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log: handle integer overflow in timestamps

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If an ident line has a ridiculous date value like (2^64)+1,
we currently just pass ULONG_MAX along to the date code,
which can produce nonsensical dates.

On systems with a signed long time_t (e.g., 64-bit glibc
systems), this actually doesn't end up too bad. The
ULONG_MAX is converted to -1, we apply the timezone field to
that, and the result ends up somewhere between Dec 31, 1969
and Jan 1, 1970.

However, there is still a few good reasons to detect the
overflow explicitly:

  1. On systems where "unsigned long" is smaller than
     time_t, we get a nonsensical date in the future.

  2. Even where it would produce "Dec 31, 1969", it's easier
     to recognize "midnight Jan 1" as a consistent sentinel
     value for "we could not parse this".

  3.  Values which do not overflow strtoul but do overflow a
      signed time_t produce nonsensical values in the past.
      For example, on a 64-bit system with a signed long
      time_t, a timestamp of 18446744073000000000 produces a
      date in 1947.

We also recognize overflow in the timezone field, which
could produce nonsensical results. In this case we show the
parsed date, but in UTC.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King
2014-02-24 02:46:37 -05:00
committed by Junio C Hamano
parent 7ca36d9398
commit 1dca155fe3
2 changed files with 24 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
pretty.c
View File

@ -401,8 +401,14 @@ static const char *show_ident_date(const struct ident_split *ident,
if (ident->date_begin && ident->date_end)
date = strtoul(ident->date_begin, NULL, 10);
if (ident->tz_begin && ident->tz_end)
tz = strtol(ident->tz_begin, NULL, 10);
if (date_overflows(date))
date = 0;
else {
if (ident->tz_begin && ident->tz_end)
tz = strtol(ident->tz_begin, NULL, 10);
if (tz == LONG_MAX || tz == LONG_MIN)
tz = 0;
}
return show_date(date, tz, mode);
}

16
t/t4212-log-corrupt.sh
View File

@ -60,4 +60,20 @@ test_expect_success 'unparsable dates produce sentinel value (%ad)' '
test_cmp expect actual
'
# date is 2^64 + 1
test_expect_success 'date parser recognizes integer overflow' '
commit=$(munge_author_date HEAD 18446744073709551617) &&
echo "Thu Jan 1 00:00:00 1970 +0000" >expect &&
git log -1 --format=%ad $commit >actual &&
test_cmp expect actual
'
# date is 2^64 - 2
test_expect_success 'date parser recognizes time_t overflow' '
commit=$(munge_author_date HEAD 18446744073709551614) &&
echo "Thu Jan 1 00:00:00 1970 +0000" >expect &&
git log -1 --format=%ad $commit >actual &&
test_cmp expect actual
'
test_done