From: Paolo Valente paolo.valente@linaro.org
commit 478de3380c1c7dbb0f65f545ee0185848413f3fe upstream.
Since commit 3726112ec731 ("block, bfq: re-schedule empty queues if they deserve I/O plugging"), to prevent the service guarantees of a bfq_queue from being violated, the bfq_queue may be left busy, i.e., scheduled for service, even if empty (see comments in __bfq_bfqq_expire() for details). But, if no process will send requests to the bfq_queue any longer, then there is no point in keeping the bfq_queue scheduled for service.
In addition, keeping the bfq_queue scheduled for service, but with no process reference any longer, may cause the bfq_queue to be freed when descheduled from service. But this is assumed to never happen, and causes a UAF if it happens. This, in turn, caused crashes [1, 2].
This commit fixes this issue by descheduling an empty bfq_queue when it remains with not process reference.
[1] https://bugzilla.redhat.com/show_bug.cgi?id=1767539 [2] https://bugzilla.kernel.org/show_bug.cgi?id=205447
Fixes: 3726112ec731 ("block, bfq: re-schedule empty queues if they deserve I/O plugging") Reported-by: Chris Evich cevich@redhat.com Reported-by: Patrick Dung patdung100@gmail.com Reported-by: Thorsten Schubert tschubert@bafh.org Tested-by: Thorsten Schubert tschubert@bafh.org Tested-by: Oleksandr Natalenko oleksandr@natalenko.name Signed-off-by: Paolo Valente paolo.valente@linaro.org Signed-off-by: Jens Axboe axboe@kernel.dk Cc: Laura Abbott labbott@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- block/bfq-iosched.c | 32 ++++++++++++++++++++++++++------ 1 file changed, 26 insertions(+), 6 deletions(-)
--- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -2699,6 +2699,28 @@ static void bfq_bfqq_save_state(struct b } }
+ +static +void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq) +{ + /* + * To prevent bfqq's service guarantees from being violated, + * bfqq may be left busy, i.e., queued for service, even if + * empty (see comments in __bfq_bfqq_expire() for + * details). But, if no process will send requests to bfqq any + * longer, then there is no point in keeping bfqq queued for + * service. In addition, keeping bfqq queued for service, but + * with no process ref any longer, may have caused bfqq to be + * freed when dequeued from service. But this is assumed to + * never happen. + */ + if (bfq_bfqq_busy(bfqq) && RB_EMPTY_ROOT(&bfqq->sort_list) && + bfqq != bfqd->in_service_queue) + bfq_del_bfqq_busy(bfqd, bfqq, false); + + bfq_put_queue(bfqq); +} + static void bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic, struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) @@ -2769,8 +2791,7 @@ bfq_merge_bfqqs(struct bfq_data *bfqd, s */ new_bfqq->pid = -1; bfqq->bic = NULL; - /* release process reference to bfqq */ - bfq_put_queue(bfqq); + bfq_release_process_ref(bfqd, bfqq); }
static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq, @@ -4885,7 +4906,7 @@ static void bfq_exit_bfqq(struct bfq_dat
bfq_put_cooperator(bfqq);
- bfq_put_queue(bfqq); /* release process reference */ + bfq_release_process_ref(bfqd, bfqq); }
static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync) @@ -4987,8 +5008,7 @@ static void bfq_check_ioprio_change(stru
bfqq = bic_to_bfqq(bic, false); if (bfqq) { - /* release process reference on this queue */ - bfq_put_queue(bfqq); + bfq_release_process_ref(bfqd, bfqq); bfqq = bfq_get_queue(bfqd, bio, BLK_RW_ASYNC, bic); bic_set_bfqq(bic, bfqq, false); } @@ -5948,7 +5968,7 @@ bfq_split_bfqq(struct bfq_io_cq *bic, st
bfq_put_cooperator(bfqq);
- bfq_put_queue(bfqq); + bfq_release_process_ref(bfqq->bfqd, bfqq); return NULL; }