Re: [PATCH bpf-next v13 4/7] landlock: Add ptrace LSM hooks

From: "Mickaël Salaün" <mic@digikod.net>
To: KP Singh <kpsingh@chromium.org>
Cc: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>,
	linux-kernel@vger.kernel.org,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Andy Lutomirski" <luto@amacapital.net>,
	"Casey Schaufler" <casey@schaufler-ca.com>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"David Drysdale" <drysdale@google.com>,
	"Florent Revest" <revest@chromium.org>,
	"James Morris" <jmorris@namei.org>, "Jann Horn" <jann@thejh.net>,
	"John Johansen" <john.johansen@canonical.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Kees Cook" <keescook@chromium.org>,
	"Michael Kerrisk" <mtk.manpages@gmail.com>,
	"Mickaël Salaün" <mickael.salaun@ssi.gouv.fr>,
	"Paul Moore" <paul@paul-moore.com>,
	"Sargun Dhillon" <sargun@sargun.me>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Stephen Smalley" <sds@tycho.nsa.gov>,
	"Tejun Heo" <tj@kernel.org>,
	"Tetsuo Handa" <penguin-kernel@I-love.SAKURA.ne.jp>,
	"Tycho Andersen" <tycho@tycho.ws>,
	"Will Drewry" <wad@chromium.org>,
	bpf@vger.kernel.org, kernel-hardening@lists.openwall.com,
	linux-api@vger.kernel.org, linux-security-module@vger.kernel.org,
	netdev@vger.kernel.org
Subject: Re: [PATCH bpf-next v13 4/7] landlock: Add ptrace LSM hooks
Date: Wed, 6 Nov 2019 17:58:46 +0100
Message-ID: <026b6f3f-d17a-d50e-4793-a76e6719cc1f@digikod.net> (raw)
In-Reply-To: <20191106101558.GA19467@chromium.org>

On 06/11/2019 11:15, KP Singh wrote:
> On 05-Nov 19:01, Mickaël Salaün wrote:
>> On 05/11/2019 18:18, Alexei Starovoitov wrote:

[...]

>>>
>>> I think the only way bpf-based LSM can land is both landlock and KRSI
>>> developers work together on a design that solves all use cases.
>>
>> As I said in a previous cover letter [1], that would be great. I think
>> that the current Landlock bases (almost everything from this series
>> except the seccomp interface) should meet both needs, but I would like
>> to have the point of view of the KRSI developers.
> 
> As I mentioned we are willing to collaborate but the current landlock
> patches does not meet the needs for KRSI:
> 
> * One program type per use-case (eg. LANDLOCK_PROG_PTRACE) as opposed to
>   a single program type. This is something that KRSI proposed in it's
>   initial design [1] and the new common "eBPF + LSM" based approach
>   [2] would maintain as well.

As ask in my previous email [1], I don't see how KRSI would efficiently
deal with other LSM hooks with a unique program (attach) type.

[1]
https://lore.kernel.org/lkml/813cedde-8ed7-2d3b-883d-909efa978d41@digikod.net/

> 
> * Landlock chooses to have multiple LSM hooks per landlock hook which is
>   more restrictive. It's not easy to write precise MAC and Audit
>   policies for a privileged LSM based on this and this ends up bloating
>   the context that needs to be maintained and requires avoidable
>   boilerplate work in the kernel.

Why do you think it is more restrictive or it adds boilerplate work? How
does KRSI will deal with more complex hooks than execve-like with
multiple kernel objects?

> 
> [1] https://lore.kernel.org/patchwork/project/lkml/list/?series=410101
> [2] https://lore.kernel.org/bpf/20191106100655.GA18815@chromium.org/T/#u
> 
> - KP Singh