block, bfq: fix uaf for bfqq in bfq_exit_icq_bfqq

Commit 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
will access 'bic->bfqq' in bic_set_bfqq(), however, bfq_exit_icq_bfqq()
can free bfqq first, and then call bic_set_bfqq(), which will cause uaf.

Fix the problem by moving bfq_exit_bfqq() behind bic_set_bfqq().

Fixes: 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20221226030605.1437081-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 16f43bb..ccf2204 100644 (file)
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5317,8 +5317,8 @@ static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
                unsigned long flags;
 
                spin_lock_irqsave(&bfqd->lock, flags);
-               bfq_exit_bfqq(bfqd, bfqq);
                bic_set_bfqq(bic, NULL, is_sync);
+               bfq_exit_bfqq(bfqd, bfqq);
                spin_unlock_irqrestore(&bfqd->lock, flags);
        }
 }