# \[PATCH v2 net 2/5\] l2tp: hold socket before dropping lock in l2tp\_ip{,6}\_recv()

- From: Guillaume Nault \<hidden\>
- Date: 2016-11-29 12:10:44 
- List: netdev
- Page: https://ratatoskr.run/netdev/2016/11/11036349
- Thread: https://ratatoskr.run/netdev/2016/11/11036346/t.md

```text
Socket must be held while under the protection of the l2tp lock; there
is no guarantee that sk remains valid after the read_unlock_bh() call.

Same issue for l2tp_ip and l2tp_ip6.

Signed-off-by: Guillaume Nault <redacted>
---
 net/l2tp/l2tp_ip.c  | 11 ++++++-----
 net/l2tp/l2tp_ip6.c | 11 ++++++-----
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index 1f57094..4d1c942 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -183,14 +183,15 @@ static int l2tp_ip_recv(struct sk_buff *skb)
 
 		read_lock_bh(&l2tp_ip_lock);
 		sk = __l2tp_ip_bind_lookup(net, iph->daddr, 0, tunnel_id);
+		if (!sk) {
+			read_unlock_bh(&l2tp_ip_lock);
+			goto discard;
+		}
+
+		sock_hold(sk);
 		read_unlock_bh(&l2tp_ip_lock);
 	}
 
-	if (sk == NULL)
-		goto discard;
-
-	sock_hold(sk);
-
 	if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
 		goto discard_put;
 
diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index af9abff..e3fc778 100644
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -198,14 +198,15 @@ static int l2tp_ip6_recv(struct sk_buff *skb)
 		read_lock_bh(&l2tp_ip6_lock);
 		sk = __l2tp_ip6_bind_lookup(net, &iph->daddr,
 					    0, tunnel_id);
+		if (!sk) {
+			read_unlock_bh(&l2tp_ip6_lock);
+			goto discard;
+		}
+
+		sock_hold(sk);
 		read_unlock_bh(&l2tp_ip6_lock);
 	}
 
-	if (sk == NULL)
-		goto discard;
-
-	sock_hold(sk);
-
 	if (!xfrm6_policy_check(sk, XFRM_POLICY_IN, skb))
 		goto discard_put;
 
-- 
2.10.2
```