dhcpcd-discuss

Hello all,

I've been having a problem with router solicitations sent out by dhcpcd 
onto a ppp interface being ignored. I did some captures and found that 
dhcpcd was adding a source address option with all zeros which is 
against my understanding of RFC4861. I've patched the router 
solicitation routine to detect an all zero hardware address and omit the 
source address option in that case. Please find attached patch.

As background the ppp interface was set up using pppd version 2.4.7 on 
Gentoo Linux 4.7.10-hardened.

Hope this is useful.

cheers

David

--- dhcpcd-6.11.3/ipv6nd.c	2016-08-15 11:53:49.000000000 +0100
+++ dhcpcd-6.11.3-r2/ipv6nd.c	2017-05-19 14:24:59.639828233 +0100
@@ -237,9 +237,17 @@
 	struct nd_router_solicit *rs;
 	struct nd_opt_hdr *nd;
 
+	size_t ihwp;
 	state = RS_STATE(ifp);
 	free(state->rs);
-	state->rslen = sizeof(*rs) + (size_t)ROUNDUP8(ifp->hwlen + 2);
+	state->rslen = sizeof(*rs);
+	/* check for hwadd full of zeros */
+	for (ihwp=0; ihwp < ifp->hwlen; ihwp++) {
+		if (ifp->hwaddr[ihwp]) {
+			state->rslen += (size_t)ROUNDUP8(ifp->hwlen + 2);
+			break;
+		}
+	}
 	state->rs = calloc(1, state->rslen);
 	if (state->rs == NULL)
 		return -1;
@@ -248,10 +256,13 @@
 	rs->nd_rs_code = 0;
 	rs->nd_rs_cksum = 0;
 	rs->nd_rs_reserved = 0;
-	nd = (struct nd_opt_hdr *)(state->rs + sizeof(*rs));
-	nd->nd_opt_type = ND_OPT_SOURCE_LINKADDR;
-	nd->nd_opt_len = (uint8_t)((ROUNDUP8(ifp->hwlen + 2)) >> 3);
-	memcpy(nd + 1, ifp->hwaddr, ifp->hwlen);
+	/* add source address option if valid hwaddr */
+	if (ihwp < ifp->hwlen) {
+		nd = (struct nd_opt_hdr *)(state->rs + sizeof(*rs));
+		nd->nd_opt_type = ND_OPT_SOURCE_LINKADDR;
+		nd->nd_opt_len = (uint8_t)((ROUNDUP8(ifp->hwlen + 2)) >> 3);
+		memcpy(nd + 1, ifp->hwaddr, ifp->hwlen);
+	}
 	return 0;
 }