linux-kernel - Re: unprivileged mounts git tree

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Message-Id: <E1KbIqL-0003QO-34@pomaz-ex.szeredi.hu>
Date:	Thu, 04 Sep 2008 19:42:05 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	serue@...ibm.com
CC:	miklos@...redi.hu, ebiederm@...ssion.com,
	akpm@...ux-foundation.org, hch@...radead.org,
	viro@...IV.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: unprivileged mounts git tree

On Thu, 4 Sep 2008, Serge E. Hallyn wrote:
> Quoting Miklos Szeredi (miklos@...redi.hu):
> > On Thu, 04 Sep 2008, Miklos Szeredi wrote:
> > > On Thu, 4 Sep 2008, Serge E. Hallyn wrote:
> > > > Are you going to revert the change forcing CL_SLAVE for
> > > > !capable(CAP_SYS_ADMIN)?  I don't think we want that - I think that
> > > > *within* a set of user mounts, propagation should be safe, right?
> > > > 
> > > > Will you be able to do this soon?  If not, should we just do the part
> > > > returning -EPERM when turning a shared mount into a user mount? 
> > > 
> > > OK, let's do that first and the tricky part (propagation vs. user
> > > mounts) later.  Will push after I've tested it.
> > 
> > Here it is:
> > 
> > git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git unprivileged-mounts
> 
> but you're still doing
> 
> 	if (IS_MNT_SHARED(old_nd.path.mnt) && !capable(CAP_SYS_ADMIN))
> 		goto out;
> 
> shouldn't it be something like
> 
> 	if (IS_MNT_SHARED(old_nd.path.mnt) && (old_nd.path.mnt & MNT_USER))
> 		goto out;
> 
> ?

Why would that be an error?  There's no real security gain to be had
from restricting a privileged user, but could cause a lot of
annoyance.  If we think this is dangerous, then protection should be
built into mount(8) with an option to override.  But not into the
kernel, IMO.

Miklos
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