Re: [PATCH] libuuid: Fix pre-1970 UUID v1 timestamp wraparound

Hey Kiran,

thanks for your patch!


Dec 14, 2025 05:04:23 Kiran Rangoon <[email protected]>:

> gregorian_to_unix now returns -1 and sets errno=EOVERFLOW
> for timestamps before the Unix epoch. uuid_time_v1 and uuid_time_v6
> now use signed arithmetic to prevent unsigned wraparound.
>
> This fixes uuidparse displaying far-future dates for historical UUIDs.

Can you add an example for the issue here?

>
> Signed-off-by: Kiran Rangoon <[email protected]>
> ---
> libuuid/src/uuid_time.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)

Could you also add some tests?

>
> diff --git a/libuuid/src/uuid_time.c b/libuuid/src/uuid_time.c
> index c7516152b..b7fcc892d 100644
> --- a/libuuid/src/uuid_time.c
> +++ b/libuuid/src/uuid_time.c
> @@ -60,15 +60,22 @@
> /* prototype to make compiler happy */
> time_t __uuid_time(const uuid_t uu, struct timeval *ret_tv);
>
> -static uint64_t gregorian_to_unix(uint64_t ts)
> +static int64_t gregorian_to_unix(uint64_t ts)
> {
> -   return ts - ((((uint64_t) 0x01B21DD2) << 32) + 0x13814000);
> +    uint64_t offset = ((((uint64_t) 0x01B21DD2) << 32) + 0x13814000);

In general, IMO we should just use a 64bit constant here instead of the calculation.
(Not your fault obviously)

> +
> +    if (ts < offset) {
> +        errno = EOVERFLOW;
> +        return -1;

Instead of erroring out here, do you think it would be possible to
gracefully handle such negative values through changes in some other places?

> +    }
> +
> +    return ts - offset;
> }
>
> static void uuid_time_v1(const struct uuid *uuid, struct timeval *tv)
> {
>     uint32_t high;
> -   uint64_t clock_reg;
> +   int64_t clock_reg;
>
>     high = uuid->time_mid | ((uuid->time_hi_and_version & 0xFFF) << 16);
>     clock_reg = uuid->time_low | ((uint64_t) high << 32);
> @@ -80,7 +87,7 @@ static void uuid_time_v1(const struct uuid *uuid, struct timeval *tv)
>
> static void uuid_time_v6(const struct uuid *uuid, struct timeval *tv)
> {
> -   uint64_t clock_reg;
> +   int64_t clock_reg;
>
>     clock_reg = uuid->time_low;
>     clock_reg <<= 16;
> --
> 2.47.3