Re: [PATCH 5/5] date: avoid overflow in approxidate relative-time multiplication
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Oct 14, 2026, 21:44 UTC
- Message-ID
- <xmqq4ieoq7n0.fsf@gitster.g>
- In-Reply-To
- <a4e602b9e726081aaaf73c627548b823a4d35477.1791958171.git.gitgitgadget@gmail.com>
"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com> writes:
Show 5 quoted lines
> On platforms where `time_t` is unsigned (and where the pre-processor > allows us to determine this fact), reject counts that are too large and > report a parse error. Narrowing them first could otherwise produce > negative or truncated values that become bogus offsets. Leave signed > `time_t` count parsing unchanged.
Does this mean that "git log -p" in a project that were made on reasonably sized platforms and then cloned to my box may cause the history traversal to stop with an error when a commit has author or committer timestamp that would not fit the time_t on my box?
It would have been horrible regression than showing the entire history with patches with bogus timestamp if it were the case.
But I do not think that is what happens. approxidate_careful() is only used to parse input by local user (e.g., "git commit --date="...", "git log @{...}"), and the changes in this patch would not affect behaviours of other uses of timestamps, so we are safe.
Show 57 quoted lines
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
> date.c | 26 ++++++++++++++++++++++++--
> 1 file changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/date.c b/date.c
> index 014065b419..0d65804d2f 100644
> --- a/date.c
> +++ b/date.c
> @@ -1298,7 +1298,18 @@ static const char *approxidate_alpha(const char *date, struct tm *tm, struct tm
> while (tl->type) {
> size_t len = strlen(tl->type);
> if (match_string(date, tl->type) >= len-1) {
> - update_tm(tm, now, tl->length * *num);
> + time_t length = tl->length, num_t = *num;
> + time_t seconds;
> +#ifndef is_unsigned_type
> + seconds = length * num_t;
> +#else
> + time_t max_val = is_unsigned_type(length)
> + ? maximum_unsigned_value_of_type(length)
> + : maximum_signed_value_of_type(length);
> + seconds = mult_overflows(length, num_t)
> + ? max_val : length * num_t;
> +#endif
> + update_tm(tm, now, seconds);
> *num = 0;
> *touched = 1;
> return end;
> @@ -1368,8 +1379,15 @@ static const char *approxidate_digit(const char *date, struct tm *tm, int *num,
> }
>
> /* Accept zero-padding only for small numbers ("Dec 02", never "Dec 0002") */
> - if (date[0] != '0' || end - date <= 2)
> + if (date[0] != '0' || end - date <= 2) {
> +#ifdef is_unsigned_type
> + if (is_unsigned_type((time_t)0) &&
> + (number > INT_MAX ||
> + number > maximum_unsigned_value_of_type((time_t)0)))
> + return NULL;
> +#endif
> *num = number;
> + }
> return end;
> }
>
> @@ -1398,6 +1416,10 @@ static timestamp_t approxidate_str(const char *date,
> if (isdigit(c)) {
> pending_number(&tm, &number);
> date = approxidate_digit(date-1, &tm, &number, time_sec);
> + if (!date) {
> + *error_ret = 1;
> + return 0;
> + }
> touched = 1;
> continue;
> }