From: Yu Kuai <yukuai3@huawei.com>

After commit 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'"),
bic->bfqq will be accessed in bic_set_bfqq(), however, in some context
bic->bfqq will be freed, and bic_set_bfqq() is called with the freed
bic->bfqq.

Fix the problem by always freeing bfqq after bic_set_bfqq().

Fixes: 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
Reported-and-tested-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 block/bfq-cgroup.c  | 2 +-
 block/bfq-iosched.c | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 7d9b15f0dbd5..0fbde0fc0628 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -769,8 +769,8 @@ static void __bfq_bic_change_cgroup(struct bfq_data *bfqd,
 				 * request from the old cgroup.
 				 */
 				bfq_put_cooperator(sync_bfqq);
-				bfq_release_process_ref(bfqd, sync_bfqq);
 				bic_set_bfqq(bic, NULL, true);
+				bfq_release_process_ref(bfqd, sync_bfqq);
 			}
 		}
 	}
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index ccf2204477a5..380e9bda2e57 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5425,9 +5425,11 @@ static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
 
 	bfqq = bic_to_bfqq(bic, false);
 	if (bfqq) {
-		bfq_release_process_ref(bfqd, bfqq);
+		struct bfq_queue *old_bfqq = bfqq;
+
 		bfqq = bfq_get_queue(bfqd, bio, false, bic, true);
 		bic_set_bfqq(bic, bfqq, false);
+		bfq_release_process_ref(bfqd, old_bfqq);
 	}
 
 	bfqq = bic_to_bfqq(bic, true);
-- 
2.31.1

On Mon, 30 Jan 2023 09:41:36 +0800, Yu Kuai wrote:
> After commit 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'"),
> bic->bfqq will be accessed in bic_set_bfqq(), however, in some context
> bic->bfqq will be freed, and bic_set_bfqq() is called with the freed
> bic->bfqq.
> 
> Fix the problem by always freeing bfqq after bic_set_bfqq().
> 
> [...]

Applied, thanks!

[1/1] block, bfq: fix uaf for bfqq in bic_set_bfqq()
      (no commit info)

Best regards,
-- 
Jens Axboe