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Date: Mon, 17 Jul 2017 19:45:07 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	kernel-hardening@...ts.openwall.com,
	keescook@...omium.org,
	alex.popov@...ux.com
Subject: [PATCH 1/1] mm/slub.c: add a naive detection of double free or corruption

Add an assertion similar to "fasttop" check in GNU C Library allocator:
an object added to a singly linked freelist should not point to itself.
That helps to detect some double free errors (e.g. CVE-2017-2636) without
slub_debug and KASAN. Testing with hackbench doesn't show any noticeable
performance penalty.

Signed-off-by: Alexander Popov <alex.popov@...ux.com>
---
 mm/slub.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/slub.c b/mm/slub.c
index 1d3f983..a106939b 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -261,6 +261,7 @@ static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
 
 static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp)
 {
+	BUG_ON(object == fp); /* naive detection of double free or corruption */
 	*(void **)(object + s->offset) = fp;
 }
 
-- 
2.7.4

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