3.16.37-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
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@xxxxxxxx>
Fixes: 320ae51feed5 ("blk-mq: new multi-queue block IO queueing mechanism")
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
block/blk-mq.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1385,7 +1385,7 @@ static struct blk_mq_tags *blk_mq_init_r
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))
this_order--;
do {
--
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