cpumask: fix slab corruption caused by alloc_cpumask_var_node()

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>		[2.6.29.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/cpumask.c b/lib/cpumask.c
index 3389e2440da0..1f71b97de0f9 100644
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -109,10 +109,10 @@ bool alloc_cpumask_var_node(cpumask_var_t *mask, gfp_t flags, int node)
 #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;