fix: DHCPv6 does not respect prefix assigned to interface (<=/64)

fixes openwrt#199

Signed-off-by: Matthias Riegler <[email protected]>

src/dhcpv6-ia.c

@@ -47,6 +47,8 @@ static void handle_addrlist_change(struct netevent_handler_info *info);
 static void start_reconf(struct dhcp_assignment *a);
 static void stop_reconf(struct dhcp_assignment *a);
 static void valid_until_cb(struct uloop_timeout *event);
+static uint32_t mask_high_for_hostid(uint8_t dhcpv6_hostid_len);
+static uint32_t mask_low_for_hostid(uint8_t dhcpv6_hostid_len);
 
 static struct netevent_handler dhcpv6_netevent_handler = { .cb = dhcpv6_netevent_cb, };
 static struct uloop_timeout valid_until_timeout = {.cb = valid_until_cb};
@@ -249,8 +251,16 @@ void dhcpv6_ia_enum_addrs(struct interface *iface, struct dhcp_assignment *c,
 			if (!ADDR_ENTRY_VALID_IA_ADDR(iface, i, m, addrs))
 				continue;
 
-			addr.s6_addr32[2] = htonl(c->assigned_host_id >> 32);
-			addr.s6_addr32[3] = htonl(c->assigned_host_id & UINT32_MAX);
+			uint32_t mask_low = mask_low_for_hostid(iface->dhcpv6_hostid_len);
+			uint32_t mask_high = mask_high_for_hostid(iface->dhcpv6_hostid_len);
+			addr.s6_addr32[2] = htonl((
+					(c->assigned_host_id >> 32) & mask_high)
+					& (~mask_high & ntohl(addrs[i].addr.in6.s6_addr32[2])
+				));
+			addr.s6_addr32[3] = htonl((
+					(c->assigned_host_id & UINT32_MAX) & mask_low)
+					& (~mask_low & ntohl(addrs[i].addr.in6.s6_addr32[3])
+				));
 		} else {
 			if (!valid_prefix_length(c, addrs[i].prefix))
 				continue;
@@ -718,6 +728,23 @@ static bool is_reserved_ipv6_iid(uint64_t iid)
 	return false;
 }
 
+static uint32_t mask_low_for_hostid(uint8_t dhcpv6_hostid_len) {
+	if (dhcpv6_hostid_len >= 32)
+		return UINT32_MAX;
+
+	return (1 << dhcpv6_hostid_len) - 1;
+}
+
+static uint32_t mask_high_for_hostid(uint8_t dhcpv6_hostid_len) {
+	if (dhcpv6_hostid_len >= 64)
+		return UINT32_MAX;
+
+  if (dhcpv6_hostid_len >= 32)
+    return (1 << (dhcpv6_hostid_len - 32)) - 1;
+
+	return return 0;
+}
+
 static bool assign_na(struct interface *iface, struct dhcp_assignment *a)
 {
 	struct dhcp_assignment *c;
@@ -744,27 +771,22 @@ static bool assign_na(struct interface *iface, struct dhcp_assignment *a)
 		uint64_t try;
 
 		if (iface->dhcpv6_hostid_len > 32) {
-			uint32_t mask_high;
-
-			if (iface->dhcpv6_hostid_len >= 64)
-				mask_high = UINT32_MAX;
-			else
-				mask_high = (1 << (iface->dhcpv6_hostid_len - 32)) - 1;
+			uint32_t mask_high = mask_high_for_hostid(iface->dhcpv6_hostid_len);
 
 			do {
 				try = (uint32_t)random();
 				try |= (uint64_t)((uint32_t)random() & mask_high) << 32;
 			} while (try < 0x100);
-		} else {
-			uint32_t mask_low;
 
-			if (iface->dhcpv6_hostid_len == 32)
-				mask_low = UINT32_MAX;
-			else
-				mask_low = (1 << iface->dhcpv6_hostid_len) - 1;
+		} else {
+			uint32_t mask_low = mask_low_for_hostid(iface->dhcpv6_hostid_len);
 			do try = ((uint32_t)random()) & mask_low; while (try < 0x100);
 		}
 
+    // If prefix is < 64 bits, we need to shift the IID to the left
+    if (iface->addr6_len < 64)
+      try <<= (64 - iface->addr6_len);
+
 		if (is_reserved_ipv6_iid(try))
 			continue;