[PATCH v3] netlink: fix null pointer dereference on nlk->groups

[Baozeng Ding <sploving1@gmail.com>]

If groups is not 0 and nlk->groups is NULL, it will not return
immediately and cause a null pointer dereference later.

Signed-off-by: Baozeng Ding <sploving1@gmail.com>
---
The v3 version adds WARN_ON, suggested by David Miller. Thanks for
David's feedback.
---
 net/netlink/af_netlink.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 59651af..f93d579 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1576,7 +1576,10 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
 		}
 	}
 
-	if (!groups && (nlk->groups == NULL || !(u32)nlk->groups[0]))
+	if (WARN_ON(!nlk->groups))
+		return 0;
+
+	if (!groups && !(u32)nlk->groups[0])
 		return 0;
 
 	netlink_table_grab();
-- 
1.9.1