netdev - Re: [Patch bpf-next v3 05/10] af_unix: implement unix_dgram_bpf

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Date:   Sat, 8 May 2021 13:43:13 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jakub Sitnicki <jakub@...udflare.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Jiang Wang <jiang.wang@...edance.com>,
        Xiongchun Duan <duanxiongchun@...edance.com>,
        Dongdong Wang <wangdongdong.6@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [Patch bpf-next v3 05/10] af_unix: implement unix_dgram_bpf_recvmsg()

On Fri, May 7, 2021 at 6:29 AM Jakub Sitnicki <jakub@...udflare.com> wrote:
>
> On Mon, Apr 26, 2021 at 04:49 AM CEST, Cong Wang wrote:
> > From: Cong Wang <cong.wang@...edance.com>
> >
> > We have to implement unix_dgram_bpf_recvmsg() to replace the
> > original ->recvmsg() to retrieve skmsg from ingress_msg.
> >
> > AF_UNIX is again special here because the lack of
> > sk_prot->recvmsg(). I simply add a special case inside
> > unix_dgram_recvmsg() to call sk->sk_prot->recvmsg() directly.
> >
> > Cc: John Fastabend <john.fastabend@...il.com>
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > Cc: Jakub Sitnicki <jakub@...udflare.com>
> > Cc: Lorenz Bauer <lmb@...udflare.com>
> > Signed-off-by: Cong Wang <cong.wang@...edance.com>
> > ---
> >  include/net/af_unix.h |  3 +++
> >  net/unix/af_unix.c    | 21 ++++++++++++++++---
> >  net/unix/unix_bpf.c   | 49 +++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 70 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/net/af_unix.h b/include/net/af_unix.h
> > index cca645846af1..e524c82794c9 100644
> > --- a/include/net/af_unix.h
> > +++ b/include/net/af_unix.h
> > @@ -82,6 +82,9 @@ static inline struct unix_sock *unix_sk(const struct sock *sk)
> >  long unix_inq_len(struct sock *sk);
> >  long unix_outq_len(struct sock *sk);
> >
> > +int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size,
> > +                      int nonblock, int flags, int *addr_len);
> > +
> >  #ifdef CONFIG_SYSCTL
> >  int unix_sysctl_register(struct net *net);
> >  void unix_sysctl_unregister(struct net *net);
> > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> > index c4afc5fbe137..08458fa9f48b 100644
> > --- a/net/unix/af_unix.c
> > +++ b/net/unix/af_unix.c
> > @@ -2088,11 +2088,11 @@ static void unix_copy_addr(struct msghdr *msg, struct sock *sk)
> >       }
> >  }
> >
> > -static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
> > -                           size_t size, int flags)
> > +int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size,
> > +                      int nonblock, int flags, int *addr_len)
> >  {
> >       struct scm_cookie scm;
> > -     struct sock *sk = sock->sk;
> > +     struct socket *sock = sk->sk_socket;
> >       struct unix_sock *u = unix_sk(sk);
> >       struct sk_buff *skb, *last;
> >       long timeo;
> > @@ -2195,6 +2195,21 @@ static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
> >       return err;
> >  }
> >
> > +static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
> > +                           int flags)
> > +{
> > +     struct sock *sk = sock->sk;
> > +     int addr_len = 0;
> > +
> > +#ifdef CONFIG_BPF_SYSCALL
> > +     if (sk->sk_prot != &unix_proto)
> > +             return sk->sk_prot->recvmsg(sk, msg, size, flags & MSG_DONTWAIT,
> > +                                         flags & ~MSG_DONTWAIT, &addr_len);
> > +#endif
> > +     return __unix_dgram_recvmsg(sk, msg, size, flags & MSG_DONTWAIT,
> > +                                 flags, &addr_len);
> > +}
> > +
>
> Nit: We can just pass NULL instead of &addr_len here it seems.

Yeah, we can actually remove this parameter for __unix_dgram_recvmsg().
Only unix_dgram_bpf_recvmsg() needs it as it is enforced by sk_prot.

Thanks.