linux-kernel - Re: [PATCH v2 7/9] seccomp: Replace smp_read_barrier_depends() with lockless

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Date:	Fri, 21 Nov 2014 08:33:40 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Pranith Kumar <bobby.prani@...il.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 7/9] seccomp: Replace smp_read_barrier_depends() with lockless_dereference()

On Fri, Nov 21, 2014 at 7:06 AM, Pranith Kumar <bobby.prani@...il.com> wrote:
> Recently lockless_dereference() was added which can be used in place of
> hard-coding smp_read_barrier_depends(). The following PATCH makes the change.
>
> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
> ---
>  kernel/seccomp.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)

Thanks!

Acked-by: Kees Cook <keescook@...omium.org>

Do you need me to carry this patch in the seccomp tree, or will
someone else be taking your entire series?

-Kees

>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 4ef9687..3729b06 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -175,17 +175,16 @@ static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
>   */
>  static u32 seccomp_run_filters(struct seccomp_data *sd)
>  {
> -       struct seccomp_filter *f = ACCESS_ONCE(current->seccomp.filter);
>         struct seccomp_data sd_local;
>         u32 ret = SECCOMP_RET_ALLOW;
> +       /* Make sure cross-thread synced filter points somewhere sane. */
> +       struct seccomp_filter *f =
> +                       lockless_dereference(current->seccomp.filter);
>
>         /* Ensure unexpected behavior doesn't result in failing open. */
>         if (unlikely(WARN_ON(f == NULL)))
>                 return SECCOMP_RET_KILL;
>
> -       /* Make sure cross-thread synced filter points somewhere sane. */
> -       smp_read_barrier_depends();
> -
>         if (!sd) {
>                 populate_seccomp_data(&sd_local);
>                 sd = &sd_local;
> --
> 1.9.1
>



-- 
Kees Cook
Chrome OS Security
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