On Wed, Oct 16, 2024 at 04:46:52PM +1100, David Gibson wrote:On Wed, Oct 16, 2024 at 02:15:19PM +1100, David Gibson wrote:Ok.. I've understood a bit more. While timing is a factor here, it looks like the main reason I wasn't seeing it on my machine is what I'd consider a bug in the Debian version of the dhclient-script: when adding an IPv6 address, it returns without waiting for DAD to complete (i.e. for the address to be non-tentative). There's also an additional bug, which doesn't cause this problem, I think, but caused some problems when I was investigating. DHCPv6 needs the link-local SLAAC address already configured and non-tentative. The Fedora dhclient-script waits for that too at the PREINIT6 stage, but the Debian one doesn't, meaning if you attempt dhclient -6 immediately after starting the namespace it will fail to bind the UDP address it needs. I still think it's a good idea not to give NA messages for the guest assigned address, but we'll need a different workaround for this issue. I guess we'll have to manually wait for DAD to complete in the DHCP tests, which will be kind of mucky :/ -- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibsonOn Thu, Oct 10, 2024 at 04:57:32PM +1100, David Gibson wrote:Hmm... no.. there's more to this. Usually DAD requests have :: as the source address, and we *do* exclude those from getting replies. In this case though, we're getting NS requests for the assigned address from what looks like the SLAAC address. So, I do think it would be wise to explicitly exclude these: we shouldn't be giving NA responses for an address that ought to belong to the guest, even if it doesn't look like a DAD. But, I'm not sure what's triggering this. Is for some reason the DHCP address not "taking", so the container is trying to locate it on the network instead? Or _is_ this DAD, but under some circumstances rather than using :: as the source address it uses another configured address.On Wed, Oct 09, 2024 at 10:44:33PM +0200, Stefano Brivio wrote: > On Wed, 9 Oct 2024 15:07:21 +0200 > Stefano Brivio <sbrivio(a)redhat.com> wrote:[snip]I reproduced the problem on passt.top, and I have a partial idea what's going on. As you say it's seeming like the address (addr_seen == addr in this case) isn't properly ready. This is over splice, but on the tap interface, I see the container sending NS messages for its own address - seems like it's doing DAD. But more importantly, we're answering those NS messages with NA messages, because we answer all NS. i.e. we're making the DAD fail. What I'm not sure of is how this ever worked at all. --config-net makes sense, since we disable DAD, but our test suite has always been using NDP+DHCP instead of --config-net. So, AFACT, we'll always fail guest DAD attempts, both IPv6, which happens most of the time and for IPv4 via ARP, which is used much more rarely. I think we need to be more selective in what NS or ARP lookups we resopnd to. The question is what approach to take:> > @@ -447,20 +447,35 @@ uint8_t fwd_nat_from_host(const struct ctx *c, uint8_t proto, > > (proto == IPPROTO_TCP || proto == IPPROTO_UDP)) { > > /* spliceable */ > > > > - /* Preserve the specific loopback adddress used, but let the > > - * kernel pick a source port on the target side > > + /* The traffic will go over the guest's 'lo' interface, but by > > + * default use its external address, so we don't inadvertently > > + * expose services that listen only on the guest's loopback > > + * address. That can be overridden by --host-lo-to-ns-lo which > > + * will instead forward to the loopback address in the guest. > > + * > > + * In either case, let the kernel pick the source address to > > + * match. > > */ > > - tgt->oaddr = ini->eaddr; > > + if (inany_v4(&ini->eaddr)) { > > + if (c->host_lo_to_ns_lo) > > + tgt->eaddr = inany_loopback4; > > + else > > + tgt->eaddr = inany_from_v4(c->ip4.addr_seen); > > + tgt->oaddr = inany_any4; > > + } else { > > + if (c->host_lo_to_ns_lo) > > + tgt->eaddr = inany_loopback6; > > + else > > + tgt->eaddr.a6 = c->ip6.addr_seen; > > Either this... > > > + tgt->oaddr = inany_any6; > > or this (and not something before this patch, up to 3/4) make the > "TCP/IPv6: host to ns (spliced): big transfer" test in pasta/tcp hang, > sometimes (about one in three/four runs), that's what I mistakenly > reported as coming from Laurent's series at:Huh, interesting. Just got back from my leave and ran that group of tests in a loop this afternoon, but didn't manage to reproduce. I have administrivia that will probably fill the rest of this week, but I'll look into this as soon as I can.