Subject: Re: [PATCH 4/5] log: handle integer overflow in timestamps

From: Junio C Hamano <[email-masked]>
Date: Mon, 24 Feb 2014 11:50:00 -0800

Jeff King <[email-masked]> writes:

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

Both are good measures to fallback to sanity, but why is that
if/else?  In other words...

> +	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;
> +	}

... don't we want to fix an input having a bogus timestamp and also
a bogus tz recorded in it?

>  	return show_date(date, tz, mode);
>  }
>  
> diff --git a/t/t4212-log-corrupt.sh b/t/t4212-log-corrupt.sh
> index 83de981..ba25a2e 100755
> --- a/t/t4212-log-corrupt.sh
> +++ b/t/t4212-log-corrupt.sh
> @@ -65,4 +65,20 @@ 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