Add client code to detect attempts to connect to 127.0.0.1 etc

We detect and reject said attempts if there is no chosen exit node or
circuit: connecting to a private addr via a randomly chosen exit node
will usually fail (if all exits reject private addresses), is always
ill-defined (you're not asking for any particular host or service),
and usually an error (you've configured all requests to go over Tor
when you really wanted to configure all _remote_ requests to go over
Tor).

This can also help detect forwarding loop requests.

Found as part of bug2279.

1 files changed, 21 insertions, 0 deletions

diff --git a/src/or/connection_edge.c b/src/or/connection_edge.c
index 73ed9fb5c3..a85943f69f 100644
--- a/src/or/connection_edge.c
+++ b/src/or/connection_edge.c
@@ -1659,6 +1659,27 @@ connection_ap_handshake_rewrite_and_attach(edge_connection_t *conn,
         connection_mark_unattached_ap(conn, END_STREAM_REASON_TORPROTOCOL);
         return -1;
       }
+      if (!conn->use_begindir && !conn->chosen_exit_name && !circ) {
+        tor_addr_t addr;
+        if (tor_addr_from_str(&addr, socks->address) >= 0 &&
+            tor_addr_is_internal(&addr, 0)) {
+          /* If this is an explicit private address with no chosen exit node,
+           * then we really don't want to try to connect to it.  That's
+           * probably an error. */
+          if (conn->is_transparent_ap) {
+            log_warn(LD_NET,
+                     "Rejecting request for anonymous connection to private "
+                     "address %s on a TransPort or NatdPort.  Possible loop "
+                     "in your NAT rules?", safe_str_client(socks->address));
+          } else {
+            log_warn(LD_NET,
+                     "Rejecting SOCKS request for anonymous connection to "
+                     "private address %s", safe_str_client(socks->address));
+          }
+          connection_mark_unattached_ap(conn, END_STREAM_REASON_PRIVATE_ADDR);
+          return -1;
+        }
+      }
 
       if (!conn->use_begindir && !conn->chosen_exit_name && !circ) {
         /* see if we can find a suitable enclave exit */