[PATCH 4.4-cip 12/23] blk-mq: fix undefined behaviour in order_to_size()

Ben Hutchings <ben.hutchings@...>

From: Bartlomiej Zolnierkiewicz <b.zolnierkie@...>

commit b3a834b1596ac668df206aa2bb1f191c31f5f5e4 upstream.

When this_order variable in blk_mq_init_rq_map() becomes zero
the code incorrectly decrements the variable and passes the result
to order_to_size() helper causing undefined behaviour:

UBSAN: Undefined behaviour in block/blk-mq.c:1459:27
shift exponent 4294967295 is too large for 32-bit type 'unsigned int'
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.6.0-rc6-00072-g33656a1 #22

Fix the code by checking this_order variable for not having the zero
value first.

Reported-by: Meelis Roos <mroos@...>
Fixes: 320ae51feed5 ("blk-mq: new multi-queue block IO queueing mechanism")
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@...>
Signed-off-by: Jens Axboe <axboe@...>
Signed-off-by: Ben Hutchings <ben.hutchings@...>
block/blk-mq.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index c3e461ec40e4..c58fdfdd9ea6 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1494,7 +1494,7 @@ static struct blk_mq_tags *blk_mq_init_rq_map(struct blk_mq_tag_set *set,
int to_do;
void *p;

- while (left < order_to_size(this_order - 1) && this_order)
+ while (this_order && left < order_to_size(this_order - 1))

do {

Ben Hutchings
Software Developer, Codethink Ltd.