From: Yu Kuai
mainline inclusion
from mainline-next-20211018
commit 52c90e0184f67eecb00b53b79bfdf75e0274f8fd
category: bugfix
issue: #I4NRS5
CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
Signed-off-by: Yu Changchun
---------------------------
There is a problem that nbd_handle_reply() might access freed request:
1) At first, a normal io is submitted and completed with scheduler:
internal_tag = blk_mq_get_tag -> get tag from sched_tags
blk_mq_rq_ctx_init
sched_tags->rq[internal_tag] = sched_tag->static_rq[internal_tag]
...
blk_mq_get_driver_tag
__blk_mq_get_driver_tag -> get tag from tags
tags->rq[tag] = sched_tag->static_rq[internal_tag]
So, both tags->rq[tag] and sched_tags->rq[internal_tag] are pointing
to the request: sched_tags->static_rq[internal_tag]. Even if the
io is finished.
2) nbd server send a reply with random tag directly:
recv_work
nbd_handle_reply
blk_mq_tag_to_rq(tags, tag)
rq = tags->rq[tag]
3) if the sched_tags->static_rq is freed:
blk_mq_sched_free_requests
blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i)
-> step 2) access rq before clearing rq mapping
blk_mq_clear_rq_mapping(set, tags, hctx_idx);
__free_pages() -> rq is freed here
4) Then, nbd continue to use the freed request in nbd_handle_reply
Fix the problem by get 'q_usage_counter' before blk_mq_tag_to_rq(),
thus request is ensured not to be freed because 'q_usage_counter' is
not zero.
Signed-off-by: Yu Kuai
Reviewed-by: Ming Lei
Link: https://lore.kernel.org/r/20210916141810.2325276-1-yukuai3@huawei.com
Signed-off-by: Jens Axboe
Reviewed-by: Jason Yan
Signed-off-by: Chen Jun
Signed-off-by: Zheng Zengkai
Signed-off-by: Yu Changchun
---
drivers/block/nbd.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 622ea52ebbdd..051ba02f996f 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -814,6 +814,7 @@ static void recv_work(struct work_struct *work)
work);
struct nbd_device *nbd = args->nbd;
struct nbd_config *config = nbd->config;
+ struct request_queue *q = nbd->disk->queue;
struct nbd_sock *nsock;
struct nbd_cmd *cmd;
struct request *rq;
@@ -824,13 +825,28 @@ static void recv_work(struct work_struct *work)
if (nbd_read_reply(nbd, args->index, &reply))
break;
+ /*
+ * Grab .q_usage_counter so request pool won't go away, then no
+ * request use-after-free is possible during nbd_handle_reply().
+ * If queue is frozen, there won't be any inflight requests, we
+ * needn't to handle the incoming garbage message.
+ */
+ if (!percpu_ref_tryget(&q->q_usage_counter)) {
+ dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
+ __func__);
+ break;
+ }
+
cmd = nbd_handle_reply(nbd, args->index, &reply);
- if (IS_ERR(cmd))
+ if (IS_ERR(cmd)) {
+ percpu_ref_put(&q->q_usage_counter);
break;
+ }
rq = blk_mq_rq_from_pdu(cmd);
if (likely(!blk_should_fake_timeout(rq->q)))
blk_mq_complete_request(rq);
+ percpu_ref_put(&q->q_usage_counter);
}
nsock = config->socks[args->index];
--
2.25.1
