Re: [RFC PATCH v1 1/2] vsock: send SIGPIPE on write to shutdowned socket

[Stefano Garzarella]

On Fri, Aug 04, 2023 at 03:46:47PM +0300, Arseniy Krasnov wrote:
> Hi Stefano,
>
> On 02.08.2023 10:46, Stefano Garzarella wrote:
> > On Tue, Aug 01, 2023 at 05:17:26PM +0300, Arseniy Krasnov wrote:
> > > POSIX requires to send SIGPIPE on write to SOCK_STREAM socket which was
> > > shutdowned with SHUT_WR flag or its peer was shutdowned with SHUT_RD
> > > flag. Also we must not send SIGPIPE if MSG_NOSIGNAL flag is set.
> > >
> > > Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
> > > ---
> > > net/vmw_vsock/af_vsock.c | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> > > index 020cf17ab7e4..013b65241b65 100644
> > > --- a/net/vmw_vsock/af_vsock.c
> > > +++ b/net/vmw_vsock/af_vsock.c
> > > @@ -1921,6 +1921,9 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
> > >             err = total_written;
> > >     }
> > > out:
> > > +    if (sk->sk_type == SOCK_STREAM)
> > > +        err = sk_stream_error(sk, msg->msg_flags, err);
> >
> > Do you know why we don't need this for SOCK_SEQPACKET and SOCK_DGRAM?
>
> Yes, here is my explanation:
>
> This function checks that input error is SIGPIPE, and if so it sends SIGPIPE to the 'current' thread
> (except case when MSG_NOSIGNAL flag is set). This behaviour is described in POSIX:
>
> Page 367 (description of defines from sys/socket.h):
> MSG_NOSIGNAL: No SIGPIPE generated when an attempt to send is made on a stream-
> oriented socket that is no longer connected.
>
> Page 497 (description of SOCK_STREAM):
> A SIGPIPE signal is raised if a thread sends on a broken stream (one that is
> no longer connected).

Okay, but I think we should do also for SEQPACKET:

https://pubs.opengroup.org/onlinepubs/009696699/functions/xsh_chap02_10.html

In 2.10.6 Socket Types:

"The SOCK_SEQPACKET socket type is similar to the SOCK_STREAM type, and
is also connection-oriented. The only difference between these types is
that record boundaries ..."

Then in  2.10.14 Signals:

"The SIGPIPE signal shall be sent to a thread that attempts to send data
on a socket that is no longer able to send. In addition, the send
operation fails with the error [EPIPE]."

It's honestly not super clear, but I assume the problem is similar with
seqpacket since it's connection-oriented, or did I miss something?

For example in sctp_sendmsg() IIUC we raise a SIGPIPE regardless of
whether the socket is STREAM or SEQPACKET.

> Page 1802 (description of 'send()' call):
> MSG_NOSIGNAL
>
> Requests not to send the SIGPIPE signal if an attempt to
> send is made on a stream-oriented socket that is no
> longer connected. The [EPIPE] error shall still be
> returned
>
> And the same for 'sendto()' and 'sendmsg()'
>
> Link to the POSIX document:
> https://www.open-std.org/jtc1/sc22/open/n4217.pdf
>
> TCP (I think we must rely on it), KCM, SMC sockets (all of them are stream) work in the same
> way by calling this function. AF_UNIX also works in the same way, but it implements SIGPIPE handling
> without this function.

I'm okay calling this function.

> The only thing that confused me a little bit, that sockets above returns EPIPE when
> we have only SEND_SHUTDOWN set, but for AF_VSOCK EPIPE is returned for RCV_SHUTDOWN
> also, but I think it is related to this patchset.

Do you mean that it is NOT related to this patchset?

Thanks,
Stefano