X-Git-Url: https://tinc-vpn.org/git/browse?p=tinc;a=blobdiff_plain;f=src%2Froute.c;h=829773180c87ab6d549e26b3d3e1577ed1c2499d;hp=5117e92f4f41ca6dbf8554e086fe8de4ebfd2a64;hb=2a538ed34332b3392f866d56accd9efecc9467ed;hpb=e4812ba9cc4262ec921944f02639ce55781d7497

diff --git a/src/route.c b/src/route.c
index 5117e92f..82977318 100644
--- a/src/route.c
+++ b/src/route.c
@@ -93,6 +93,53 @@ static bool checklength(node_t *source, vpn_packet_t *packet, length_t length) {
 		return true;
 }
 
+void clamp_mss(node_t *source, node_t *via, vpn_packet_t *packet) {
+	int i;
+	int len = ((packet->data[46] >> 4) - 5) * 4;
+
+	for(int i = 0; i < len;) {
+		if(packet->data[54 + i] == 0)
+			break;
+
+		if(packet->data[54 + i] == 1) {
+			i++;
+			continue;
+		}
+
+		if(i > len - 2 || i > len - packet->data[55 + i])
+			break;
+
+		if(packet->data[54 + i] != 2) {
+			if(packet->data[55 + i] < 2)
+				break;
+			i += packet->data[55 + i];
+			continue;
+		}
+
+		if(packet->data[55] != 4)
+			break;
+
+		uint16_t oldmss = packet->data[56 + i] << 8 | packet->data[57 + i];
+		uint16_t newmss = via->mtu - 54;
+		uint16_t csum = packet->data[50] << 8 | packet->data[51];
+
+		if(oldmss <= newmss)
+			break;
+		
+		ifdebug(TRAFFIC) logger(LOG_INFO, "Clamping MSS of packet from %s to %s to %d", source->name, via->name, newmss);
+
+		packet->data[56 + i] = newmss >> 8;
+		packet->data[57 + i] = newmss & 0xff;
+		csum ^= 0xffff;
+		csum -= oldmss;
+		csum += newmss;
+		csum ^= 0xffff;
+		packet->data[50] = csum >> 8;
+		packet->data[51] = csum & 0xff;
+		break;
+	}
+}
+
 static void swap_mac_addresses(vpn_packet_t *packet) {
 	mac_t tmp;
 	memcpy(&tmp, &packet->data[0], sizeof tmp);
@@ -328,6 +375,9 @@ static void route_ipv4_unicast(node_t *source, vpn_packet_t *packet) {
 		return;
 	}
 
+	if(via && via != myself && packet->data[23] == 6 && packet->len >= 58 && (packet->data[46] >> 4) > 5)
+		clamp_mss(source, via, packet);
+ 
 	send_packet(subnet->owner, packet);
 }
 
@@ -740,6 +790,9 @@ static void route_mac(node_t *source, vpn_packet_t *packet) {
 		}
 	}
 
+	if(via && via != myself && (packet->data[12] << 8 | packet->data[13]) == ETH_P_IP && packet->len >= 58 && packet->data[23] == 6 && (packet->data[46] >> 4) > 5)
+		clamp_mss(source, via, packet);
+ 
 	send_packet(subnet->owner, packet);
 }