[PATCH 3.16.y-ckt 147/168] slab: fix nodeid bounds check for non-contiguous node IDs

From: Luis Henriques
Date: Mon Dec 15 2014 - 09:34:25 EST

3.16.7-ckt3 -stable review patch. If anyone has any objections, please let me know.


From: Paul Mackerras <paulus@xxxxxxxxx>

commit 7c3fbbdd04a681a1992ad6a3d7a36a63ff668753 upstream.

The bounds check for nodeid in ____cache_alloc_node gives false
positives on machines where the node IDs are not contiguous, leading to
a panic at boot time. For example, on a POWER8 machine the node IDs are
typically 0, 1, 16 and 17. This means that num_online_nodes() returns
4, so when ____cache_alloc_node is called with nodeid = 16 the VM_BUG_ON
triggers, like this:

kernel BUG at /home/paulus/kernel/kvm/mm/slab.c:3079!
Call Trace:
.____cache_alloc_node+0x5c/0x270 (unreliable)

To fix this, we instead compare the nodeid with MAX_NUMNODES, and
additionally make sure it isn't negative (since nodeid is an int). The
check is there mainly to protect the array dereference in the get_node()
call in the next line, and the array being dereferenced is of size
MAX_NUMNODES. If the nodeid is in range but invalid (for example if the
node is off-line), the BUG_ON in the next line will catch that.

Fixes: 14e50c6a9bc2 ("mm: slab: Verify the nodeid passed to ____cache_alloc_node")
Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
Reviewed-by: Pekka Enberg <penberg@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
mm/slab.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slab.c b/mm/slab.c
index c9103e4cf2c2..92dbea7e7132 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3225,7 +3225,7 @@ static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags,
void *obj;
int x;

- VM_BUG_ON(nodeid > num_online_nodes());
+ VM_BUG_ON(nodeid < 0 || nodeid >= MAX_NUMNODES);
n = cachep->node[nodeid];


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