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

[Michael j Theall]

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

> From: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
> To: Miklos Szeredi <miklos@xxxxxxxxxx>
> Cc: fuse-devel@xxxxxxxxxxxxxxxxxxxxx, "Serge H. Hallyn" 
> <serge.hallyn@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Seth 
> Forshee <seth.forshee@xxxxxxxxxxxxx>, "Eric W. Biederman" 
> <ebiederm@xxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx
> 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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