linux-kernel - Re: [PATCH v5 2/4] fuse: Support fuse filesystems outside of init_user

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Date:	Tue, 11 Nov 2014 15:04:54 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Seth Forshee <seth.forshee@...onical.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Serge H. Hallyn" <serge.hallyn@...ntu.com>,
	Andy Lutomirski <luto@...capital.net>,
	Michael j Theall <mtheall@...ibm.com>,
	fuse-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v5 2/4] fuse: Support fuse filesystems outside of
 init_user_ns

On Wed, Oct 22, 2014 at 04:24:18PM -0500, Seth Forshee wrote:
> Update fuse to translate uids and gids to/from the user namspace
> of the process servicing requests on /dev/fuse. Any ids which do
> not map into the namespace will result in errors. inodes will
> also be marked bad when unmappable ids are received from
> userspace.

Okay.

> Due to security concerns the namespace used should be fixed,
> otherwise a user might be able to gain elevated privileges or
> influence processes that the user would otherwise be unable to
> manipulate. Thus the namespace of the mounting process is used
> for all translations, and this namespace is required to be the
> same as the one in use when /dev/fuse was opened.

Maybe I'm being dense, but can someone give a concrete example of such an
attack?

That might also help me understand how exactly user/pid namespaces work...

Patch otherwise looks okay.

Thanks,
Miklos
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