linux-kernel - Re: [fuse-devel] [PATCH v4 4/5] fuse: Support privileged xattrs only with a mount option

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Message-ID: <OFD40DA8DF.F78EA39D-ON86257D71.0057C4DC-86257D71.0064055D@us.ibm.com>
Date:	Tue, 14 Oct 2014 13:12:26 -0500
From:	Michael j Theall <mtheall@...ibm.com>
To:	Seth Forshee <seth.forshee@...onical.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	fuse-devel@...ts.sourceforge.net, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Miklos Szeredi <miklos@...redi.hu>,
	"Serge H. Hallyn" <serge.hallyn@...ntu.com>
Subject: Re: [fuse-devel] [PATCH v4 4/5] fuse: Support privileged xattrs only	with a
 mount option

Seth Forshee <seth.forshee@...onical.com> wrote on 10/14/2014 09:25:55 AM:

> From: Seth Forshee <seth.forshee@...onical.com>
> To: Miklos Szeredi <miklos@...redi.hu>
> Cc: fuse-devel@...ts.sourceforge.net, "Serge H. Hallyn" 
> <serge.hallyn@...ntu.com>, linux-kernel@...r.kernel.org, Seth 
> Forshee <seth.forshee@...onical.com>, "Eric W. Biederman" 
> <ebiederm@...ssion.com>, linux-fsdevel@...r.kernel.org
> Date: 10/14/2014 09:27 AM
> Subject: [fuse-devel] [PATCH v4 4/5] fuse: Support privileged xattrs
> only with a mount option
> 
> Allowing unprivileged users to provide arbitrary xattrs via fuse
> mounts bypasses the normal restrictions on setting xattrs. Such
> mounts should be restricted to reading and writing xattrs in the
> user.* namespace.
> 

Can you explain how the normal restrictions on setting xattrs are 
bypassed?
My filesystem still needs security.* and system.*, and it looks like
xattr_permission already prevents non-privileged users from accessing
trusted.*

> It's difficult though to tell whether a mount is being performed
> on behalf of an unprivileged user since fuse mounts are ususally
> done via a suid root helper. Thus a new mount option,
> privileged_xattrs, is added to indicated that xattrs from other
> namespaces are allowed. This option can only be supplied by
> system-wide root; supplying the option as an unprivileged user
> will cause the mount to fail.

I can't say I'm convinced that this is the right direction to head.

Regards,
Michael Theall

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