linux-kernel - Re: [PATCH 0/6] File Sealing & memfd

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Date:	Tue, 08 Apr 2014 15:00:28 +0200
From:	Florian Weimer <fweimer@...hat.com>
To:	David Herrmann <dh.herrmann@...il.com>,
	linux-kernel@...r.kernel.org
CC:	Hugh Dickins <hughd@...gle.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Matthew Wilcox <matthew@....cx>,
	Karol Lewandowski <k.lewandowsk@...sung.com>,
	Kay Sievers <kay@...y.org>, Daniel Mack <zonque@...il.com>,
	Lennart Poettering <lennart@...ttering.net>,
	Kristian Høgsberg <krh@...planet.net>,
	john.stultz@...aro.org, Greg Kroah-Hartman <greg@...ah.com>,
	Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	dri-devel@...ts.freedesktop.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ryan Lortie <desrt@...rt.ca>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Subject: Re: [PATCH 0/6] File Sealing & memfd_create()

On 03/19/2014 08:06 PM, David Herrmann wrote:

> Unlike existing techniques that provide similar protection, sealing allows
> file-sharing without any trust-relationship. This is enforced by rejecting seal
> modifications if you don't own an exclusive reference to the given file. So if
> you own a file-descriptor, you can be sure that no-one besides you can modify
> the seals on the given file. This allows mapping shared files from untrusted
> parties without the fear of the file getting truncated or modified by an
> attacker.

How do you keep these promises on network and FUSE file systems?  Surely 
there is still some trust involved for such descriptors?

What happens if you create a loop device on a sealed descriptor?

Why does memfd_create not create a file backed by a memory region in the 
current process?  Wouldn't this be a far more generic primitive? 
Creating aliases of memory regions would be interesting for many things 
(not just libffi bypassing SELinux-enforced NX restrictions :-).

-- 
Florian Weimer / Red Hat Product Security Team
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