linux-kernel - Re: [PATCH 0/3] Taming execve, setuid, and LSMs

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Message-ID: <20100420143545.GA19513@us.ibm.com>
Date:	Tue, 20 Apr 2010 09:35:45 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Andrew Lutomirski <luto@....edu>
Cc:	Stephen Smalley <sds@...ho.nsa.gov>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Eric Biederman <ebiederm@...ssion.com>,
	"Andrew G. Morgan" <morgan@...nel.org>
Subject: Re: [PATCH 0/3] Taming execve, setuid, and LSMs

Quoting Andrew Lutomirski (luto@....edu):
> On Tue, Apr 20, 2010 at 8:37 AM, Stephen Smalley <sds@...ho.nsa.gov> wrote:
> > On Mon, 2010-04-19 at 16:39 -0500, Serge E. Hallyn wrote:
> >> Quoting Andrew Lutomirski (luto@....edu):
> 
> >> > and LSM  transitions.  I
> >> > think this is a terrible idea for two reasons:
> >> >   1. LSM transitions already scare me enough, and if anyone relies on
> >> > them working in concert with setuid, then the mere act of separating
> >> > them might break things, even if the "privileged" (by LSM) app in
> >> > question is well-written.
> >>
> >> hmm...
> >>
> >> A good point.
> >
> > At least in the case of SELinux, context transitions upon execve are
> > already disabled in the nosuid case, and Eric's patch updated the
> > SELinux test accordingly.
> >
> 
> True,  but I think it's still asking for trouble -- other LSMs could
> (and almost certainly will, especially the out-of-tree ones) do
> something, and I think that any action at all that an LSM takes in the
> bprm_set_creds hook for a nosuid (or whatever it's called) process is
> wrong or at best misguided.

I could be wrong, but I think the point is that your reasoning is
correct, and that the same reasoning must apply if we're just
executing a file out of an fs which has been mounted with '-o nosuid'.

> Can you think of anything that an LSM should do (or even should be
> able to do) when a nosuid process calls exec, other than denying the
> request outright?  With my patch, LSMs can still reject the open_exec
> call.
> 
> --Andy
> --
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