From: Guus Sliepen <guus@tinc-vpn.org>
Date: Sun, 28 Feb 2010 17:20:13 +0000 (+0100)
Subject: Clamp MSS to miminum MTU in both directions.
X-Git-Tag: import-tinc-1.1~558^2~11
X-Git-Url: https://git.meshlink.io/?a=commitdiff_plain;h=3cb91d75f874e3398c35cd4280c1e0a1ceeedabc;p=meshlink

Clamp MSS to miminum MTU in both directions.

Clamp MSS of both incoming and outgoing packets, and use the minimum of the
PMTU of both directions when clamping.
---

diff --git a/src/route.c b/src/route.c
index 664fed89..6c381ccf 100644
--- a/src/route.c
+++ b/src/route.c
@@ -94,9 +94,13 @@ static bool checklength(node_t *source, vpn_packet_t *packet, length_t length) {
 }
 
 static void clamp_mss(const node_t *source, const node_t *via, vpn_packet_t *packet) {
-	if(!via || via == myself || !(via->options & OPTION_CLAMP_MSS))
+	if(!source || !via || !(via->options & OPTION_CLAMP_MSS))
 		return;
 
+	uint16_t mtu = source->mtu;
+	if(via != myself && via->mtu < mtu)
+		mtu = via->mtu;
+
 	/* Find TCP header */
 	int start = 0;
 	uint16_t type = packet->data[12] << 8 | packet->data[13];
@@ -140,7 +144,7 @@ static void clamp_mss(const node_t *source, const node_t *via, vpn_packet_t *pac
 
 		/* Found it */
 		uint16_t oldmss = packet->data[start + 22 + i] << 8 | packet->data[start + 23 + i];
-		uint16_t newmss = via->mtu - start - 20;
+		uint16_t newmss = mtu - start - 20;
 		uint16_t csum = packet->data[start + 16] << 8 | packet->data[start + 17];
 
 		if(oldmss <= newmss)