From 4e57613ae19a71a0f180f0648223a139f48c932c Mon Sep 17 00:00:00 2001
From: Florian Forster <octo@noris.net>
Date: Fri, 6 Mar 2009 16:53:28 +0100
Subject: [PATCH] rrdtool plugin: Fix a possible race condition at startup.

On a very busy system, if the network plugin was initialized before the
rrdtool plugin, `rrd_cache_insert' may be called before the RRDtool
plugin is initialized. It would then pass `cache == NULL' to
`c_avl_get', resulting in a segmentation fault.
---
 src/rrdtool.c       | 34 +++++++++++++++++++++++++++-------
 src/utils_avltree.c |  2 ++
 2 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/src/rrdtool.c b/src/rrdtool.c
index e1c7902b..27e64c11 100644
--- a/src/rrdtool.c
+++ b/src/rrdtool.c
@@ -621,6 +621,7 @@ static void *rrd_queue_thread (void *data)
 		rrd_cache_t *cache_entry;
 		char **values;
 		int    values_num;
+		int    status;
 		int    i;
 
                 pthread_mutex_lock (&queue_lock);
@@ -628,7 +629,6 @@ static void *rrd_queue_thread (void *data)
                 while (true)
                 {
                   struct timespec ts_wait;
-                  int status;
 
                   while ((flushq_head == NULL) && (queue_head == NULL)
                       && (do_shutdown == 0))
@@ -704,17 +704,28 @@ static void *rrd_queue_thread (void *data)
 		 * we make a copy of it's values */
 		pthread_mutex_lock (&cache_lock);
 
-		c_avl_get (cache, queue_entry->filename, (void *) &cache_entry);
+		status = c_avl_get (cache, queue_entry->filename,
+				(void *) &cache_entry);
 
-		values = cache_entry->values;
-		values_num = cache_entry->values_num;
+		if (status == 0)
+		{
+			values = cache_entry->values;
+			values_num = cache_entry->values_num;
 
-		cache_entry->values = NULL;
-		cache_entry->values_num = 0;
-		cache_entry->flags = FLAG_NONE;
+			cache_entry->values = NULL;
+			cache_entry->values_num = 0;
+			cache_entry->flags = FLAG_NONE;
+		}
 
 		pthread_mutex_unlock (&cache_lock);
 
+		if (status != 0)
+		{
+			sfree (queue_entry->filename);
+			sfree (queue_entry);
+			continue;
+		}
+
 		/* Update `tv_next_update' */
 		if (write_rate > 0.0) 
                 {
@@ -968,6 +979,15 @@ static int rrd_cache_insert (const char *filename,
 
 	pthread_mutex_lock (&cache_lock);
 
+	/* This shouldn't happen, but it did happen at least once, so we'll be
+	 * careful. */
+	if (cache == NULL)
+	{
+		pthread_mutex_unlock (&cache_lock);
+		WARNING ("rrdtool plugin: cache == NULL.");
+		return (-1);
+	}
+
 	c_avl_get (cache, filename, (void *) &rc);
 
 	if (rc == NULL)
diff --git a/src/utils_avltree.c b/src/utils_avltree.c
index 9f0b7968..3e258e95 100644
--- a/src/utils_avltree.c
+++ b/src/utils_avltree.c
@@ -581,6 +581,8 @@ int c_avl_get (c_avl_tree_t *t, const void *key, void **value)
 {
 	c_avl_node_t *n;
 
+	assert (t != NULL);
+
 	n = search (t, key);
 	if (n == NULL)
 		return (-1);
-- 
2.30.2