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From: "Mickaël Salaün" <mic@digikod.net>
To: Andy Lutomirski <luto@kernel.org>
Cc: Tycho Andersen <tycho@tycho.ws>,
	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>, 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: [PATCH bpf-next v8 00/11] Landlock LSM: Toward unprivileged sandboxing
Date: Mon, 2 Apr 2018 00:04:36 +0200	[thread overview]
Message-ID: <0f355079-7ee2-c06a-2d47-a7a2fa6d98fe@digikod.net> (raw)
In-Reply-To: <CALCETrUwkV4_65y7UjSgrq5WHOcZZ=+znKArehvhb1xEGG9HXw@mail.gmail.com>


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On 03/09/2018 12:53 AM, Andy Lutomirski wrote:
> On Thu, Mar 8, 2018 at 11:51 PM, Mickaël Salaün <mic@digikod.net> wrote:
>>
>> On 07/03/2018 02:21, Andy Lutomirski wrote:
>>> On Tue, Mar 6, 2018 at 11:06 PM, Mickaël Salaün <mic@digikod.net> wrote:
>>>>
>>>> On 06/03/2018 23:46, Tycho Andersen wrote:
>>>>> On Tue, Mar 06, 2018 at 10:33:17PM +0000, Andy Lutomirski wrote:
>>>>>>>> Suppose I'm writing a container manager.  I want to run "mount" in the
>>>>>>>> container, but I don't want to allow moun() in general and I want to
>>>>>>>> emulate certain mount() actions.  I can write a filter that catches
>>>>>>>> mount using seccomp and calls out to the container manager for help.
>>>>>>>> This isn't theoretical -- Tycho wants *exactly* this use case to be
>>>>>>>> supported.
>>>>>>>
>>>>>>> Well, I think this use case should be handled with something like
>>>>>>> LD_PRELOAD and a helper library. FYI, I did something like this:
>>>>>>> https://github.com/stemjail/stemshim
>>>>>>
>>>>>> I doubt that will work for containers.  Containers that use user
>>>>>> namespaces and, for example, setuid programs aren't going to honor
>>>>>> LD_PRELOAD.
>>>>>
>>>>> Or anything that calls syscalls directly, like go programs.
>>>>
>>>> That's why the vDSO-like approach. Enforcing an access control is not
>>>> the issue here, patching a buggy userland (without patching its code) is
>>>> the issue isn't it?
>>>>
>>>> As far as I remember, the main problem is to handle file descriptors
>>>> while "emulating" the kernel behavior. This can be done with a "shim"
>>>> code mapped in every processes. Chrome used something like this (in a
>>>> previous sandbox mechanism) as a kind of emulation (with the current
>>>> seccomp-bpf ). I think it should be doable to replace the (userland)
>>>> emulation code with an IPC wrapper receiving file descriptors through
>>>> UNIX socket.
>>>>
>>>
>>> Can you explain exactly what you mean by "vDSO-like"?
>>>
>>> When a 64-bit program does a syscall, it just executes the SYSCALL
>>> instruction.  The vDSO isn't involved at all.  32-bit programs usually
>>> go through the vDSO, but not always.
>>>
>>> It could be possible to force-load a DSO into an entire container and
>>> rig up seccomp to intercept all SYSCALLs not originating from the DSO
>>> such that they merely redirect control to the DSO, but that seems
>>> quite messy.
>>
>> vDSO is a code mapped for all processes. As you said, these processes
>> may use it or not. What I was thinking about is to use the same concept,
>> i.e. map a "shim" code into each processes pertaining to a particular
>> hierarchy (the same way seccomp filters are inherited across processes).
>> With a seccomp filter matching some syscall (e.g. mount, open), it is
>> possible to jump back to the shim code thanks to SECCOMP_RET_TRAP. This
>> shim code should then be able to emulate/patch what is needed, even
>> faking a file opening by receiving a file descriptor through a UNIX
>> socket. As did the Chrome sandbox, the seccomp filter may look at the
>> calling address to allow the shim code to call syscalls without being
>> catched, if needed. However, relying on SIGSYS may not fit with
>> arbitrary code. Using a new SECCOMP_RET_EMULATE (?) may be used to jump
>> to a specific process address, to emulate the syscall in an easier way
>> than only relying on a {c,e}BPF program.
>>
> 
> This could indeed be done, but I think that Tycho's approach is much
> cleaner and probably faster.
> 

I like it too but how does this handle file descriptors?


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  reply	other threads:[~2018-04-01 22:06 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-27  0:41 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
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 [this message]
2018-04-02  0:39                       ` Tycho Andersen

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