Improve packet source detection.

When no UDP communication has been done yet, tinc establishes a guess
for the UDP address+port of each node. However, when there are multiple nodes
behind a NAT, tinc will guess the exact same address+port combination
for them, because it doesn't know about the NAT mappings yet. So when
receiving a packet, don't trust that guess unless we have confirmed UDP
communication.

This ensures try_harder() is called in such cases. However, this
function was actually very inefficient, trying to verify packets
multiple times for nodes with multiple edges. Only call try_mac() at
most once per node.

diff --git a/src/net_packet.c b/src/net_packet.c
index e9e2172..abd83a9 100644 (file)
--- a/src/net_packet.c
+++ b/src/net_packet.c
@@ -257,7 +257,7 @@ static bool try_mac(node_t *n, const vpn_packet_t *inpkt) {
 #ifdef DISABLE_LEGACY
        return false;
 #else
-       if(!digest_active(n->indigest) || inpkt->len < sizeof(seqno_t) + digest_length(n->indigest))
+       if(!n->status.validkey_in || !digest_active(n->indigest) || inpkt->len < sizeof(seqno_t) + digest_length(n->indigest))
                return false;
 
        return digest_verify(n->indigest, SEQNO(inpkt), inpkt->len - digest_length(n->indigest), DATA(inpkt) + inpkt->len - digest_length(n->indigest));
@@ -1263,33 +1263,52 @@ void broadcast_packet(const node_t *from, vpn_packet_t *packet) {
        }
 }
 
+/* We got a packet from some IP address, but we don't know who sent it.  Try to
+   verify the message authentication code against all active session keys.
+   Since this is actually an expensive operation, we only do a full check once
+   a minute, the rest of the time we only check against nodes for which we know
+   an IP address that matches the one from the packet.  */
+
 static node_t *try_harder(const sockaddr_t *from, const vpn_packet_t *pkt) {
-       node_t *n = NULL;
+       node_t *match = NULL;
        bool hard = false;
        static time_t last_hard_try = 0;
 
-       for splay_each(edge_t, e, edge_weight_tree) {
-               if(!e->to->status.reachable || e->to == myself)
+       for splay_each(node_t, n, node_tree) {
+               if(!n->status.reachable || n == myself)
+                       continue;
+
+               if((n->status.sptps && !n->sptps.instate) || !n->status.validkey_in)
                        continue;
 
-               if(sockaddrcmp_noport(from, &e->address)) {
+               bool soft = false;
+
+               for splay_each(edge_t, e, n->edge_tree) {
+                       if(!e->reverse)
+                               continue;
+                       if(!sockaddrcmp_noport(from, &e->reverse->address)) {
+                               soft = true;
+                               break;
+                       }
+               }
+
+               if(!soft) {
                        if(last_hard_try == now.tv_sec)
                                continue;
                        hard = true;
                }
 
-               if(!try_mac(e->to, pkt))
+               if(!try_mac(n, pkt))
                        continue;
 
-               n = e->to;
+               match = n;
                break;
        }
 
        if(hard)
                last_hard_try = now.tv_sec;
 
-       last_hard_try = now.tv_sec;
-       return n;
+       return match;
 }
 
 void handle_incoming_vpn_data(void *data, int flags) {
@@ -1319,6 +1338,9 @@ void handle_incoming_vpn_data(void *data, int flags) {
 
        node_t *n = lookup_node_udp(&addr);
 
+       if(n && !n->status.udp_confirmed)
+               n = NULL; // Don't believe it if we don't have confirmation yet.
+
        if(!n) {
                // It might be from a 1.1 node, which might have a source ID in the packet.
                pkt.offset = 2 * sizeof(node_id_t);