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

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Date:	Mon, 16 Mar 2009 14:21:45 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Igor Zhbanov <izh1979@...il.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
	neilb@...e.de, Trond.Myklebust@...app.com,
	David Howells <dhowells@...hat.com>,
	Andrew Morgan <morgan@...nel.org>,
	James Morris <jmorris@...ei.org>,
	linux-security-module@...r.kernel.org,
	SELinux <selinux@...ho.nsa.gov>
Subject: Re: Ответ: VFS, NFS
 security bug? Should CAP_MKNOD and CAP_LINUX_IMMUTABLE be added to
 CAP_FS_MASK?

On Fri, 2009-03-13 at 14:00 -0500, Serge E. Hallyn wrote:
> Quoting Igor Zhbanov (izh1979@...il.com):
> > But ordinary users can't create devices. It seems to me that in time
> > of implementation of capabilities in kernel 2.4, capabilities related
> > to filesystem was added first. And mark for them contains all above in
> > header file. And when CAP_MKNOD was added later, author just forget to
> > update mask.
> > 
> > If mask was designed to drop all filesystem related capabilities, then
> > it must be expanded, because ordinary users cannot create devices etc.
> 
> I think you thought Bruce was saying we shouldn't change the set of
> capabilities, but he was just asking exactly what changes Michael was
> interested in.
> 
> Igor, thanks for finding this.  I never got your original message.  Do
> you have a patdch to add the two capabilities?  Do you think the
> other two I mentioned (CAP_SYS_ADMIN and CAP_SETFCAP) need to be
> added too?
> 
> I've added Andrew Morgan, LSM and SELinux mailing lists to get another
> opinion about adding those two.  In particular, we'd be adding them
> to the fs_masks becuase CAP_SYS_ADMIN lets you change the selinux
> label, and CAP_SETFCAP lets you change the file capabilities.

I'd be inclined against adding CAP_SYS_ADMIN to the mask; note that it
is only checked for setting SELinux security contexts (or more broadly
any attributes in the security namespace) when SELinux is disabled.  In
the SELinux-enabled case, we are checking SELinux-specific permissions
when setting the SELinux attributes, whether on the client or the
server.

-- 
Stephen Smalley
National Security Agency

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