/**
 * Copyright (C) 2012-2013 Steven Barth <steven@midlink.org>
 *
 * 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 <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <errno.h>

#include <fcntl.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <net/ethernet.h>
#include <netinet/ip6.h>
#include <netinet/icmp6.h>
#include <netpacket/packet.h>

#include <linux/filter.h>
#include <linux/neighbour.h>

#include "dhcpv6.h"
#include "odhcpd.h"


static void ndp_netevent_cb(unsigned long event, struct netevent_handler_info *info);
static void setup_route(struct in6_addr *addr, struct interface *iface, bool add);
static void setup_addr_for_relaying(struct in6_addr *addr, struct interface *iface, bool add);
static void handle_solicit(void *addr, void *data, size_t len,
		struct interface *iface, void *dest);

static int ping_socket = -1;

// Filter ICMPv6 messages of type neighbor soliciation
static struct sock_filter bpf[] = {
	BPF_STMT(BPF_LD | BPF_B | BPF_ABS, offsetof(struct ip6_hdr, ip6_nxt)),
	BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, IPPROTO_ICMPV6, 0, 3),
	BPF_STMT(BPF_LD | BPF_B | BPF_ABS, sizeof(struct ip6_hdr) +
			offsetof(struct icmp6_hdr, icmp6_type)),
	BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, ND_NEIGHBOR_SOLICIT, 0, 1),
	BPF_STMT(BPF_RET | BPF_K, 0xffffffff),
	BPF_STMT(BPF_RET | BPF_K, 0),
};
static const struct sock_fprog bpf_prog = {sizeof(bpf) / sizeof(*bpf), bpf};
static struct netevent_handler ndp_netevent_handler = { .cb = ndp_netevent_cb, };

// Initialize NDP-proxy
int ndp_init(void)
{
	int val = 2;

	// Open ICMPv6 socket
	ping_socket = socket(AF_INET6, SOCK_RAW | SOCK_CLOEXEC, IPPROTO_ICMPV6);
	if (ping_socket < 0) {
		syslog(LOG_ERR, "Unable to open raw socket: %m");
			return -1;
	}

	setsockopt(ping_socket, IPPROTO_RAW, IPV6_CHECKSUM, &val, sizeof(val));

	// This is required by RFC 4861
	val = 255;
	setsockopt(ping_socket, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &val, sizeof(val));
	setsockopt(ping_socket, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &val, sizeof(val));

	// Filter all packages, we only want to send
	struct icmp6_filter filt;
	ICMP6_FILTER_SETBLOCKALL(&filt);
	setsockopt(ping_socket, IPPROTO_ICMPV6, ICMP6_FILTER, &filt, sizeof(filt));

	netlink_add_netevent_handler(&ndp_netevent_handler);

	return 0;
}

int ndp_setup_interface(struct interface *iface, bool enable)
{
	int ret = 0, procfd;
	bool dump_neigh = false;
	char procbuf[64];

	snprintf(procbuf, sizeof(procbuf), "/proc/sys/net/ipv6/conf/%s/proxy_ndp", iface->ifname);
	procfd = open(procbuf, O_WRONLY);

	if (procfd < 0) {
		ret = -1;
		goto out;
	}

	if (iface->ndp_event.uloop.fd > 0) {
		uloop_fd_delete(&iface->ndp_event.uloop);
		close(iface->ndp_event.uloop.fd);
		iface->ndp_event.uloop.fd = -1;

		if (!enable || iface->ndp != MODE_RELAY)
			if (write(procfd, "0\n", 2) < 0) {}

		dump_neigh = true;
	}

	if (enable && iface->ndp == MODE_RELAY) {
		if (write(procfd, "1\n", 2) < 0) {}

		int sock = socket(AF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC, htons(ETH_P_IPV6));
		if (sock < 0) {
			syslog(LOG_ERR, "Unable to open packet socket: %m");
			ret = -1;
			goto out;
		}

#ifdef PACKET_RECV_TYPE
		int pktt = 1 << PACKET_MULTICAST;
		setsockopt(sock, SOL_PACKET, PACKET_RECV_TYPE, &pktt, sizeof(pktt));
#endif

		if (setsockopt(sock, SOL_SOCKET, SO_ATTACH_FILTER,
				&bpf_prog, sizeof(bpf_prog))) {
			syslog(LOG_ERR, "Failed to set BPF: %m");
			ret = -1;
			goto out;
		}

		struct sockaddr_ll ll = {
			.sll_family = AF_PACKET,
			.sll_ifindex = iface->ifindex,
			.sll_protocol = htons(ETH_P_IPV6),
			.sll_hatype = 0,
			.sll_pkttype = 0,
			.sll_halen = 0,
			.sll_addr = {0},
		};
		bind(sock, (struct sockaddr*)&ll, sizeof(ll));

		struct packet_mreq mreq = {iface->ifindex, PACKET_MR_ALLMULTI, ETH_ALEN, {0}};
		setsockopt(sock, SOL_PACKET, PACKET_ADD_MEMBERSHIP, &mreq, sizeof(mreq));

		iface->ndp_event.uloop.fd = sock;
		iface->ndp_event.handle_dgram = handle_solicit;
		odhcpd_register(&iface->ndp_event);

		// If we already were enabled dump is unnecessary, if not do dump
		if (!dump_neigh)
			netlink_dump_neigh_table(false);
		else
			dump_neigh = false;
	}

	if (dump_neigh)
		netlink_dump_neigh_table(true);

out:
	if (procfd >= 0)
		close(procfd);

	return ret;
}

static void ndp_netevent_cb(unsigned long event, struct netevent_handler_info *info)
{
	struct interface *iface = info->iface;
	bool add = true;

	if (!iface || iface->ndp == MODE_DISABLED)
		return;

	switch (event) {
	case NETEV_ADDR6_DEL:
		add = false;
		netlink_dump_neigh_table(false);
		/* fall through */
	case NETEV_ADDR6_ADD:
		setup_addr_for_relaying(&info->addr.in6, iface, add);
		break;
	case NETEV_NEIGH6_DEL:
		add = false;
		/* fall through */
	case NETEV_NEIGH6_ADD:
		if (info->neigh.flags & NTF_PROXY) {
			if (add) {
				netlink_setup_proxy_neigh(&info->neigh.dst.in6, iface->ifindex, false);
				setup_route(&info->neigh.dst.in6, iface, false);
				netlink_dump_neigh_table(false);
			}
			break;
		}

		if (add &&
		    !(info->neigh.state &
		      (NUD_REACHABLE|NUD_STALE|NUD_DELAY|NUD_PROBE|NUD_PERMANENT|NUD_NOARP)))
			break;

		setup_addr_for_relaying(&info->neigh.dst.in6, iface, add);
		setup_route(&info->neigh.dst.in6, iface, add);

		if (!add)
			netlink_dump_neigh_table(false);
		break;
	default:
		break;
	}
}

// Send an ICMP-ECHO. This is less for actually pinging but for the
// neighbor cache to be kept up-to-date.
static void ping6(struct in6_addr *addr,
		const struct interface *iface)
{
	struct sockaddr_in6 dest = { .sin6_family = AF_INET6, .sin6_addr = *addr, .sin6_scope_id = iface->ifindex, };
	struct icmp6_hdr echo = { .icmp6_type = ICMP6_ECHO_REQUEST };
	struct iovec iov = { .iov_base = &echo, .iov_len = sizeof(echo) };
	char ipbuf[INET6_ADDRSTRLEN];

	inet_ntop(AF_INET6, addr, ipbuf, sizeof(ipbuf));
	syslog(LOG_NOTICE, "Pinging for %s%%%s", ipbuf, iface->ifname);

	netlink_setup_route(addr, 128, iface->ifindex, NULL, 128, true);
	odhcpd_send(ping_socket, &dest, &iov, 1, iface);
	netlink_setup_route(addr, 128, iface->ifindex, NULL, 128, false);
}

// Handle solicitations
static void handle_solicit(void *addr, void *data, size_t len,
		struct interface *iface, _unused void *dest)
{
	struct ip6_hdr *ip6 = data;
	struct nd_neighbor_solicit *req = (struct nd_neighbor_solicit*)&ip6[1];
	struct sockaddr_ll *ll = addr;
	char ipbuf[INET6_ADDRSTRLEN];
	uint8_t mac[6];

	// Solicitation is for duplicate address detection
	bool ns_is_dad = IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src);

	// Don't process solicit messages on non relay interfaces
	// Don't forward any non-DAD solicitation for external ifaces
	// TODO: check if we should even forward DADs for them
	if (iface->ndp != MODE_RELAY || (iface->external && !ns_is_dad))
		return;

	if (len < sizeof(*ip6) + sizeof(*req))
		return; // Invalid reqicitation

	if (IN6_IS_ADDR_LINKLOCAL(&req->nd_ns_target) ||
			IN6_IS_ADDR_LOOPBACK(&req->nd_ns_target) ||
			IN6_IS_ADDR_MULTICAST(&req->nd_ns_target))
		return; // Invalid target

	inet_ntop(AF_INET6, &req->nd_ns_target, ipbuf, sizeof(ipbuf));
	syslog(LOG_DEBUG, "Got a NS for %s%%%s", ipbuf, iface->ifname);

	odhcpd_get_mac(iface, mac);
	if (!memcmp(ll->sll_addr, mac, sizeof(mac)))
		return; // Looped back

	struct interface *c;
	list_for_each_entry(c, &interfaces, head)
		if (iface != c && c->ndp == MODE_RELAY &&
				(ns_is_dad || !c->external))
			ping6(&req->nd_ns_target, c);
}

// Use rtnetlink to modify kernel routes
static void setup_route(struct in6_addr *addr, struct interface *iface, bool add)
{
	char ipbuf[INET6_ADDRSTRLEN];

	inet_ntop(AF_INET6, addr, ipbuf, sizeof(ipbuf));
	syslog(LOG_NOTICE, "%s about %s%s%%%s",
			(add) ? "Learning" : "Forgetting",
			iface->learn_routes ? "proxy routing for " : "",
			ipbuf, iface->ifname);

	if (iface->learn_routes)
		netlink_setup_route(addr, 128, iface->ifindex, NULL, 1024, add);
}

static void setup_addr_for_relaying(struct in6_addr *addr, struct interface *iface, bool add)
{
	struct interface *c;
	char ipbuf[INET6_ADDRSTRLEN];

	inet_ntop(AF_INET6, addr, ipbuf, sizeof(ipbuf));

	list_for_each_entry(c, &interfaces, head) {
		if (iface == c || (c->ndp != MODE_RELAY && !add))
			continue;

		bool neigh_add = (c->ndp == MODE_RELAY ? add : false);

		if (netlink_setup_proxy_neigh(addr, c->ifindex, neigh_add))
			syslog(LOG_DEBUG, "Failed to %s proxy neighbour entry %s%%%s",
				neigh_add ? "add" : "delete", ipbuf, c->ifname);
		else
			syslog(LOG_DEBUG, "%s proxy neighbour entry %s%%%s",
				neigh_add ? "Added" : "Deleted", ipbuf, c->ifname);
	}
}