Detect and handle NULL returns from (gm/local)time_r

These functions can return NULL for otherwise-valid values of
time_t.  Notably, the glibc gmtime manpage says it can return NULL
if the year if greater than INT_MAX, and the windows MSDN gmtime
page says it can return NULL for negative time_t values.

Also, our formatting code is not guaranteed to correctly handle
years after 9999 CE.

This patch tries to correct this by detecting NULL values from
gmtime/localtime_r, and trying to clip them to a reasonable end of
the scale.  If they are in the middle of the scale, we call it a
downright error.

Arguably, it's a bug to get out-of-bounds dates like this to begin
with.  But we've had bugs of this kind in the past, and warning when
we see a bug is much kinder than doing a NULL-pointer dereference.

Boboper found this one too.

1 files changed, 0 insertions, 9 deletions

diff --git a/src/common/compat.h b/src/common/compat.h
index 550c08b533..af795ffba9 100644
--- a/src/common/compat.h
+++ b/src/common/compat.h
@@ -321,17 +321,8 @@ struct timeval {
 
 void tor_gettimeofday(struct timeval *timeval);
 
-#ifdef HAVE_LOCALTIME_R
-#define tor_localtime_r localtime_r
-#else
 struct tm *tor_localtime_r(const time_t *timep, struct tm *result);
-#endif
-
-#ifdef HAVE_GMTIME_R
-#define tor_gmtime_r gmtime_r
-#else
 struct tm *tor_gmtime_r(const time_t *timep, struct tm *result);
-#endif
 
 #ifndef timeradd
 /** Replacement for timeradd on platforms that do not have it: sets tvout to