From: Yu Kuai yukuai3@huawei.com
mainline inclusion from mainline-next-20211018 commit 52c90e0184f67eecb00b53b79bfdf75e0274f8fd category: bugfix bugzilla: 49890 CVE: NA ---------------------------
There is a problem that nbd_handle_reply() might access freed request:
1) At first, a normal io is submitted and completed with scheduler:
internel_tag = blk_mq_get_tag -> get tag from sched_tags blk_mq_rq_ctx_init sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag] ... blk_mq_get_driver_tag __blk_mq_get_driver_tag -> get tag from tags tags->rq[tag] = sched_tag->static_rq[internel_tag]
So, both tags->rq[tag] and sched_tags->rq[internel_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 yukuai3@huawei.com Reviewed-by: Ming Lei ming.lei@redhat.com Link: https://lore.kernel.org/r/20210916141810.2325276-1-yukuai3@huawei.com Signed-off-by: Jens Axboe axboe@kernel.dk Reviewed-by: Jason Yan yanaijie@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- 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 8c2e3224cdd65..45e6ae6add382 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -772,6 +772,7 @@ 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;
@@ -781,11 +782,26 @@ 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; + }
blk_mq_complete_request(blk_mq_rq_from_pdu(cmd)); + percpu_ref_put(&q->q_usage_counter); }
nsock = config->socks[args->index];