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

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

[Sabrina Dubroca]

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;
 
-- 
2.27.0

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

[Jakub Sitnicki]

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>

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

[Alexei Starovoitov]

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

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

[John Fastabend]

Alexei Starovoitov wrote:
> 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

Thanks for the patch. LGTM, I guess we should also break the
copy loop in __tcp_bpf_recvmsg if RCV_SHUTDOWN is set it
looks like TCP stack does. I'll send a follow up thanks!