+static int append_peer_ipv6_address(unsigned int iface, struct in6_addr *local_addr, struct in6_addr *remote_addr)
+{
+ struct msghdr msg;
+ struct sockaddr_nl sa;
+ struct iovec iov;
+ struct nlmsghdr *nlmsg;
+ struct ifaddrmsg *ifa;
+ struct rtattr *local_rta;
+ struct rtattr *remote_rta;
+ char buf[NLMSG_LENGTH(sizeof(*ifa) + RTA_LENGTH(sizeof(*local_addr)) + RTA_LENGTH(sizeof(*remote_addr)))];
+ ssize_t nlmsg_len;
+ struct nlmsgerr *errmsg;
+ int one;
+ int fd;
+
+ fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+ if (fd < 0)
+ return 0;
+
+ /*
+ * Tell kernel to not send to us payload of acknowledgment error message.
+ * NETLINK_CAP_ACK option is supported since Linux kernel version 4.3 and
+ * older kernel versions always send full payload in acknowledgment netlink
+ * message. We ignore payload of this message as we need only error code,
+ * to check if our set remote peer address request succeeded or failed.
+ * So ignore return value from the following setsockopt() call as setting
+ * option NETLINK_CAP_ACK means for us just a kernel hint / optimization.
+ */
+ one = 1;
+ setsockopt(fd, SOL_NETLINK, NETLINK_CAP_ACK, &one, sizeof(one));
+
+ memset(&sa, 0, sizeof(sa));
+ sa.nl_family = AF_NETLINK;
+ sa.nl_pid = 0;
+ sa.nl_groups = 0;
+
+ if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
+ close(fd);
+ return 0;
+ }
+
+ memset(buf, 0, sizeof(buf));
+
+ nlmsg = (struct nlmsghdr *)buf;
+ nlmsg->nlmsg_len = NLMSG_LENGTH(sizeof(*ifa) + RTA_LENGTH(sizeof(*local_addr)) + RTA_LENGTH(sizeof(*remote_addr)));
+ nlmsg->nlmsg_type = RTM_NEWADDR;
+ nlmsg->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | NLM_F_REPLACE;
+ nlmsg->nlmsg_seq = 1;
+ nlmsg->nlmsg_pid = 0;
+
+ ifa = NLMSG_DATA(nlmsg);
+ ifa->ifa_family = AF_INET6;
+ ifa->ifa_prefixlen = 128;
+ ifa->ifa_flags = IFA_F_NODAD | IFA_F_PERMANENT;
+ ifa->ifa_scope = RT_SCOPE_LINK;
+ ifa->ifa_index = iface;
+
+ local_rta = IFA_RTA(ifa);
+ local_rta->rta_len = RTA_LENGTH(sizeof(*local_addr));
+ local_rta->rta_type = IFA_LOCAL;
+ memcpy(RTA_DATA(local_rta), local_addr, sizeof(*local_addr));
+
+ remote_rta = (struct rtattr *)((char *)local_rta + local_rta->rta_len);
+ remote_rta->rta_len = RTA_LENGTH(sizeof(*remote_addr));
+ remote_rta->rta_type = IFA_ADDRESS;
+ memcpy(RTA_DATA(remote_rta), remote_addr, sizeof(*remote_addr));
+
+ memset(&sa, 0, sizeof(sa));
+ sa.nl_family = AF_NETLINK;
+ sa.nl_pid = 0;
+ sa.nl_groups = 0;
+
+ memset(&iov, 0, sizeof(iov));
+ iov.iov_base = nlmsg;
+ iov.iov_len = nlmsg->nlmsg_len;
+
+ memset(&msg, 0, sizeof(msg));
+ msg.msg_name = &sa;
+ msg.msg_namelen = sizeof(sa);
+ msg.msg_iov = &iov;
+ msg.msg_iovlen = 1;
+ msg.msg_control = NULL;
+ msg.msg_controllen = 0;
+ msg.msg_flags = 0;
+
+ if (sendmsg(fd, &msg, 0) < 0) {
+ close(fd);
+ return 0;
+ }
+
+ memset(&iov, 0, sizeof(iov));
+ iov.iov_base = buf;
+ iov.iov_len = sizeof(buf);
+
+ memset(&msg, 0, sizeof(msg));
+ msg.msg_name = NULL;
+ msg.msg_namelen = 0;
+ msg.msg_iov = &iov;
+ msg.msg_iovlen = 1;
+ msg.msg_control = NULL;
+ msg.msg_controllen = 0;
+ msg.msg_flags = 0;
+
+ nlmsg_len = recvmsg(fd, &msg, 0);
+ close(fd);
+
+ if (nlmsg_len < 0)
+ return 0;
+
+ if ((size_t)nlmsg_len < sizeof(*nlmsg)) {
+ errno = EINVAL;
+ return 0;
+ }
+
+ nlmsg = (struct nlmsghdr *)buf;
+
+ /* acknowledgment packet for NLM_F_ACK is NLMSG_ERROR */
+ if (nlmsg->nlmsg_type != NLMSG_ERROR) {
+ errno = EINVAL;
+ return 0;
+ }
+
+ if ((size_t)nlmsg_len < NLMSG_LENGTH(sizeof(*errmsg))) {
+ errno = EINVAL;
+ return 0;
+ }
+
+ errmsg = NLMSG_DATA(nlmsg);
+
+ /* error == 0 indicates success */
+ if (errmsg->error == 0)
+ return 1;
+
+ errno = -errmsg->error;
+ return 0;
+}
+