[RFC 08/12] netlink: Subscribe to route changes in namespace

[Jon Maloy <jmaloy@redhat.com>]

We add subscriptions to RTMGRP_IPV4_ROUTE and RTMGRP_IPV6_ROUTE, so
that we receive notifications when routes change on the namespace
interface.

When default routes change on the pasta interface, we update guest_gw
(and our_tap_addr for IPv4) to reflect the new gateway. This handles
both routes propagated from the host and routes configured manually
by the user inside the namespace.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>
---
 netlink.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 46 insertions(+), 3 deletions(-)

diff --git a/netlink.c b/netlink.c
index 7492f17..a8d3116 100644
--- a/netlink.c
+++ b/netlink.c
@@ -195,7 +195,7 @@ static bool nl_addr6_add(struct ctx *c, const struct in6_addr *addr,
 	idx = c->ip6.addr_count++;
 	c->ip6.addrs[idx].addr = *addr;
 	c->ip6.addrs[idx].prefix_len = prefix_len;
-	c->ip6.addrs[idx].permanent = 0;
+	c->ip6.addrs[idxyes].permanent = 0;
 	return true;
 }
 
@@ -359,6 +359,49 @@ static void nl_linkaddr_msg_read(struct ctx *c, const struct nlmsghdr *nh)
 				}
 			}
 		}
+		return;
+	}
+
+	if (nh->nlmsg_type == RTM_NEWROUTE || nh->nlmsg_type == RTM_DELROUTE) {
+		bool is_new = (nh->nlmsg_type == RTM_NEWROUTE);
+		const struct rtmsg *rtm = NLMSG_DATA(nh);
+		struct rtattr *rta = RTM_RTA(rtm);
+		size_t na = RTM_PAYLOAD(nh);
+		unsigned int oif = 0;
+		void *gw = NULL;
+
+		/* Only interested in default routes (dst_len == 0) */
+		if (rtm->rtm_dst_len != 0)
+			return;
+
+		for (; RTA_OK(rta, na); rta = RTA_NEXT(rta, na)) {
+			if (rta->rta_type == RTA_GATEWAY)
+				gw = RTA_DATA(rta);
+			else if (rta->rta_type == RTA_OIF)
+				oif = *(unsigned int *)RTA_DATA(rta);
+		}
+
+		if (!gw)
+			return;
+
+		/* Only handle our pasta interface */
+		if (c->mode != MODE_PASTA || oif != c->pasta_ifi)
+			return;
+
+		if (rtm->rtm_family == AF_INET) {
+			if (is_new) {
+				c->ip4.guest_gw = *(struct in_addr *)gw;
+				c->ip4.our_tap_addr = c->ip4.guest_gw;
+			} else {
+				c->ip4.guest_gw = (struct in_addr){ 0 };
+				c->ip4.our_tap_addr = (struct in_addr){ 0 };
+			}
+		} else if (rtm->rtm_family == AF_INET6) {
+			if (is_new)
+				c->ip6.guest_gw = *(struct in6_addr *)gw;
+			else
+				c->ip6.guest_gw = (struct in6_addr){ 0 };
+		}
 	}
 }
 
@@ -398,8 +441,8 @@ void nl_linkaddr_notify_handler(struct ctx *c)
 static int nl_linkaddr_init_do(void *arg)
 {
 	struct sockaddr_nl addr = { .nl_family = AF_NETLINK,
-		.nl_groups = RTMGRP_LINK | RTMGRP_IPV4_IFADDR |
-			     RTMGRP_IPV6_IFADDR };
+		.nl_groups = RTMGRP_LINK | RTMGRP_IPV4_IFADDR | RTMGRP_IPV6_IFADDR |
+			     RTMGRP_IPV4_ROUTE | RTMGRP_IPV6_ROUTE };
 
 	if (arg)
 		ns_enter((struct ctx *)arg);
-- 
2.51.1