[PATCH] block, bfq: fix uaf for bfqq in bic_set_bfqq()

[Yu Kuai]

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 first, 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@xxxxxxx>
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 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 a6e8da5f5cfd..feb13ac25557 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -749,8 +749,8 @@ static void bfq_sync_bfqq_move(struct bfq_data *bfqd,
 		 * old cgroup.
 		 */
 		bfq_put_cooperator(sync_bfqq);
-		bfq_release_process_ref(bfqd, sync_bfqq);
 		bic_set_bfqq(bic, NULL, true, act_idx);
+		bfq_release_process_ref(bfqd, sync_bfqq);
 	}
 }
 
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 815b884d6c5a..2ddf831221c4 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5581,9 +5581,11 @@ static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
 
 	bfqq = bic_to_bfqq(bic, false, bfq_actuator_index(bfqd, bio));
 	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_actuator_index(bfqd, bio));
+		bfq_release_process_ref(bfqd, old_bfqq);
 	}
 
 	bfqq = bic_to_bfqq(bic, true, bfq_actuator_index(bfqd, bio));
-- 
2.31.1