Date:   Tue, 23 Jun 2020 08:29:36 -0500
From:   Corey Minyard <minyard@....org>
To:     Xin Long <lucien.xin@...il.com>
Cc:     Michael Tuexen <Michael.Tuexen@...chi.franken.de>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        linux-sctp@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: Strange problem with SCTP+IPv6

On Tue, Jun 23, 2020 at 06:13:30PM +0800, Xin Long wrote:
> On Tue, Jun 23, 2020 at 2:34 AM Michael Tuexen
> <Michael.Tuexen@...chi.franken.de> wrote:
> >
> > > On 22. Jun 2020, at 20:32, Marcelo Ricardo Leitner <marcelo.leitner@...il.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@....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@....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;

This does not compile in the latest mainline.  sk is not defined.
Also, if you could send a normal git patch, that would be easier to 
manage.

Thanks,

-corey

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

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