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Date:   Mon, 22 Jun 2020 11:57:59 -0500
From:   Corey Minyard <minyard@acm.org>
To:     Xin Long <lucien.xin@gmail.com>
Cc:     Vlad Yasevich <vyasevich@gmail.com>,
        Neil Horman <nhorman@tuxdriver.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
        linux-sctp@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: Strange problem with SCTP+IPv6
Message-ID: <20200622165759.GA3235@minyard.net>
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On Mon, Jun 22, 2020 at 08:01:23PM +0800, Xin Long wrote:
> On Sun, Jun 21, 2020 at 11:56 PM Corey Minyard <minyard@acm.org> wrote:
> >
> > I've stumbled upon a strange problem with SCTP and IPv6.  If I create an
> > sctp listening socket on :: and set the IPV6_V6ONLY socket option on it,
> > then I make a connection to it using ::1, the connection will drop after
> > 2.5 seconds with an ECONNRESET error.
> >
> > It only happens on SCTP, it doesn't have the issue if you connect to a
> > full IPv6 address instead of ::1, and it doesn't happen if you don't
> > set IPV6_V6ONLY.  I have verified current end of tree kernel.org.
> > I tried on an ARM system and x86_64.
> >
> > I haven't dug into the kernel to see if I could find anything yet, but I
> > thought I would go ahead and report it.  I am attaching a reproducer.
> > Basically, compile the following code:
> The code only set IPV6_V6ONLY on server side, so the client side will
> still bind all the local ipv4 addresses (as you didn't call bind() to
> bind any specific addresses ). Then after the connection is created,
> the client will send HB on the v4 paths to the server. The server
> will abort the connection, as it can't support v4.
> 
> So you can work around it by either:
> 
>   - set IPV6_V6ONLY on client side.
> 
> or
> 
>   - bind to the specific v6 addresses on the client side.
> 
> I don't see RFC said something about this.
> So it may not be a good idea to change the current behaviour
> to not establish the connection in this case, which may cause regression.

Ok, I understand this.  It's a little strange, but I see why it works
this way.

Thanks,

-corey

> 
> >
> >   gcc -g -o sctptest -Wall sctptest.c
> >
> > and run it in one window as a server:
> >
> >   ./sctptest a
> >
> > (Pass in any option to be the server) and run the following in another
> > window as the client:
> >
> >   ./sctptest
> >
> > It disconnects after about 2.5 seconds.  If it works, it should just sit
> > there forever.
> >
> > -corey
> >
> >
> > #include <stdio.h>
> > #include <stdbool.h>
> > #include <string.h>
> > #include <unistd.h>
> > #include <fcntl.h>
> > #include <sys/select.h>
> > #include <arpa/inet.h>
> > #include <netinet/sctp.h>
> > #include <sys/types.h>
> > #include <sys/socket.h>
> > #include <netdb.h>
> >
> > static int
> > getaddr(const char *addr, const char *port, bool listen,
> >         struct addrinfo **rai)
> > {
> >     struct addrinfo *ai, hints;
> >
> >     memset(&hints, 0, sizeof(hints));
> >     hints.ai_flags = AI_ADDRCONFIG;
> >     if (listen)
> >         hints.ai_flags |= AI_PASSIVE;
> >     hints.ai_family = AF_UNSPEC;
> >     hints.ai_socktype = SOCK_STREAM;
> >     hints.ai_protocol = IPPROTO_SCTP;
> >     if (getaddrinfo(addr, port, &hints, &ai)) {
> >         perror("getaddrinfo");
> >         return -1;
> >     }
> >
> >     *rai = ai;
> >     return 0;
> > }
> >
> > static int
> > waitread(int s)
> > {
> >     char data[1];
> >     ssize_t rv;
> >
> >     rv = read(s, data, sizeof(data));
> >     if (rv == -1) {
> >         perror("read");
> >         return -1;
> >     }
> >     printf("Read %d bytes\n", (int) rv);
> >     return 0;
> > }
> >
> > static int
> > do_server(void)
> > {
> >     int err, ls, s, optval;
> >     struct addrinfo *ai;
> >
> >     printf("Server\n");
> >
> >     err = getaddr("::", "3023", true, &ai);
> >     if (err)
> >         return err;
> >
> >     ls = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
> >     if (ls == -1) {
> >         perror("socket");
> >         return -1;
> >     }
> >
> >     optval = 1;
> >     if (setsockopt(ls, SOL_SOCKET, SO_REUSEADDR,
> >                    (void *)&optval, sizeof(optval)) == -1) {
> >         perror("setsockopt reuseaddr");
> >         return -1;
> >     }
> >
> >     /* Comment this out and it will work. */
> >     if (setsockopt(ls, IPPROTO_IPV6, IPV6_V6ONLY, &optval,
> >                    sizeof(optval)) == -1) {
> >         perror("setsockopt ipv6 only");
> >         return -1;
> >     }
> >
> >     err = bind(ls, ai->ai_addr, ai->ai_addrlen);
> >     if (err == -1) {
> >         perror("bind");
> >         return -1;
> >     }
> >
> >     err = listen(ls, 5);
> >     if (err == -1) {
> >         perror("listen");
> >         return -1;
> >     }
> >
> >     s = accept(ls, NULL, NULL);
> >     if (s == -1) {
> >         perror("accept");
> >         return -1;
> >     }
> >
> >     close(ls);
> >
> >     err = waitread(s);
> >     close(s);
> >     return err;
> > }
> >
> > static int
> > do_client(void)
> > {
> >     int err, s;
> >     struct addrinfo *ai;
> >
> >     printf("Client\n");
> >
> >     err = getaddr("::1", "3023", false, &ai);
> >     if (err)
> >         return err;
> >
> >     s = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
> >     if (s == -1) {
> >         perror("socket");
> >         return -1;
> >     }
> >
> >     err = connect(s, ai->ai_addr, ai->ai_addrlen);
> >     if (err == -1) {
> >         perror("connect");
> >         return -1;
> >     }
> >
> >     err = waitread(s);
> >     close(s);
> >     return err;
> > }
> >
> > int
> > main(int argc, char *argv[])
> > {
> >     int err;
> >
> >     if (argc > 1)
> >         err = do_server();
> >     else
> >         err = do_client();
> >     return !!err;
> > }
> >