From 628bc3e5a1beae395b5b515998396c60559ed3a9 Mon Sep 17 00:00:00 2001 From: Samuel Thibault Date: Mon, 6 May 2024 23:53:35 +0200 Subject: [PATCH] l2tp: Support several sockets with same IP/port quadruple Some l2tp providers will use 1701 as origin port and open several tunnels for the same origin and target. On the Linux side, this may mean opening several sockets, but then trafic will go to only one of them, losing the trafic for the tunnel of the other socket (or leaving it up to userland, consuming a lot of cpu%). This can also happen when the l2tp provider uses a cluster, and load-balancing happens to migrate from one origin IP to another one, for which a socket was already established. Managing reassigning tunnels from one socket to another would be very hairy for userland. Lastly, as documented in l2tpconfig(1), as client it may be necessary to use 1701 as origin port for odd firewalls reasons, which could prevent from establishing several tunnels to a l2tp server, for the same reason: trafic would get only on one of the two sockets. With the V2 protocol it is however easy to route trafic to the proper tunnel, by looking up the tunnel number in the network namespace. This fixes the three cases altogether. Signed-off-by: Samuel Thibault Link: https://lore.kernel.org/r/20240506215336.1470009-1-samuel.thibault@ens-lyon.org Signed-off-by: Paolo Abeni --- net/l2tp/l2tp_core.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 8d21ff25f160..2ab45e3f48bf 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -794,6 +794,7 @@ static void l2tp_session_queue_purge(struct l2tp_session *session) static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb) { struct l2tp_session *session = NULL; + struct l2tp_tunnel *orig_tunnel = tunnel; unsigned char *ptr, *optr; u16 hdrflags; u32 tunnel_id, session_id; @@ -845,6 +846,20 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb) /* Extract tunnel and session ID */ tunnel_id = ntohs(*(__be16 *)ptr); ptr += 2; + + if (tunnel_id != tunnel->tunnel_id) { + /* We are receiving trafic for another tunnel, probably + * because we have several tunnels between the same + * IP/port quadruple, look it up. + */ + struct l2tp_tunnel *alt_tunnel; + + alt_tunnel = l2tp_tunnel_get(tunnel->l2tp_net, tunnel_id); + if (!alt_tunnel || alt_tunnel->version != L2TP_HDR_VER_2) + goto pass; + tunnel = alt_tunnel; + } + session_id = ntohs(*(__be16 *)ptr); ptr += 2; } else { @@ -875,6 +890,9 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb) l2tp_recv_common(session, skb, ptr, optr, hdrflags, length); l2tp_session_dec_refcount(session); + if (tunnel != orig_tunnel) + l2tp_tunnel_dec_refcount(tunnel); + return 0; invalid: @@ -884,6 +902,9 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb) /* Put UDP header back */ __skb_push(skb, sizeof(struct udphdr)); + if (tunnel != orig_tunnel) + l2tp_tunnel_dec_refcount(tunnel); + return 1; }