From 6f04a5c390b7a47a30c4ccc96b3dfe9dddfcd1e6 Mon Sep 17 00:00:00 2001
From: Samuel Thibault <samuel.thibault@ens-lyon.org>
Date: Sat, 8 Mar 2025 23:13:23 +0100
Subject: [PATCH] l2tp: Add Last Sent/Received LCP ConfReq in ICCN

To support proxy LCP negotiation.
---
 l2tpns.c | 14 ++++++++++++++
 l2tpns.h | 10 ++++++++++
 ppp.c    | 30 ++++++++++++++++++++++++++++++
 3 files changed, 54 insertions(+)

diff --git a/l2tpns.c b/l2tpns.c
index 941e81e..a001823 100644
--- a/l2tpns.c
+++ b/l2tpns.c
@@ -4841,6 +4841,8 @@ void processudp(uint8_t *buf, int len, struct sockaddr_in *addr, uint16_t indexu
 
 						session[s].ppp.phase = Establish;
 						session[s].ppp.lcp = Starting;
+						sess_local[s].lcp_last_received_confreq_n = 0;
+						sess_local[s].lcp_last_sent_confreq_n = 0;
 
 						STAT(session_created);
 						break;
@@ -4867,6 +4869,7 @@ void processudp(uint8_t *buf, int len, struct sockaddr_in *addr, uint16_t indexu
 				LOG(3, s, t, "Received ICRP\n");
 				if (session[s].forwardtosession)
 				{
+					sessionidt fs = session[s].forwardtosession;
 					controlt *c = controlnew(12); // ICCN
 
 					session[s].opened = time_now;
@@ -4879,6 +4882,17 @@ void processudp(uint8_t *buf, int len, struct sockaddr_in *addr, uint16_t indexu
 
 					control32(c, 19, 1, 1); // Framing Type
 					control32(c, 24, 10000000, 1); // Tx Connect Speed
+
+					if (sess_local[fs].lcp_last_sent_confreq_n)
+						// Last Sent LCP ConfReq
+						controlb(c, 27, sess_local[fs].lcp_last_sent_confreq,
+						                sess_local[fs].lcp_last_sent_confreq_n, 0);
+
+					if (sess_local[fs].lcp_last_received_confreq_n)
+						// Last Received LCP ConfReq
+						controlb(c, 28, sess_local[fs].lcp_last_received_confreq,
+						                sess_local[fs].lcp_last_received_confreq_n, 0);
+
 					controladd(c, asession, t); // send the message
 					LOG(3, s, t, "Sending ICCN\n");
 				}
diff --git a/l2tpns.h b/l2tpns.h
index 8a54fc5..0ca23be 100644
--- a/l2tpns.h
+++ b/l2tpns.h
@@ -393,6 +393,9 @@ fragmentationt;
 #define AUTHPAP		1	// allow PAP
 #define AUTHCHAP	2	// allow CHAP
 
+#define MAXLCPLENGTH 128 // Arbitrary, not too large to avoid consuming too
+                         // much memory, but not too short for actual uses
+
 typedef struct
 {
 	// packet counters
@@ -416,6 +419,13 @@ typedef struct
 	// authentication to use
 	int lcp_authtype;
 
+	// Last Received LCP ConfReq and its length
+	uint8_t lcp_last_received_confreq[MAXLCPLENGTH];
+	int lcp_last_received_confreq_n;
+	// Last Sent LCP ConfReq and its length
+	uint8_t lcp_last_sent_confreq[MAXLCPLENGTH];
+	int lcp_last_sent_confreq_n;
+
 	// our MRU
 	uint16_t ppp_mru;
 
diff --git a/ppp.c b/ppp.c
index 57b4340..c40b858 100644
--- a/ppp.c
+++ b/ppp.c
@@ -425,6 +425,8 @@ void lcp_open(sessionidt s, tunnelidt t)
 void lcp_restart(sessionidt s)
 {
 	session[s].ppp.phase = Establish;
+	sess_local[s].lcp_last_received_confreq_n = 0;
+	sess_local[s].lcp_last_sent_confreq_n = 0;
 	// This-Layer-Down
 	change_state(s, ipcp, Initial);
 	change_state(s, ipv6cp, Initial);
@@ -851,6 +853,18 @@ void processlcp(sessionidt s, tunnelidt t, uint8_t *p, uint16_t l)
 		LOG(3, s, t, "LCP: send %s\n", ppp_code(*response));
 		if (config->debug > 3) dumplcp(response, l);
 
+		if (*response == ConfigAck && l - 4 <= sizeof(sess_local[s].lcp_last_received_confreq))
+		{
+			memcpy(sess_local[s].lcp_last_received_confreq, p + 4, l - 4);
+			sess_local[s].lcp_last_received_confreq_n = l - 4;
+		}
+		else
+		{
+			LOG(3, s, t, "their LCP ConfigReq is too long for proxying\n");
+			dumplcp(p, l);
+			sess_local[s].lcp_last_received_confreq_n = 0;
+		}
+
 		tunnelsend(b, l + (response - b), t);
 	}
 	else if (*p == ConfigNak || *p == ConfigRej)
@@ -859,6 +873,10 @@ void processlcp(sessionidt s, tunnelidt t, uint8_t *p, uint16_t l)
 		uint8_t *o = (p + 4);
 		int authtype = -1;
 
+		// They didn't like our config
+
+		sess_local[s].lcp_last_sent_confreq_n = 0;
+
 		while (x > 2)
 		{
 			int type = o[0];
@@ -2800,6 +2818,18 @@ void sendlcp(sessionidt s, tunnelidt t)
 	LOG_HEX(5, "PPPLCP", q, l - q);
 	if (config->debug > 3) dumplcp(q, l - q);
 
+	if (l - (q + 4) <= sizeof(sess_local[s].lcp_last_sent_confreq))
+	{
+		memcpy(sess_local[s].lcp_last_sent_confreq, q + 4, l - (q + 4));
+		sess_local[s].lcp_last_sent_confreq_n = l - (q + 4);
+	}
+	else
+	{
+		LOG(3, s, t, "our LCP ConfigReq is too long for proxying\n");
+		dumplcp(q, l - q);
+		sess_local[s].lcp_last_sent_confreq_n = 0;
+	}
+
 	tunnelsend(b, (l - b), t);
 	restart_timer(s, lcp);
 }