The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x 1ba0403ac6447f2d63914fb760c44a3b19c44eaf # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024100220-swagger-freehand-6d91@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

1ba0403ac644 ("block, bfq: fix uaf for accessing waker_bfqq after splitting") fd571df0ac5b ("block, bfq: turn bfqq_data into an array in bfq_io_cq") a61230470c8c ("block, bfq: move io_cq-persistent bfqq data into a dedicated struct") 9778369a2d6c ("block, bfq: split sync bfq_queues on a per-actuator basis") 246cf66e300b ("block, bfq: fix uaf for bfqq in bfq_exit_icq_bfqq") 337366e02b37 ("block, bfq: replace 0/1 with false/true in bic apis") 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'") a1795c2ccb1e ("bfq: fix waker_bfqq inconsistency crash")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1ba0403ac6447f2d63914fb760c44a3b19c44eaf Mon Sep 17 00:00:00 2001 From: Yu Kuai yukuai3@huawei.com Date: Mon, 9 Sep 2024 21:41:48 +0800 Subject: [PATCH] block, bfq: fix uaf for accessing waker_bfqq after splitting

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@huawei.com Link: https://lore.kernel.org/r/20240909134154.954924-2-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe axboe@kernel.dk

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); }