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devip: don't send and ignore MLD messages for invalid multicast groups

RFC2710 states that MLD messages should never
be sent for scope 0 and 1 mcast addresses
as well as FF02::1.

--- a/sys/src/9/ip/igmp.c

+++ b/sys/src/9/ip/igmp.c

@@ -128,6 +128,25 @@

 	ipoput4(f, bp, nil, 1, DFLTTOS, nil);	/* TTL of 1 */

 }

+static int

+mldvalidgroup(uchar *group)

+{

+	if(ipismulticast(group) != V6)

+		return 0;

+

+	/*

+	 * MLD messages are never sent for multicast addresses

+	 * whos scope is 0 (reserved) or 1 (node-local).

+	 * MLD messages ARE sent for multicast addresses whose

+	 * scope is 2 (link-local) ... except all-nodes address.

+	 */

+	if((group[1] & 0xF) < Link_local_scop

+	|| ipcmp(group, v6allnodesL) == 0)

+		return 0;

+

+	return 1;

+}

+

 static void

 mldsendreport(Fs *f, uchar *src, uchar *dst, uchar *group, int done)

 {

@@ -137,6 +156,9 @@

 	if(!islinklocal(src))

 		return;

+	if(!mldvalidgroup(group))

+		return;

+

 	bp = allocb(sizeof(mldhbhopt)+MLDPKTSZ);

 	bp->wp += sizeof(mldhbhopt)+MLDPKTSZ;

 	bp->rp += sizeof(mldhbhopt);

@@ -358,8 +380,7 @@

 	hnputs(p->ploadlen, MLDPKTSZ-IP6HDR);

 	if(ptclcsum(bp, 0, MLDPKTSZ))

 		goto error;

-

-	if(ipcmp(p->group, IPnoaddr) != 0 && ipismulticast(p->group) != V6)

+	if(ipcmp(p->group, IPnoaddr) != 0 && !mldvalidgroup(p->group))

 		goto error;

 	switch(p->type){

-- 

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