linux-kernel - [RFC][PATCH 1/5] mm/slab_common: allow NULL cache pointer in kmem_cache

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Date:	Tue,  9 Jun 2015 21:04:49 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Minchan Kim <minchan@...nel.org>, Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Michal Hocko <mhocko@...e.cz>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, sergey.senozhatsky.work@...il.com,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: [RFC][PATCH 1/5] 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.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Reported-by: Andrew Morton <akpm@...ux-foundation.org>
LKML-reference: https://lkml.org/lkml/2015/6/8/583
---
 mm/slab_common.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 8873985..ea69b13 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -641,6 +641,9 @@ 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();
-- 
2.4.3.368.g7974889

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