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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: "Mickaël Salaün" <mic@digikod.net>
Cc: 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>,
	"KP Singh" <kpsingh@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: Tue, 5 Nov 2019 11:34:47 -0800
Message-ID: <20191105193446.s4pswwwhrmgk6hcx@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <23acf523-dbc4-855b-ca49-2bbfa5e7117e@digikod.net>

On Tue, Nov 05, 2019 at 07:01:41PM +0100, Mickaël Salaün wrote:
> 
> On 05/11/2019 18:18, Alexei Starovoitov wrote:
> > On Mon, Nov 04, 2019 at 06:21:43PM +0100, Mickaël Salaün wrote:
> >> Add a first Landlock hook that can be used to enforce a security policy
> >> or to audit some process activities.  For a sandboxing use-case, it is
> >> needed to inform the kernel if a task can legitimately debug another.
> >> ptrace(2) can also be used by an attacker to impersonate another task
> >> and remain undetected while performing malicious activities.
> >>
> >> Using ptrace(2) and related features on a target process can lead to a
> >> privilege escalation.  A sandboxed task must then be able to tell the
> >> kernel if another task is more privileged, via ptrace_may_access().
> >>
> >> Signed-off-by: Mickaël Salaün <mic@digikod.net>
> > ...
> >> +static int check_ptrace(struct landlock_domain *domain,
> >> +		struct task_struct *tracer, struct task_struct *tracee)
> >> +{
> >> +	struct landlock_hook_ctx_ptrace ctx_ptrace = {
> >> +		.prog_ctx = {
> >> +			.tracer = (uintptr_t)tracer,
> >> +			.tracee = (uintptr_t)tracee,
> >> +		},
> >> +	};
> > 
> > So you're passing two kernel pointers obfuscated as u64 into bpf program
> > yet claiming that the end goal is to make landlock unprivileged?!
> > The most basic security hole in the tool that is aiming to provide security.
> 
> How could you used these pointers without dedicated BPF helpers? This
> context items are typed as PTR_TO_TASK and can't be used without a
> dedicated helper able to deal with ARG_PTR_TO_TASK. Moreover, pointer
> arithmetic is explicitly forbidden (and I added tests for that). Did I
> miss something?

It's a pointer leak.

> 
> > 
> > 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.
> 
> [1] https://lore.kernel.org/lkml/20191029171505.6650-1-mic@digikod.net/
> 
> > BPF is capable
> > to be a superset of all existing LSMs whereas landlock and KRSI propsals today
> > are custom solutions to specific security concerns. BPF subsystem was extended
> > with custom things in the past. In networking we have lwt, skb, tc, xdp, sk
> > program types with a lot of overlapping functionality. We couldn't figure out
> > how to generalize them into single 'networking' program. Now we can and we
> > should. Accepting two partially overlapping bpf-based LSMs would be repeating
> > the same mistake again.
> 
> I'll let the LSM maintainers comment on whether BPF could be a superset
> of all LSM, but given the complexity of an access-control system, I have
> some doubts though. Anyway, we need to start somewhere and then iterate.
> This patch series is a first step.

I would like KRSI folks to speak up. So far I don't see any sharing happening
between landlock and KRSI. You're claiming this set is a first step. They're
claiming the same about their patches. I'd like to set a patchset that was
jointly developed.


  reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-04 17:21 [PATCH bpf-next v13 0/7] Landlock LSM Mickaël Salaün
2019-11-04 17:21 ` [PATCH bpf-next v13 1/7] bpf,landlock: Define an eBPF program type for Landlock hooks Mickaël Salaün
2019-11-04 17:21 ` [PATCH bpf-next v13 2/7] landlock: Add the management of domains Mickaël Salaün
2019-11-04 17:21 ` [PATCH bpf-next v13 3/7] landlock,seccomp: Apply Landlock programs to process hierarchy Mickaël Salaün
2019-11-04 17:21 ` [PATCH bpf-next v13 4/7] landlock: Add ptrace LSM hooks Mickaël Salaün
2019-11-05 17:18   ` Alexei Starovoitov
2019-11-05 17:55     ` Casey Schaufler
2019-11-05 19:31       ` Alexei Starovoitov
2019-11-05 19:55         ` Casey Schaufler
2019-11-05 21:54           ` Alexei Starovoitov
2019-11-05 22:32             ` Casey Schaufler
2019-11-05 18:01     ` Mickaël Salaün
2019-11-05 19:34       ` Alexei Starovoitov [this message]
2019-11-05 22:18         ` Mickaël Salaün
2019-11-06 10:06         ` KP Singh
2019-11-06 16:55           ` Mickaël Salaün
2019-11-06 21:45             ` KP Singh
2019-11-08 14:08               ` Mickaël Salaün
2019-11-08 14:34                 ` Daniel Borkmann
2019-11-08 15:39                   ` Mickaël Salaün
2019-11-08 15:27                 ` KP Singh
2019-11-06 10:15       ` KP Singh
2019-11-06 16:58         ` Mickaël Salaün
2019-11-04 17:21 ` [PATCH bpf-next v13 5/7] bpf,landlock: Add task_landlock_ptrace_ancestor() helper Mickaël Salaün
2019-11-04 17:21 ` [PATCH bpf-next v13 6/7] bpf,landlock: Add tests for the Landlock ptrace program type Mickaël Salaün
2019-11-04 17:21 ` [PATCH bpf-next v13 7/7] landlock: Add user and kernel documentation for Landlock Mickaël Salaün

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