From eed47d19d9362bdd958e4ab56af480b9dbf6b2b6 Mon Sep 17 00:00:00 2001 From: Paolo Valente Date: Wed, 10 Apr 2019 10:38:33 +0200 Subject: block, bfq: fix use after free in bfq_bfqq_expire The function bfq_bfqq_expire() invokes the function __bfq_bfqq_expire(), and the latter may free the in-service bfq-queue. If this happens, then no other instruction of bfq_bfqq_expire() must be executed, or a use-after-free will occur. Basing on the assumption that __bfq_bfqq_expire() invokes bfq_put_queue() on the in-service bfq-queue exactly once, the queue is assumed to be freed if its refcounter is equal to one right before invoking __bfq_bfqq_expire(). But, since commit 9dee8b3b057e ("block, bfq: fix queue removal from weights tree") this assumption is false. __bfq_bfqq_expire() may also invoke bfq_weights_tree_remove() and, since commit 9dee8b3b057e ("block, bfq: fix queue removal from weights tree"), also the latter function may invoke bfq_put_queue(). So __bfq_bfqq_expire() may invoke bfq_put_queue() twice, and this is the actual case where the in-service queue may happen to be freed. To address this issue, this commit moves the check on the refcounter of the queue right around the last bfq_put_queue() that may be invoked on the queue. Fixes: 9dee8b3b057e ("block, bfq: fix queue removal from weights tree") Reported-by: Dmitrii Tcvetkov Reported-by: Douglas Anderson Tested-by: Dmitrii Tcvetkov Tested-by: Douglas Anderson Signed-off-by: Paolo Valente Signed-off-by: Jens Axboe --- block/bfq-iosched.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'block/bfq-iosched.h') diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h index 062e1c4787f4..86394e503ca9 100644 --- a/block/bfq-iosched.h +++ b/block/bfq-iosched.h @@ -995,7 +995,7 @@ bool __bfq_deactivate_entity(struct bfq_entity *entity, bool ins_into_idle_tree); bool next_queue_may_preempt(struct bfq_data *bfqd); struct bfq_queue *bfq_get_next_queue(struct bfq_data *bfqd); -void __bfq_bfqd_reset_in_service(struct bfq_data *bfqd); +bool __bfq_bfqd_reset_in_service(struct bfq_data *bfqd); void bfq_deactivate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq, bool ins_into_idle_tree, bool expiration); void bfq_activate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq); -- cgit v1.2.3-55-g7522