l2tp: fix race in l2tp_recv_common()

[mirror_ubuntu-bionic-kernel.git] / net / l2tp / l2tp_ip.c

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index c59712057dc838170f47f917cc3676f9f06f958b..4d322c1b7233e5b546ff75a585a3603503e076bc 100644 (file)
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -143,19 +143,19 @@ static int l2tp_ip_recv(struct sk_buff *skb)
        }
 
        /* Ok, this is a data packet. Lookup the session. */
-       session = l2tp_session_find(net, NULL, session_id);
-       if (session == NULL)
+       session = l2tp_session_get(net, NULL, session_id, true);
+       if (!session)
                goto discard;
 
        tunnel = session->tunnel;
-       if (tunnel == NULL)
-               goto discard;
+       if (!tunnel)
+               goto discard_sess;
 
        /* Trace packet contents, if enabled */
        if (tunnel->debug & L2TP_MSG_DATA) {
                length = min(32u, skb->len);
                if (!pskb_may_pull(skb, length))
-                       goto discard;
+                       goto discard_sess;
 
                /* Point to L2TP header */
                optr = ptr = skb->data;
@@ -165,6 +165,7 @@ static int l2tp_ip_recv(struct sk_buff *skb)
        }
 
        l2tp_recv_common(session, skb, ptr, optr, 0, skb->len, tunnel->recv_payload_hook);
+       l2tp_session_dec_refcount(session);
 
        return 0;
 
@@ -178,9 +179,10 @@ 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);
@@ -202,6 +204,12 @@ pass_up:
 
        return sk_receive_skb(sk, skb, 1);
 
+discard_sess:
+       if (session->deref)
+               session->deref(session);
+       l2tp_session_dec_refcount(session);
+       goto discard;
+
 discard_put:
        sock_put(sk);
 
@@ -388,7 +396,7 @@ static int l2tp_ip_backlog_recv(struct sock *sk, struct sk_buff *skb)
 drop:
        IP_INC_STATS(sock_net(sk), IPSTATS_MIB_INDISCARDS);
        kfree_skb(skb);
-       return -1;
+       return 0;
 }
 
 /* Userspace will call sendmsg() on the tunnel socket to send L2TP