linux-kernel - Re: implement-file-posix-capabilities.patch

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Date:	Thu, 28 Jun 2007 10:38:44 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Casey Schaufler <casey@...aufler-ca.com>
Cc:	Andrew Morgan <morgan@...nel.org>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Andrew Morgan <agm@...gle.com>,
	Andrew Morton <akpm@...gle.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	James Morris <jmorris@...ei.org>,
	linux-security-module@...r.kernel.org,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: implement-file-posix-capabilities.patch

Quoting Casey Schaufler (casey@...aufler-ca.com):
> 
> --- Andrew Morgan <morgan@...nel.org> wrote:
> 
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > Serge E. Hallyn wrote:
> > >> Does that explain it?
> > > 
> > > Yes, thanks, but then it still could come in handy to have fE be a full
> > > bitset, so the application gets some eff caps automatically, while
> > > others it has to manually set...
> > 
> > [We touched on this a number of emails back.]
> > 
> > If an application is capability aware, it can manipulate its own
> > capabilities and should have fE=0.
> > 
> > If an application is not capability aware, it needs to have *all* of its
> > capabilities enabled at exec() time. Otherwise, it won't work.
> 
> The intent of the fE vector in the POSIX draft is that those capabilities
> are set on exec (lower vectors permitting). There are cases where it
> does make sense to raise just some (e.g. ping). 
> 
> > The only reason for having an fE bitmap is to allow a capability-aware
> > program (you really trust to do its privileged operations carefully) to
> > be lazy and get some of its capabilities raised for free. Perhaps you
> > can clarify why this is a desirable thing? :-)
> 
> No, it's to allow you to grant a subset of the available capabilities
> to a program that is not aware of capabilities. You can give "date"
> the capability to reset the clock without giving it the capability
> to remove other people's files without changing the code or running
> it setuid.

Would there be a difference between that and setting either fI or fP
(depending on your intent) to those caps, and setting fE=1 in Andrew's
scheme?

thanks,
-serge
-
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