linux-kernel - Re: [PATCH v2 0/3] seccomp: add PR_SECCOMP_EXT and SECCOMP_EXT_ACT

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Message-ID: <CAGXu5jKfBz2siheK7mbghsVc_ynW=4Bc31AyHcvQ=Ux-veQe=A@mail.gmail.com>
Date:	Thu, 17 Apr 2014 11:18:57 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	John Johansen <john.johansen@...onical.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Will Drewry <wad@...omium.org>,
	Julien Tinnes <jln@...omium.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	LSM List <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v2 0/3] seccomp: add PR_SECCOMP_EXT and SECCOMP_EXT_ACT_TSYNC

On Thu, Apr 17, 2014 at 11:13 AM, Andy Lutomirski <luto@...capital.net> wrote:
> On Thu, Apr 17, 2014 at 11:05 AM, Kees Cook <keescook@...omium.org> 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.

-Kees

-- 
Kees Cook
Chrome OS Security
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