linux-kernel - Re: [PATCH net-next v2] sctp: add bpf_bypass

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Message-ID: <CAEivzxennLfeh=pbMBA2Qj_DQXLMijGKVcRiKuraacCxc=9mgA@mail.gmail.com>
Date:   Thu, 11 May 2023 15:26:31 +0200
From:   Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     nhorman@...driver.com, davem@...emloft.net,
        Daniel Borkmann <daniel@...earbox.net>,
        Christian Brauner <brauner@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Xin Long <lucien.xin@...il.com>, linux-sctp@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2] sctp: add bpf_bypass_getsockopt proto callback

On Thu, May 11, 2023 at 3:12 PM Marcelo Ricardo Leitner
<marcelo.leitner@...il.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 fdtable.
> >
> > This patch was born as a result of discussion around a new SCM_PIDFD interface:
> > https://lore.kernel.org/all/20230413133355.350571-3-aleksandr.mikhalitsyn@canonical.com/
>
> Cool, but the description is mentioning the CONNECTX3 sockopt.
>
> >
> > Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks")
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > Cc: Christian Brauner <brauner@...nel.org>
> > Cc: Stanislav Fomichev <sdf@...gle.com>
> > Cc: Neil Horman <nhorman@...driver.com>
> > Cc: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> > Cc: Xin Long <lucien.xin@...il.com>
> > Cc: linux-sctp@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > Cc: netdev@...r.kernel.org
> > Suggested-by: Stanislav Fomichev <sdf@...gle.com>
> > Acked-by: Stanislav Fomichev <sdf@...gle.com>
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
> > ---
> >  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 == SOL_SCTP) {
> > +             switch (optname) {
> > +             /*
> > +              * 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 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 reasonable to skip
> > +              * bpf getsockopt hook for this sockopt too. Because internaly, it
> > +              * triggers connect() and if error will be masked userspace 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 = {
> >       .shutdown    =  sctp_shutdown,
> >       .setsockopt  =  sctp_setsockopt,
> >       .getsockopt  =  sctp_getsockopt,
> > +     .bpf_bypass_getsockopt  = sctp_bpf_bypass_getsockopt,
> >       .sendmsg     =  sctp_sendmsg,
> >       .recvmsg     =  sctp_recvmsg,
> >       .bind        =  sctp_bind,
> > @@ -9705,6 +9735,7 @@ struct proto sctpv6_prot = {
> >       .shutdown       = sctp_shutdown,
> >       .setsockopt     = sctp_setsockopt,
> >       .getsockopt     = sctp_getsockopt,
> > +     .bpf_bypass_getsockopt  = sctp_bpf_bypass_getsockopt,
> >       .sendmsg        = sctp_sendmsg,
> >       .recvmsg        = sctp_recvmsg,
> >       .bind           = sctp_bind,
> > --
> > 2.34.1
> >