From 3942d29918522ba6a393c19388301ec04df429cd Mon Sep 17 00:00:00 2001
From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Date: Tue, 8 Sep 2015 15:00:50 -0700
Subject: [PATCH] mm/slab_common: allow NULL cache pointer in
 kmem_cache_destroy()

kmem_cache_destroy() does not tolerate a NULL kmem_cache pointer argument
and performs a NULL-pointer dereference.  This requires additional
attention and effort from developers/reviewers and forces all
kmem_cache_destroy() callers (200+ as of 4.1) to do a NULL check

    if (cache)
        kmem_cache_destroy(cache);

Or, otherwise, be invalid kmem_cache_destroy() users.

Tweak kmem_cache_destroy() and NULL-check the pointer there.

Proposed by Andrew Morton.

Link: https://lkml.org/lkml/2015/6/8/583
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/slab_common.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index c26829fe4e37..bde04a699ab6 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -640,6 +640,9 @@ void kmem_cache_destroy(struct kmem_cache *s)
 	bool need_rcu_barrier = false;
 	bool busy = false;
 
+	if (unlikely(!s))
+		return;
+
 	BUG_ON(!is_root_cache(s));
 
 	get_online_cpus();