linux-kernel - Re: [PATCH v7 2/9] seccomp: split filter prep from check and apply

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Message-ID: <CAGXu5j+CxPPj2m+mgAR99O9PmDF0Pg4vKEXqN6SOdawQ7X_q8g@mail.gmail.com>
Date:	Fri, 27 Jun 2014 11:45:23 -0700
From:	Kees Cook <keescook@...omium.org>
To:	David Drysdale <drysdale@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Alexei Starovoitov <ast@...mgrid.com>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Will Drewry <wad@...omium.org>,
	Julien Tinnes <jln@...omium.org>,
	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 v7 2/9] seccomp: split filter prep from check and apply

On Thu, Jun 26, 2014 at 5:37 AM, David Drysdale <drysdale@...gle.com> wrote:
> On Mon, Jun 23, 2014 at 02:58:06PM -0700, Kees Cook wrote:
>> In preparation for adding seccomp locking, move filter creation away
>> from where it is checked and applied. This will allow for locking where
>> no memory allocation is happening. The validation, filter attachment,
>> and seccomp mode setting can all happen under the future locks.
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>  kernel/seccomp.c |   97 +++++++++++++++++++++++++++++++++++++-----------------
>>  1 file changed, 67 insertions(+), 30 deletions(-)
>>
>> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
>> index afb916c7e890..edc8c79ed16d 100644
>> --- a/kernel/seccomp.c
>> +++ b/kernel/seccomp.c
>> @@ -515,6 +551,7 @@ static long seccomp_set_mode(unsigned long seccomp_mode, char __user *filter)
>>       current->seccomp.mode = seccomp_mode;
>>       set_thread_flag(TIF_SECCOMP);
>>  out:
>> +     seccomp_filter_free(prepared);
>>       return ret;
>>  }
>
> I think this needs to be inside #ifdef CONFIG_SECCOMP_FILTER to match
> the definition of seccomp_filter_free:
>
> ../kernel/seccomp.c:554:2: error: implicit declaration of function ‘seccomp_filter_free’ [-Werror=implicit-function-declaration]

Thanks for catching that! I've ended up rearranging the patch series
so the prepare/attach split happens after I've split the set_mode
functions now, so I've managed to avoid this condition now. :)

-Kees

-- 
Kees Cook
Chrome OS Security
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