Re: [gentoo-user] User eix-sync permissions problem

[Kerin Millar <kerframil@fastmail.co.uk>]

On 11/02/2014 01:23, Walter Dnes wrote:
> On Tue, Feb 11, 2014 at 12:28:43AM +0000, Kerin Millar wrote
>> On 10/02/2014 23:57, Walter Dnes wrote:
>>>
>>>     What's the point, if you still have to run as root (or su or sudo) for
>>> the emerge update process?
>>
>> It's the principle of least privilege. Is there any specific reason for
>> portage to fork and exec rsync as root? Is rsync sandboxed? Should rsync
>> have unfettered read/write access to all mounted filesystems? Can it be
>> guaranteed that rsync hasn't been compromised? Can it be guaranteed that
>> PORTAGE_RSYNC_OPTS will contain safe options at all times?
>>
>> The answer to all of these questions is "no". Basically, the combination
>> of usersync and non-root ownership of PORTDIR hardens the process in a
>> sensible way while conferring no disadvantage.
>
>    If /usr/portage is owned by portage:portage, then wouldn't a user
> (member of portage) be able to do mischief by tweaking ebuilds?  E.g.
> modify an ebuild to point to a tarball located on a usb stick, at
> http://127.0.0.1/media/sdc1/my_tarball.tgz.  This would allow a local
> user to supply code that gets built and then installed in /usr/bin, or
> /sbin, etc.

Yes, but only if the group write bit is set throughout PORTDIR. By 
default, rsync - as invoked by portage - preserves the permission bits 
from the remote and the files stored by the mirrors do not have this bit 
set.

What I have described elsewhere is a method for ensuring that the group 
write bit is set. In that case, your concern is justified; you would 
definitely not want to grant membership of the portage group to anyone 
that you couldn't trust in this context.

--Kerin