Re: [PATCH bpf] bpf: tcp: recv() should return 0 when the peer socket is closed

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Jakub Sitnicki <jakub@cloudflare.com>
Cc: Sabrina Dubroca <sd@queasysnail.net>,
	Network Development <netdev@vger.kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	Daniel Borkmann <daniel@iogearbox.net>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH bpf] bpf: tcp: recv() should return 0 when the peer socket is closed
Date: Fri, 12 Jun 2020 15:13:14 -0700	[thread overview]
Message-ID: <CAADnVQKYHg-ZmzEibZ7TtZdyfNK+r7FQfv_DuJK44LdRuATDGw@mail.gmail.com> (raw)
In-Reply-To: <20200612121526.4810a073@toad>

On Fri, Jun 12, 2020 at 3:18 AM Jakub Sitnicki <jakub@cloudflare.com> wrote:
>
> On Wed, 10 Jun 2020 12:19:43 +0200
> Sabrina Dubroca <sd@queasysnail.net> wrote:
>
> > If the peer is closed, we will never get more data, so
> > tcp_bpf_wait_data will get stuck forever. In case we passed
> > MSG_DONTWAIT to recv(), we get EAGAIN but we should actually get
> > 0.
> >
> > From man 2 recv:
> >
> >     RETURN VALUE
> >
> >     When a stream socket peer has performed an orderly shutdown, the
> >     return value will be 0 (the traditional "end-of-file" return).
> >
> > This patch makes tcp_bpf_wait_data always return 1 when the peer
> > socket has been shutdown. Either we have data available, and it would
> > have returned 1 anyway, or there isn't, in which case we'll call
> > tcp_recvmsg which does the right thing in this situation.
> >
> > Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
> > Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
> > ---
> >  net/ipv4/tcp_bpf.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
> > index 2b915aafda42..7aa68f4aae6c 100644
> > --- a/net/ipv4/tcp_bpf.c
> > +++ b/net/ipv4/tcp_bpf.c
> > @@ -245,6 +245,9 @@ static int tcp_bpf_wait_data(struct sock *sk, struct sk_psock *psock,
> >       DEFINE_WAIT_FUNC(wait, woken_wake_function);
> >       int ret = 0;
> >
> > +     if (sk->sk_shutdown & RCV_SHUTDOWN)
> > +             return 1;
> > +
> >       if (!timeo)
> >               return ret;
> >
>
> Acked-by: Jakub Sitnicki <jakub@cloudflare.com>

Applied. Thanks