Re: Strange problem with SCTP+IPv6

[Michael Tuexen <Michael.Tuexen@lurchi.franken.de>]

> 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.

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;
>>>>> }
>>>>> 
>>