/**
 * Copyright (C) 2012-2014 Steven Barth <steven@midlink.org>
 * Copyright (C) 2017-2018 Hans Dedecker <dedeckeh@gmail.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License v2 as published by
 * the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 */

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <signal.h>
#include <string.h>
#include <stddef.h>
#include <stdbool.h>
#include <syslog.h>
#include <unistd.h>
#include <resolv.h>
#include <alloca.h>

#include <net/if.h>
#include <arpa/inet.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/icmp6.h>

#include <linux/rtnetlink.h>

#ifndef SOL_NETLINK
#define SOL_NETLINK 270
#endif

#ifndef NETLINK_ADD_MEMBERSHIP
#define NETLINK_ADD_MEMBERSHIP 1
#endif

#ifndef IFF_LOWER_UP
#define IFF_LOWER_UP 0x10000
#endif

#include "odhcp6c.h"
#include "ra.h"

static bool nocarrier = false;
static bool ptp_link = false;

static int sock = -1, rtnl = -1;
static int if_index = 0;
static char if_name[IF_NAMESIZE] = {0};
static volatile int rs_attempt = 0;
static struct in6_addr lladdr = IN6ADDR_ANY_INIT;
static unsigned int ra_options = 0;
static unsigned int ra_holdoff_interval = 0;
static int ra_hoplimit = 0;
static int ra_mtu = 0;
static int ra_reachable = 0;
static int ra_retransmit = 0;

struct {
	struct icmp6_hdr hdr;
	struct icmpv6_opt lladdr;
} rs = {
	.hdr = {ND_ROUTER_SOLICIT, 0, 0, {{0}}},
	.lladdr = {ND_OPT_SOURCE_LINKADDR, 1, {0}},
};

static void ra_send_rs(int signal __attribute__((unused)));

int ra_init(const char *ifname, const struct in6_addr *ifid,
		unsigned int options, unsigned int holdoff_interval)
{
	struct ifreq ifr;

	ra_options = options;
	ra_holdoff_interval = holdoff_interval;

	const pid_t ourpid = getpid();
	sock = socket(AF_INET6, SOCK_RAW | SOCK_CLOEXEC, IPPROTO_ICMPV6);
	if (sock < 0)
		goto failure;

	memset(&ifr, 0, sizeof(ifr));
	strncpy(ifr.ifr_name, ifname, sizeof(ifr.ifr_name) - 1);
	if (ioctl(sock, SIOCGIFFLAGS, &ifr) < 0)
		goto failure;

	ptp_link = !!(ifr.ifr_flags & IFF_POINTOPOINT);

	memset(&ifr, 0, sizeof(ifr));
	strncpy(ifr.ifr_name, ifname, sizeof(ifr.ifr_name) - 1);
	if (ioctl(sock, SIOCGIFINDEX, &ifr) < 0)
		goto failure;

	if_index = ifr.ifr_ifindex;
	lladdr = *ifid;

	rtnl = socket(AF_NETLINK, SOCK_DGRAM | SOCK_CLOEXEC, NETLINK_ROUTE);
	if (rtnl < 0)
		goto failure;

	struct sockaddr_nl rtnl_kernel = { .nl_family = AF_NETLINK };
	if (connect(rtnl, (const struct sockaddr*)&rtnl_kernel, sizeof(rtnl_kernel)) < 0)
		goto failure;

	int val = RTNLGRP_LINK;
	if (setsockopt(rtnl, SOL_NETLINK, NETLINK_ADD_MEMBERSHIP, &val, sizeof(val)) < 0)
		goto failure;

	if (fcntl(rtnl, F_SETOWN, ourpid) < 0)
		goto failure;

	if (fcntl(rtnl, F_SETFL, fcntl(sock, F_GETFL) | O_ASYNC) < 0)
		goto failure;

	struct {
		struct nlmsghdr hdr;
		struct ifinfomsg ifi;
	} req = {
		.hdr = {sizeof(req), RTM_GETLINK, NLM_F_REQUEST, 1, 0},
		.ifi = {.ifi_index = if_index}
	};
	if (send(rtnl, &req, sizeof(req), 0) < 0)
		goto failure;

	ra_link_up();

	// Filter ICMPv6 package types
	struct icmp6_filter filt;
	ICMP6_FILTER_SETBLOCKALL(&filt);
	ICMP6_FILTER_SETPASS(ND_ROUTER_ADVERT, &filt);
	if (setsockopt(sock, IPPROTO_ICMPV6, ICMP6_FILTER, &filt, sizeof(filt)) < 0)
		goto failure;

	// Bind to all-nodes
	struct ipv6_mreq an = {ALL_IPV6_NODES, if_index};
	if (setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &an, sizeof(an)) < 0)
		goto failure;

	// Let the kernel compute our checksums
	val = 2;
	if (setsockopt(sock, IPPROTO_RAW, IPV6_CHECKSUM, &val, sizeof(val)) < 0)
		goto failure;

	// This is required by RFC 4861
	val = 255;
	if (setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &val, sizeof(val)) < 0)
		goto failure;

	// Receive multicast hops
	val = 1;
	if (setsockopt(sock, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &val, sizeof(val)) < 0)
		goto failure;

	// Bind to one device
	if (setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, ifname, strlen(ifname)) < 0)
		goto failure;

	// Add async-mode
	if (fcntl(sock, F_SETOWN, ourpid) < 0)
		goto failure;

	val = fcntl(sock, F_GETFL);
	if (val < 0)
		goto failure;

	if (fcntl(sock, F_SETFL, val | O_ASYNC) < 0)
		goto failure;

	// Send RS
	signal(SIGALRM, ra_send_rs);
	ra_send_rs(SIGALRM);

	return 0;

failure:
	if (sock >= 0)
		close(sock);

	if (rtnl >= 0)
		close(rtnl);

	return -1;
}

static void ra_send_rs(int signal __attribute__((unused)))
{
	const struct sockaddr_in6 dest = {AF_INET6, 0, 0, ALL_IPV6_ROUTERS, if_index};
	const struct icmpv6_opt llnull = {ND_OPT_SOURCE_LINKADDR, 1, {0}};
	size_t len;

	if ((rs_attempt % 2 == 0) && memcmp(&rs.lladdr, &llnull, sizeof(llnull)))
		len = sizeof(rs);
	else
		len = sizeof(struct icmp6_hdr);

	if (sendto(sock, &rs, len, MSG_DONTWAIT, (struct sockaddr*)&dest, sizeof(dest)) < 0)
		syslog(LOG_ERR, "Failed to send RS (%s)",  strerror(errno));

	if (++rs_attempt <= 3)
		alarm(4);
}

static int16_t pref_to_priority(uint8_t flags)
{
	flags = (flags >> 3) & 0x03;

	return (flags == 0x0) ? 512 : (flags == 0x1) ? 384 :
			(flags == 0x3) ? 640 : -1;
}

bool ra_link_up(void)
{
	static bool firstcall = true;
	struct {
		struct nlmsghdr hdr;
		struct ifinfomsg msg;
		uint8_t pad[4000];
	} resp;
	bool ret = false;
	ssize_t read;

	do {
		read = recv(rtnl, &resp, sizeof(resp), MSG_DONTWAIT);

		if (read < 0 || !NLMSG_OK(&resp.hdr, (size_t)read) ||
				resp.hdr.nlmsg_type != RTM_NEWLINK ||
				resp.msg.ifi_index != if_index)
			continue;

		ssize_t alen = NLMSG_PAYLOAD(&resp.hdr, sizeof(resp.msg));
		for (struct rtattr *rta = (struct rtattr*)(resp.pad);
				RTA_OK(rta, alen); rta = RTA_NEXT(rta, alen)) {
			if (rta->rta_type == IFLA_ADDRESS &&
					RTA_PAYLOAD(rta) >= sizeof(rs.lladdr.data))
				memcpy(rs.lladdr.data, RTA_DATA(rta), sizeof(rs.lladdr.data));
		}

		bool hascarrier = resp.msg.ifi_flags & IFF_LOWER_UP;
		if (!firstcall && nocarrier != !hascarrier)
			ret = true;

		nocarrier = !hascarrier;
		firstcall = false;
	} while (read > 0);

	if (ret) {
		syslog(LOG_NOTICE, "carrier => %i event on %s", (int)!nocarrier, if_name);

		rs_attempt = 0;
		ra_send_rs(SIGALRM);
	}

	return ret;
}

static bool ra_icmpv6_valid(struct sockaddr_in6 *source, int hlim, uint8_t *data, size_t len)
{
	struct icmp6_hdr *hdr = (struct icmp6_hdr*)data;
	struct icmpv6_opt *opt, *end = (struct icmpv6_opt*)&data[len];

	if (hlim != 255 || len < sizeof(*hdr) || hdr->icmp6_code)
		return false;

	switch (hdr->icmp6_type) {
	case ND_ROUTER_ADVERT:
		if (!IN6_IS_ADDR_LINKLOCAL(&source->sin6_addr))
			return false;

		opt = (struct icmpv6_opt*)((struct nd_router_advert*)data + 1);
		break;

	default:
		return false;
	}

	icmpv6_for_each_option(opt, opt, end)
		;

	return opt == end;
}

static bool ra_set_hoplimit(int val)
{
	if (val > 0 && val != ra_hoplimit) {
		ra_hoplimit = val;
		return true;
	}

	return false;
}

static bool ra_set_mtu(int val)
{
	if (val >= 1280 && val <= 65535 && ra_mtu != val) {
		ra_mtu = val;
		return true;
	}

	return false;
}

static bool ra_set_reachable(int val)
{
	if (val > 0 && val <= 3600000 && ra_reachable != val) {
		ra_reachable = val;
		return true;
	}

	return false;
}

static bool ra_set_retransmit(int val)
{
	if (val > 0 && val <= 60000 && ra_retransmit != val) {
		ra_retransmit = val;
		return true;
	}

	return false;
}

int ra_get_hoplimit(void)
{
	return ra_hoplimit;
}

int ra_get_mtu(void)
{
	return ra_mtu;
}

int ra_get_reachable(void)
{
	return ra_reachable;
}

int ra_get_retransmit(void)
{
	return ra_retransmit;
}

bool ra_process(void)
{
	bool found = false;
	bool changed = false;
	uint8_t buf[1500] _aligned(4);
	union {
		struct cmsghdr hdr;
		uint8_t buf[CMSG_SPACE(sizeof(int))];
	} cmsg_buf;
	struct nd_router_advert *adv = (struct nd_router_advert*)buf;
	struct odhcp6c_entry *entry = alloca(sizeof(*entry) + 256);
	const struct in6_addr any = IN6ADDR_ANY_INIT;

	memset(entry, 0, sizeof(*entry));

	if (IN6_IS_ADDR_UNSPECIFIED(&lladdr)) {
		struct sockaddr_in6 addr = {AF_INET6, 0, 0, ALL_IPV6_ROUTERS, if_index};
		socklen_t alen = sizeof(addr);
		int sock = socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6);

		if (sock >= 0) {
			if (!connect(sock, (struct sockaddr*)&addr, sizeof(addr)) &&
					!getsockname(sock, (struct sockaddr*)&addr, &alen))
				lladdr = addr.sin6_addr;

			close(sock);
		}
	}

	while (true) {
		struct sockaddr_in6 from;
		struct iovec iov = {buf, sizeof(buf)};
		struct msghdr msg = {
			.msg_name = (void *) &from,
			.msg_namelen = sizeof(from),
			.msg_iov = &iov,
			.msg_iovlen = 1,
			.msg_control = cmsg_buf.buf,
			.msg_controllen = sizeof(cmsg_buf),
			.msg_flags = 0
		};
		struct icmpv6_opt *opt;
		uint32_t router_valid;
		int hlim = 0;

		ssize_t len = recvmsg(sock, &msg, MSG_DONTWAIT);
		if (len <= 0)
			break;

		if (IN6_IS_ADDR_UNSPECIFIED(&lladdr))
			continue;

		for (struct cmsghdr *ch = CMSG_FIRSTHDR(&msg); ch != NULL;
				ch = CMSG_NXTHDR(&msg, ch))
			if (ch->cmsg_level == IPPROTO_IPV6 &&
					ch->cmsg_type == IPV6_HOPLIMIT)
				memcpy(&hlim, CMSG_DATA(ch), sizeof(hlim));

		if (!ra_icmpv6_valid(&from, hlim, buf, len))
			continue;

		if (!found) {
			odhcp6c_expire(false);
			found = true;
		}

		router_valid = ntohs(adv->nd_ra_router_lifetime);

		/* RFC4861 §6.3.7
		 * Once the host sends a Router Solicitation, and receives a valid
		 * Router Advertisement with a non-zero Router Lifetime, the host MUST
		 * desist from sending additional solicitations on that interface
		 * Moreover, a host SHOULD send at least one solicitation in the case
		 * where an advertisement is received prior to having sent a solicitation.
		 */
		if (rs_attempt > 0 && router_valid > 0) {
			alarm(0);
			rs_attempt = 0;
		}

		// Parse default route
		entry->target = any;
		entry->length = 0;
		entry->router = from.sin6_addr;
		entry->priority = pref_to_priority(adv->nd_ra_flags_reserved);
		if (entry->priority < 0)
			entry->priority = pref_to_priority(0);

		entry->valid = router_valid;
		entry->preferred = entry->valid;
		changed |= odhcp6c_update_entry(STATE_RA_ROUTE, entry,
						0, ra_holdoff_interval);

		// Parse hoplimit
		changed |= ra_set_hoplimit(adv->nd_ra_curhoplimit);

		// Parse ND parameters
		changed |= ra_set_reachable(ntohl(adv->nd_ra_reachable));
		changed |= ra_set_retransmit(ntohl(adv->nd_ra_retransmit));

		// Evaluate options
		icmpv6_for_each_option(opt, &adv[1], &buf[len]) {
			if (opt->type == ND_OPT_MTU) {
				uint32_t *mtu = (uint32_t*)&opt->data[2];
				changed |= ra_set_mtu(ntohl(*mtu));
			} else if (opt->type == ND_OPT_ROUTE_INFORMATION && opt->len <= 3) {
				struct icmpv6_opt_route_info *ri = (struct icmpv6_opt_route_info *)opt;

				if (ri->prefix_len > 128) {
					continue;
				} else if (ri->prefix_len > 64) {
					if (ri->len < 2)
						continue;
				} else if (ri->prefix_len > 0) {
					if (ri->len < 1)
						continue;
				}

				entry->router = from.sin6_addr;
				entry->target = any;
				entry->priority = pref_to_priority(ri->flags);
				entry->length = ri->prefix_len;
				entry->valid = ntohl(ri->lifetime);
				memcpy(&entry->target, ri->prefix, (ri->len - 1) * 8);

				if (IN6_IS_ADDR_LINKLOCAL(&entry->target)
						|| IN6_IS_ADDR_LOOPBACK(&entry->target)
						|| IN6_IS_ADDR_MULTICAST(&entry->target))
					continue;

				if (entry->priority > 0)
					changed |= odhcp6c_update_entry(STATE_RA_ROUTE, entry,
									0, ra_holdoff_interval);
			} else if (opt->type == ND_OPT_PREFIX_INFORMATION && opt->len == 4) {
				struct nd_opt_prefix_info *pinfo = (struct nd_opt_prefix_info*)opt;
				entry->router = any;
				entry->target = pinfo->nd_opt_pi_prefix;
				entry->priority = 256;
				entry->length = pinfo->nd_opt_pi_prefix_len;
				entry->valid = ntohl(pinfo->nd_opt_pi_valid_time);
				entry->preferred = ntohl(pinfo->nd_opt_pi_preferred_time);

				if (entry->length > 128 || IN6_IS_ADDR_LINKLOCAL(&entry->target)
						|| IN6_IS_ADDR_LOOPBACK(&entry->target)
						|| IN6_IS_ADDR_MULTICAST(&entry->target)
						|| entry->valid < entry->preferred)
					continue;

				if ((pinfo->nd_opt_pi_flags_reserved & ND_OPT_PI_FLAG_ONLINK) &&
				    !ptp_link)
					changed |= odhcp6c_update_entry(STATE_RA_ROUTE, entry,
									7200, ra_holdoff_interval);

				if (!(pinfo->nd_opt_pi_flags_reserved & ND_OPT_PI_FLAG_AUTO) ||
						pinfo->nd_opt_pi_prefix_len != 64)
					continue;

				entry->target.s6_addr32[2] = lladdr.s6_addr32[2];
				entry->target.s6_addr32[3] = lladdr.s6_addr32[3];

				changed |= odhcp6c_update_entry(STATE_RA_PREFIX, entry,
								7200, ra_holdoff_interval);
			} else if (opt->type == ND_OPT_RECURSIVE_DNS && opt->len > 2) {
				entry->router = from.sin6_addr;
				entry->priority = 0;
				entry->length = 128;
				uint32_t *valid = (uint32_t*)&opt->data[2];
				entry->valid = ntohl(*valid);
				entry->preferred = 0;

				for (ssize_t i = 0; i < (opt->len - 1) / 2; ++i) {
					memcpy(&entry->target, &opt->data[6 + i * sizeof(entry->target)],
							sizeof(entry->target));
					changed |= odhcp6c_update_entry(STATE_RA_DNS, entry,
									0, ra_holdoff_interval);
				}
			} else if (opt->type == ND_OPT_DNSSL && opt->len > 1) {
				uint32_t *valid = (uint32_t*)&opt->data[2];
				uint8_t *buf = &opt->data[6];
				uint8_t *end = &buf[(opt->len - 1) * 8];

				entry->router = from.sin6_addr;
				entry->valid = ntohl(*valid);

				while (buf < end) {
					int len = dn_expand(buf, end, buf, (char*)entry->auxtarget, 256);
					if (len < 1)
						break;

					buf = &buf[len];
					entry->auxlen = strlen((char*)entry->auxtarget);

					if (entry->auxlen == 0)
						continue;

					changed |= odhcp6c_update_entry(STATE_RA_SEARCH, entry,
									0, ra_holdoff_interval);
					entry->auxlen = 0;
				}
			}
		}

		if (ra_options & RA_RDNSS_DEFAULT_LIFETIME) {
			int states[2] = {STATE_RA_DNS, STATE_RA_SEARCH};

			for (size_t i = 0; i < 2; ++i) {
				size_t ra_dns_len;
				uint8_t *start = odhcp6c_get_state(states[i], &ra_dns_len);

				for (struct odhcp6c_entry *c = (struct odhcp6c_entry*)start;
							(uint8_t*)c < &start[ra_dns_len] &&
							(uint8_t*)odhcp6c_next_entry(c) <= &start[ra_dns_len];
							c = odhcp6c_next_entry(c)) {
					if (IN6_ARE_ADDR_EQUAL(&c->router, &from.sin6_addr) &&
							c->valid > router_valid)
						c->valid = router_valid;
				}
			}
		}
	}

	if (found)
		odhcp6c_expire(false);

	return found && changed;
}