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

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Date:	Tue, 20 Apr 2010 10:23:06 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Stephen Smalley <sds@...ho.nsa.gov>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	"Serge E. Hallyn" <serue@...ibm.com>, 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

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.

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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