[PATCH 09/16] FIX [1/2] slub: Do not dereference NULL pointer in node_match

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

From: Christoph Lameter <cl@linux.com>

The variables accessed in slab_alloc are volatile and therefore
the page pointer passed to node_match can be NULL. The processing
of data in slab_alloc is tentative until either the cmpxhchg
succeeds or the __slab_alloc slowpath is invoked. Both are
able to perform the same allocation from the freelist.

Check for the NULL pointer in node_match.

A false positive will lead to a retry of the loop in __slab_alloc.

Signed-off-by: Christoph Lameter <cl@linux.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bigeasy@linutronix: replace page with c->page]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 mm/slub.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index 5710788..08eb4c1 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2038,7 +2038,7 @@ static void flush_all(struct kmem_cache *s)
 static inline int node_match(struct kmem_cache_cpu *c, int node)
 {
 #ifdef CONFIG_NUMA
-	if (node != NUMA_NO_NODE && c->node != node)
+	if (!c->page || (node != NUMA_NO_NODE && c->node != node))
 		return 0;
 #endif
 	return 1;
-- 
1.7.10.4