Re: [PATCH v2 0/3] seccomp: add PR_SECCOMP_EXT and SECCOMP_EXT_ACT_TSYNC

[Kees Cook]

On Thu, Apr 17, 2014 at 11:31 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Thu, Apr 17, 2014 at 11:18 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>> On Thu, Apr 17, 2014 at 11:13 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>>> On Thu, Apr 17, 2014 at 11:05 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>>>> This adds the ability for threads to request seccomp filter
>>>> synchronization across their thread group. To support this,
>>>> seccomp locking on writes is introduced, along with refactoring
>>>> of no_new_privs. Races with thread creation are handled via the
>>>> tasklist_list.
>>>>
>>>> I think all the concerns raised during the discussion[1] of the first
>>>> version of this patch have been addressed. However, the races involved
>>>> have tricked me before. :)
>>>>
>>>
>>> Would this be easier to use if there were a single syscall to set a
>>> seccomp filter and sync threads?  That way you wouldn't have to write
>>> your filter such that it gives permission to sync threads.
>>
>> That would be even cleaner, yes. I was hoping to see the new bpf jump
>> tables before expanding into new filter calls, with the hope of doing
>> it all at the same time. However, I guess we could just include a
>> version number in the new call to indicate which filter type it was,
>> and include flags (like "threadgroup sync") in there? I'm trying to
>> imagine what would be the least painful for future-proofing.
>
> What's the time frame on the new bpf stuff?  If it'll be ready for
> 3.16, it might not matter.

I don't think seccomp will be extended to deal with that for a while,
since it'd require a lot of coordination first. So, for now, I think
adding a "flags" field should be sufficient. I'll work that up.

-Kees

-- 
Kees Cook
Chrome OS Security
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