blk-mq: fix use-after-free in blk_mq_exit_sched

tagset can't be used after blk_cleanup_queue() is returned because
freeing tagset usually follows blk_clenup_queue(). Commit d97e594c5166
("blk-mq: Use request queue-wide tags for tagset-wide sbitmap") adds
check on q->tag_set->flags in blk_mq_exit_sched(), and causes
use-after-free.

Fixes it by using hctx->flags.

Reported-by: syzbot+77ba3d171a25c56756ea@syzkaller.appspotmail.com
Fixes: d97e594c5166 ("blk-mq: Use request queue-wide tags for tagset-wide sbitmap")
Cc: John Garry <john.garry@huawei.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Tested-by: John Garry <john.garry@huawei.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Link: https://lore.kernel.org/r/20210609063046.122843-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index a9182d2f8ad38648a2a1c96f0657b523877f27f5..80273245d11a68ab98d702f57360818971838c48 100644 (file)
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -680,6 +680,7 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
 {
        struct blk_mq_hw_ctx *hctx;
        unsigned int i;
+       unsigned int flags = 0;
 
        queue_for_each_hw_ctx(q, hctx, i) {
                blk_mq_debugfs_unregister_sched_hctx(hctx);
@@ -687,12 +688,13 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
                        e->type->ops.exit_hctx(hctx, i);
                        hctx->sched_data = NULL;
                }
+               flags = hctx->flags;
        }
        blk_mq_debugfs_unregister_sched(q);
        if (e->type->ops.exit_sched)
                e->type->ops.exit_sched(e);
        blk_mq_sched_tags_teardown(q);
-       if (blk_mq_is_sbitmap_shared(q->tag_set->flags))
+       if (blk_mq_is_sbitmap_shared(flags))
                blk_mq_exit_sched_shared_sbitmap(q);
        q->elevator = NULL;
 }