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authorPaolo Valente <paolo.valente@linaro.org>2019-04-10 10:38:33 +0200
committerJens Axboe <axboe@kernel.dk>2019-04-10 07:54:38 -0600
commiteed47d19d9362bdd958e4ab56af480b9dbf6b2b6 (patch)
treeebb19cdcb30d8e16135544007babceb40da2d08b /block/bfq-wf2q.c
parent3ec482d15cb986bf08b923f9193eeddb3b9ca69f (diff)
downloadlinux-eed47d19d9362bdd958e4ab56af480b9dbf6b2b6.tar.bz2
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 <demfloro@demfloro.ru> Reported-by: Douglas Anderson <dianders@chromium.org> Tested-by: Dmitrii Tcvetkov <demfloro@demfloro.ru> Tested-by: Douglas Anderson <dianders@chromium.org> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/bfq-wf2q.c')
-rw-r--r--block/bfq-wf2q.c17
1 files changed, 15 insertions, 2 deletions
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,