linux-kernel - Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

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Date:	Wed, 09 Jan 2008 09:47:31 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	nigel@...el.suspend2.net
CC:	pavel@....cz, akpm@...ux-foundation.org, hch@...radead.org,
	serue@...ibm.com, viro@....linux.org.uk, ebiederm@...ssion.com,
	kzak@...hat.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, containers@...ts.osdl.org,
	util-linux-ng@...r.kernel.org
Subject: Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

> >> On Tue 2008-01-08 12:35:09, Miklos Szeredi wrote:
> >>> From: Miklos Szeredi <mszeredi@...e.cz>
> >>>
> >>> Use FS_SAFE for "fuse" fs type, but not for "fuseblk".
> >>>
> >>> FUSE was designed from the beginning to be safe for unprivileged users.  This
> >>> has also been verified in practice over many years.  In addition unprivileged
> >> Eh? So 'kill -9 no longer works' and 'suspend no longer works' is not
> >> considered important enough to even mention?
> > 
> > No.  Because in practice they don't seem to matter.  Also because
> > there's no way in which fuse could be done differently to address
> > these issues.
> 
> Could you clarify, please? I hope I'm getting the wrong end of the stick
> - it sounds to me like you and Pavel are saying that this patch breaks
> suspending to ram (and hibernating?) but you want to push it anyway
> because you haven't been able to produce an instance, don't think
> suspending or hibernating matter and couldn't fix fuse anyway?

This patch has nothing to do with suspend or hibernate.  What this
patchset does, is help get rid of fusermount, a suid-root mount
helper.  It also opens up new possibilities, which are not fuse
related.

Fuse has bad interactions with the freezer, theoretically.  In
practice, I remember just one bug report (that sparked off this whole
"do we need freezer, or don't we" flamefest), that actually got fixed
fairly quickly, ...maybe.  Rafael probably remembers better.

> > The 'kill -9' thing is basically due to VFS level locking not being
> > interruptible.  It could be changed, but I'm not sure it's worth it.
> > 
> > For the suspend issue, there are also no easy solutions.
> 
> What are the non-easy solutions?

The ability to freeze tasks in uninterruptible sleep, or more
generally at any preempt point (except when drivers are poking
hardware).

I know this doesn't play well with userspace hibernate, and I don't
think it can be resolved without going the kexec way.

Miklos
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