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

From: Ludovic Courtès
Subject: bug#10021: [PATCH id] Add error-checking on GNU
Date: Mon, 14 Nov 2011 14:33:56 +0100
User-agent: Gnus/5.110018 (No Gnus v0.18) Emacs/24.0.90 (gnu/linux)

Hi Jim,

Jim Meyering <address@hidden> skribis:

> Ludovic Courtès wrote:
>> Hi Paul,
>> Paul Eggert <address@hidden> 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!


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