l2tp: hold tunnel socket when handling control frames in l2tp_ip and l2tp_ip6

The code following l2tp_tunnel_find() expects that a new reference is
held on sk. Either sk_receive_skb() or the discard_put error path will
drop a reference from the tunnel's socket.

This issue exists in both l2tp_ip and l2tp_ip6.

Fixes: a3c18422a4b4 ("l2tp: hold socket before dropping lock in l2tp_ip{, 6}_recv()")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 6 insertions, 4 deletions

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index d25038cfd64e..7208fbe5856b 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -178,9 +178,10 @@ pass_up:
 
         tunnel_id = ntohl(*(__be32 *) &skb->data[4]);
         tunnel = l2tp_tunnel_find(net, tunnel_id);
-        if (tunnel != NULL)
+        if (tunnel) {
                 sk = tunnel->sock;
-        else {
+                sock_hold(sk);
+        } else {
                 struct iphdr *iph = (struct iphdr *) skb_network_header(skb);
 
                 read_lock_bh(&l2tp_ip_lock);
diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index a4abcbc4c09a..516d7ce24ba7 100644
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -191,9 +191,10 @@ pass_up:
 
         tunnel_id = ntohl(*(__be32 *) &skb->data[4]);
         tunnel = l2tp_tunnel_find(net, tunnel_id);
-        if (tunnel != NULL)
+        if (tunnel) {
                 sk = tunnel->sock;
-        else {
+                sock_hold(sk);
+        } else {
                 struct ipv6hdr *iph = ipv6_hdr(skb);
 
                 read_lock_bh(&l2tp_ip6_lock);