linux-kernel - Re: [PATCH v4 10/11] seccomp: Switch addfd to Extensible Argument ioctl

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Date:   Tue, 16 Jun 2020 08:55:46 -0600
From:   Tycho Andersen <tycho@...ho.ws>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Sargun Dhillon <sargun@...gun.me>,
        Christian Brauner <christian@...uner.io>,
        "David S. Miller" <davem@...emloft.net>,
        Christoph Hellwig <hch@....de>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Aleksa Sarai <cyphar@...har.com>,
        Matt Denton <mpdenton@...gle.com>,
        Jann Horn <jannh@...gle.com>, Chris Palmer <palmer@...gle.com>,
        Robert Sesek <rsesek@...gle.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, Shuah Khan <shuah@...nel.org>,
        netdev@...r.kernel.org, containers@...ts.linux-foundation.org,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 10/11] seccomp: Switch addfd to Extensible Argument
 ioctl

On Mon, Jun 15, 2020 at 08:25:23PM -0700, Kees Cook wrote:
> This patch is based on discussions[1] with Sargun Dhillon, Christian
> Brauner, and David Laight. Instead of building size into the addfd
> structure, make it a function of the ioctl command (which is how sizes are
> normally passed to ioctls). To support forward and backward compatibility,
> just mask out the direction and size, and match everything. The size (and
> any future direction) checks are done along with copy_struct_from_user()
> logic. Also update the selftests to check size bounds.
> 
> [1] https://lore.kernel.org/lkml/20200612104629.GA15814@ircssh-2.c.rugged-nimbus-611.internal
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  include/uapi/linux/seccomp.h                  |  2 -
>  kernel/seccomp.c                              | 21 ++++++----
>  tools/testing/selftests/seccomp/seccomp_bpf.c | 40 ++++++++++++++++---
>  3 files changed, 49 insertions(+), 14 deletions(-)
> 
> diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
> index c347160378e5..473a61695ac3 100644
> --- a/include/uapi/linux/seccomp.h
> +++ b/include/uapi/linux/seccomp.h
> @@ -118,7 +118,6 @@ struct seccomp_notif_resp {
>  
>  /**
>   * struct seccomp_notif_addfd
> - * @size: The size of the seccomp_notif_addfd structure
>   * @id: The ID of the seccomp notification
>   * @flags: SECCOMP_ADDFD_FLAG_*
>   * @srcfd: The local fd number
> @@ -126,7 +125,6 @@ struct seccomp_notif_resp {
>   * @newfd_flags: The O_* flags the remote FD should have applied
>   */
>  struct seccomp_notif_addfd {
> -	__u64 size;

Huh? Won't this break builds?

Tycho