diff mbox series

[PATCHv2] l2tp: Support several sockets with same IP/port quadruple

Message ID 20240506215336.1470009-1-samuel.thibault@ens-lyon.org (mailing list archive)
State Accepted
Commit 628bc3e5a1beae395b5b515998396c60559ed3a9
Delegated to: Netdev Maintainers
Headers show
Series [PATCHv2] l2tp: Support several sockets with same IP/port quadruple | expand

Checks

Context Check Description
netdev/series_format warning Single patches do not need cover letters; Target tree name not specified in the subject
netdev/tree_selection success Guessed tree name to be net-next
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 926 this patch: 926
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers warning 1 maintainers not CCed: willemb@google.com
netdev/build_clang success Errors and warnings before: 937 this patch: 937
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 937 this patch: 937
netdev/checkpatch warning WARNING: line length of 81 exceeds 80 columns WARNING: line length of 82 exceeds 80 columns
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
netdev/contest success net-next-2024-05-08--03-00 (tests: 1005)

Commit Message

Samuel Thibault May 6, 2024, 9:53 p.m. UTC 
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 <samuel.thibault@ens-lyon.org>
---

Diff from v1:
- do not check for tunnel->l2tp_net != NULL, it cannot not be
- check for tunnel version

 net/l2tp/l2tp_core.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

Comments

patchwork-bot+netdevbpf@kernel.org May 9, 2024, 2 p.m. UTC | #1 
Hello:

This patch was applied to netdev/net-next.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Mon,  6 May 2024 23:53:35 +0200 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [PATCHv2] l2tp: Support several sockets with same IP/port quadruple
    https://git.kernel.org/netdev/net-next/c/628bc3e5a1be

You are awesome, thank you!
diff mbox series

Patch

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;
 }