Re: bug#10021: [PATCH id] Add error-checking on GNU

[Ludovic Courtès]

Hi Jim,

Jim Meyering <jim@meyering.net> skribis:

> Ludovic Courtès wrote:
>
>> Hi Paul,
>>
>> Paul Eggert <eggert@cs.ucla.edu> skribis:
>>
>>> On 11/12/11 13:48, Ludovic Courtès wrote:
>>>> +#ifdef __GNU__
>>>> +      if (euid == -1 && !use_real
>>>> +          && !just_group && !just_group_list && !just_context)
>>>> +        error (EXIT_FAILURE, errno, _("cannot get effective UID"));
>>>> +#endif
>>>
>>> I suggest removing the "#ifdef __GNU__" here and in its other
>>> three uses in the patch, as functions like as geteuid() can fail on
>>> a few non-GNU systems too.  See:
>>>
>>> http://publib.boulder.ibm.com/infocenter/iseries/v5r3/index.jsp?topic=%2Fapis%2Fgeteuid.htm
>>>
>>> For this particular application (the 'id' program) I doubt whether
>>> it's worth our time to configure this stuff at compile-time,
>>> and that it's fine to do a run-time check on all platforms.
>>
>> OTOH, on POSIX-conforming systems (which includes GNU/Linux, so it may
>> be the majority of systems in use), -1 may well be a valid UID/GID.
>>
>> That’s why I was conservative and decided to ifdef that.  This ifdef
>> also served as a documentation that this is a GNU extension to POSIX.
>>
>> Perhaps it’d be safer to keep an ifdef and list all the OSes known to
>> have this behavior?
>
> Thanks for persevering.
> I tested this on a gnu/linux system and found that I could indeed create a
> user with a UID of 2^32-1 (though not directly via adduser -- it imposes
> a maximum of 2^32-2), and that without something like those #ifdefs,
> GNU id would mistakenly fail for such a user:
>
>     id: cannot get effective UID: No such file or directory
>
> However, with the patch below, it does this:
>
>     $ ./id -u
>     4294967295

OK, good to know.  Thank *you* for persevering!

Ludo’.