linux-kernel - Re: VFS, NFS security bug? Should CAP_MKNOD and CAP_LINUX_IMMUTABLE be added to CAP_FS

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Message-ID: <20090312190039.GA6901@fieldses.org>
Date:	Thu, 12 Mar 2009 15:00:39 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Igor Zhbanov <izh1979@...il.com>, linux-kernel@...r.kernel.org,
	viro@...iv.linux.org.uk, neilb@...e.de, Trond.Myklebust@...app.com,
	David Howells <dhowells@...hat.com>,
	James Morris <jmorris@...ei.org>
Subject: Re: VFS, NFS security bug? Should CAP_MKNOD and
	CAP_LINUX_IMMUTABLE be added to CAP_FS_MASK?

On Thu, Mar 12, 2009 at 11:10:47AM -0500, Serge E. Hallyn wrote:
> Quoting J. Bruce Fields (bfields@...ldses.org):
> > On Wed, Mar 11, 2009 at 03:53:34PM +0300, Igor Zhbanov wrote:
> > > Hello!
> > > 
> > > It seems that CAP_MKNOD and CAP_LINUX_IMMUTABLE were forgotten to be
> > > added to CAP_FS_MASK_B0 in linux-2.6.x and to CAP_FS_MASK in
> > > linux-2.4.x. Both capabilities affects file system and can be
> > > considered file system capabilities.
> > 
> > Sounds right to me--I'd expect rootsquash to guarantee that new device
> > nodes can't be created from the network.  Cc'ing random people from the
> > git log for include/linux/capability.h in hopes they can help.
> 
> Yeah it seems reasonable.  If it is, then does that mean that we
> also need CAP_SYS_ADMIN (to write selinux labels) and CAP_SETFCAP
> (to set file capabilities) as well?

For nfsd at least we should be droppping anything that concerns the
filesystem and would normally require root privileges.

We need to trace up through the users of CAP_FS_SET and figure out what
other users need.

--b.
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