nfs: nfs4clinet: check the return value of kstrdup()

stable inclusion
from linux-4.19.230
commit 2c9587f72ff4b502c2fd15eb3ccff388eae12d07

--------------------------------

[ Upstream commit fbd2057e ]

kstrdup() returns NULL when some internal memory errors happen, it is
better to check the return value of it so to catch the memory error in
time.
Signed-off-by: NXiaoke Wang <xkernel.wang@foxmail.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>
Signed-off-by: NLaibin Qiu <qiulaibin@huawei.com>

fs/nfs/nfs4client.c

@@ -1276,8 +1276,11 @@ int nfs4_update_server(struct nfs_server *server, const char *hostname,
 	}
 	nfs_put_client(clp);
 
-	if (server->nfs_client->cl_hostname == NULL)
+	if (server->nfs_client->cl_hostname == NULL) {
 		server->nfs_client->cl_hostname = kstrdup(hostname, GFP_KERNEL);
+		if (server->nfs_client->cl_hostname == NULL)
+			return -ENOMEM;
+	}
 	nfs_server_insert_lists(server);
 
 	return nfs_probe_destination(server);