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[2a10:fc81:a806:d6a9::1]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-371898abf2csm1184863f8f.107.2024.08.15.03.59.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Aug 2024 03:59:34 -0700 (PDT) Date: Thu, 15 Aug 2024 12:59:32 +0200 From: Stefano Brivio To: David Gibson Subject: Re: [PATCH v2 4/7] netlink, pasta: Disable DAD for link-local addresses on namespace interface Message-ID: <20240815125932.53f38296@elisabeth> In-Reply-To: References: <20240815083649.4188007-1-sbrivio@redhat.com> <20240815083649.4188007-5-sbrivio@redhat.com> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.41; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: 4RXTNRDFA5PPP5TXIZIEUTELG3NHYLH4 X-Message-ID-Hash: 4RXTNRDFA5PPP5TXIZIEUTELG3NHYLH4 X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: passt-dev@passt.top, Paul Holzinger X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Thu, 15 Aug 2024 20:38:17 +1000 David Gibson wrote: > On Thu, Aug 15, 2024 at 10:36:46AM +0200, Stefano Brivio wrote: > > It makes no sense for a container or a guest to try and perform > > duplicate address detection for their link-local address, as we'll > > anyway not relay neighbour solicitations with an unspecified source > > address. > > > > While they perform duplicate address detection, the link-local address > > is not usable, which prevents us from bringing up especially > > containers and communicate with them right away via IPv6. > > > > This is not enough to prevent DAD and reach the container right away: > > we'll need a couple more patches. > > > > As we send NLM_F_REPLACE requests right away, while we still have to > > read out other addresses on the same socket, we can't use nl_do(): > > keep a count of messages we send (addresses we change) and deal with > > the answer to those NLM_F_REPLACE requests in a separate loop, later. > > > > Link: https://github.com/containers/podman/pull/23561#discussion_r1711639663 > > Signed-off-by: Stefano Brivio > > --- > > netlink.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > netlink.h | 1 + > > pasta.c | 6 ++++++ > > 3 files changed, 62 insertions(+) > > > > diff --git a/netlink.c b/netlink.c > > index 873e6c7..59f2fd9 100644 > > --- a/netlink.c > > +++ b/netlink.c > > @@ -673,6 +673,61 @@ int nl_route_dup(int s_src, unsigned int ifi_src, > > return 0; > > } > > > > +/** > > + * nl_addr_set_ll_nodad() - Set IFA_F_NODAD on IPv6 link-local addresses > > + * @s: Netlink socket > > + * @ifi: Interface index in target namespace > > + * > > + * Return: 0 on success, negative error code on failure > > + */ > > +int nl_addr_set_ll_nodad(int s, unsigned int ifi) > > +{ > > + struct req_t { > > + struct nlmsghdr nlh; > > + struct ifaddrmsg ifa; > > + } req = { > > + .ifa.ifa_family = AF_INET6, > > + .ifa.ifa_index = ifi, > > + }; > > + unsigned ll_addrs = 0; > > + struct nlmsghdr *nh; > > + char buf[NLBUFSIZ]; > > + ssize_t status; > > + uint32_t seq; > > + > > + seq = nl_send(s, &req, RTM_GETADDR, NLM_F_DUMP, sizeof(req)); > > + nl_foreach_oftype(nh, status, s, buf, seq, RTM_NEWADDR) { > > + struct ifaddrmsg *ifa = (struct ifaddrmsg *)NLMSG_DATA(nh); > > + struct rtattr *rta; > > + size_t na; > > + > > + if (ifa->ifa_index != ifi || ifa->ifa_scope != RT_SCOPE_LINK) > > + continue; > > + > > + ifa->ifa_flags |= IFA_F_NODAD; > > + > > + for (rta = IFA_RTA(ifa), na = IFA_PAYLOAD(nh); RTA_OK(rta, na); > > + rta = RTA_NEXT(rta, na)) { > > + /* If 32-bit flags are used, add IFA_F_NODAD there */ > > + if (rta->rta_type == IFA_FLAGS) > > + *(uint32_t *)RTA_DATA(rta) |= IFA_F_NODAD; > > + } > > + > > + nl_send(s, nh, RTM_NEWADDR, NLM_F_REPLACE, nh->nlmsg_len); > > + ll_addrs++; > > + } > > + > > + if (status < 0) > > + return status; > > Ah... one gotcha with the nl_send() in the loop. We should make sure > we get the responses from any of those we sent, even if the original > request failed. Otherwise we'll be out of sync on the netlink socket again. I'm ignoring the return code of nl_send(), so, minus the issue you're raising about nl_foreach() below, that should already be sorted, right? > > + seq += ll_addrs; > > + > > + nl_foreach(nh, status, s, buf, seq) > > + warn("netlink: Unexpected response message"); > > I don't think this will work right if there's > 1 address. It will be > looking for the last sequence number on the first iteration and will > die in nl_status() when it mismatches. Ah, oops, right. > Maybe just loop on nl_next() until you get the last seq number, then > call nl_status()? How do I check for errors on the answers before the next one? I mean, nl_foreach() should fit here, it's just that I need to start from the right sequence number. > That also means you could just save the seq each > time you nl_send(), overwriting the previous one, rather than relying > on the fact that we allocate seqs, well, sequentially. I don't understand how this fits with calling nl_next() until I get to the last sequence number. Letting that aside, can't I simply use nl_foreach(), but start with the sequence of the first nl_send() instead of the last one? -- Stefano