From: Marcelo Ricardo Leitner > Sent: 22 June 2020 19:33 > On Mon, Jun 22, 2020 at 08:01:24PM +0200, Michael Tuexen wrote: > > > 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? > > 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." Does it even make sense to mix IPv4 and IPv6 addresses on the same connection? I don't remember ever seeing both types of address in a message, but may not have looked. I also wonder whether the connection should be dropped for an error response on a path that has never been validated. OTOH the whole 'multi-homing' part of SCTP sucks. The IP addresses a server needs to bind to depend on where the incoming connection will come from. A local connection may be able to use a 192.168.x.x address but a remote connection must not - as it may be defined locally at the remote system. But both connections can come into the public (routable) address. We have to tell customers to explicitly configure the local IP addresses - which means the application has to know what they are. Fortunately these apps are pretty static - usually M3UA. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
