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/NDP table.
We add this feature here.
Signed-off-by: Jon Maloy
---
netlink.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
netlink.h | 2 ++
2 files changed, 81 insertions(+)
diff --git a/netlink.c b/netlink.c
index 8f82e73..cf7debc 100644
--- a/netlink.c
+++ b/netlink.c
@@ -800,6 +800,85 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
return status;
}
+/**
+ * nl_neigh_mac_get() - Get neighbor MAC address from the kernel neigh table
+ * @s: Netlink socket fd
+ * @addr: IPv4 or IPv6 address
+ * @ifi: Interface index
+ * @mac: Buffer for Ethernet MAC, left unchanged if not found/usable
+ *
+ * Return: <0 on netlink error; 0 otherwise (drains all replies for @seq).
+ */
+int nl_neigh_mac_get(int s, const union inany_addr *addr,
+ int ifi, unsigned char *mac)
+{
+ const void *ip = inany_v4(addr);
+ struct req_t {
+ struct nlmsghdr nlh;
+ struct ndmsg ndm;
+ struct rtattr rta;
+ char ip[RTA_ALIGN(sizeof(struct in6_addr))];
+ } req;
+ struct nlmsghdr *nh;
+ char buf[NLBUFSIZ];
+ ssize_t status;
+ uint32_t seq;
+ int msglen;
+ int iplen;
+
+ memset(&req, 0, sizeof(req));
+ req.ndm.ndm_ifindex = ifi;
+ req.rta.rta_type = NDA_DST;
+
+ if (ip) {
+ req.ndm.ndm_family = AF_INET;
+ iplen = sizeof(struct in_addr);
+ } else {
+ req.ndm.ndm_family = AF_INET6;
+ ip = &addr;
+ iplen = sizeof(struct in6_addr);
+ }
+
+ req.rta.rta_len = RTA_LENGTH(iplen);
+ memcpy(RTA_DATA(&req.rta), ip, iplen);
+ msglen = NLMSG_ALIGN(sizeof(req.nlh) + sizeof(req.ndm) + RTA_LENGTH(iplen));
+ seq = nl_send(s, &req, RTM_GETNEIGH, 0, msglen);
+
+ /* Drain all RTM_NEWNEIGH replies for this seq */
+ nl_foreach_oftype(nh, status, s, buf, seq, RTM_NEWNEIGH) {
+ struct ndmsg *ndm = NLMSG_DATA(nh);
+ struct rtattr *rta = (struct rtattr *)(ndm + 1);
+ const uint8_t *lladdr = NULL;
+ size_t na = RTM_PAYLOAD(nh);
+ const void *dst = NULL;
+ size_t lladdr_len = 0;
+ size_t dstlen = 0;
+
+ 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 && dstlen == (size_t)iplen && memcmp(dst, ip, iplen) == 0) {
+ /* Only copy Ethernet-style addresses; leave unchanged otherwise */
+ if (lladdr && lladdr_len == ETH_ALEN)
+ memcpy(mac, lladdr, ETH_ALEN);
+ }
+ }
+
+ return status;
+}
+
/**
* nl_addr_get_ll() - Get first IPv6 link-local address for a given interface
* @s: Netlink socket
diff --git a/netlink.h b/netlink.h
index b51e99c..026c64f 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);
+int 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);
--
2.50.1