On 在 2021/09/14 15:46, Ming Lei wrote:
If the above can happen, blk_mq_find_and_get_req() may not fix it too, just
wondering why not take the following simpler way for avoiding the UAF?
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 5170a630778d..dfa5cce71f66 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -795,9 +795,13 @@ 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_cmd *cmd;
struct request *rq;
+ if (!percpu_ref_tryget(&q->q_usage_counter))
+ return;
+
while (1) {
cmd = nbd_read_stat(nbd, args->index);
if (IS_ERR(cmd)) {
@@ -813,6 +817,7 @@ static void recv_work(struct work_struct *work)
if (likely(!blk_should_fake_timeout(rq->q)))
blk_mq_complete_request(rq);
}
+ blk_queue_exit(q);
nbd_config_put(nbd);
atomic_dec(&config->recv_threads);
wake_up(&config->recv_wq);
Hi, Ming
This apporch is wrong.
If blk_mq_freeze_queue() is called, and nbd is waiting for all
request to complete. percpu_ref_tryget() will fail here, and deadlock
will occur because request can't complete in recv_work().
Thanks,
Kuai
