linux-kernel - Re: [PATCH v3 1/4] seccomp: Add sysctl to display available actions

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Message-ID: <5ebcdb7f-4aca-34a0-abbd-81eb5372776d@canonical.com>
Date:   Thu, 16 Feb 2017 14:05:41 -0600
From:   Tyler Hicks <tyhicks@...onical.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Paul Moore <paul@...l-moore.com>, Eric Paris <eparis@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Will Drewry <wad@...omium.org>, linux-audit@...hat.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        John Crispin <john@...ozen.org>
Subject: Re: [PATCH v3 1/4] seccomp: Add sysctl to display available actions

On 02/16/2017 01:01 PM, Andy Lutomirski wrote:
> On Thu, Feb 16, 2017 at 10:47 AM, Tyler Hicks <tyhicks@...onical.com> wrote:
>> On 02/15/2017 09:14 PM, Andy Lutomirski wrote:
>>> On Mon, Feb 13, 2017 at 7:45 PM, Tyler Hicks <tyhicks@...onical.com> wrote:
>>>> This patch creates a read-only sysctl containing an ordered list of
>>>> seccomp actions that the kernel supports. The ordering, from left to
>>>> right, is the lowest action value (kill) to the highest action value
>>>> (allow). Currently, a read of the sysctl file would return "kill trap
>>>> errno trace allow". The contents of this sysctl file can be useful for
>>>> userspace code as well as the system administrator.
>>>
>>> Would this make more sense as a new seccomp(2) mode a la
>>> SECCOMP_HAS_ACTION?  Then sandboxy things that have no fs access could
>>> use it.
>>>
>>
>> It would make sense for code that needs to check which actions are
>> available. It wouldn't make sense for administrators that need to check
>> which actions are available unless libseccomp provided a wrapper utility.
>>
>> Is this a theoretical concern or do you know of a sandboxed piece of
>> code that cannot access the sysctl before constructing a seccomp filter?
>>
> 
> It's semi-theoretical.  But suppose I unshare namespaces, unmount a
> bunch of stuff, then ask libseccomp to install a filter.  (I've
> written code that does exactly that.)   libseccomp won't be able to
> read the sysctl.

That's a good point. It seems like we might need both mechanisms
(SECCOMP_HAS_ACTION for code and actions_avail for humans).

Tyler

> 
> --Andy
> 




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