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Date:   Sat, 28 Dec 2019 13:06:43 +1100
From:   Aleksa Sarai <cyphar@cyphar.com>
To:     Sargun Dhillon <sargun@sargun.me>
Cc:     linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        tycho@tycho.ws, jannh@google.com, christian.brauner@ubuntu.com,
        keescook@chromium.org
Subject: Re: [PATCH v2 2/2] seccomp: Check that seccomp_notif is zeroed out
 by the user
Message-ID: <20191228020643.jb2kn5wztwnrpr74@yavin.dot.cyphar.com>
References: <20191228014849.GA31783@ircssh-2.c.rugged-nimbus-611.internal>
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On 2019-12-28, Sargun Dhillon <sargun@sargun.me> wrote:
> This patch is a small change in enforcement of the uapi for
> SECCOMP_IOCTL_NOTIF_RECV ioctl. Specifically, the datastructure which
> is passed (seccomp_notif) must be zeroed out. Previously any of its
> members could be set to nonsense values, and we would ignore it.
>=20
> This ensures all fields are set to their zero value.
>=20
> This relies on the seccomp_notif datastructure to not have
> any unnamed padding, as it is valid to initialize the datastructure
> as:
>=20
>   struct seccomp_notif notif =3D {};
>=20
> This only initializes named members to their 0-value [1].
>=20
> [1]: https://lore.kernel.org/lkml/20191227023131.klnobtlfgeqcmvbb@yavin.d=
ot.cyphar.com/
>=20
> Signed-off-by: Sargun Dhillon <sargun@sargun.me>
> Cc: Kees Cook <keescook@chromium.org>

Looks good.

Reviewed-by: Aleksa Sarai <cyphar@cyphar.com>

> ---
>  kernel/seccomp.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>=20
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 12d2227e5786..4fd73cbdd01e 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -1026,6 +1026,12 @@ static long seccomp_notify_recv(struct seccomp_fil=
ter *filter,
>  	struct seccomp_notif unotif;
>  	ssize_t ret;
> =20
> +	ret =3D check_zeroed_user(buf, sizeof(unotif));
> +	if (ret < 0)
> +		return ret;
> +	if (!ret)
> +		return -EINVAL;
> +
>  	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
<https://www.cyphar.com/>

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