[PATCH v10 1/9] netlink: add subsciption on changes in NDP/ARP table

[Jon Maloy <jmaloy@redhat.com>]

The solution to bug https://bugs.passt.top/show_bug.cgi?id=120
requires the ability to translate from an IP address to its
corresponding MAC address in cases where those are present in
the ARP or NDP tables.

To keep track of the contents of these tables we add a netlink
based neighbour subscription feature.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>

---
v3: - Added an attribute contianing NDA_DST to sent message, so
      that we let the kernel do the filtering of the IP address
      and return only one entry.
    - Added interface index to the call signature. Since the only
      interface we know is the template interface, this limits
      the number of hosts that will be seen as 'network segment
      local' from a PASST viewpoint.
v4: - Made loop independent of attribute order.
    - Ignoring L2 addresses which are not of size ETH_ALEN.
v5: - Changed return value of new function, so caller can know if
      a MAC address really was found.
v6: - Removed warning printout which had ended up in the wrong
      commit.
v8: - Changed to neighbour event subscription model
    - netlink: arp/ndp table subscription
v10:- Updated according to David's latest comments on v8
    - Added functionaly where we initially read current
      state of ARP/NDP tables
---
 epoll_type.h |   2 +
 netlink.c    | 180 +++++++++++++++++++++++++++++++++++++++++++++++++++
 netlink.h    |   4 ++
 passt.c      |   8 +++
 4 files changed, 194 insertions(+)

diff --git a/epoll_type.h b/epoll_type.h
index 12ac59b..a90ffb6 100644
--- a/epoll_type.h
+++ b/epoll_type.h
@@ -44,6 +44,8 @@ enum epoll_type {
 	EPOLL_TYPE_REPAIR_LISTEN,
 	/* TCP_REPAIR helper socket */
 	EPOLL_TYPE_REPAIR,
+	/* Netlink neighbour subscription socket */
+	EPOLL_TYPE_NL_NEIGH,
 
 	EPOLL_NUM_TYPES,
 };
diff --git a/netlink.c b/netlink.c
index c436780..0dc4e9d 100644
--- a/netlink.c
+++ b/netlink.c
@@ -26,6 +26,7 @@
 #include <arpa/inet.h>
 #include <netinet/in.h>
 #include <netinet/if_ether.h>
+#include <net/if_arp.h>
 
 #include <linux/netlink.h>
 #include <linux/rtnetlink.h>
@@ -40,6 +41,10 @@
 #define RTNH_NEXT_AND_DEC(rtnh, attrlen)				\
 	((attrlen) -= RTNH_ALIGN((rtnh)->rtnh_len), RTNH_NEXT(rtnh))
 
+/* Convenience macro borrowed from kernel */
+#define NUD_VALID (NUD_PERMANENT | NUD_NOARP |		\
+		   NUD_REACHABLE | NUD_PROBE | NUD_STALE)
+
 /* Netlink expects a buffer of at least 8kiB or the system page size,
  * whichever is larger.  32kiB is recommended for more efficient.
  * Since the largest page size on any remotely common Linux setup is
@@ -53,6 +58,7 @@
 int nl_sock	= -1;
 int nl_sock_ns	= -1;
 static int nl_seq = 1;
+static int nl_sock_neigh = -1;
 
 /**
  * nl_sock_init_do() - Set up netlink sockets in init or target namespace
@@ -1103,3 +1109,177 @@ int nl_link_set_flags(int s, unsigned int ifi,
 
 	return nl_do(s, &req, RTM_NEWLINK, 0, sizeof(req));
 }
+
+/**
+ * nl_neigh_msg_read() - Interpret a neigbour state message from netlink
+ *
+ */
+static void nl_neigh_msg_read(const struct ctx *c, struct nlmsghdr *nh)
+{
+	struct ndmsg *ndm = NLMSG_DATA(nh);
+	struct rtattr *rta = (struct rtattr *)(ndm + 1);
+	size_t na = NLMSG_PAYLOAD(nh, sizeof(*ndm));
+	char ip_str[INET6_ADDRSTRLEN];
+	char mac_str[ETH_ADDRSTRLEN];
+	const uint8_t *lladdr = NULL;
+	const void *dst = NULL;
+	size_t lladdr_len = 0;
+	uint8_t mac[ETH_ALEN];
+	union inany_addr addr;
+	size_t dstlen = 0;
+
+	if (nh->nlmsg_type == NLMSG_DONE)
+		return;
+
+	if (nh->nlmsg_type == NLMSG_ERROR) {
+		warn("NLMSG type error");
+		return;
+	}
+
+	if (nh->nlmsg_type != RTM_NEWNEIGH &&
+	    nh->nlmsg_type != RTM_DELNEIGH)
+		return;
+
+	for (; RTA_OK(rta, na); rta = RTA_NEXT(rta, na)) {
+		switch (rta->rta_type) {
+		case NDA_DST:
+			dst = RTA_DATA(rta);
+			dstlen = RTA_PAYLOAD(rta);
+			break;
+		case NDA_LLADDR:
+			lladdr = RTA_DATA(rta);
+			lladdr_len = RTA_PAYLOAD(rta);
+			break;
+		default:
+			break;
+		}
+	}
+
+	if (!dst)
+		return;
+
+	if (!lladdr || lladdr_len != ETH_ALEN)
+		return;
+
+	if (ndm->ndm_type != ARPHRD_ETHER)
+		return;
+
+	memcpy(mac, lladdr, ETH_ALEN);
+	eth_ntop(mac, mac_str, sizeof(mac_str));
+
+	if (ndm->ndm_family == AF_INET &&
+	    (dstlen != sizeof(struct in_addr) ||
+	     ndm->ndm_ifindex != c->ifi4))
+		return;
+
+	if (ndm->ndm_family == AF_INET6 &&
+	    (dstlen != sizeof(struct in6_addr) ||
+	     ndm->ndm_ifindex != c->ifi6))
+		return;
+
+	if (ndm->ndm_family == AF_INET)
+		addr = inany_from_v4(*(struct in_addr *) dst);
+	else if (ndm->ndm_family == AF_INET6)
+		addr.a6 = *(struct in6_addr *) dst;
+	else
+		return;
+
+	inet_ntop(ndm->ndm_family, dst, ip_str, sizeof(ip_str));
+
+	if (nh->nlmsg_type == RTM_NEWNEIGH &&
+	    ndm->ndm_state & NUD_VALID) {
+		trace("neigh table update: %s / %s", ip_str, mac_str);
+	} else {
+		trace("neigh table delete: %s / %s", ip_str, mac_str);
+	}
+}
+
+/**
+ * nl_neigh_subscr_sync() - Read current contents ARP/NDP tables
+ *
+ */
+static void nl_neigh_subscr_sync(const struct ctx *c, int proto, int ifi)
+{
+	struct {
+		struct nlmsghdr nlh;
+		struct ndmsg ndm;
+	} req = { 0 };
+	struct nlmsghdr *nh;
+	char buf[NLBUFSIZ];
+	ssize_t status;
+	uint32_t seq;
+
+	req.ndm.ndm_family = proto;
+	req.ndm.ndm_ifindex = ifi;
+	seq = nl_send(nl_sock_neigh, &req, RTM_GETNEIGH, NLM_F_DUMP, sizeof(req));
+	nl_foreach_oftype(nh, status, nl_sock_neigh, buf, seq, RTM_NEWNEIGH)
+		nl_neigh_msg_read(c, nh);
+}
+
+/**
+ * nl_neigh_subscr_handler() - Non-blocking drain of pending neighbour updates
+ * @c:	       Execution context
+ */
+void nl_neigh_subscr_handler(struct ctx *c)
+{
+	struct nlmsghdr *nh;
+	char buf[NLBUFSIZ];
+	ssize_t n;
+
+	for (;;) {
+		n = recv(nl_sock_neigh, buf, sizeof(buf), MSG_DONTWAIT);
+		if (n < 0) {
+			if (errno != EAGAIN)
+				warn_perror("Failed to read from netlink sock");
+			return;
+		}
+		nh = (struct nlmsghdr *)buf;
+		for (; NLMSG_OK(nh, n); nh = NLMSG_NEXT(nh, n))
+			nl_neigh_msg_read(c, nh);
+	}
+}
+
+/**
+ * nl_neigh_subscr_init() - Open netlink sock and subscribe to neighbour events
+ *
+ * Return: 0 on success, -1 on failure
+ */
+int nl_neigh_subscr_init(struct ctx *c)
+{
+	union epoll_ref ref = {
+		.type = EPOLL_TYPE_NL_NEIGH
+	};
+	struct epoll_event ev = {
+		.events = EPOLLIN
+	};
+	struct sockaddr_nl addr = {
+		.nl_family = AF_NETLINK,
+		.nl_groups = RTMGRP_NEIGH,
+	};
+
+	if (nl_sock_neigh >= 0)
+		return 0;
+
+	nl_sock_neigh = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
+	if (nl_sock_neigh < 0)
+		return -1;
+
+	if (bind(nl_sock_neigh, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
+		close(nl_sock_neigh);
+		nl_sock_neigh = -1;
+		return -1;
+	}
+
+	ref.fd = nl_sock_neigh;
+	ev.data.u64 = ref.u64;
+	if (epoll_ctl(c->epollfd, EPOLL_CTL_ADD, nl_sock_neigh, &ev) == -1) {
+		close(nl_sock_neigh);
+		nl_sock_neigh = -1;
+		return -1;
+	}
+
+	nl_neigh_subscr_sync(c, AF_INET, c->ifi4);
+	nl_neigh_subscr_sync(c, AF_INET6, c->ifi6);
+
+	return 0;
+}
diff --git a/netlink.h b/netlink.h
index b51e99c..a7d3506 100644
--- a/netlink.h
+++ b/netlink.h
@@ -17,6 +17,8 @@ int nl_route_dup(int s_src, unsigned int ifi_src,
 		 int s_dst, unsigned int ifi_dst, sa_family_t af);
 int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
 		void *addr, int *prefix_len, void *addr_l);
+bool nl_neigh_mac_get(int s, const union inany_addr *addr, int ifi,
+		      unsigned char *mac);
 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);
@@ -28,5 +30,7 @@ int nl_link_set_mac(int s, unsigned int ifi, const void *mac);
 int nl_link_set_mtu(int s, unsigned int ifi, int mtu);
 int nl_link_set_flags(int s, unsigned int ifi,
 		      unsigned int set, unsigned int change);
+int nl_neigh_subscr_init(struct ctx *c);
+void nl_neigh_subscr_handler(struct ctx *c);
 
 #endif /* NETLINK_H */
diff --git a/passt.c b/passt.c
index 31fbb75..e20bbad 100644
--- a/passt.c
+++ b/passt.c
@@ -53,6 +53,7 @@
 #include "vu_common.h"
 #include "migrate.h"
 #include "repair.h"
+#include "netlink.h"
 
 #define EPOLL_EVENTS		8
 
@@ -79,6 +80,7 @@ char *epoll_type_str[] = {
 	[EPOLL_TYPE_VHOST_KICK]		= "vhost-user kick socket",
 	[EPOLL_TYPE_REPAIR_LISTEN]	= "TCP_REPAIR helper listening socket",
 	[EPOLL_TYPE_REPAIR]		= "TCP_REPAIR helper socket",
+	[EPOLL_TYPE_NL_NEIGH]		= "netlink neighbour subscription socket",
 };
 static_assert(ARRAY_SIZE(epoll_type_str) == EPOLL_NUM_TYPES,
 	      "epoll_type_str[] doesn't match enum epoll_type");
@@ -322,6 +324,9 @@ int main(int argc, char **argv)
 
 	pcap_init(&c);
 
+	if (nl_neigh_subscr_init(&c) < 0)
+		warn("Failed to subscribe to RTMGRP_NEIGH");
+
 	if (!c.foreground) {
 		if ((devnull_fd = open("/dev/null", O_RDWR | O_CLOEXEC)) < 0)
 			die_perror("Failed to open /dev/null");
@@ -414,6 +419,9 @@ loop:
 		case EPOLL_TYPE_REPAIR:
 			repair_handler(&c, eventmask);
 			break;
+		case EPOLL_TYPE_NL_NEIGH:
+			nl_neigh_subscr_handler(&c);
+			break;
 		default:
 			/* Can't happen */
 			ASSERT(0);
-- 
2.50.1