Merge remote-tracking branch 'public/feature9777_024_squashed'

Conflicts:
	src/or/circuitbuild.c

4 files changed, 81 insertions, 10 deletions

diff --git a/changes/feature9777 b/changes/feature9777
new file mode 100644
index 000000000..312b5e034
--- /dev/null
+++ b/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.
diff --git a/src/or/circuitbuild.c b/src/or/circuitbuild.c
index 8e6bb59ef..ffcca4666 100644
--- a/src/or/circuitbuild.c
+++ b/src/or/circuitbuild.c
@@ -57,6 +57,9 @@ static crypt_path_t *onion_next_hop_in_cpath(crypt_path_t *cpath);
 static int onion_extend_cpath(origin_circuit_t *circ);
 static int count_acceptable_nodes(smartlist_t *routers);
 static int onion_append_hop(crypt_path_t **head_ptr, extend_info_t *choice);
+#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
@@ -269,21 +272,74 @@ 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);
-  if (r < 0) {
-    log_info(LD_CIRC,"Generating cpath hop failed.");
-    return -1;
+  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 == 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);
+    }
   }
-  if (r == 0)
-    goto again;
-  return 0; /* if r == 1 */
+  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
@@ -1946,6 +2002,9 @@ 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)
diff --git a/src/or/circuitlist.c b/src/or/circuitlist.c
index c31bc49d0..22224db54 100644
--- a/src/or/circuitlist.c
+++ b/src/or/circuitlist.c
@@ -796,7 +796,7 @@ 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;
@@ -807,6 +807,14 @@ 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)
diff --git a/src/or/circuitlist.h b/src/or/circuitlist.h
index bf3d1b467..1c8cf7de2 100644
--- a/src/or/circuitlist.h
+++ b/src/or/circuitlist.h
@@ -56,6 +56,7 @@ 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);