[PATCH] blk-mq: fix use-after-free in blk_mq_free_tag_set()

[Junichi Nomura <j-nomura@ce.jp.nec.com>]

tags is freed in blk_mq_free_rq_map() and should not be used after that.
The problem doesn't manifest if CONFIG_CPUMASK_OFFSTACK is false because
free_cpumask_var() is nop.

tags->cpumask is allocated in blk_mq_init_tags() so it's natural to
free cpumask in its counter part, blk_mq_free_tags().

Fixes: f26cdc8536ad ("blk-mq: Shared tag enhancements")
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Jens Axboe <axboe@fb.com>
---
 block/blk-mq-tag.c | 1 +
 block/blk-mq.c     | 4 +---
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index ed96474..ec2d119 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -641,6 +641,7 @@ void blk_mq_free_tags(struct blk_mq_tags *tags)
 {
 	bt_free(&tags->bitmap_tags);
 	bt_free(&tags->breserved_tags);
+	free_cpumask_var(tags->cpumask);
 	kfree(tags);
 }
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7785ae9..85f0143 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2296,10 +2296,8 @@ void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
 	int i;
 
 	for (i = 0; i < set->nr_hw_queues; i++) {
-		if (set->tags[i]) {
+		if (set->tags[i])
 			blk_mq_free_rq_map(set, set->tags[i], i);
-			free_cpumask_var(set->tags[i]->cpumask);
-		}
 	}
 
 	kfree(set->tags);
-- 
2.1.0