Merge remote-tracking branch 'public/feature9777_024_squashed' into maint-0.2.4

changes/feature9777

@@ -0,0 +1,3 @@
+  o Minor features:
+    - Avoid using circuit paths if no node in the path supports the ntor
+      circuit extension handshake. Implements ticket 9777.

src/or/circuitbuild.c

@@ -72,6 +72,9 @@ static void pathbias_count_use_failed(origin_circuit_t *circ);
 static void pathbias_measure_use_rate(entry_guard_t *guard);
 static void pathbias_measure_close_rate(entry_guard_t *guard);
 static void pathbias_scale_use_rates(entry_guard_t *guard);
+#ifdef CURVE25519_ENABLED
+static int circuits_can_use_ntor(void);
+#endif
 
 /** This function tries to get a channel to the specified endpoint,
  * and then calls command_setup_channel() to give it the right
@@ -284,21 +287,74 @@ circuit_rep_hist_note_result(origin_circuit_t *circ)
   } while (hop!=circ->cpath);
 }
 
+#ifdef CURVE25519_ENABLED
+/** Return 1 iff at least one node in circ's cpath supports ntor. */
+static int
+circuit_cpath_supports_ntor(const origin_circuit_t *circ)
+{
+  crypt_path_t *head = circ->cpath, *cpath = circ->cpath;
+
+  cpath = head;
+  do {
+    if (cpath->extend_info &&
+        !tor_mem_is_zero(
+            (const char*)cpath->extend_info->curve25519_onion_key.public_key,
+            CURVE25519_PUBKEY_LEN))
+      return 1;
+
+    cpath = cpath->next;
+  } while (cpath != head);
+
+  return 0;
+}
+#else
+#define circuit_cpath_supports_ntor(circ) 0
+#endif
+
 /** Pick all the entries in our cpath. Stop and return 0 when we're
  * happy, or return -1 if an error occurs. */
 static int
 onion_populate_cpath(origin_circuit_t *circ)
 {
-  int r;
- again:
-  r = onion_extend_cpath(circ);
+  int n_tries = 0;
+#ifdef CURVE25519_ENABLED
+  const int using_ntor = circuits_can_use_ntor();
+#else
+  const int using_ntor = 0;
+#endif
+
+#define MAX_POPULATE_ATTEMPTS 32
+
+  while (1) {
+    int r = onion_extend_cpath(circ);
     if (r < 0) {
       log_info(LD_CIRC,"Generating cpath hop failed.");
       return -1;
     }
-  if (r == 0)
-    goto again;
-  return 0; /* if r == 1 */
+    if (r == 1) {
+      /* This circuit doesn't need/shouldn't be forced to have an ntor hop */
+      if (circ->build_state->desired_path_len <= 1 || ! using_ntor)
+        return 0;
+
+      /* This circuit has an ntor hop. great! */
+      if (circuit_cpath_supports_ntor(circ))
+        return 0;
+
+      /* No node in the circuit supports ntor.  Have we already tried too many
+       * times? */
+      if (++n_tries >= MAX_POPULATE_ATTEMPTS)
+        break;
+
+      /* Clear the path and retry */
+      circuit_clear_cpath(circ);
+    }
+  }
+  log_warn(LD_CIRC, "I tried for %d times, but I couldn't build a %d-hop "
+           "circuit with at least one node that supports ntor.",
+           MAX_POPULATE_ATTEMPTS,
+           circ->build_state->desired_path_len);
+
+  return -1;
 }
 
 /** Create and return a new origin circuit. Initialize its purpose and
@@ -3475,6 +3531,9 @@ onion_next_hop_in_cpath(crypt_path_t *cpath)
 
 /** Choose a suitable next hop in the cpath <b>head_ptr</b>,
  * based on <b>state</b>. Append the hop info to head_ptr.
+ *
+ * Return 1 if the path is complete, 0 if we successfully added a hop,
+ * and -1 on error.
  */
 static int
 onion_extend_cpath(origin_circuit_t *circ)

src/or/circuitlist.c

@@ -709,7 +709,7 @@ circuit_free_cpath(crypt_path_t *cpath)
   if (!cpath)
     return;
 
-  /* it's a doubly linked list, so we have to notice when we've
+  /* it's a circular list, so we have to notice when we've
    * gone through it once. */
   while (cpath->next && cpath->next != head) {
     victim = cpath;
@@ -720,6 +720,14 @@ circuit_free_cpath(crypt_path_t *cpath)
   circuit_free_cpath_node(cpath);
 }
 
+/** Remove all the items in the cpath on <b>circ</b>.*/
+void
+circuit_clear_cpath(origin_circuit_t *circ)
+{
+  circuit_free_cpath(circ->cpath);
+  circ->cpath = NULL;
+}
+
 /** Release all storage held by circuits. */
 void
 circuit_free_all(void)

src/or/circuitlist.h

@@ -50,6 +50,7 @@ void circuit_mark_all_dirty_circs_as_unusable(void);
 void circuit_mark_for_close_(circuit_t *circ, int reason,
                              int line, const char *file);
 int circuit_get_cpath_len(origin_circuit_t *circ);
+void circuit_clear_cpath(origin_circuit_t *circ);
 crypt_path_t *circuit_get_cpath_hop(origin_circuit_t *circ, int hopnum);
 void circuit_get_all_pending_on_channel(smartlist_t *out,
                                         channel_t *chan);