[PATCH] blk-mq-sched: Don't reference queue tagset in blk_mq_sched_tags_teardown()

[John Garry]

We should not reference the queue tagset in blk_mq_sched_tags_teardown()
(see function comment) for the blk-mq flags, so use the passed flags
instead.

This solves a use-after-free, similarly fixed earlier (and since broken
again) in commit f0c1c4d2864e ("blk-mq: fix use-after-free in
blk_mq_exit_sched").

Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>
Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Tested-by: Anders Roxell <anders.roxell@xxxxxxxxxx>
Fixes: e155b0c238b2 ("blk-mq: Use shared tags for shared sbitmap support")
Signed-off-by: John Garry <john.garry@xxxxxxxxxx>

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index e85b7556b096..6a9444848e3a 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -541,7 +541,7 @@ static void blk_mq_sched_tags_teardown(struct request_queue *q, unsigned int fla
 
 	queue_for_each_hw_ctx(q, hctx, i) {
 		if (hctx->sched_tags) {
-			if (!blk_mq_is_shared_tags(q->tag_set->flags))
+			if (!blk_mq_is_shared_tags(flags))
 				blk_mq_free_rq_map(hctx->sched_tags);
 			hctx->sched_tags = NULL;
 		}
-- 
2.17.1