From b5c198ae873150ffc54bfd32f6342c37ef7d6636 Mon Sep 17 00:00:00 2001
From: Samuel Thibault <samuel.thibault@ens-lyon.org>
Date: Sun, 9 Mar 2025 17:08:13 +0100
Subject: [PATCH] l2tplac: fast-forward session that triggered tunnel creation

Previously, when we got a call to be forwarded to another LNS and we didn't
have a tunnel to it yet, we would wait for a PAP/CHAP re-send to trigger the
creation of a session in the fresh tunnel. We do not have to wait, we can
trigger that on SCCCN ack.
---
 l2tplac.c | 6 +++++-
 l2tpns.c  | 7 +++++++
 l2tpns.h  | 2 ++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/l2tplac.c b/l2tplac.c
index f515d85..2af1570 100644
--- a/l2tplac.c
+++ b/l2tplac.c
@@ -341,6 +341,8 @@ static int lac_create_tunnelsession(tunnelidt t, sessionidt s, confrlnsidt i_con
 		tunnel[t].window = 4; // default window
 		tunnel[t].isremotelns = i_conf;
 		tunnel[t].indexudp = config->indexlacudpfd;
+		tunn_local[t].initialsession = s;
+		strncpy(tunn_local[t].initialuser, puser, sizeof(tunn_local[t].initialuser) - 1);
 		STAT(tunnel_created);
 
 		random_data(pconfigrlns[i_conf].auth, sizeof(pconfigrlns[i_conf].auth));
@@ -354,7 +356,9 @@ static int lac_create_tunnelsession(tunnelidt t, sessionidt s, confrlnsidt i_con
 	}
 	else
 	{
-		/** TODO **/
+		/** TODO: ideally we would queue all sessions waiting for the tunnel to
+		 * be finished creating, to trigger forwarding them all on SCCCN ack,
+		 * not just the initial one **/
 		LOG(1, 0, t, "(REMOTE LNS) tunnel is not open\n");
 	}
 
diff --git a/l2tpns.c b/l2tpns.c
index bc215e2..f82fa08 100644
--- a/l2tpns.c
+++ b/l2tpns.c
@@ -4289,6 +4289,13 @@ void processudp(uint8_t *buf, int len, struct sockaddr_in *addr, uint16_t indexu
 				LOG(3, s, t, "REMOTE LNS acked our SCCCN %d\n", tunn_local[t].scccn);
 				tunn_local[t].scccn = -1;
 				tunnel[t].state = TUNNELOPEN;
+
+				if (tunn_local[t].initialsession)
+				{
+					// Forward the call that triggered the tunnel creation
+					lac_create_session(t, tunn_local[t].initialsession, tunn_local[t].initialuser);
+					tunn_local[t].initialsession = 0;
+				}
 			}
 		}
 		if (l)
diff --git a/l2tpns.h b/l2tpns.h
index d468d22..e182597 100644
--- a/l2tpns.h
+++ b/l2tpns.h
@@ -520,6 +520,8 @@ typedef struct
 	int32_t scccn;		// seq number of last sccn waiting for an ack (-1 if none)
 	controlt *controlr;	// queue of OoO-received messages
 	int l2tp_fd;		// kernel acceleration UDP socket
+	sessionidt initialsession;	// initial session that triggered creating the tunnel to another LNS
+	char initialuser[MAXUSER];	// user of initial session
 }
 tunnellocalt;