linux-kernel - Re: [PATCH 3/3] CRED: Move the effective capabilities into the cred struct

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Date:	Thu, 20 Sep 2007 08:36:57 -0700 (PDT)
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Trond Myklebust <Trond.Myklebust@...app.com>,
	Andrew Morgan <morgan@...nel.org>
Cc:	David Howells <dhowells@...hat.com>, viro@....linux.org.uk,
	hch@...radead.org, sds@...ho.nsa.gov, casey@...aufler-ca.com,
	linux-kernel@...r.kernel.org, selinux@...ho.nsa.gov,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 3/3] CRED: Move the effective capabilities into the cred struct


--- Trond Myklebust <Trond.Myklebust@...app.com> wrote:

> On Wed, 2007-09-19 at 21:11 -0700, Andrew Morgan wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > David Howells wrote:
> > > Move the effective capabilities mask from the task struct into the
> credentials
> > > record.
> > > 
> > > Note that the effective capabilities mask in the cred struct shadows that
> in
> > > the task_struct because a thread can have its capabilities masks changed
> by
> > > another thread.  The shadowing is performed by update_current_cred()
> which is
> > > invoked on entry to any system call that might need it.
> > 
> > OOC If we were to simply drop support for one process changing the
> > capabilities of another, would we need this patch?
> 
> No. This has nothing to do about one process changing some other
> process' capabilities. It has to do with being able to pass security
> information around the kernel beyond the confines of the task struct.
> 
> This is needed in order to deal with asynchronous i/o where security
> checks may have to be deferred, and where the task struct may no longer
> be available.
> One example would be a failover situation when doing deferred writes: if
> the first choice of storage medium is unavailable, and the kernel tries
> to fail the write over to another storage. On NFS that might involve
> having to build up a new RPCSEC_GSS security context for the new server.
> Currently, you cannot do this safely because all the security info is
> cached in the task struct and much of it cannot be copied.

Ok, what can't be copied, and why can't it be copied?


Casey Schaufler
casey@...aufler-ca.com
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