[Rpm-maint] Verify when two usernames use the same UID

Panu Matilainen pmatilai at laiskiainen.org
Fri Jun 6 08:19:40 UTC 2014

On 06/06/2014 10:42 AM, Panu Matilainen wrote:
> On 06/05/2014 07:15 PM, Archie Cobbs wrote:
>> I'd like a second opinion from this list on http://rpm.org/ticket/872
>> which
>> was just closed as invalid. I don't agree (and I also don't understand
>> the
>> closing comment).
>> The issue is that rpm --verify fails 50% of the time when one of the
>> RPM's
>> files is owned by a user 'aaa' who happens to share the same UID as
>> another
>> user 'bbb', even though the RPM is completely unchanged from its original
>> installation. This just seems wrong.
>> In UNIX the username -> UID relationship is a many-to-one mapping. Or
>> have
>> I been mistaken all these years?
>> Simply put, rpm --verify is incorrectly assuming that this
>> relationship is
>> one-to-one.
>> Either rpm has a bug or I'm missing something very basic...
> Rpm has many bugs but I dont think this is one of them.
> Pretty much the whole POSIX API assumes username <-> uid relation being
> one-to-one, getpwnam() and getpwuid() have no provisions to return more
> than one entry. What happens when duplicates are present is not
> described in any standard I know of (feel free to educate me if I'm just
> ignorant here) but I'd assume the behavior to be implementation
> dependent at best.
> Oh and just FWIW, what you describe in the ticket as the algorithm rpm
> should use is actually exactly what rpm does: it stat()'s the file,
> looks up the the username from st.st_uid and compares that with what is
> stored in the package for that file.

Come to think of it, in the scenario described in the ticket doing the 
exact opposite (looking up expected UID based on the username from 
package and comparing with on-disk UID) would do the right thing.

But when there are multiple UIDs with same name, that would get 
unreliable results whereas the current "algorithm" gets it right.

As mentioned in the closing comment, there is no right or wrong answer 
when there are duplicates. What rpm *could* do is try both ways and 
issue warnings about duplicates though. It might not be entirely in 
rpm's "domain" but...

	- Panu -

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