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: <20090313175848.GB27891@fieldses.org>
Date:	Fri, 13 Mar 2009 13:58:48 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Michael Kerrisk <mtk.manpages@...il.com>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	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 Fri, Mar 13, 2009 at 09:21:23AM +1300, Michael Kerrisk wrote:
> On Fri, Mar 13, 2009 at 5:10 AM, Serge E. Hallyn <serue@...ibm.com> 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?
> 
> If a change is made to CAP_FS_MASK, please do remember to CC
> mtk.manpages@...il.com, and linux-api@.

OK, that's because the exact set of capabilities that is dropped on
setfsuid is documented in capabilities(7)?  (Anywhere else?)

--b.

> 
> Cheers,
> 
> Michael
> 
> 
> -- 
> Michael Kerrisk Linux man-pages maintainer;
> http://www.kernel.org/doc/man-pages/ Found a documentation bug?
> http://www.kernel.org/doc/man-pages/reporting_bugs.html
> --
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