Don't trust the port in the source address of requests.

At least one client gets it wrong: always send to the client port for
clients, and the server port for relays.

src/dhcp6.c

@@ -75,6 +75,7 @@ void dhcp6_packet(time_t now)
   ssize_t sz; 
   struct ifreq ifr;
   struct iname *tmp;
+  unsigned short port;
 
   msg.msg_control = control_u.control6;
   msg.msg_controllen = sizeof(control_u);
@@ -84,7 +85,7 @@ void dhcp6_packet(time_t now)
   msg.msg_iov =  &daemon->dhcp_packet;
   msg.msg_iovlen = 1;
   
-  if ((sz = recv_dhcp_packet(daemon->dhcp6fd, &msg)) == -1 || sz <= 4)
+  if ((sz = recv_dhcp_packet(daemon->dhcp6fd, &msg)) == -1)
     return;
   
   for (cmptr = CMSG_FIRSTHDR(&msg); cmptr; cmptr = CMSG_NXTHDR(&msg, cmptr))
@@ -134,15 +135,23 @@ void dhcp6_packet(time_t now)
   
   lease_prune(NULL, now); /* lose any expired leases */
 
-  sz = dhcp6_reply(parm.current, if_index, ifr.ifr_name, &parm.fallback, 
-		   sz, IN6_IS_ADDR_MULTICAST(&from.sin6_addr), now);
+  port = dhcp6_reply(parm.current, if_index, ifr.ifr_name, &parm.fallback, 
+		     sz, IN6_IS_ADDR_MULTICAST(&from.sin6_addr), now);
   
   lease_update_file(now);
   lease_update_dns();
   
-  if (sz != 0)
-    while (sendto(daemon->dhcp6fd, daemon->outpacket.iov_base, sz, 0, (struct sockaddr *)&from, sizeof(from)) == -1 &&
+  /* The port in the source address of the original request should
+     be correct, but at least once client sends from the server port,
+     so we explicitly send to the client port to a client, and the
+     server port to a relay. */
+  if (port != 0)
+    {
+      from.sin6_port = htons(port);
+      while (sendto(daemon->dhcp6fd, daemon->outpacket.iov_base, save_counter(0), 
+		    0, (struct sockaddr *)&from, sizeof(from)) == -1 &&
 	   retry_send());
+    }
 }
 
 static int complete_context6(struct in6_addr *local,  int prefix,

src/dnsmasq.h

@@ -1053,8 +1053,8 @@ void make_duid(time_t now);
 
 /* rfc3315.c */
 #ifdef HAVE_DHCP6
-size_t dhcp6_reply(struct dhcp_context *context, int interface, char *iface_name,  
-		   struct in6_addr *fallback, size_t sz, int is_multicast, time_t now);
+unsigned short dhcp6_reply(struct dhcp_context *context, int interface, char *iface_name,  
+			   struct in6_addr *fallback, size_t sz, int is_multicast, time_t now);
 #endif
 
 /* dhcp-common.c */

src/rfc3315.c

@@ -34,12 +34,18 @@ static unsigned int opt6_uint(unsigned char *opt, int offset, int size);
 #define opt6_ptr(opt, i) ((void *)&(((unsigned char *)(opt))[4+(i)]))
 
 
-size_t dhcp6_reply(struct dhcp_context *context, int interface, char *iface_name,
-		   struct in6_addr *fallback, size_t sz, int is_unicast, time_t now)
+unsigned short dhcp6_reply(struct dhcp_context *context, int interface, char *iface_name,
+			   struct in6_addr *fallback, size_t sz, int is_unicast, time_t now)
 {
   struct dhcp_netid *relay_tags = NULL;
   struct dhcp_vendor *vendor;
-
+  int msg_type;
+  
+  if (sz <= 4)
+    return 0;
+  
+  msg_type = *((unsigned char *)daemon->dhcp_packet.iov_base);
+  
   /* Mark these so we only match each at most once, to avoid tangled linked lists */
   for (vendor = daemon->dhcp_vendors; vendor; vendor = vendor->next)
     vendor->netid.next = &vendor->netid;
@@ -47,7 +53,7 @@ size_t dhcp6_reply(struct dhcp_context *context, int interface, char *iface_name
   save_counter(0);
   
   if (dhcp6_maybe_relay(NULL, &relay_tags, context, interface, iface_name, fallback, daemon->dhcp_packet.iov_base, sz, is_unicast, now))
-    return save_counter(0);
+    return msg_type == DHCP6RELAYFORW ? DHCPV6_SERVER_PORT : DHCPV6_CLIENT_PORT;
 
   return 0;
 }
@@ -764,10 +770,15 @@ static int dhcp6_no_relay(int msg_type, struct in6_addr *link_address, struct dh
 		    
 		    end_opt6(o);
 		    	
-		    o = new_opt6(OPTION6_PREFERENCE);
-		    put_opt6_char(0);
-		    end_opt6(o);
-
+		    if (address_assigned) 
+		      {
+			/* If --dhcp-authoritative is set, we can tell client not to wait for
+			   other possible servers */
+			o = new_opt6(OPTION6_PREFERENCE);
+			put_opt6_char(option_bool(OPT_AUTHORITATIVE) ? 255 : 0);
+			end_opt6(o);
+		      }
+		    
 		    break;
 		  }
 	      }