netdev - Re: [RFC v3 11/22] seccomp,landlock: Handle Landlock hooks per process hierarchy

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Message-ID: <57D9D06C.2020007@digikod.net>
Date:   Thu, 15 Sep 2016 00:34:20 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Daniel Mack <daniel@...que.org>,
        David Drysdale <drysdale@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Elena Reshetova <elena.reshetova@...el.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        James Morris <james.l.morris@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        Paul Moore <pmoore@...hat.com>,
        Sargun Dhillon <sargun@...gun.me>,
        "Serge E . Hallyn" <serge@...lyn.com>, Tejun Heo <tj@...nel.org>,
        Will Drewry <wad@...omium.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC v3 11/22] seccomp,landlock: Handle Landlock hooks per
 process hierarchy


On 14/09/2016 20:43, Andy Lutomirski wrote:
> On Wed, Sep 14, 2016 at 12:24 AM, Mickaël Salaün <mic@...ikod.net> wrote:
>> A Landlock program will be triggered according to its subtype/origin
>> bitfield. The LANDLOCK_FLAG_ORIGIN_SECCOMP value will trigger the
>> Landlock program when a seccomp filter will return RET_LANDLOCK.
>> Moreover, it is possible to return a 16-bit cookie which will be
>> readable by the Landlock programs in its context.
> 
> Are you envisioning that the filters will return RET_LANDLOCK most of
> the time or rarely?  If it's most of the time, then maybe this could
> be simplified a bit by unconditionally calling the landlock filter and
> letting the landlock filter access a struct seccomp_data if needed.

Exposing seccomp_data in a Landlock context may be a good idea. The main
implication is that Landlock programs may then be architecture specific
(if dealing with data) as seccomp filters are. Another point is that it
remove any direct binding between seccomp filters and Landlock programs.
I will try this (more simple) approach.

> 
>>
>> Only seccomp filters loaded from the same thread and before a Landlock
>> program can trigger it through LANDLOCK_FLAG_ORIGIN_SECCOMP. Multiple
>> Landlock programs can be triggered by one or more seccomp filters. This
>> way, each RET_LANDLOCK (with specific cookie) will trigger all the
>> allowed Landlock programs once.
> 
> This interface seems somewhat awkward.  Should we not have a way to
> atomicaly install a whole pile of landlock filters and associated
> seccomp filter all at once?

I can change the seccomp(2) use in this way: instead of loading a
Landlock program, (atomically) load an array of Landlock programs.

However, exposing seccomp_data to Landlock programs looks like a better
way to deal with it. This does not needs to manage an array of Landlock
programs.

 Mickaël



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