From: Yu Kuai <yukuai3@xxxxxxxxxx>
Before commit fd571df0ac5b ("block, bfq: turn bfqq_data into an array
in bfq_io_cq"), process reference is read before bfq_put_stable_ref(),
and it's safe if bfq_put_stable_ref() put the last reference, because
process reference will be 0 and 'stable_merge_bfqq' won't be accessed
in this case. However, the commit changed the order and will cause
uaf for 'stable_merge_bfqq'.
In order to emphasize that bfq_put_stable_ref() can drop the last
reference, fix the problem by moving bfq_put_stable_ref() to the end of
bfq_setup_stable_merge().
Fixes: fd571df0ac5b ("block, bfq: turn bfqq_data into an array in bfq_io_cq")
Reported-and-tested-by: Shinichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
Link: https://lore.kernel.org/linux-block/20230307071448.rzihxbm4jhbf5krj@shindev/
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
block/bfq-iosched.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 8a8d4441519c..d9ed3108c17a 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2854,11 +2854,11 @@ bfq_setup_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
{
int proc_ref = min(bfqq_process_refs(bfqq),
bfqq_process_refs(stable_merge_bfqq));
- struct bfq_queue *new_bfqq;
+ struct bfq_queue *new_bfqq = NULL;
- if (idling_boosts_thr_without_issues(bfqd, bfqq) ||
- proc_ref == 0)
- return NULL;
+ bfqq_data->stable_merge_bfqq = NULL;
+ if (idling_boosts_thr_without_issues(bfqd, bfqq) || proc_ref == 0)
+ goto out;
/* next function will take at least one ref */
new_bfqq = bfq_setup_merge(bfqq, stable_merge_bfqq);
@@ -2873,6 +2873,11 @@ bfq_setup_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
new_bfqq_data->stably_merged = true;
}
}
+
+out:
+ /* deschedule stable merge, because done or aborted here */
+ bfq_put_stable_ref(stable_merge_bfqq);
+
return new_bfqq;
}
@@ -2933,11 +2938,6 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
struct bfq_queue *stable_merge_bfqq =
bfqq_data->stable_merge_bfqq;
- /* deschedule stable merge, because done or aborted here */
- bfq_put_stable_ref(stable_merge_bfqq);
-
- bfqq_data->stable_merge_bfqq = NULL;
-
return bfq_setup_stable_merge(bfqd, bfqq,
stable_merge_bfqq,
bfqq_data);
--
2.31.1
