Bug 2121099

It is also unclear what is the timezone in use here, perhaps that should be filed as another bug? Consider a case of 4 IdM servers where two of them are on different timezone than the others. What is the UTC time when the password will actually expire? Thanks.

The issue is easily reproduced by setting the expiration date using ipa user-mod --password-expiration=DATE.

(In reply to Marko Myllynen from comment #0)
> If the given date is too distant in the future then I would have expected it
> to be rejected. However, this does not look like a 2038 issue as e.g.
> 2089-12-31 23:59:59 does not cause such a warning.

It is a similar issue because the check is evaluating a delta between 2 timestamps, now and the expiration date, and if the delta overflows the buffer we have unpredictable behavior. The delta is also represented as a signed 32 bit integer, meaning the buffer overflow happens if the 2 dates are distant of more than ~68 years, which fits nicely with the behavior described here (2022 + 68 = 2090 is the pivot point).


Relevant code:
--------------
https://github.com/krb5/krb5/blob/70f61d417261ca17efe3d60d180033bea2da60b0/src/lib/krb5/krb/get_in_tkt.c#L1567-L1571
    delta = ts_delta(pw_exp, now);
    if (delta < 3600) {
        snprintf(banner, sizeof(banner),
                 _("Warning: Your password will expire in less than one hour "
                   "on %s"), ts);

and the definition of ts_delta:
https://github.com/krb5/krb5/blob/70f61d417261ca17efe3d60d180033bea2da60b0/src/include/k5-int.h#L2319-L2325
/* Return the delta between two timestamps (a - b) as a signed 32-bit value,
 * without relying on undefined behavior. */
static inline krb5_deltat
ts_delta(krb5_timestamp a, krb5_timestamp b)
{
    return (krb5_deltat)((uint32_t)a - (uint32_t)b);
}


krb5_deltat is defined in https://github.com/krb5/krb5/blob/70f61d417261ca17efe3d60d180033bea2da60b0/src/include/krb5/krb5.hin:

typedef int32_t krb5_int32;
typedef krb5_int32      krb5_deltat;


Moving the issue to krb5 component.

I guess either we switch the type of krb5_deltat from int32_t to int64_t, or we add an extra test to detect integer wrapping before the delta is calculated.

I think the first option is better, but it may have some implications in the rest of the code. We will discuss this issue upstream.

The krb5_timestamp and krb5_deltat types are widely used in the MIT krb5 codebase. Their underlying type is int32_t, but krb5_timestamp is actually used as an unsigned 32-bit integer to support later dates in the future. Changing the underlying type would definitely require a lot of changes, including in the ABI, so I simply opened a PR to cast the delta as uint32_t:

https://github.com/krb5/krb5/pull/1266

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (Moderate: krb5 security, bug fix, and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2023:2570