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

[Chris Wright]

-stable review patch.  If anyone has any objections, please let us know.
---------------------

From: Jack Steiner <steiner@xxxxxxx>

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@xxxxxxx>
Acked-by: Mike Travis <travis@xxxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
---
 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;

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