[PATCH] nvmet-fcloop: fail LS request synchronously when remote port is gone

[Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com>]

fcloop_t2h_ls_req() handles a missing remoteport by queueing the request
on tport->ls_list and completing it with -ECONNREFUSED from a work item.

nvmet_fc_delete_assoc_work() sends the Disconnect Association LS this
way. When it runs during nvmet_fc_unregister_targetport(), the work is
queued after flush_workqueue() has started, so it is not waited for.
nvmet_fc_free_pending_reqs() then frees the still-pending lsop and the
late work item calls lsreq->done() on freed memory:

  BUG: KASAN: slab-use-after-free in fcloop_rport_lsrqst_work+0x242/0x2e0
  Workqueue: nvmet-wq fcloop_tport_lsrqst_work
  Allocated by nvmet_fc_xmt_disconnect_assoc
  Freed by nvmet_fc_free_pending_reqs
           nvmet_fc_unregister_targetport
           fcloop_delete_target_port

Return -ECONNREFUSED directly instead. __nvmet_fc_send_ls_req() unwinds
and nvmet_fc_xmt_disconnect_assoc() frees the lsop, so no completion is
left outstanding.

Reported-by: syzbot+77955102efac681ec73b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=77955102efac681ec73b
Fixes: bbccbf791e6f ("nvmet-fc: free pending reqs on tgtport unregister")
Signed-off-by: Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com>
---
 drivers/nvme/target/fcloop.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/drivers/nvme/target/fcloop.c b/drivers/nvme/target/fcloop.c
index b63af3b643a6..9f9fb40f8a97 100644
--- a/drivers/nvme/target/fcloop.c
+++ b/drivers/nvme/target/fcloop.c
@@ -456,21 +456,18 @@ fcloop_t2h_ls_req(struct nvmet_fc_target_port *targetport, void *hosthandle,
 	 * 1:1 tgtport vs remoteport
 	 */
 
+	/*
+	 * Fail synchronously: an async completion can run after
+	 * nvmet_fc_unregister_targetport() has freed the pending lsreq.
+	 */
+	if (!tport->remoteport)
+		return -ECONNREFUSED;
+
 	tls_req = kmem_cache_alloc(lsreq_cache, GFP_KERNEL);
 	if (!tls_req)
 		return -ENOMEM;
 	tls_req->lsreq = lsreq;
 	INIT_LIST_HEAD(&tls_req->ls_list);
-
-	if (!tport->remoteport) {
-		tls_req->status = -ECONNREFUSED;
-		spin_lock(&tport->lock);
-		list_add_tail(&tls_req->ls_list, &tport->ls_list);
-		spin_unlock(&tport->lock);
-		queue_work(nvmet_wq, &tport->ls_work);
-		return ret;
-	}
-
 	tls_req->status = 0;
 	ret = nvme_fc_rcv_ls_req(tport->remoteport, &tls_req->ls_rsp,
 				 lsreq->rqstaddr, lsreq->rqstlen);
-- 
2.43.0