[PATCH v1 net-next 06/15] vxlan: Fix potential null-ptr-deref in vxlan_gro_prepare_receive().

[Kuniyuki Iwashima <kuniyu@google.com>]

udp_tunnel_sock_release() could set sk->sk_user_data to NULL
while vxlan_gro_prepare_receive() is running.

Let's check if rcu_dereference_sk_user_data() is NULL after
skb_gro_remcsum_init().

Fixes: 5602c48cf875 ("vxlan: change vxlan to use UDP socket GRO")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
This is 10 years old bug...
---
 drivers/net/vxlan/vxlan_core.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c
index 0ea88232b985..abf3ae04d75b 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -657,14 +657,18 @@ static struct vxlanhdr *vxlan_gro_prepare_receive(struct sock *sk,
 						  struct sk_buff *skb,
 						  struct gro_remcsum *grc)
 {
-	struct sk_buff *p;
 	struct vxlanhdr *vh, *vh2;
 	unsigned int hlen, off_vx;
-	struct vxlan_sock *vs = rcu_dereference_sk_user_data(sk);
+	struct vxlan_sock *vs;
+	struct sk_buff *p;
 	__be32 flags;
 
 	skb_gro_remcsum_init(grc);
 
+	vs = rcu_dereference_sk_user_data(sk);
+	if (!vs)
+		return NULL;
+
 	off_vx = skb_gro_offset(skb);
 	hlen = off_vx + sizeof(*vh);
 	vh = skb_gro_header(skb, hlen, off_vx);
-- 
2.54.0.545.g6539524ca2-goog