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-wf2q.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) (limited to 'block/bfq-wf2q.c') diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c index a11bef75483d..ae4d000ac0af 100644 --- a/block/bfq-wf2q.c +++ b/block/bfq-wf2q.c @@ -1605,7 +1605,8 @@ struct bfq_queue *bfq_get_next_queue(struct bfq_data *bfqd) return bfqq; } -void __bfq_bfqd_reset_in_service(struct bfq_data *bfqd) +/* returns true if the in-service queue gets freed */ +bool __bfq_bfqd_reset_in_service(struct bfq_data *bfqd) { struct bfq_queue *in_serv_bfqq = bfqd->in_service_queue; struct bfq_entity *in_serv_entity = &in_serv_bfqq->entity; @@ -1629,8 +1630,20 @@ void __bfq_bfqd_reset_in_service(struct bfq_data *bfqd) * service tree either, then release the service reference to * the queue it represents (taken with bfq_get_entity). */ - if (!in_serv_entity->on_st) + if (!in_serv_entity->on_st) { + /* + * If no process is referencing in_serv_bfqq any + * longer, then the service reference may be the only + * reference to the queue. If this is the case, then + * bfqq gets freed here. + */ + int ref = in_serv_bfqq->ref; bfq_put_queue(in_serv_bfqq); + if (ref == 1) + return true; + } + + return false; } void bfq_deactivate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq, -- cgit