date: check date overflow against time_t

When we check whether a timestamp has overflowed, we check
only against ULONG_MAX, meaning that strtoul has overflowed.
However, we also feed these timestamps to system functions
like gmtime, which expect a time_t. On many systems, time_t
is actually smaller than "unsigned long" (e.g., because it
is signed), and we would overflow when using these
functions.  We don't know the actual size or signedness of
time_t, but we can easily check for truncation with a simple
assignment.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/cache.h b/cache.h
index bb71bf8..9a2c377 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -909,6 +909,7 @@ void datestamp(char *buf, int bufsize);
 unsigned long approxidate_careful(const char *, int *);
 unsigned long approxidate_relative(const char *date, const struct timeval *now);
 enum date_mode parse_date_format(const char *format);
+int date_overflows(unsigned long date);
 
 #define IDENT_STRICT          1
 #define IDENT_NO_DATE         2

diff --git a/date.c b/date.c
index 57331ed..2dae471 100644 (file)
--- a/date.c
+++ b/date.c
@@ -1085,3 +1085,20 @@ unsigned long approxidate_careful(const char *date, int *error_ret)
        gettimeofday(&tv, NULL);
        return approxidate_str(date, &tv, error_ret);
 }
+
+int date_overflows(unsigned long t)
+{
+       time_t sys;
+
+       /* If we overflowed our unsigned long, that's bad... */
+       if (t == ULONG_MAX)
+               return 1;
+
+       /*
+        * ...but we also are going to feed the result to system
+        * functions that expect time_t, which is often "signed long".
+        * Make sure that we fit into time_t, as well.
+        */
+       sys = t;
+       return t != sys || (t < 1) != (sys < 1);
+}

diff --git a/fsck.c b/fsck.c
index 760e072..64bf279 100644 (file)
--- a/fsck.c
+++ b/fsck.c
@@ -266,7 +266,7 @@ static int fsck_ident(char **ident, struct object *obj, fsck_error error_func)
        (*ident)++;
        if (**ident == '0' && (*ident)[1] != ' ')
                return error_func(obj, FSCK_ERROR, "invalid author/committer line - zero-padded date");
-       if (strtoul(*ident, &end, 10) == ULONG_MAX)
+       if (date_overflows(strtoul(*ident, &end, 10)))
                return error_func(obj, FSCK_ERROR, "invalid author/committer line - date causes integer overflow");
        if (end == *ident || *end != ' ')
                return error_func(obj, FSCK_ERROR, "invalid author/committer line - bad date");