linux-kernel - Re: [PATCH] fs: Make /proc/sys inodes be owned by global root.

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Date:   Thu, 29 Nov 2018 17:09:28 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Radoslaw Burny <rburny@...gle.com>,
        Seth Forshee <seth.forshee@...onical.com>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        jsperbeck@...gle.com
Subject: Re: [PATCH] fs: Make /proc/sys inodes be owned by global root.

On Mon, Nov 26, 2018 at 11:29:40PM -0600, Eric W. Biederman wrote:
> Luis Chamberlain <mcgrof@...nel.org> writes:
> > Thanks for the description of how to run into the issue described but
> > is there also a practical use case today where this is happening? I ask
> > as it would be good to know the severity of the issue in the real world
> > today.
> 
> People trying to run containers without a root user in the container.
> It atypical but something doable.  

My question was if there are generic tools / propreitary tools which are
doing this widely *today*. Or is this just a custom setup some folks
use?

> We spoke about this at LPC.  And this is the correct behavioral change.
> 
> The problem is there is a default value for i_uid and i_gid that is
> correct in the general case.  That default value is not corect for
> sysctl, because proc is weird.  As the sysctl permission check in
> test_perm are all against GLOBAL_ROOT_UID and GLOBAL_ROOT_GID we did not
> notice that i_uid and i_gid were being set wrong.
> 
> So all this patch does is fix the default values i_uid and i_gid.
> 
> The commit comment seems worth cleaning up.  But for the
> content of the code.

The logic seems sensible then, but are we implicating what a container
does with its sysctl values onto the entire system? If so, sure, it
seems you want this for networking purposes as there are a series of
sysctl values a container may want to muck with, but are we sure we
want the same for *all* sysctl entries?

  Luis