Be more willing to use an unsuitable circuit for exit.

Specifically, there are two cases: a) are we willing to start a new
circuit at a node not in your ExitNodes config option, and b) are we
willing to make use of a circuit that's already established but has an
unsuitable exit.

Now we discard all your circuits when you set ExitNodes, so the only
way you could end up with an exit circuit that ends at an unsuitable
place is if we explicitly ran out of exit nodes, StrictNodes was 0,
and we built this circuit to solve a stream that needs solving.

Fixes bug in dc322931, which would ignore the just-built circuit because
it has an unsuitable exit.

1 files changed, 20 insertions, 1 deletions

diff --git a/src/or/connection_edge.c b/src/or/connection_edge.c
index b1e952d465..47230da2e0 100644
--- a/src/or/connection_edge.c
+++ b/src/or/connection_edge.c
@@ -2840,9 +2840,13 @@ connection_edge_is_rendezvous_stream(edge_connection_t *conn)
  * to exit from it, or 0 if it probably will not allow it.
  * (We might be uncertain if conn's destination address has not yet been
  * resolved.)
+ *
+ * If <b>excluded_means_no</b> is 1 and Exclude*Nodes is set and excludes
+ * this relay, return 0.
  */
 int
-connection_ap_can_use_exit(edge_connection_t *conn, routerinfo_t *exit)
+connection_ap_can_use_exit(edge_connection_t *conn, routerinfo_t *exit,
+                           int excluded_means_no)
 {
   tor_assert(conn);
   tor_assert(conn->_base.type == CONN_TYPE_AP);
@@ -2889,6 +2893,21 @@ connection_ap_can_use_exit(edge_connection_t *conn, routerinfo_t *exit)
     if (!conn->chosen_exit_name && policy_is_reject_star(exit->exit_policy))
       return 0;
   }
+  if (options->_ExcludeExitNodesUnion &&
+      (options->StrictNodes || excluded_means_no) &&
+      routerset_contains_router(options->_ExcludeExitNodesUnion, exit)) {
+    /* If we are trying to avoid this node as exit, and we have StrictNodes
+     * set, then this is not a suitable exit. Refuse it.
+     *
+     * If we don't have StrictNodes set, then this function gets called in
+     * two contexts. First, we've got a circuit open and we want to know
+     * whether we can use it. In that case, we somehow built this circuit
+     * despite having the last hop in ExcludeExitNodes, so we should be
+     * willing to use it. Second, we are evaluating whether this is an
+     * acceptable exit for a new circuit. In that case, skip it. */
+    return 0;
+  }
+
   return 1;
 }