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authorPaolo Valente <paolo.valente@linaro.org>2019-11-14 10:33:11 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-11-24 08:16:59 +0100
commit50c97a0b3f189ca9d37781fab4089f96c1169570 (patch)
treeb75d08ce4fb5dc18209d4897bf36066912dae8f4
parentc6e0ab4169163865190912628c81759252a18135 (diff)
block, bfq: deschedule empty bfq_queues not referred by any process
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>
-rw-r--r--block/bfq-iosched.c32
1 files changed, 26 insertions, 6 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 70bcbd02edcb..aabc8c1ab0cd 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2699,6 +2699,28 @@ static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
}
}
+
+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, struct bfq_io_cq *bic,
*/
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_data *bfqd, struct bfq_queue *bfqq)
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(struct bfq_io_cq *bic, struct bio *bio)
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, struct bfq_queue *bfqq)
bfq_put_cooperator(bfqq);
- bfq_put_queue(bfqq);
+ bfq_release_process_ref(bfqq->bfqd, bfqq);
return NULL;
}