linux-kernel - Re: [PATCH v8 3/9] seccomp: introduce writer locking

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Date:	Fri, 27 Jun 2014 10:27:05 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Will Drewry <wad@...omium.org>,
	Julien Tinnes <jln@...omium.org>,
	David Drysdale <drysdale@...gle.com>,
	Linux API <linux-api@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-mips@...ux-mips.org,
	linux-arch <linux-arch@...r.kernel.org>,
	linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v8 3/9] seccomp: introduce writer locking

On Wed, Jun 25, 2014 at 11:07 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 06/24, Kees Cook wrote:
>>
>> +static void copy_seccomp(struct task_struct *p)
>> +{
>> +#ifdef CONFIG_SECCOMP
>> +     /*
>> +      * Must be called with sighand->lock held, which is common to
>> +      * all threads in the group. Regardless, nothing special is
>> +      * needed for the child since it is not yet in the tasklist.
>> +      */
>> +     BUG_ON(!spin_is_locked(&current->sighand->siglock));
>> +
>> +     get_seccomp_filter(current);
>> +     p->seccomp = current->seccomp;
>> +
>> +     if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
>> +             set_tsk_thread_flag(p, TIF_SECCOMP);
>> +#endif
>> +}
>
> Wait. But what about no_new_privs? We should copy it as well...
>
> Perhaps this helper should be updated a bit and moved into seccomp.c so
> that seccomp_sync_threads() could use it too.

Ah! Yes. I had been thinking it had been copied during the task_struct
duplication, but that would have been before holding sighand->lock, so
it needs explicit recopying. Thanks!

-Kees

-- 
Kees Cook
Chrome OS Security
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