Commit b3a834b1 authored by Bartlomiej Zolnierkiewicz's avatar Bartlomiej Zolnierkiewicz Committed by Jens Axboe

blk-mq: fix undefined behaviour in order_to_size()

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-g33656a1f #22

Fix the code by checking this_order variable for not having the zero
value first.
Reported-by: default avatarMeelis Roos <>
Fixes: 320ae51f ("blk-mq: new multi-queue block IO queueing mechanism")
Signed-off-by: default avatarBartlomiej Zolnierkiewicz <>
Signed-off-by: default avatarJens Axboe <>
parent 59fa0224
......@@ -1495,7 +1495,7 @@ 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 {
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