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References: <20230511123148.332043-1-aleksandr.mikhalitsyn@canonical.com> <ZFzpqZCV6V+hwKjI@t14s.localdomain>
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From:   Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Date:   Thu, 11 May 2023 15:26:31 +0200
Message-ID: <CAEivzxennLfeh=pbMBA2Qj_DQXLMijGKVcRiKuraacCxc=9mgA@mail.gmail.com>
Subject: Re: [PATCH net-next v2] sctp: add bpf_bypass_getsockopt proto callback
To:     Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc:     nhorman@tuxdriver.com, davem@davemloft.net,
        Daniel Borkmann <daniel@iogearbox.net>,
        Christian Brauner <brauner@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Xin Long <lucien.xin@gmail.com>, linux-sctp@vger.kernel.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org
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On Thu, May 11, 2023 at 3:12=E2=80=AFPM Marcelo Ricardo Leitner
<marcelo.leitner@gmail.com> wrote:
>
> Hi,

Hi Marcelo,

thanks! Fixed in -v3.

Kind regards,
Alex

>
> Two things:
>
> On Thu, May 11, 2023 at 02:31:48PM +0200, Alexander Mikhalitsyn 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 f=
dtable.
> >
> > This patch was born as a result of discussion around a new SCM_PIDFD in=
terface:
> > https://lore.kernel.org/all/20230413133355.350571-3-aleksandr.mikhalits=
yn@canonical.com/
>
> Cool, but the description is mentioning the CONNECTX3 sockopt.
>
> >
> > 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
> > Suggested-by: Stanislav Fomichev <sdf@google.com>
> > Acked-by: Stanislav Fomichev <sdf@google.com>
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.c=
om>
> > ---
> >  net/sctp/socket.c | 31 +++++++++++++++++++++++++++++++
> >  1 file changed, 31 insertions(+)
> >
> > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > index cda8c2874691..a211a203003c 100644
> > --- a/net/sctp/socket.c
> > +++ b/net/sctp/socket.c
> > @@ -8281,6 +8281,35 @@ static int sctp_getsockopt(struct sock *sk, int =
level, int optname,
> >       return retval;
> >  }
> >
> > +static bool sctp_bpf_bypass_getsockopt(int level, int optname)
> > +{
> > +     if (level =3D=3D SOL_SCTP) {
> > +             switch (optname) {
> > +             /*
> > +              * These options do fd_install(), and if BPF_CGROUP_RUN_P=
ROG_GETSOCKOPT
> > +              * hook returns an error after success of the original ha=
ndler
> > +              * sctp_getsockopt(...), userspace will receive an error =
from getsockopt
> > +              * syscall and will be not aware that fd was successfully=
 installed into fdtable.
> > +              *
> > +              * Let's prevent bpf cgroup hook from running on them.
> > +              */
>
> This and..
>
> > +             case SCTP_SOCKOPT_PEELOFF:
> > +             case SCTP_SOCKOPT_PEELOFF_FLAGS:
> > +             /*
> > +              * As pointed by Marcelo Ricardo Leitner it seems reasona=
ble to skip
> > +              * bpf getsockopt hook for this sockopt too. Because inte=
rnaly, it
> > +              * triggers connect() and if error will be masked userspa=
ce can be confused.
> > +              */
>
> ..this comments can be removed, as they are easily visible on the
> description later on for who is interested on why such lines were
> added.
>
> Thanks,
> Marcelo
>
> > +             case SCTP_SOCKOPT_CONNECTX3:
> > +                     return true;
> > +             default:
> > +                     return false;
> > +             }
> > +     }
> > +
> > +     return false;
> > +}
> > +
> >  static int sctp_hash(struct sock *sk)
> >  {
> >       /* STUB */
> > @@ -9650,6 +9679,7 @@ 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 +9735,7 @@ 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
> >