From e2f2a39452c43b64ea3191642a2661cb8d03827a Mon Sep 17 00:00:00 2001 From: Yu Kuai Date: Wed, 8 Mar 2023 10:32:08 +0800 Subject: block, bfq: fix uaf for 'stable_merge_bfqq' 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 Link: https://lore.kernel.org/linux-block/20230307071448.rzihxbm4jhbf5krj@shindev/ Signed-off-by: Yu Kuai Reviewed-by: Jan Kara Signed-off-by: Jens Axboe --- 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); -- cgit v1.2.3