Re: Strange problem with SCTP+IPv6

[Michael Tuexen]

> On 22. Jun 2020, at 18:57, Corey Minyard <minyard@xxxxxxx> 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@xxxxxxx> 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?

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;
>>> }
>>>