is a static file handle that can be set to NULL by any
other thread, while current thread is blocked by
pthread_mutex_lock(). This commit fixes this race condition.

Signed-off-by: Umer Saleem <usaleem@ixsystems.com>
---

diff --git a/src/rrd_daemon.c b/src/rrd_daemon.c
index 3ad3a66f..cf125476 100644
--- a/src/rrd_daemon.c
+++ b/src/rrd_daemon.c
@@ -3412,10 +3412,12 @@ static int journal_write(
 {                       /* {{{ */
     int       chars;
 
-    if (journal_fh == NULL)
+    pthread_mutex_lock(&journal_lock);
+    if (journal_fh == NULL) {
+        pthread_mutex_unlock(&journal_lock);
         return 0;
+    }
 
-    pthread_mutex_lock(&journal_lock);
     chars = fprintf(journal_fh, "%s %s\n", cmd, args);
     journal_size += chars;