X-Git-Url: https://tinc-vpn.org/git/browse?p=tinc;a=blobdiff_plain;f=src%2Froute.c;h=70c5806b28c83343e0406add00f395dd2b56cfe4;hp=27851469555040a0d0b8326410494194262b0d60;hb=0c7e0210d900185d4c1a9ffd969dc2a26d9523a9;hpb=04fc19112da5e7fcefefcf6e490987cdcfb6f620

diff --git a/src/route.c b/src/route.c
index 27851469..70c5806b 100644
--- a/src/route.c
+++ b/src/route.c
@@ -164,7 +164,7 @@ static void clamp_mss(const node_t *source, const node_t *via, vpn_packet_t *pac
 		/* Found it */
 		uint16_t oldmss = DATA(packet)[start + 22 + i] << 8 | DATA(packet)[start + 23 + i];
 		uint16_t newmss = mtu - start - 20;
-		uint16_t csum = DATA(packet)[start + 16] << 8 | DATA(packet)[start + 17];
+		uint32_t csum = DATA(packet)[start + 16] << 8 | DATA(packet)[start + 17];
 
 		if(oldmss <= newmss)
 			break;
@@ -175,11 +175,13 @@ static void clamp_mss(const node_t *source, const node_t *via, vpn_packet_t *pac
 		DATA(packet)[start + 22 + i] = newmss >> 8;
 		DATA(packet)[start + 23 + i] = newmss & 0xff;
 		csum ^= 0xffff;
-		csum -= oldmss;
+		csum += oldmss ^ 0xffff;
 		csum += newmss;
+		csum = (csum & 0xffff) + (csum >> 16);
+		csum += csum >> 16;
 		csum ^= 0xffff;
 		DATA(packet)[start + 16] = csum >> 8;
-		DATA(packet)[start + 17] = csum & 0xff;
+		DATA(packet)[start + 17] = csum;
 		break;
 	}
 }