6.6-stable review patch. If anyone has any objections, please let me know.
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From: Yu Kuai yukuai3@huawei.com
[ Upstream commit 1ba0403ac6447f2d63914fb760c44a3b19c44eaf ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 2c09c298d8940..055ba1f98009d 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -6823,6 +6823,31 @@ 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 @@ -6884,7 +6909,7 @@ 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)) @@ -6904,7 +6929,7 @@ 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;
/* @@ -6914,7 +6939,7 @@ 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); }