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6in4: ingress filter multicast and link-local, but allow relay traffic

--- a/sys/src/cmd/ip/6in4.c

+++ b/sys/src/cmd/ip/6in4.c

@@ -381,7 +381,6 @@

 {

 	int n, m;

 	char buf[64*1024];

-	uchar a[IPaddrlen];

 	Ip6hdr *op;

 	Iphdr *ip;

@@ -419,14 +418,10 @@

 		op = (Ip6hdr*)(buf + IPaddrlen + STFHDR);

 		n -= STFHDR;

-		/*

-		 * don't relay: just accept packets for local host/subnet

-		 * (this blocks link-local and multicast addresses as well)

-		 */

-		maskip(op->dst, localmask, a);

-		if (!equivip6(a, localnet)) {

-			syslog(0, "6in4", "ingress filtered %I -> %I; "

-				"dst not on local net", op->src, op->dst);

+		/* filter multicast and link-local, but allow relay traffic */

+		if (badipv6(op->src) || badipv6(op->dst)) {

+			syslog(0, "6in4", "ingress filtered %I -> %I; bad src/dst",

+				op->src, op->dst);

 			continue;

 		}

 		if (debug > 1)