[PATCH net] bareudp: fix NULL pointer dereference in bareudp_fill_metadata_dst()

[Weiming Shi <bestswngs@gmail.com>]

bareudp_fill_metadata_dst() passes bareudp->sock to
udp_tunnel6_dst_lookup() in the IPv6 path without a NULL check.
The socket is only created in bareudp_open() and NULLed in
bareudp_stop(), so calling this function while the device is down
triggers a NULL dereference via sock->sk.

 BUG: kernel NULL pointer dereference, address: 0000000000000018
 RIP: 0010:udp_tunnel6_dst_lookup (net/ipv6/ip6_udp_tunnel.c:160)
 Call Trace:
  <TASK>
  bareudp_fill_metadata_dst (drivers/net/bareudp.c:532)
  do_execute_actions (net/openvswitch/actions.c:901)
  ovs_execute_actions (net/openvswitch/actions.c:1589)
  ovs_packet_cmd_execute (net/openvswitch/datapath.c:700)
  genl_family_rcv_msg_doit (net/netlink/genetlink.c:1114)
  genl_rcv_msg (net/netlink/genetlink.c:1209)
  netlink_rcv_skb (net/netlink/af_netlink.c:2550)
  </TASK>

Add a NULL check returning -ESHUTDOWN, consistent with the xmit paths
in the same driver.

Fixes: 571912c69f0e ("net: UDP tunnel encapsulation module for tunnelling different protocols like MPLS, IP, NSH etc.")
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
 drivers/net/bareudp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/bareudp.c b/drivers/net/bareudp.c
index 0df3208783ad..da5866ba0699 100644
--- a/drivers/net/bareudp.c
+++ b/drivers/net/bareudp.c
@@ -529,6 +529,9 @@ static int bareudp_fill_metadata_dst(struct net_device *dev,
 		struct in6_addr saddr;
 		struct socket *sock = rcu_dereference(bareudp->sock);
 
+		if (!sock)
+			return -ESHUTDOWN;
+
 		dst = udp_tunnel6_dst_lookup(skb, dev, bareudp->net, sock,
 					     0, &saddr, &info->key,
 					     sport, bareudp->port, info->key.tos,
-- 
2.43.0