Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230510131527.1244929-1-aleksandr.mikhalitsyn@canonical.com>
In-Reply-To: <20230510131527.1244929-1-aleksandr.mikhalitsyn@canonical.com>
From:   Stanislav Fomichev <sdf@google.com>
Date:   Wed, 10 May 2023 07:31:55 -0700
Message-ID: <CAKH8qBuzWHoEiABvTgM2qnx5Av127VMHnncGtU5EZq+ffT9eGg@mail.gmail.com>
Subject: Re: [PATCH net-next] sctp: add bpf_bypass_getsockopt proto callback
To:     Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Cc:     nhorman@tuxdriver.com, davem@davemloft.net,
        Daniel Borkmann <daniel@iogearbox.net>,
        Christian Brauner <brauner@kernel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
        Xin Long <lucien.xin@gmail.com>, linux-sctp@vger.kernel.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Wed, May 10, 2023 at 6:15=E2=80=AFAM Alexander Mikhalitsyn
<aleksandr.mikhalitsyn@canonical.com> wrote:
>
> Add bpf_bypass_getsockopt proto callback and filter out
> SCTP_SOCKOPT_PEELOFF and SCTP_SOCKOPT_PEELOFF_FLAGS socket options
> from running eBPF hook on them.
>
> These options do fd_install(), and if BPF_CGROUP_RUN_PROG_GETSOCKOPT
> hook returns an error after success of the original handler
> sctp_getsockopt(...), userspace will receive an error from getsockopt
> syscall and will be not aware that fd was successfully installed into fdt=
able.
>
> This patch was born as a result of discussion around a new SCM_PIDFD inte=
rface:
> https://lore.kernel.org/all/20230413133355.350571-3-aleksandr.mikhalitsyn=
@canonical.com/
>
> Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks")
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: Stanislav Fomichev <sdf@google.com>
> Cc: Neil Horman <nhorman@tuxdriver.com>
> Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> Cc: Xin Long <lucien.xin@gmail.com>
> Cc: linux-sctp@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: netdev@vger.kernel.org
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com=
>

Acked-by: Stanislav Fomichev <sdf@google.com>

with a small nit below

> ---
>  net/sctp/socket.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index cda8c2874691..a9a0ababea90 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -8281,6 +8281,29 @@ static int sctp_getsockopt(struct sock *sk, int le=
vel, int optname,
>         return retval;
>  }
>

[...]

> +bool sctp_bpf_bypass_getsockopt(int level, int optname)

static bool ... ? You're not making it indirect-callable, so seems
fine to keep private to this compilation unit?

> +{
> +       /*
> +        * These options do fd_install(), and if BPF_CGROUP_RUN_PROG_GETS=
OCKOPT
> +        * hook returns an error after success of the original handler
> +        * sctp_getsockopt(...), userspace will receive an error from get=
sockopt
> +        * syscall and will be not aware that fd was successfully install=
ed into fdtable.
> +        *
> +        * Let's prevent bpf cgroup hook from running on them.
> +        */
> +       if (level =3D=3D SOL_SCTP) {
> +               switch (optname) {
> +               case SCTP_SOCKOPT_PEELOFF:
> +               case SCTP_SOCKOPT_PEELOFF_FLAGS:
> +                       return true;
> +               default:
> +                       return false;
> +               }
> +       }
> +
> +       return false;
> +}
> +
>  static int sctp_hash(struct sock *sk)
>  {
>         /* STUB */
> @@ -9650,6 +9673,7 @@ struct proto sctp_prot =3D {
>         .shutdown    =3D  sctp_shutdown,
>         .setsockopt  =3D  sctp_setsockopt,
>         .getsockopt  =3D  sctp_getsockopt,
> +       .bpf_bypass_getsockopt  =3D sctp_bpf_bypass_getsockopt,
>         .sendmsg     =3D  sctp_sendmsg,
>         .recvmsg     =3D  sctp_recvmsg,
>         .bind        =3D  sctp_bind,
> @@ -9705,6 +9729,7 @@ struct proto sctpv6_prot =3D {
>         .shutdown       =3D sctp_shutdown,
>         .setsockopt     =3D sctp_setsockopt,
>         .getsockopt     =3D sctp_getsockopt,
> +       .bpf_bypass_getsockopt  =3D sctp_bpf_bypass_getsockopt,
>         .sendmsg        =3D sctp_sendmsg,
>         .recvmsg        =3D sctp_recvmsg,
>         .bind           =3D sctp_bind,
> --
> 2.34.1
>