From: James Rouzier <jrouzier@inverse.ca>
Date: Tue, 28 Oct 2014 21:13:43 +0000 (-0400)
Subject: Lock thread_pool.wait_mutex before forking to avoid a race condition between rad_fork... 
X-Git-Tag: release_2_2_6~15^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F824%2Fhead;p=thirdparty%2Ffreeradius-server.git

Lock thread_pool.wait_mutex before forking to avoid a race condition between rad_fork, rad_waitpid and reap_children.

There is a race condition that can occur under high load where a child is reaped before being added to the waiters list.
---

diff --git a/src/main/threads.c b/src/main/threads.c
index 72d849fc03..d4de4ff436 100644
--- a/src/main/threads.c
+++ b/src/main/threads.c
@@ -1142,6 +1142,7 @@ pid_t rad_fork(void)
 	/*
 	 *	Fork & save the PID for later reaping.
 	 */
+	pthread_mutex_lock(&thread_pool.wait_mutex);
 	child_pid = fork();
 	if (child_pid > 0) {
 		int rcode;
@@ -1152,9 +1153,7 @@ pid_t rad_fork(void)
 
 		tf->pid = child_pid;
 
-		pthread_mutex_lock(&thread_pool.wait_mutex);
 		rcode = fr_hash_table_insert(thread_pool.waiters, tf);
-		pthread_mutex_unlock(&thread_pool.wait_mutex);
 
 		if (!rcode) {
 			radlog(L_ERR, "Failed to store PID, creating what will be a zombie process %d",
@@ -1162,6 +1161,12 @@ pid_t rad_fork(void)
 			free(tf);
 		}
 	}
+	/*
+	 *	Do not unlock in child process
+	 */
+	if(child_pid != 0 ) {
+		pthread_mutex_unlock(&thread_pool.wait_mutex);
+	}
 
 	/*
 	 *	Return whatever we were told.