From: Yu Kuai <yukuai3@xxxxxxxxxx>
After commit 42c306ed7233 ("block, bfq: don't break merge chain in
bfq_split_bfqq()"), if the current procress is the last holder of bfqq,
the bfqq can be freed after bfq_split_bfqq(). Hence recored the bfqq and
then access bfqq->waker_bfqq may trigger UAF. What's more, the waker_bfqq
may in the merge chain of bfqq, hence just recored waker_bfqq is still
not safe.
Fix the problem by adding a helper bfq_waker_bfqq() to check if
bfqq->waker_bfqq is in the merge chain, and current procress is the only
holder.
Fixes: 42c306ed7233 ("block, bfq: don't break merge chain in bfq_split_bfqq()")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
block/bfq-iosched.c | 31 ++++++++++++++++++++++++++++---
1 file changed, 28 insertions(+), 3 deletions(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index d1bf2b8a3576..d5d39974c674 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -6825,6 +6825,31 @@ static void bfq_prepare_request(struct request *rq)
rq->elv.priv[0] = rq->elv.priv[1] = NULL;
}
+static struct bfq_queue *bfq_waker_bfqq(struct bfq_queue *bfqq)
+{
+ struct bfq_queue *new_bfqq = bfqq->new_bfqq;
+ struct bfq_queue *waker_bfqq = bfqq->waker_bfqq;
+
+ if (!waker_bfqq)
+ return NULL;
+
+ while (new_bfqq) {
+ if (new_bfqq == waker_bfqq) {
+ /*
+ * If waker_bfqq is in the merge chain, and current
+ * is the only procress.
+ */
+ if (bfqq_process_refs(waker_bfqq) == 1)
+ return NULL;
+ break;
+ }
+
+ new_bfqq = new_bfqq->new_bfqq;
+ }
+
+ return waker_bfqq;
+}
+
/*
* If needed, init rq, allocate bfq data structures associated with
* rq, and increment reference counters in the destination bfq_queue
@@ -6886,7 +6911,7 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
/* If the queue was seeky for too long, break it apart. */
if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq) &&
!bic->bfqq_data[a_idx].stably_merged) {
- struct bfq_queue *old_bfqq = bfqq;
+ struct bfq_queue *waker_bfqq = bfq_waker_bfqq(bfqq);
/* Update bic before losing reference to bfqq */
if (bfq_bfqq_in_large_burst(bfqq))
@@ -6906,7 +6931,7 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
bfqq_already_existing = true;
if (!bfqq_already_existing) {
- bfqq->waker_bfqq = old_bfqq->waker_bfqq;
+ bfqq->waker_bfqq = waker_bfqq;
bfqq->tentative_waker_bfqq = NULL;
/*
@@ -6916,7 +6941,7 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
* woken_list of the waker. See
* bfq_check_waker for details.
*/
- if (bfqq->waker_bfqq)
+ if (waker_bfqq)
hlist_add_head(&bfqq->woken_list_node,
&bfqq->waker_bfqq->woken_list);
}
--
2.39.2
