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From: Andy Lutomirski <luto@kernel.org>
To: "Mickaël Salaün" <mic@digikod.net>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Casey Schaufler <casey@schaufler-ca.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	David Drysdale <drysdale@google.com>,
	"David S . Miller" <davem@davemloft.net>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	James Morris <james.l.morris@oracle.com>,
	Jann Horn <jann@thejh.net>, Jonathan Corbet <corbet@lwn.net>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	Paul Moore <paul@paul-moore.com>,
	Sargun Dhillon <sargun@sargun.me>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	Shuah Khan <shuah@kernel.org>, Tejun Heo <tj@kernel.org>,
	Thomas Graf <tgraf@suug.ch>, Tycho Andersen <tycho@tycho.ws>,
	Will Drewry <wad@chromium.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Linux API <linux-api@vger.kernel.org>,
	LSM List <linux-security-module@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next v8 08/11] landlock: Add ptrace restrictions
Date: Tue, 27 Feb 2018 23:02:16 +0000	[thread overview]
Message-ID: <CALCETrUTiUeV71jgYWup0CZwG8eQ3=W7X5FgJqmgPxnYbFsccw@mail.gmail.com> (raw)
In-Reply-To: <0e7d0512-12a3-568d-aa55-3def4b91c6d0@digikod.net>

On Tue, Feb 27, 2018 at 10:14 PM, Mickaël Salaün <mic@digikod.net> wrote:
>
> On 27/02/2018 06:01, Andy Lutomirski wrote:
>>
>>
>>> On Feb 26, 2018, at 8:17 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>>
>>>> On Tue, Feb 27, 2018 at 12:41 AM, Mickaël Salaün <mic@digikod.net> wrote:
>>>> A landlocked process has less privileges than a non-landlocked process
>>>> and must then be subject to additional restrictions when manipulating
>>>> processes. To be allowed to use ptrace(2) and related syscalls on a
>>>> target process, a landlocked process must have a subset of the target
>>>> process' rules.
>>>>
>>>> Signed-off-by: Mickaël Salaün <mic@digikod.net>
>>>> Cc: Alexei Starovoitov <ast@kernel.org>
>>>> Cc: Andy Lutomirski <luto@amacapital.net>
>>>> Cc: Daniel Borkmann <daniel@iogearbox.net>
>>>> Cc: David S. Miller <davem@davemloft.net>
>>>> Cc: James Morris <james.l.morris@oracle.com>
>>>> Cc: Kees Cook <keescook@chromium.org>
>>>> Cc: Serge E. Hallyn <serge@hallyn.com>
>>>> ---
>>>>
>>>> Changes since v6:
>>>> * factor out ptrace check
>>>> * constify pointers
>>>> * cleanup headers
>>>> * use the new security_add_hooks()
>>>> ---
>>>> security/landlock/Makefile       |   2 +-
>>>> security/landlock/hooks_ptrace.c | 124 +++++++++++++++++++++++++++++++++++++++
>>>> security/landlock/hooks_ptrace.h |  11 ++++
>>>> security/landlock/init.c         |   2 +
>>>> 4 files changed, 138 insertions(+), 1 deletion(-)
>>>> create mode 100644 security/landlock/hooks_ptrace.c
>>>> create mode 100644 security/landlock/hooks_ptrace.h
>>>>
>>>> diff --git a/security/landlock/Makefile b/security/landlock/Makefile
>>>> index d0f532a93b4e..605504d852d3 100644
>>>> --- a/security/landlock/Makefile
>>>> +++ b/security/landlock/Makefile
>>>> @@ -3,4 +3,4 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
>>>> landlock-y := init.o chain.o task.o \
>>>>        tag.o tag_fs.o \
>>>>        enforce.o enforce_seccomp.o \
>>>> -       hooks.o hooks_cred.o hooks_fs.o
>>>> +       hooks.o hooks_cred.o hooks_fs.o hooks_ptrace.o
>>>> diff --git a/security/landlock/hooks_ptrace.c b/security/landlock/hooks_ptrace.c
>>>> new file mode 100644
>>>> index 000000000000..f1b977b9c808
>>>> --- /dev/null
>>>> +++ b/security/landlock/hooks_ptrace.c
>>>> @@ -0,0 +1,124 @@
>>>> +/*
>>>> + * Landlock LSM - ptrace hooks
>>>> + *
>>>> + * Copyright © 2017 Mickaël Salaün <mic@digikod.net>
>>>> + *
>>>> + * This program is free software; you can redistribute it and/or modify
>>>> + * it under the terms of the GNU General Public License version 2, as
>>>> + * published by the Free Software Foundation.
>>>> + */
>>>> +
>>>> +#include <asm/current.h>
>>>> +#include <linux/errno.h>
>>>> +#include <linux/kernel.h> /* ARRAY_SIZE */
>>>> +#include <linux/lsm_hooks.h>
>>>> +#include <linux/sched.h> /* struct task_struct */
>>>> +#include <linux/seccomp.h>
>>>> +
>>>> +#include "common.h" /* struct landlock_prog_set */
>>>> +#include "hooks.h" /* landlocked() */
>>>> +#include "hooks_ptrace.h"
>>>> +
>>>> +static bool progs_are_subset(const struct landlock_prog_set *parent,
>>>> +               const struct landlock_prog_set *child)
>>>> +{
>>>> +       size_t i;
>>>> +
>>>> +       if (!parent || !child)
>>>> +               return false;
>>>> +       if (parent == child)
>>>> +               return true;
>>>> +
>>>> +       for (i = 0; i < ARRAY_SIZE(child->programs); i++) {
>>>
>>> ARRAY_SIZE(child->programs) seems misleading.  Is there no define
>>> NUM_LANDLOCK_PROG_TYPES or similar?
>>>
>>>> +               struct landlock_prog_list *walker;
>>>> +               bool found_parent = false;
>>>> +
>>>> +               if (!parent->programs[i])
>>>> +                       continue;
>>>> +               for (walker = child->programs[i]; walker;
>>>> +                               walker = walker->prev) {
>>>> +                       if (walker == parent->programs[i]) {
>>>> +                               found_parent = true;
>>>> +                               break;
>>>> +                       }
>>>> +               }
>>>> +               if (!found_parent)
>>>> +                       return false;
>>>> +       }
>>>> +       return true;
>>>> +}
>>>
>>> If you used seccomp, you'd get this type of check for free, and it
>>> would be a lot easier to comprehend.  AFAICT the only extra leniency
>>> you're granting is that you're agnostic to the order in which the
>>> rules associated with different program types were applied, which
>>> could easily be added to seccomp.
>>
>> On second thought, this is all way too complicated.  I think the correct logic is either "if you are filtered by Landlock, you cannot ptrace anything" or to delete this patch entirely.
>
> This does not fit a lot of use cases like running a container
> constrained with some Landlock programs. We should not deny users the
> ability to debug their stuff.
>
> This patch add the minimal protection which are needed to have
> meaningful Landlock security policy. Without it, they may be easily
> bypassable, hence useless.
>

I think you're wrong here.  Any sane container trying to use Landlock
like this would also create a PID namespace.  Problem solved.  I still
think you should drop this patch.

>
>> If something like Tycho's notifiers goes in, then it's not obvious that, just because you have the same set of filters, you have the same privilege.  Similarly, if a feature that lets a filter query its cgroup goes in (and you proposed this once!) then the logic you implemented here is wrong.
>
> I don't get your point. Please take a look at the tests (patch 10).

I don't know what you want me to look at.

What I'm saying is: suppose I write a filter like this:

bool allow_some_action(void)
{
  int value_from_container_manager = call_out_to_user_notifier();
  return value_from_container_manager == 42;
}

or

bool allow_some_action(void)
{
  return my_cgroup_is("/foo/bar");
}

In both of these cases, your code will do the wrong thing.

>
>>
>> Or you could just say that it's the responsibility of a Landlock user to properly filter ptrace() just like it's the responsibility of seccomp users to filter ptrace if needed.
>
> A user should be able to enforce a security policy on ptrace as well,
> but this patch enforce a minimal set of security boundaries. It will be
> easy to add a new Landlock program type to get this kind of access control.

It sounds like you want Landlock to be a complete container system all
by itself.  I disagree with that design goal.

  reply	other threads:[~2018-02-27 23:02 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-27  0:41 [PATCH bpf-next v8 00/11] Landlock LSM: Toward unprivileged sandboxing Mickaël Salaün
2018-02-27  0:41 ` [PATCH bpf-next v8 01/11] fs,security: Add a security blob to nameidata Mickaël Salaün
2018-02-27  0:57   ` Al Viro
2018-02-27  1:23     ` Al Viro
2018-03-11 20:14       ` Mickaël Salaün
2018-02-28 16:27   ` kbuild test robot
2018-02-28 16:58   ` kbuild test robot
2018-02-27  0:41 ` [PATCH bpf-next v8 02/11] fs,security: Add a new file access type: MAY_CHROOT Mickaël Salaün
2018-02-27  0:41 ` [PATCH bpf-next v8 03/11] bpf: Add eBPF program subtype and is_valid_subtype() verifier Mickaël Salaün
2018-02-27  0:41 ` [PATCH bpf-next v8 04/11] bpf,landlock: Define an eBPF program type for Landlock hooks Mickaël Salaün
2018-02-27  0:41 ` [PATCH bpf-next v8 05/11] seccomp,landlock: Enforce Landlock programs per process hierarchy Mickaël Salaün
2018-02-27  2:08   ` Alexei Starovoitov
2018-02-27  4:40     ` Andy Lutomirski
2018-02-27  4:54       ` Alexei Starovoitov
2018-02-27  5:20         ` Andy Lutomirski
2018-02-27  5:32           ` Alexei Starovoitov
2018-02-27 16:39             ` Andy Lutomirski
2018-02-27 17:30               ` Casey Schaufler
2018-02-27 17:36                 ` Andy Lutomirski
2018-02-27 18:03                   ` Casey Schaufler
2018-02-27 21:48               ` Mickaël Salaün
2018-04-08 13:13                 ` Mickaël Salaün
2018-04-08 21:06                   ` Andy Lutomirski
2018-04-08 22:01                     ` Mickaël Salaün
2018-04-10  4:48                       ` Alexei Starovoitov
2018-04-11 22:18                         ` Mickaël Salaün
2018-02-27  0:41 ` [PATCH bpf-next v8 06/11] bpf,landlock: Add a new map type: inode Mickaël Salaün
2018-02-28 17:35   ` kbuild test robot
2018-02-27  0:41 ` [PATCH bpf-next v8 07/11] landlock: Handle filesystem access control Mickaël Salaün
2018-02-27  0:41 ` [PATCH bpf-next v8 08/11] landlock: Add ptrace restrictions Mickaël Salaün
2018-02-27  4:17   ` Andy Lutomirski
2018-02-27  5:01     ` Andy Lutomirski
2018-02-27 22:14       ` Mickaël Salaün
2018-02-27 23:02         ` Andy Lutomirski [this message]
2018-02-27 23:23           ` Andy Lutomirski
2018-02-28  0:00             ` Mickaël Salaün
2018-02-28  0:09               ` Andy Lutomirski
2018-03-06 22:28                 ` Mickaël Salaün
2018-04-01 22:48                   ` Mickaël Salaün
2018-02-27 22:18     ` Mickaël Salaün
2018-02-27  0:41 ` [PATCH bpf-next v8 09/11] bpf: Add a Landlock sandbox example Mickaël Salaün
2018-02-27  0:41 ` [PATCH bpf-next v8 10/11] bpf,landlock: Add tests for Landlock Mickaël Salaün
2018-02-27  0:41 ` [PATCH bpf-next v8 11/11] landlock: Add user and kernel documentation " Mickaël Salaün
2018-02-27  4:36 ` [PATCH bpf-next v8 00/11] Landlock LSM: Toward unprivileged sandboxing Andy Lutomirski
2018-02-27 22:03   ` Mickaël Salaün
2018-02-27 23:09     ` Andy Lutomirski
2018-03-06 22:25       ` Mickaël Salaün
2018-03-06 22:33         ` Andy Lutomirski
2018-03-06 22:46           ` Tycho Andersen
2018-03-06 23:06             ` Mickaël Salaün
2018-03-07  1:21               ` Andy Lutomirski
2018-03-08 23:51                 ` Mickaël Salaün
2018-03-08 23:53                   ` Andy Lutomirski
2018-04-01 22:04                     ` Mickaël Salaün
2018-04-02  0:39                       ` Tycho Andersen

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