From: Yu Kuai <yukuai3@xxxxxxxxxx> commit 1ba0403ac6447f2d63914fb760c44a3b19c44eaf upstream. 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> Link: https://lore.kernel.org/r/20240909134154.954924-2-yukuai1@xxxxxxxxxxxxxxx Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- block/bfq-iosched.c | 31 ++++++++++++++++++++++++++++--- 1 file changed, 28 insertions(+), 3 deletions(-) --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -6568,6 +6568,31 @@ static void bfq_prepare_request(struct r 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 @@ -6628,7 +6653,7 @@ static struct bfq_queue *bfq_init_rq(str /* If the queue was seeky for too long, break it apart. */ if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq) && !bic->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)) @@ -6647,7 +6672,7 @@ static struct bfq_queue *bfq_init_rq(str 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; /* @@ -6657,7 +6682,7 @@ static struct bfq_queue *bfq_init_rq(str * 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); } Patches currently in stable-queue which might be from yukuai3@xxxxxxxxxx are queue-5.15/block-bfq-fix-possible-uaf-for-bfqq-bic-with-merge-c.patch queue-5.15/block-bfq-choose-the-last-bfqq-from-merge-chain-in-b.patch queue-5.15/block-bfq-don-t-break-merge-chain-in-bfq_split_bfqq.patch queue-5.15/block-bfq-fix-uaf-for-accessing-waker_bfqq-after-splitting.patch