[tor-bugs] #16980 [Tor]: Implicit time range assumption breaks Tor in Shadow

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#16980: Implicit time range assumption breaks Tor in Shadow
----------------------------+--------------------------------
     Reporter:  robgjansen  |      Owner:
         Type:  defect      |     Status:  new
     Priority:  normal      |  Milestone:
    Component:  Tor         |    Version:  Tor: 0.2.7.2-alpha
   Resolution:              |   Keywords:
Actual Points:              |  Parent ID:
       Points:              |
----------------------------+--------------------------------

Comment (by nickm):

 We do indeed assume that time_t is signed; see this section in
 configure.ac:

 {{{
 AX_CHECK_SIGN([time_t],
        [ AC_DEFINE(TIME_T_IS_SIGNED, 1, [Define if time_t is signed]) ],
        [ : ], [
 #ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>
 #endif
 #ifdef HAVE_SYS_TIME_H
 #include <sys/time.h>
 #endif
 #ifdef HAVE_TIME_H
 #include <time.h>
 #endif
 ])

 if test "$ax_cv_decl_time_t_signed" = no; then
   AC_MSG_WARN([You have an unsigned time_t; some things will probably
 break. Please tell the Tor developers about your interesting platform.])
 fi
 }}}

 We can safely turn that WARN into an ERR I think.

 But refactoring crypto_rand_time_range() that way doesn't seem so safe to
 me; it doesn't actually do the right thing with negative inputs. What
 about something more like:
 {{{
    tor_assert(min < max);
    return min + (time_t)crypto_rand_uint64(max-min);
 }}}


 (Also, I am far from convinced that this is the last thing that will break
 if time() starts out at 0 -- I never really considered what would happen
 if you tried to run Tor in 1970 before, and there may well be other things
 that break.  I wonder if, as a kludge, you wouldn't be better off starting
 Shadow's time() at 1971 or 1980 or 2000 or something -- I bet there are
 other programs out there that make similar assumptions not needing to run
 at times before they were written.)

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16980#comment:3>
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