[PATCH v3 6/7] pasta: Disable neighbour solicitations on device up to prevent DAD

[Stefano Brivio <sbrivio@redhat.com>]

As soon as we the kernel notifier for IPv6 address configuration
(addrconf_notify()) sees that we bring the target interface up
(NETDEV_UP), it will schedule duplicate address detection, so, by
itself, setting the nodad flag later is useless, because that won't
stop a detection that's already in progress.

However, if we disable neighbour solicitations with IFF_NOARP (which
is a misnomer for IPv6 interfaces, but there's no possibility of
mixing things up), the notifier will not trigger DAD, because it can't
be done, of course, without neighbour solicitations.

Set IFF_NOARP as we bring up the device, and drop it after we had a
chance to set the nodad attribute on the link.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
---
 netlink.c | 22 ++++++++++++----------
 pasta.c   | 11 ++++++++++-
 2 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/netlink.c b/netlink.c
index 06a3816..9592b1b 100644
--- a/netlink.c
+++ b/netlink.c
@@ -689,11 +689,10 @@ int nl_addr_set_ll_nodad(int s, unsigned int ifi)
 		.ifa.ifa_family    = AF_INET6,
 		.ifa.ifa_index     = ifi,
 	};
-	unsigned ll_addrs = 0;
+	uint32_t seq, last_seq = 0;
+	ssize_t status, ret = 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) {
@@ -713,19 +712,22 @@ int nl_addr_set_ll_nodad(int s, unsigned int ifi)
 				*(uint32_t *)RTA_DATA(rta) |= IFA_F_NODAD;
 		}
 
-		nl_send(s, nh, RTM_NEWADDR, NLM_F_REPLACE, nh->nlmsg_len);
-		ll_addrs++;
+		last_seq = nl_send(s, nh, RTM_NEWADDR, NLM_F_REPLACE,
+				   nh->nlmsg_len);
 	}
 
 	if (status < 0)
-		return status;
+		ret = status;
 
-	seq += ll_addrs;
+	for (seq = seq + 1; seq <= last_seq; seq++) {
+		nl_foreach(nh, status, s, buf, seq)
+			warn("netlink: Unexpected response message");
 
-	nl_foreach(nh, status, s, buf, seq)
-		warn("netlink: Unexpected response message");
+		if (!ret && status < 0)
+			ret = status;
+	}
 
-	return status;
+	return ret;
 }
 
 /**
diff --git a/pasta.c b/pasta.c
index e8883bd..1142f03 100644
--- a/pasta.c
+++ b/pasta.c
@@ -303,10 +303,15 @@ void pasta_ns_conf(struct ctx *c)
 		    strerror(-rc));
 
 	if (c->pasta_conf_ns) {
+		unsigned int flags = IFF_UP;
+
 		if (c->mtu != -1)
 			nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
 
-		nl_link_set_flags(nl_sock_ns, c->pasta_ifi, IFF_UP, IFF_UP);
+		if (c->ifi6) /* Avoid duplicate address detection on link up */
+			flags |= IFF_NOARP;
+
+		nl_link_set_flags(nl_sock_ns, c->pasta_ifi, flags, flags);
 
 		if (c->ifi4) {
 			if (c->ip4.no_copy_addrs) {
@@ -353,6 +358,10 @@ void pasta_ns_conf(struct ctx *c)
 				    strerror(-rc));
 			}
 
+			/* We dodged DAD: re-enable neighbour solicitations */
+			nl_link_set_flags(nl_sock_ns, c->pasta_ifi,
+					  0, IFF_NOARP);
+
 			if (c->ip6.no_copy_addrs) {
 				rc = nl_addr_set(nl_sock_ns, c->pasta_ifi,
 						 AF_INET6, &c->ip6.addr, 64);
-- 
@@ -303,10 +303,15 @@ void pasta_ns_conf(struct ctx *c)
 		    strerror(-rc));
 
 	if (c->pasta_conf_ns) {
+		unsigned int flags = IFF_UP;
+
 		if (c->mtu != -1)
 			nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
 
-		nl_link_set_flags(nl_sock_ns, c->pasta_ifi, IFF_UP, IFF_UP);
+		if (c->ifi6) /* Avoid duplicate address detection on link up */
+			flags |= IFF_NOARP;
+
+		nl_link_set_flags(nl_sock_ns, c->pasta_ifi, flags, flags);
 
 		if (c->ifi4) {
 			if (c->ip4.no_copy_addrs) {
@@ -353,6 +358,10 @@ void pasta_ns_conf(struct ctx *c)
 				    strerror(-rc));
 			}
 
+			/* We dodged DAD: re-enable neighbour solicitations */
+			nl_link_set_flags(nl_sock_ns, c->pasta_ifi,
+					  0, IFF_NOARP);
+
 			if (c->ip6.no_copy_addrs) {
 				rc = nl_addr_set(nl_sock_ns, c->pasta_ifi,
 						 AF_INET6, &c->ip6.addr, 64);
-- 
2.43.0