linux-kernel - Re: [PATCH] seccomp: do not reject initial filter using TSYNC

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Date:	Thu, 17 Jul 2014 10:53:40 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Kees Cook <keescook@...omium.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	LSM List <linux-security-module@...r.kernel.org>,
	James Morris <jmorris@...ei.org>,
	Oleg Nesterov <oleg@...hat.com>,
	David Drysdale <drysdale@...gle.com>
Subject: Re: [PATCH] seccomp: do not reject initial filter using TSYNC

On Thu, Jul 17, 2014 at 10:49 AM, Kees Cook <keescook@...omium.org> wrote:
> There was an unneeded sanity check in the TSYNC code that was causing
> the first filter applied to not allow the TSYNC flag. Additionally,
> this optimizes the thread loops to skip "current". It was harmless, but
> better to not cause problems in the future.
>
> Reported-by: David Drysdale <drysdale@...gle.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> This goes on top of the v11 seccomp-tsync series. If I should respin
> as v12, please let me know.
>
> Thanks!
> ---
>  kernel/seccomp.c |   11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 2125b83ccfd4..0e0c6905b81d 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -255,14 +255,15 @@ static inline pid_t seccomp_can_sync_threads(void)
>         BUG_ON(!mutex_is_locked(&current->signal->cred_guard_mutex));
>         BUG_ON(!spin_is_locked(&current->sighand->siglock));
>
> -       if (current->seccomp.mode != SECCOMP_MODE_FILTER)
> -               return -EACCES;
> -
>         /* Validate all threads being eligible for synchronization. */
>         caller = current;
>         for_each_thread(caller, thread) {
>                 pid_t failed;
>
> +               /* Skip current, since it is initiating the sync. */
> +               if (thread == current)
> +                       continue;
> +

Should that be "thread == caller"?

--Andy
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