Re: [PATCH 0/6] File Sealing & memfd_create()

[Florian Weimer]

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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