linux-kernel - [PATCH 4.2.y-ckt 194/206] blk-mq: fix undefined behaviour in order_to

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Message-Id: <1465507015-23052-195-git-send-email-kamal@canonical.com>
Date:	Thu,  9 Jun 2016 14:16:43 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Jens Axboe <axboe@...com>, Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 194/206] blk-mq: fix undefined behaviour in order_to_size()

4.2.8-ckt12 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

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

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@...ux.ee>
Fixes: 320ae51feed5 ("blk-mq: new multi-queue block IO queueing mechanism")
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Signed-off-by: Jens Axboe <axboe@...com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 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 0990d4c..7d5f8cb 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1488,7 +1488,7 @@ 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 {
-- 
2.7.4