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

From: Tycho Andersen <tycho@tycho.ws>
To: Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org, Sargun Dhillon <sargun@sargun.me>,
	Christian Brauner <christian@brauner.io>,
	"David S. Miller" <davem@davemloft.net>,
	Christoph Hellwig <hch@lst.de>, Jakub Kicinski <kuba@kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Aleksa Sarai <cyphar@cyphar.com>,
	Matt Denton <mpdenton@google.com>, Jann Horn <jannh@google.com>,
	Chris Palmer <palmer@google.com>,
	Robert Sesek <rsesek@google.com>,
	Giuseppe Scrivano <gscrivan@redhat.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Will Drewry <wad@chromium.org>, Shuah Khan <shuah@kernel.org>,
	netdev@vger.kernel.org, containers@lists.linux-foundation.org,
	linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v4 10/11] seccomp: Switch addfd to Extensible Argument ioctl
Date: Tue, 16 Jun 2020 10:18:59 -0600	[thread overview]
Message-ID: <20200616161859.GL2893648@cisco> (raw)
In-Reply-To: <202006160904.A30F2C5B9E@keescook>

On Tue, Jun 16, 2020 at 09:05:29AM -0700, Kees Cook wrote:
> On Tue, Jun 16, 2020 at 08:55:46AM -0600, Tycho Andersen wrote:
> > 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@chromium.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?
> 
> Only if they use addfd without this patch? :) Are you saying I should
> collapse this patch into the main addfd and test patches?

Oh, derp, I see :) Yeah, maybe that would be good.

Tycho