linux-kernel - Re: Upstream first policy

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Message-ID: <m1d3zbecqt.fsf@fess.ebiederm.org>
Date:	Wed, 10 Mar 2010 19:52:26 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, James Morris <jmorris@...ei.org>,
	linux-kernel@...r.kernel.org, Kyle McMartin <kyle@...artin.ca>,
	Alexander Viro <viro@....linux.org.uk>
Subject: Re: Upstream first policy


Weird.  Somehow I only got a copy of this from lkml.

Alan Cox <alan@...rguk.ukuu.org.uk> writes:

>> time.  If pathnames were not fundamentally important we could apply
>> a patch like the one below and allow unprivileged users to unshare
>> the mount namespace and mount filesystems wherever.  There is nothing
>> fundamental about those operations that require root privileges except
>> that you are manipulating the pathnames of objects.
>
> And in a purely SELinux enviromnment your patch would work out because
> you could use labels to control this stuff.
>  
>
>> -	if (!capable(CAP_SYS_ADMIN))
>> -		return -EPERM;
>> -
>
> It does raise the question about whether you can do it if you had a
> namespace property of "ignore suidness". I'm not sure thats enough
> however.

The long term plan is to change that to.

	if (nscapable(mnt_ns->user_ns, CAP_SYS_ADMIN))
		return -EPERM.

That is.
- Create a new user/credential namespace (ultimately an unprivileged operation).
- Have the root user of the new user namespace create a new mount namespace.
- Over that new mount namespace the root user of the new user namespace
  has full control.

It is a little convoluted but it maintains backwards compatibility.  Unfortunately
there is still a long ways to go before we get there.

Eric
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