Re: Strange problem with SCTP+IPv6

[Xin Long <lucien.xin@gmail.com>]

On Tue, Jun 23, 2020 at 2:34 AM Michael Tuexen
<Michael.Tuexen@lurchi.franken.de> wrote:
>
> > On 22. Jun 2020, at 20:32, Marcelo Ricardo Leitner <marcelo.leitner@gmail.com> wrote:
> >
> > 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."
> I agree.
Then we need a fix in sctp_bind_addrs_to_raw():

@@ -238,6 +240,9 @@ union sctp_params sctp_bind_addrs_to_raw(const
struct sctp_bind_addr *bp,
        addrparms = retval;

        list_for_each_entry(addr, &bp->address_list, list) {
+               if ((PF_INET6 = sk->sk_family) && inet_v6_ipv6only(sk) &&
+                   (AF_INET = addr->a.sa.sa_family))
+                       continue;
                af = sctp_get_af_specific(addr->a.v4.sin_family);
                len = af->to_addr_param(&addr->a, &rawaddr);
                memcpy(addrparms.v, &rawaddr, len);

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