[patch 029/100] cpumask: fix slab corruption caused by alloc_cpumask_var_node()

Chris Wright
2009-04-23T07:40:01Z

[-- Attachment #1: cpumask-fix-slab-corruption-caused-by-alloc_cpumask_var_node.patch --]
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-stable review patch. If anyone has any objections, please let us know.
---------------------

From: Jack Steiner <steiner@sgi.com>

upstream commit: 4f032ac4122a77dbabf7a24b2739b2790448180f

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

The function zeros out cpumask bits beyond the last possible cpu. The
starting point for zeroing should be the beginning of the mask offset by a
byte count derived from the number of possible cpus. The offset was
calculated in bits instead of bytes. This resulted in overwriting the end
of the cpumask.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Acked-by: Mike Travis <travis@sgi.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
lib/cpumask.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -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;