Recover better when our clock jumps back many hours

like might happen for Tails or Whonix users who start with a very wrong
hardware clock, use Tor to discover a more accurate time, and then
fix their clock.

Resolves part of ticket 8766.

(There are still some timers in various places that aren't addressed yet.)

changes/ticket8766

+  o Minor features:
+    - Recover better when our clock jumps back many hours, like might
+      happen for Tails or Whonix users who start with a very wrong
+      hardware clock, use Tor to discover a more accurate time, and then
+      fix their clock. Resolves part of ticket 8766.
+      [I'd call this a major feature if it actually fixed all of the issues.]
+

src/or/circuitbuild.c

@@ -1049,6 +1049,10 @@ circuit_note_clock_jumped(int seconds_elapsed)
                               "CLOCK_JUMPED");
   circuit_mark_all_unused_circs();
   circuit_mark_all_dirty_circs_as_unusable();
+  if (seconds_elapsed < 0) {
+    /* Restart all the timers in case we jumped a long way into the past. */
+    reset_all_main_loop_timers();
+  }
 }
 
 /** Take the 'extend' <b>cell</b>, pull out addr/port plus the onion

src/or/main.c

@@ -1227,6 +1227,15 @@ typedef struct {
 
 static time_to_t time_to = { 0 };
 
+/** Reset all the time_to's so we'll do all our actions again as if we
+ * just started up.
+ * Useful if our clock just moved back a long time from the future,
+ * so we don't wait until that future arrives again before acting.
+ */
+void reset_all_main_loop_timers(void) {
+  memset(&time_to, 0, sizeof(time_to_t));
+}
+
 /**
  * Update our schedule so that we'll check whether we need to update our
  * descriptor immediately, rather than after up to CHECK_DESCRIPTOR_INTERVAL
@@ -1768,8 +1777,6 @@ second_elapsed_callback(periodic_timer_t *timer, void *arg)
   if (seconds_elapsed < -NUM_JUMPED_SECONDS_BEFORE_WARN ||
       seconds_elapsed >= NUM_JUMPED_SECONDS_BEFORE_WARN) {
     circuit_note_clock_jumped(seconds_elapsed);
-    /* XXX if the time jumps *back* many months, do our events in
-     * run_scheduled_events() recover? I don't think they do. -RD */
   } else if (seconds_elapsed > 0)
     stats_n_seconds_working += seconds_elapsed;
 

src/or/main.h

@@ -52,6 +52,7 @@ void directory_info_has_arrived(time_t now, int from_cache);
 
 void ip_address_changed(int at_interface);
 void dns_servers_relaunch_checks(void);
+void reset_all_main_loop_timers(void);
 void reschedule_descriptor_update_check(void);
 
 MOCK_DECL(long,get_uptime,(void));