Commit e2f2a394 authored by Yu Kuai's avatar Yu Kuai Committed by Jens Axboe
Browse files

block, bfq: fix uaf for 'stable_merge_bfqq' 



Before commit fd571df0 ("block, bfq: turn bfqq_data into an array
in bfq_io_cq"), process reference is read before bfq_put_stable_ref(),
and it's safe if bfq_put_stable_ref() put the last reference, because
process reference will be 0 and 'stable_merge_bfqq' won't be accessed
in this case. However, the commit changed the order and  will cause
uaf for 'stable_merge_bfqq'.

In order to emphasize that bfq_put_stable_ref() can drop the last
reference, fix the problem by moving bfq_put_stable_ref() to the end of
bfq_setup_stable_merge().

Fixes: fd571df0 ("block, bfq: turn bfqq_data into an array in bfq_io_cq")
Reported-and-tested-by: default avatarShinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Link: https://lore.kernel.org/linux-block/20230307071448.rzihxbm4jhbf5krj@shindev/


Signed-off-by: default avatarYu Kuai <yukuai3@huawei.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent e3306221

block/bfq-iosched.c

+9 −9
Original line number Diff line number Diff line
@@ -2854,11 +2854,11 @@ bfq_setup_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq, 
{

	int proc_ref = min(bfqq_process_refs(bfqq),

			   bfqq_process_refs(stable_merge_bfqq));

	struct bfq_queue *new_bfqq;

	struct bfq_queue *new_bfqq = NULL;



	if (idling_boosts_thr_without_issues(bfqd, bfqq) ||

	    proc_ref == 0)

		return NULL;

	bfqq_data->stable_merge_bfqq = NULL;

	if (idling_boosts_thr_without_issues(bfqd, bfqq) || proc_ref == 0)

		goto out;



	/* next function will take at least one ref */

	new_bfqq = bfq_setup_merge(bfqq, stable_merge_bfqq);
@@ -2873,6 +2873,11 @@ bfq_setup_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq, 
			new_bfqq_data->stably_merged = true;

		}

	}



out:

	/* deschedule stable merge, because done or aborted here */

	bfq_put_stable_ref(stable_merge_bfqq);



	return new_bfqq;

}
@@ -2933,11 +2938,6 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, 
			struct bfq_queue *stable_merge_bfqq =

				bfqq_data->stable_merge_bfqq;



			/* deschedule stable merge, because done or aborted here */

			bfq_put_stable_ref(stable_merge_bfqq);



			bfqq_data->stable_merge_bfqq = NULL;



			return bfq_setup_stable_merge(bfqd, bfqq,

						      stable_merge_bfqq,

						      bfqq_data);