linux-kernel - Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF

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Date:	Thu, 12 Jan 2012 11:46:37 -0800
From:	Andrew Lutomirski <luto@....edu>
To:	Will Drewry <wad@...omium.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, keescook@...omium.org,
	john.johansen@...onical.com, serge.hallyn@...onical.com,
	coreyb@...ux.vnet.ibm.com, pmoore@...hat.com, eparis@...hat.com,
	djm@...drot.org, segoon@...nwall.com, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	viro@...iv.linux.org.uk, mingo@...e.hu, akpm@...ux-foundation.org,
	khilman@...com, borislav.petkov@....com, amwang@...hat.com,
	oleg@...hat.com, ak@...ux.intel.com, eric.dumazet@...il.com,
	gregkh@...e.de, dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com
Subject: Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF

On Thu, Jan 12, 2012 at 11:40 AM, Will Drewry <wad@...omium.org> wrote:
> On Thu, Jan 12, 2012 at 12:44 PM, Andrew Lutomirski <luto@....edu> wrote:
>> On Thu, Jan 12, 2012 at 10:32 AM, Linus Torvalds
>> <torvalds@...ux-foundation.org> wrote:
>>> On Thu, Jan 12, 2012 at 10:18 AM, Andrew Lutomirski <luto@....edu> wrote:
>>>>
>>>> Like this?
>>>>
>>>> http://lkml.indiana.edu/hypermail/linux/kernel/1003.3/01225.html
>>>
>>> I don't know the execve_nosecurity patches, so the diff makes little
>>> sense to me, but yeah, I wouldn't expect it to be more than a couple
>>> of lines. Exactly *how* you set the bit etc is not something I care
>>> deeply about, prctl seems about as good as anything.
>>>
>>>> Note that there's a huge can of worms if execve is allowed but
>>>> suid/sgid is not: selinux may elevate privileges on exec of pretty
>>>> much anything.  (I think that this is a really awful idea, but it's in
>>>> the kernel, so we're stuck with it.)
>>>
>>> You can do any amount of crazy things with selinux, but the other side
>>> of the coin is that it would also be trivial to teach selinux about
>>> this same "restricted environment" bit, and just say that a process
>>> with that bit set doesn't get to match whatever selinux privilege
>>> escalation rules..
>>>
>>> I really don't think this is just about "execve cannot do setuid". I
>>> think it's about the process being marked as restricted.
>>>
>>> So in your patch, I think that "PR_RESTRICT_EXEC" bit is wrong. It
>>> should simply be "PR_RESTRICT_ME", and be done with it, and not try to
>>> artificially limit it to be some "execve feature", and more think of
>>> it as a "this is a process that has *no* extra privileges at all, and
>>> can never get them".
>>
>> Fair enough.  I'll submit the simpler patch tonight.
>
> This sounds cool.  Do you think you'll go for a new task_struct member
> or will it a securebit?  (Seems like securebits might be too tied to
> posix file caps, but I figured I'd ask).
>
> I'm planning on going ahead and mocking up your potential patch so I
> can respin this series using it and make sure I understand the
> interactions.

I think securebits and cred didn't exist the first time I did this,
and sticking it in struct cred might unnecessarily prevent sharing
cred (assuming that even happens).  So I'd say task_struct.

--Andy
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