linux-kernel - Re: [PATCH] userns: honour no_new_privs for cap

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Date:   Fri, 22 Dec 2017 13:17:34 +1100
From:   Aleksa Sarai <asarai@...e.de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Maciej Żenczykowski <zenczykowski@...il.com>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        linux-security-module@...r.kernel.org,
        Mahesh Bandewar <maheshb@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH] userns: honour no_new_privs for cap_bset during user ns
 creation/switch

On 2017-12-21, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> Good point about CAP_DAC_OVERRIDE on files you own.
> 
> I think there is an argument that you are playing dangerous games with
> the permission system there, as it isn't effectively a file you own if
> you can't read it, and you can't change it's permissions.

This problem reminds me of the whole "unmapped group" problem. If you
have access to a file through an unmapped group you can still access a
file -- which to me is wrong. I understand the need for checking
unmapped groups in order to fix the "chmod 707" problem, but I think
that unmapped groups should only *block* access and never *grant* it.

I was working on a patch for that issue a while ago but it touched more
VFS than I was comfortable with. Eric, is that a fix you would be
interested in?

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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