From mboxrd@z Thu Jan 1 00:00:00 1970 From: Aleksa Sarai Subject: Re: [PATCH] seccomp: Check flags on seccomp_notif is unset Date: Fri, 27 Dec 2019 01:32:29 +1100 Message-ID: <20191226143229.sbopynwut2hhsiwn@yavin.dot.cyphar.com> References: <20191225214530.GA27780@ircssh-2.c.rugged-nimbus-611.internal> <20191226115245.usf7z5dkui7ndp4w@wittgenstein> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="fgt5mo6icnbxpigg" Return-path: Content-Disposition: inline In-Reply-To: <20191226115245.usf7z5dkui7ndp4w@wittgenstein> Sender: linux-kernel-owner@vger.kernel.org To: Christian Brauner Cc: Sargun Dhillon , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, tycho@tycho.ws, jannh@google.com, keescook@chromium.org List-Id: linux-api@vger.kernel.org --fgt5mo6icnbxpigg Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-12-26, Christian Brauner wrote: > On Wed, Dec 25, 2019 at 09:45:33PM +0000, Sargun Dhillon wrote: > > This patch is a small change in enforcement of the uapi for > > SECCOMP_IOCTL_NOTIF_RECV ioctl. Specificaly, the datastructure which is > > passed (seccomp_notif), has a flags member. Previously that could be > > set to a nonsense value, and we would ignore it. This ensures that > > no flags are set. > >=20 > > Signed-off-by: Sargun Dhillon > > Cc: Kees Cook >=20 > I'm fine with this since we soon want to make use of the flag argument > when we add a flag to get a pidfd from the seccomp notifier on receive. > The major users I could identify already pass in seccomp_notif with all > fields set to 0. If we really break users we can always revert; this > seems very unlikely to me though. >=20 > One more question below, otherwise: >=20 > Reviewed-by: Christian Brauner >=20 > > --- > > kernel/seccomp.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > >=20 > > diff --git a/kernel/seccomp.c b/kernel/seccomp.c > > index 12d2227e5786..455925557490 100644 > > --- a/kernel/seccomp.c > > +++ b/kernel/seccomp.c > > @@ -1026,6 +1026,13 @@ static long seccomp_notify_recv(struct seccomp_f= ilter *filter, > > struct seccomp_notif unotif; > > ssize_t ret; > > =20 > > + if (copy_from_user(&unotif, buf, sizeof(unotif))) > > + return -EFAULT; > > + > > + /* flags is reserved right now, make sure it's unset */ > > + if (unotif.flags) > > + return -EINVAL; > > + >=20 > Might it make sense to use >=20 > err =3D copy_struct_from_user(&unotif, sizeof(unotif), buf, sizeof(unoti= f)); > if (err) > return err; >=20 > This way we check that the whole struct is 0 and report an error as soon > as one of the members is non-zero. That's more drastic but it'd ensure > that other fields can be used in the future for whatever purposes. > It would also let us get rid of the memset() below.=20 Given that this isn't an extensible struct, it would be simpler to just do check_zeroed_user() -- copy_struct_from_user() is overkill. That would also remove the need for any copy_from_user()s and the memset can be dropped by just doing struct seccomp_notif unotif =3D {}; > > memset(&unotif, 0, sizeof(unotif)); > > =20 > > ret =3D down_interruptible(&filter->notif->request); > > --=20 > > 2.20.1 > >=20 --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --fgt5mo6icnbxpigg Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXgTEegAKCRCdlLljIbnQ EuTpAP4wZYtJyKgXrPhPg8m27dR0ZKvSVhgLQW+sH93GxA3prgEAq+3iCvwDomHL 7hxWTJqkQIAvqUejPuQZqKRMQ6qd5gw= =uj2S -----END PGP SIGNATURE----- --fgt5mo6icnbxpigg--