[PATCH v4 5/7] netlink, pasta: Fetch link-local address from namespace interface once it's up

[Stefano Brivio <sbrivio@redhat.com>]

As soon as we bring up the interface, the Linux kernel will set up a
link-local address for it, so we can fetch it and start using right
away, if we need a link-local address to communicate to the container
before we see any traffic coming from it.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
---
 netlink.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 netlink.h |  1 +
 pasta.c   |  7 +++++++
 3 files changed, 55 insertions(+)

diff --git a/netlink.c b/netlink.c
index 5a5af14..9592b1b 100644
--- a/netlink.c
+++ b/netlink.c
@@ -796,6 +796,53 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
 	return status;
 }
 
+/**
+ * nl_addr_get_ll() - Get first IPv6 link-local address for a given interface
+ * @s:		Netlink socket
+ * @ifi:	Interface index in outer network namespace
+ * @addr:	Link-local address to fill
+ *
+ * Return: 0 on success, negative error code on failure
+ */
+int nl_addr_get_ll(int s, unsigned int ifi, struct in6_addr *addr)
+{
+	struct req_t {
+		struct nlmsghdr nlh;
+		struct ifaddrmsg ifa;
+	} req = {
+		.ifa.ifa_family		= AF_INET6,
+		.ifa.ifa_index		= ifi,
+	};
+	struct nlmsghdr *nh;
+	bool found = false;
+	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 ||
+		    found)
+			continue;
+
+		for (rta = IFA_RTA(ifa), na = IFA_PAYLOAD(nh); RTA_OK(rta, na);
+		     rta = RTA_NEXT(rta, na)) {
+			if (rta->rta_type != IFA_ADDRESS)
+				continue;
+
+			if (!found) {
+				memcpy(addr, RTA_DATA(rta), RTA_PAYLOAD(rta));
+				found = true;
+			}
+		}
+	}
+	return status;
+}
+
 /**
  * nl_add_set() - Set IP addresses for given interface and address family
  * @s:		Netlink socket
diff --git a/netlink.h b/netlink.h
index 66a44ad..b51e99c 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_get_ll(int s, unsigned int ifi, struct in6_addr *addr);
 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);
diff --git a/pasta.c b/pasta.c
index 17eed15..e8883bd 100644
--- a/pasta.c
+++ b/pasta.c
@@ -340,6 +340,13 @@ void pasta_ns_conf(struct ctx *c)
 		}
 
 		if (c->ifi6) {
+			rc = nl_addr_get_ll(nl_sock_ns, c->pasta_ifi,
+					    &c->ip6.addr_ll_seen);
+			if (rc < 0) {
+				warn("Can't get LL address from namespace: %s",
+				    strerror(-rc));
+			}
+
 			rc = nl_addr_set_ll_nodad(nl_sock_ns, c->pasta_ifi);
 			if (rc < 0) {
 				warn("Can't set nodad for LL in namespace: %s",
-- 
@@ -340,6 +340,13 @@ void pasta_ns_conf(struct ctx *c)
 		}
 
 		if (c->ifi6) {
+			rc = nl_addr_get_ll(nl_sock_ns, c->pasta_ifi,
+					    &c->ip6.addr_ll_seen);
+			if (rc < 0) {
+				warn("Can't get LL address from namespace: %s",
+				    strerror(-rc));
+			}
+
 			rc = nl_addr_set_ll_nodad(nl_sock_ns, c->pasta_ifi);
 			if (rc < 0) {
 				warn("Can't set nodad for LL in namespace: %s",
-- 
2.43.0