Re: Strange problem with SCTP+IPv6

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

On Mon, Jun 22, 2020 at 08:01:24PM +0200, Michael Tuexen wrote:
> > On 22. Jun 2020, at 18:57, Corey Minyard <minyard@acm.org> wrote:
> > 
> > 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.
> I don't. I would expect it to work as I described in my email.
> Could someone explain me how and why it is behaving different from
> my expectation?

It looks like a bug to me. Testing with this test app here, I can see
the INIT_ACK being sent with a bunch of ipv4 addresses in it and
that's unexpected for a v6only socket. As is, it's the server saying
"I'm available at these other addresses too, but not."

Thanks,
Marcelo

> 
> Best regards
> Michael
> > 
> > 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;
> >>> }
> >>> 
>