linux-kernel - Re: ioctl CAP_LINUX_IMMUTABLE is checked in the wrong namespace

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Message-ID: <20140430004000.GC28969@ubuntumail>
Date:	Wed, 30 Apr 2014 00:40:00 +0000
From:	Serge Hallyn <serge.hallyn@...ntu.com>
To:	Theodore Ts'o <tytso@....edu>,
	Andy Lutomirski <luto@...capital.net>,
	Marian Marinov <mm@...com>,
	containers@...ts.linux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	lxc-devel <lxc-devel@...ts.sourceforge.net>
Subject: Re: ioctl CAP_LINUX_IMMUTABLE is checked in the wrong namespace

Quoting Theodore Ts'o (tytso@....edu):
> On Wed, Apr 30, 2014 at 12:16:41AM +0000, Serge Hallyn wrote:
> > I forget the details, but there was another case where I wanted to
> > have the userns which 'owns' the whole fs available.  I guess we'd
> > have to check against that instead of using inode_capable.
> 
> Yes, that sounds right.
> 
> And *please* tell me that that under no circumstances can anyone other
> than root@...t_user_ns is allowed to use mknod....

That's the case.  We've considered making exceptions for things like
/dev/null, but in practice bind-mounting devices from the host has
worked out just fine.
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