linux-kernel - Re: [PATCH 3/7] fs: Ignore file caps in mounts from other user namespaces

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Message-ID: <20150716130607.GA77715@ubuntu-hedt>
Date:	Thu, 16 Jul 2015 08:06:07 -0500
From:	Seth Forshee <seth.forshee@...onical.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	James Morris <james.l.morris@...cle.com>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	LSM List <linux-security-module@...r.kernel.org>,
	SELinux-NSA <selinux@...ho.nsa.gov>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/7] fs: Ignore file caps in mounts from other user
 namespaces

On Wed, Jul 15, 2015 at 06:23:01PM -0700, Andy Lutomirski wrote:
> > So if we have the s_user_ns check in get_file_caps the mnt_may_suid pass
> > isn't strictly necessary, but I still think it is useful as a mitigation
> > to the "leaks" Eric mentions. It _should_ be impossible for a user to
> > gain access to another user's mount namespace,
> 
> No, it's very easy with SCM_RIGHTS.  We should make sure it's safe.

Sure, what I really meant was that an attacker shouldn't be able to do
so without cooperation from the other user's processes. But I think
we're all in agreement that making it safe is a good idea.

Seth
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