linux-kernel - [PATCH] - Fix slab corruption caused by alloc_cpumask_var

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Message-ID: <20090402212751.GA11495@sgi.com>
Date:	Thu, 2 Apr 2009 16:27:51 -0500
From:	Jack Steiner <steiner@....com>
To:	akpm@...ux-foundation.org, mingo@...e.hu, rusty@...tcorp.com.au,
	sfr@...b.auug.org.au
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] - Fix slab corruption caused by alloc_cpumask_var_node()

Fix for slab corruption caused by alloc_cpumask_var_node() overwriting
the tail end of an off-stack cpumask.

Signed-off-by: Jack Steiner <steiner@....com>
Acked-by: Mike Travis <travis.sgi.com>


---

Corrruption was found in latest linux-next (4/1)
	v2.6.29-12081-g421a9f3



 lib/cpumask.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux/lib/cpumask.c
===================================================================
--- linux.orig/lib/cpumask.c	2009-04-02 15:30:05.000000000 -0500
+++ linux/lib/cpumask.c	2009-04-02 15:57:44.000000000 -0500
@@ -109,10 +109,10 @@ bool alloc_cpumask_var_node(cpumask_var_
 #endif
 	/* FIXME: Bandaid to save us from old primitives which go to NR_CPUS. */
 	if (*mask) {
+		unsigned char *ptr = (unsigned char *)cpumask_bits(*mask);
 		unsigned int tail;
 		tail = BITS_TO_LONGS(NR_CPUS - nr_cpumask_bits) * sizeof(long);
-		memset(cpumask_bits(*mask) + cpumask_size() - tail,
-		       0, tail);
+		memset(ptr + cpumask_size() - tail, 0, tail);
 	}
 
 	return *mask != NULL;
--
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