Commit b3a834b1 authored May 16, 2016 by Bartlomiej Zolnierkiewicz Committed by Jens Axboe May 16, 2016

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-g33656a1 #22

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

Reported-by: Meelis Roos <mroos@linux.ee>
Fixes: 320ae51f ("blk-mq: new multi-queue block IO queueing mechanism")
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent 59fa0224

block/blk-mq.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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))
		this_order--;

		do {

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