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From: "Mickaël Salaün" <mic@digikod.net>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	Alexei Starovoitov <ast@kernel.org>, Tejun Heo <tj@kernel.org>,
	Sargun Dhillon <sargun@sargun.me>,
	Network Development <netdev@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>,
	LSM List <linux-security-module@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"open list:CONTROL GROUP (CGROUP)" <cgroups@vger.kernel.org>,
	"David S . Miller" <davem@davemloft.net>,
	Daniel Mack <daniel@zonque.org>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [RFC v2 09/10] landlock: Handle cgroups (performance)
Date: Tue, 30 Aug 2016 22:33:31 +0200	[thread overview]
Message-ID: <57C5ED9B.3040303@digikod.net> (raw)
In-Reply-To: <CALCETrWAYyx_5Axyeqiz6tQa0kqTeNTuHRrERcM2G8ROhaphVw@mail.gmail.com>


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On 30/08/2016 22:23, Andy Lutomirski wrote:
> On Tue, Aug 30, 2016 at 1:20 PM, Mickaël Salaün <mic@digikod.net> wrote:
>>
>> On 30/08/2016 20:55, Andy Lutomirski wrote:
>>> On Sun, Aug 28, 2016 at 2:42 AM, Mickaël Salaün <mic@digikod.net> wrote:
>>>>
>>>>
>>>> On 28/08/2016 10:13, Andy Lutomirski wrote:
>>>>> On Aug 27, 2016 11:14 PM, "Mickaël Salaün" <mic@digikod.net> wrote:
>>>>>>
>>>>>>
>>>>>> On 27/08/2016 22:43, Alexei Starovoitov wrote:
>>>>>>> On Sat, Aug 27, 2016 at 09:35:14PM +0200, Mickaël Salaün wrote:
>>>>>>>> On 27/08/2016 20:06, Alexei Starovoitov wrote:
>>>>>>>>> On Sat, Aug 27, 2016 at 04:06:38PM +0200, Mickaël Salaün wrote:
>>>>>>>>>> As said above, Landlock will not run an eBPF programs when not strictly
>>>>>>>>>> needed. Attaching to a cgroup will have the same performance impact as
>>>>>>>>>> attaching to a process hierarchy.
>>>>>>>>>
>>>>>>>>> Having a prog per cgroup per lsm_hook is the only scalable way I
>>>>>>>>> could come up with. If you see another way, please propose.
>>>>>>>>> current->seccomp.landlock_prog is not the answer.
>>>>>>>>
>>>>>>>> Hum, I don't see the difference from a performance point of view between
>>>>>>>> a cgroup-based or a process hierarchy-based system.
>>>>>>>>
>>>>>>>> Maybe a better option should be to use an array of pointers with N
>>>>>>>> entries, one for each supported hook, instead of a unique pointer list?
>>>>>>>
>>>>>>> yes, clearly array dereference is faster than link list walk.
>>>>>>> Now the question is where to keep this prog_array[num_lsm_hooks] ?
>>>>>>> Since we cannot keep it inside task_struct, we have to allocate it.
>>>>>>> Every time the task is creted then. What to do on the fork? That
>>>>>>> will require changes all over. Then the obvious optimization would be
>>>>>>> to share this allocated array of prog pointers across multiple tasks...
>>>>>>> and little by little this new facility will look like cgroup.
>>>>>>> Hence the suggestion to put this array into cgroup from the start.
>>>>>>
>>>>>> I see your point :)
>>>>>>
>>>>>>>
>>>>>>>> Anyway, being able to attach an LSM hook program to a cgroup thanks to
>>>>>>>> the new BPF_PROG_ATTACH seems a good idea (while keeping the possibility
>>>>>>>> to use a process hierarchy). The downside will be to handle an LSM hook
>>>>>>>> program which is not triggered by a seccomp-filter, but this should be
>>>>>>>> needed anyway to handle interruptions.
>>>>>>>
>>>>>>> what do you mean 'not triggered by seccomp' ?
>>>>>>> You're not suggesting that this lsm has to enable seccomp to be functional?
>>>>>>> imo that's non starter due to overhead.
>>>>>>
>>>>>> Yes, for now, it is triggered by a new seccomp filter return value
>>>>>> RET_LANDLOCK, which can take a 16-bit value called cookie. This must not
>>>>>> be needed but could be useful to bind a seccomp filter security policy
>>>>>> with a Landlock one. Waiting for Kees's point of view…
>>>>>>
>>>>>
>>>>> I'm not Kees, but I'd be okay with that.  I still think that doing
>>>>> this by process hierarchy a la seccomp will be easier to use and to
>>>>> understand (which is quite important for this kind of work) than doing
>>>>> it by cgroup.
>>>>>
>>>>> A feature I've wanted to add for a while is to have an fd that
>>>>> represents a seccomp layer, the idea being that you would set up your
>>>>> seccomp layer (with syscall filter, landlock hooks, etc) and then you
>>>>> would have a syscall to install that layer.  Then an unprivileged
>>>>> sandbox manager could set up its layer and still be able to inject new
>>>>> processes into it later on, no cgroups needed.
>>>>
>>>> A nice thing I didn't highlight about Landlock is that a process can
>>>> prepare a layer of rules (arraymap of handles + Landlock programs) and
>>>> pass the file descriptors of the Landlock programs to another process.
>>>> This process could then apply this programs to get sandboxed. However,
>>>> for now, because a Landlock program is only triggered by a seccomp
>>>> filter (which do not follow the Landlock programs as a FD), they will be
>>>> useless.
>>>>
>>>> The FD referring to an arraymap of handles can also be used to update a
>>>> map and change the behavior of a Landlock program. A master process can
>>>> then add or remove restrictions to another process hierarchy on the fly.
>>>
>>> Maybe this could be extended a little bit.  The fd could hold the
>>> seccomp filter *and* the LSM hook filters.  FMODE_EXECUTE could give
>>> the ability to install it and FMODE_WRITE could give the ability to
>>> modify it.
>>>
>>
>> This is interesting! It should be possible to append the seccomp stack
>> of a source process to the seccomp stack of the target process when a
>> Landlock program is passed and then activated through seccomp(2).
>>
>> For the FMODE_EXECUTE/FMODE_WRITE, are you suggesting to manage
>> permission of the eBPF program FD in a specific way?
>>
> 
> This wouldn't be an eBPF program FD -- it would be an FD encapsulating
> an entire configuration including seccomp BPF program, whatever
> landlock stuff is associated, and eventual seccomp monitor
> configuration (once I write that code), etc.
> 
> You wouldn't say "attach this process's seccomp stack to me" -- you'd
> say "attach this seccomp layer to me".
> 
> A decision that we'd have to make would be whether the FD links to the
> parent layer or whether it can be attached without regard to what the
> parent layer is.

OK, I like that, but I think it could be done on a second time. :)


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  reply	other threads:[~2016-08-30 20:34 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-25 10:32 [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 01/10] landlock: Add Kconfig Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 02/10] bpf: Move u64_to_ptr() to BPF headers and inline it Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 03/10] bpf,landlock: Add a new arraymap type to deal with (Landlock) handles Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 04/10] seccomp: Split put_seccomp_filter() with put_seccomp() Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 05/10] seccomp: Handle Landlock Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 06/10] landlock: Add LSM hooks Mickaël Salaün
2016-08-30 18:56   ` Andy Lutomirski
2016-08-30 20:10     ` Mickaël Salaün
2016-08-30 20:18       ` Andy Lutomirski
2016-08-30 20:27         ` Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 07/10] landlock: Add errno check Mickaël Salaün
2016-08-25 11:13   ` Andy Lutomirski
2016-08-25 10:32 ` [RFC v2 08/10] landlock: Handle file system comparisons Mickaël Salaün
2016-08-25 11:12   ` Andy Lutomirski
2016-08-25 14:10     ` Mickaël Salaün
2016-08-26 14:57       ` Andy Lutomirski
2016-08-27 13:45         ` Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 09/10] landlock: Handle cgroups Mickaël Salaün
2016-08-25 11:09   ` Andy Lutomirski
2016-08-25 14:44     ` Mickaël Salaün
2016-08-26 12:55       ` Tejun Heo
2016-08-26 14:20       ` Andy Lutomirski
2016-08-26 15:50         ` Tejun Heo
2016-08-26  2:14   ` Alexei Starovoitov
2016-08-26 15:10     ` Mickaël Salaün
2016-08-26 23:05       ` Alexei Starovoitov
2016-08-27  7:30         ` Andy Lutomirski
2016-08-27 18:11           ` Alexei Starovoitov
2016-08-28  8:14             ` Andy Lutomirski
2016-08-27 14:06         ` [RFC v2 09/10] landlock: Handle cgroups (performance) Mickaël Salaün
2016-08-27 18:06           ` Alexei Starovoitov
2016-08-27 19:35             ` Mickaël Salaün
2016-08-27 20:43               ` Alexei Starovoitov
2016-08-27 21:14                 ` Mickaël Salaün
2016-08-28  8:13                   ` Andy Lutomirski
2016-08-28  9:42                     ` Mickaël Salaün
2016-08-30 18:55                       ` Andy Lutomirski
2016-08-30 20:20                         ` Mickaël Salaün
2016-08-30 20:23                           ` Andy Lutomirski
2016-08-30 20:33                             ` Mickaël Salaün [this message]
2016-08-30 20:55                               ` Alexei Starovoitov
2016-08-30 21:45                                 ` Andy Lutomirski
2016-08-31  1:36                                   ` Alexei Starovoitov
2016-08-31  3:29                                     ` Andy Lutomirski
2016-08-27 14:19         ` [RFC v2 09/10] landlock: Handle cgroups (netfilter match) Mickaël Salaün
2016-08-27 18:32           ` Alexei Starovoitov
2016-08-27 14:34         ` [RFC v2 09/10] landlock: Handle cgroups (program types) Mickaël Salaün
2016-08-27 18:19           ` Alexei Starovoitov
2016-08-27 19:55             ` Mickaël Salaün
2016-08-27 20:56               ` Alexei Starovoitov
2016-08-27 21:18                 ` Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 10/10] samples/landlock: Add sandbox example Mickaël Salaün
2016-08-25 11:05 ` [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Andy Lutomirski
2016-08-25 13:57   ` Mickaël Salaün
2016-08-27  7:40 ` Andy Lutomirski
2016-08-27 15:10   ` Mickaël Salaün
2016-08-27 15:21     ` [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing (cgroup delegation) Mickaël Salaün
2016-08-30 16:06 ` [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Andy Lutomirski
2016-08-30 19:51   ` Mickaël Salaün
2016-08-30 19:55     ` Andy Lutomirski
2016-09-15  9:19 ` Pavel Machek
2016-09-20 17:08   ` Mickaël Salaün
2016-09-24  7:45     ` Pavel Machek
2016-10-03 22:56     ` Kees Cook
2016-10-05 20:30       ` Mickaël Salaün

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