[tor-commits] [tor/master] Warn when the system clock is set back in time

[nickm at torproject.org]

commit cd279ca7f59cba46a319854c9e7f65fbb6f0a0af
Author: teor (Tim Wilson-Brown) <teor2345 at gmail.com>
Date:   Wed Sep 30 13:33:56 2015 +0200

    Warn when the system clock is set back in time
    
    Warn when the state file was last written in the future.
    Tor doesn't know that consensuses have expired if the clock is in the past.
    
    Patch by "teor". Implements ticket #17188.
---
 changes/warn-when-time-goes-backwards |    5 +++++
 src/or/statefile.c                    |   12 ++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/changes/warn-when-time-goes-backwards b/changes/warn-when-time-goes-backwards
new file mode 100644
index 0000000..d7e584d
--- /dev/null
+++ b/changes/warn-when-time-goes-backwards
@@ -0,0 +1,5 @@
+  o Minor features (security, clock):
+    - Warn when the system clock is set back in time (when the
+      state file was last written in the future). Tor doesn't know
+      that consensuses have expired if the clock is in the past.
+      Patch by "teor". Implements ticket #17188.
diff --git a/src/or/statefile.c b/src/or/statefile.c
index dd1894b..a904c41 100644
--- a/src/or/statefile.c
+++ b/src/or/statefile.c
@@ -372,6 +372,18 @@ or_state_load(void)
     new_state = or_state_new();
   } else if (contents) {
     log_info(LD_GENERAL, "Loaded state from \"%s\"", fname);
+    /* Warn the user if their clock has been set backwards,
+     * they could be tricked into using old consensuses */
+    if (new_state->LastWritten > time(NULL)) {
+      char last_written_str[ISO_TIME_LEN+1];
+      char now_str[ISO_TIME_LEN+1];
+      format_iso_time(last_written_str, new_state->LastWritten),
+      format_iso_time(now_str, time(NULL));
+      log_warn(LD_GENERAL, "Your system clock has been set back in time. "
+               "Tor needs an accurate clock to know when the consensus "
+               "expires. Clock time is %s, state file time is %s.",
+               now_str, last_written_str);
+    }
   } else {
     log_info(LD_GENERAL, "Initialized state");
   }