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[2a10:fc81:a806:d6a9::1]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-7c6b636946bsm561981a12.82.2024.08.14.23.53.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Aug 2024 23:53:01 -0700 (PDT) Date: Thu, 15 Aug 2024 08:52:58 +0200 From: Stefano Brivio To: David Gibson Subject: Re: [PATCH 4/7] netlink, pasta: Disable DAD for link-local addresses on namespace interface Message-ID: <20240815085258.553a14be@elisabeth> In-Reply-To: References: <20240814225429.3707908-1-sbrivio@redhat.com> <20240814225429.3707908-5-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: IOOB5KBL6HJTO76HD7TD5I7ZG2ENWBHC X-Message-ID-Hash: IOOB5KBL6HJTO76HD7TD5I7ZG2ENWBHC 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 13:01:08 +1000 David Gibson wrote: > On Thu, Aug 15, 2024 at 12:54:26AM +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. > > > > A large part of the function setting the nodad attribute is copied^W > > vendored from nl_routes_dup(), and we could probably refactor things > > to avoid code duplication, eventually, but keep this simple for the > > moment. > > I don't really care about the duplication, but I'm not sure > nl_routes_dup() was the right thing to vendor. > > > Link: https://github.com/containers/podman/pull/23561#discussion_r1711639663 > > Signed-off-by: Stefano Brivio > > --- > > netlink.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > netlink.h | 1 + > > pasta.c | 6 ++++ > > 3 files changed, 104 insertions(+) > > > > diff --git a/netlink.c b/netlink.c > > index 873e6c7..4b49de1 100644 > > --- a/netlink.c > > +++ b/netlink.c > > @@ -673,6 +673,103 @@ 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, > > + }; > > + ssize_t nlmsgs_size, left, status; > > + unsigned ll_addrs = 0; > > + struct nlmsghdr *nh; > > + char buf[NLBUFSIZ]; > > + uint32_t seq; > > + unsigned i; > > + > > + seq = nl_send(s, &req, RTM_GETADDR, NLM_F_DUMP, sizeof(req)); > > + > > + /* nl_foreach() will step through multiple response datagrams, > > + * which we don't want here because we need to have all the > > + * addresses in the buffer at once. See also nl_route_dup(). > > Hmm.. do we need them all in the buffer at once, though? For > routes_dup we needed it because we take multiple passes through the > whole list, and that's not the case here. Right, we don't need that, I shouldn't have vendored the comment as it was. > I guess we can't do an nl_do() within the loop, because that will > expect the response to its own command while we're still getting > reponses from the original NLM_F_DUMP. Exactly, that's why. > nl_addr_dup() gets away with it because the nl_do()s are on a > different netlink socket. Correct. > But.. I think we could nl_send() each NODAD request as we construct > it, keep a count, then wait for all the queued responses. Oh, I didn't think of doing that. It's definitely worth a try. > It means we can't easily match an error response to which thing > caused it, but doesn't look like we were reporting in that much > detail anyway. Right, I don't think we should care about that here. > > > + */ > > + nh = nl_next(s, buf, NULL, &nlmsgs_size); > > + for (left = nlmsgs_size; > > + NLMSG_OK(nh, left) && (status = nl_status(nh, left, seq)) > 0; > > + nh = NLMSG_NEXT(nh, left)) { > > + struct ifaddrmsg *ifa = (struct ifaddrmsg *)NLMSG_DATA(nh); > > + bool discard = false; > > + struct rtattr *rta; > > + size_t na; > > + > > + if (nh->nlmsg_type != RTM_NEWADDR) > > + continue; > > + > > + if (ifa->ifa_index != ifi || ifa->ifa_scope != RT_SCOPE_LINK) > > + discard = true; > > + > > + 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; > > + } > > + > > + if (discard) > > + nh->nlmsg_type = NLMSG_NOOP; > > + else > > + ll_addrs++; > > + } > > + > > + if (!NLMSG_OK(nh, left)) { > > + /* Process any remaining datagrams in a different > > + * buffer so we don't overwrite the first one. > > + */ > > + char tail[NLBUFSIZ]; > > + unsigned extra = 0; > > + > > + nl_foreach_oftype(nh, status, s, tail, seq, RTM_NEWADDR) > > + extra++; > > + > > + if (extra) { > > + err("netlink: Too many link-local addresses"); > > + return -E2BIG; > > + } > > + } > > + > > + if (status < 0) > > + return status; > > + > > + for (i = 0; i < ll_addrs; i++) { > > + for (nh = (struct nlmsghdr *)buf, left = nlmsgs_size; > > + NLMSG_OK(nh, left); > > + nh = NLMSG_NEXT(nh, left)) { > > + int rc; > > + > > + if (nh->nlmsg_type != RTM_NEWADDR) > > + continue; > > + > > + rc = nl_do(s, nh, RTM_NEWADDR, NLM_F_REPLACE, > > + nh->nlmsg_len); > > + if (rc < 0) > > + return rc; > > + } > > + } > > + > > + return 0; > > +} > > + > > /** > > * nl_addr_get() - Get most specific global address, given interface and family > > * @s: Netlink socket > > diff --git a/netlink.h b/netlink.h > > index 178f8ae..66a44ad 100644 > > --- a/netlink.h > > +++ b/netlink.h > > @@ -19,6 +19,7 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af, > > void *addr, int *prefix_len, void *addr_l); > > int nl_addr_set(int s, unsigned int ifi, sa_family_t af, > > const void *addr, int prefix_len); > > +int nl_addr_set_ll_nodad(int s, unsigned int ifi); > > int nl_addr_dup(int s_src, unsigned int ifi_src, > > int s_dst, unsigned int ifi_dst, sa_family_t af); > > int nl_link_get_mac(int s, unsigned int ifi, void *mac); > > diff --git a/pasta.c b/pasta.c > > index 96545b1..838bbb3 100644 > > --- a/pasta.c > > +++ b/pasta.c > > @@ -340,6 +340,12 @@ void pasta_ns_conf(struct ctx *c) > > } > > > > if (c->ifi6) { > > + rc = nl_addr_set_ll_nodad(nl_sock_ns, c->pasta_ifi); > > + if (rc < 0) { > > + die("Can't disable DAD for LL in namespace: %s", > > + strerror(-rc)); > > So... I'm usually the one arguing *for* ASSERT()s and die()s, but in > this case it seems overly drastic. If we're unable to set DAD it will > slow things down, but mostly things should still work. I'd prefer to > see this as just a warn(). Definitely, yeah. -- Stefano