[PATCH] block: fix potential dereference null pointer

[cgel . zte]

From: Lv Ruyi <lv.ruyi@xxxxxxxxxx>

rcu_dereference may return NULL, so check the returned pointer.

Reported-by: Zeal Robot <zealci@xxxxxxxxxx>
Signed-off-by: Lv Ruyi <lv.ruyi@xxxxxxxxxx>
---
 drivers/block/drbd/drbd_req.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index e1e58e91ee58..8ab6da155e2f 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -577,6 +577,10 @@ int __req_mod(struct drbd_request *req, enum drbd_req_event what,
 		D_ASSERT(device, !(req->rq_state & RQ_NET_MASK));
 		rcu_read_lock();
 		nc = rcu_dereference(connection->net_conf);
+		if (!nc) {
+			rcu_read_unlock();
+			break;
+		}
 		p = nc->wire_protocol;
 		rcu_read_unlock();
 		req->rq_state |=
@@ -690,6 +694,10 @@ int __req_mod(struct drbd_request *req, enum drbd_req_event what,
 		/* close the epoch, in case it outgrew the limit */
 		rcu_read_lock();
 		nc = rcu_dereference(connection->net_conf);
+		if (!nc) {
+			rcu_read_unlock();
+			break;
+		}
 		p = nc->max_epoch_size;
 		rcu_read_unlock();
 		if (connection->current_tle_writes >= p)
-- 
2.25.1