Re: [PATCH] blk-mq: fix use-after-free in blk_mq_exit_sched

[Ming Lei <ming.lei@redhat.com>]

On Wed, Jun 09, 2021 at 02:30:46PM +0800, Ming Lei wrote:
> 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>
> ---
>  block/blk-mq-sched.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index a9182d2f8ad3..80273245d11a 100644
> --- 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;
>  }

Hello Jens,

Any chance to merge this fix?


Thanks,
Ming