Roll back the path_state for circs if we detatch a stream.

An adversary could let the first stream request succeed (ie the resolve), but
then tag and timeout the remainder (via cell dropping), forcing them on new
circuits.

Rolling back the state will cause us to probe such circuits, which should lead
to probe failures in the event of such tagging due to either unrecognized
cells coming in while we wait for the probe, or the cipher state getting out
of sync in the case of dropped cells.

src/or/connection_edge.c

@@ -637,6 +637,16 @@ connection_ap_expire_beginning(void)
     }
     if (circ->purpose == CIRCUIT_PURPOSE_C_REND_JOINED) {
       if (seconds_idle >= options->SocksTimeout) {
+        /* Path bias: We need to probe the circuit to ensure validity.
+         * Roll its state back if it succeeded so that we do so upon close. */
+        if (TO_ORIGIN_CIRCUIT(circ)->path_state == PATH_STATE_USE_SUCCEEDED) {
+          log_info(LD_CIRC,
+                   "Rolling back pathbias use state to 'attempted' for timed "
+                   "out rend circ %d",
+                   TO_ORIGIN_CIRCUIT(circ)->global_identifier);
+          TO_ORIGIN_CIRCUIT(circ)->path_state = PATH_STATE_USE_ATTEMPTED;
+        }
+
         log_fn(severity, LD_REND,
                "Rend stream is %d seconds late. Giving up on address"
                " '%s.onion'.",
@@ -806,6 +816,15 @@ connection_ap_detach_retriable(entry_connection_t *conn,
   control_event_stream_status(conn, STREAM_EVENT_FAILED_RETRIABLE, reason);
   ENTRY_TO_CONN(conn)->timestamp_lastread = time(NULL);
 
+  /* Path bias: We need to probe the circuit to ensure validity.
+   * Roll its state back if it succeeded so that we do so upon close. */
+  if (circ->path_state == PATH_STATE_USE_SUCCEEDED) {
+    log_info(LD_CIRC,
+             "Rolling back pathbias use state to 'attempted' for detached "
+             "circuit %d", circ->global_identifier);
+    circ->path_state = PATH_STATE_USE_ATTEMPTED;
+  }
+
   if (conn->pending_optimistic_data) {
     generic_buffer_set_to_copy(&conn->sending_optimistic_data,
                                conn->pending_optimistic_data);