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block, bfq: fix uaf for accessing waker_bfqq after splitting

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After commit 42c306ed72 ("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: 42c306ed72 ("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>
This commit is contained in:
Yu Kuai 2024-09-09 21:41:48 +08:00 committed by Jens Axboe
parent 29390bb566
commit 1ba0403ac6
1 changed files with 28 additions and 3 deletions
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31
block/bfq-iosched.c
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@ -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);
}