On Tue, Jun 23, 2020 at 01:17:28PM +0000, David Laight wrote: > 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. That's an interesting question. Do the RFCs say anything? I would assume it was ok unless ipv6only was set. > > I also wonder whether the connection should be dropped for an error > response on a path that has never been validated. That actually bothered me a bit more. Shouldn't it stay up if any path is up? That's kind of the whole point of multihoming. > > OTOH the whole 'multi-homing' part of SCTP sucks. I don't think so. > 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. Umm, no, If you have a private address, it better be behind a firewall, and the firewall should handle rewriting the packet to fix the addresses. It doesn't appear that Linux netfilter does this. There is a TODO in the code for this. But that's how it *should* work. -corey > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) >
