2012/8/21 Gordon Ross <[email protected]>:
> On Fri, Aug 17, 2012 at 5:44 AM, Frank Lahm <[email protected]> wrote:
>> 2012/8/17 James Relph <[email protected]>:
> [...]
>>>
>>> Thanks very much for that confirmation, really doesn't seem obvious in a 
>>> lot of the documentation!  I don't have a system handy to test today (will 
>>> do over the weekend) but I'll try and get a better idea of how that works 
>>> over the weekend (in particular after a reboot, what UID/GID will a 
>>> file/folder show (ie. with ls) until the same user logs in again and the 
>>> new ephemeral mapping is created?).
>>
>> ephemeral ids break setuid/seteuid because they are not static on a
>> _running_ system. They may change anytime. Thus any POSIX compliant
>> application relying on these functions for privileges can not use
>> them.
>
> Really?

Yes. By using `getent group AD-GROUP` an existing user uid mapping
(which a process was using with seteuid at that time) changed which
badly affected that process.

> Where is your evidence?

I don't care proving this. Imo the lesson to learn is that as there's
no written guarantee of id mapping stability I will not bet my horse
on this.

> I don't think I've ever seen one
> change except after a reboot.

I bet you (and nobody else) has ever done serious testing using the
mapped ids in UNIX processes with POSIX calls like seteuid.

-f

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