/* PASST - Plug A Simple Socket Transport
 *
 * passt.c - Daemon implementation
 *
 * Author: Stefano Brivio <sbrivio@redhat.com>
 * License: GPLv2
 *
 * Grab Ethernet frames via AF_UNIX socket, build AF_INET/AF_INET6 sockets for
 * each 5-tuple from ICMP, TCP, UDP packets, perform connection tracking and
 * forward them with destination address NAT. Forward packets received on
 * sockets back to the UNIX domain socket (typically, a tap file descriptor from
 * qemu).
 *
 * TODO:
 * - steal packets from AF_INET/AF_INET6 sockets (using eBPF/XDP, or a new
 *   socket option): currently, incoming packets are also handled by in-kernel
 *   protocol handlers, so every incoming untracked TCP packet gets a RST.
 *   Workaround:
 *	iptables -A OUTPUT -m state --state INVALID,NEW,ESTABLISHED \
 *				-p tcp --tcp-flags RST RST -j DROP
 *	ip6tables -A OUTPUT -m state --state INVALID,NEW,ESTABLISHED \
 *				-p tcp --tcp-flags RST RST -j DROP
 * - and use XDP sockmap on top of that to improve performance
 * - aging and timeout/RST bookkeeping for connection tracking entries
 */

#include <stdio.h>
#include <sys/epoll.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#include <ifaddrs.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/icmpv6.h>
#include <linux/if_link.h>
#include <net/ethernet.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <netdb.h>
#include <string.h>
#include <errno.h>
#include <linux/ip.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>

#include "passt.h"
#include "arp.h"
#include "dhcp.h"
#include "ndp.h"
#include "util.h"

#define EPOLL_EVENTS	10

/**
 * sock_unix() - Create and bind AF_UNIX socket, add to epoll list
 *
 * Return: newly created socket, doesn't return on error
 */
static int sock_unix(void)
{
	int fd = socket(AF_UNIX, SOCK_STREAM, 0);
	struct sockaddr_un addr = {
		.sun_family = AF_UNIX,
		.sun_path = UNIX_SOCK_PATH,
	};

	if (fd < 0) {
		perror("UNIX socket");
		exit(EXIT_FAILURE);
	}

	unlink(UNIX_SOCK_PATH);
	if (bind(fd, (const struct sockaddr *)&addr, sizeof(addr)) < 0) {
		perror("UNIX socket bind");
		exit(EXIT_FAILURE);
	}
	return fd;
}

/**
 * struct nl_request - Netlink request filled and sent by get_routes()
 * @nlh:	Netlink message header
 * @rtm:	Routing Netlink message
 */
struct nl_request {
	struct nlmsghdr nlh;
	struct rtmsg rtm;
};

/**
 * get_routes() - Get default route and fill in routable interface name
 * @c:		Execution context
 */
static void get_routes(struct ctx *c)
{
	struct nl_request req = {
		.nlh.nlmsg_type = RTM_GETROUTE,
		.nlh.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP | NLM_F_EXCL,
		.nlh.nlmsg_len = sizeof(struct nl_request),
		.nlh.nlmsg_seq = 1,
		.rtm.rtm_family = AF_INET,
		.rtm.rtm_table = RT_TABLE_MAIN,
		.rtm.rtm_scope = RT_SCOPE_UNIVERSE,
		.rtm.rtm_type = RTN_UNICAST,
	};
	struct sockaddr_nl addr = {
		.nl_family = AF_NETLINK,
	};
	struct nlmsghdr *nlh;
	struct rtattr *rta;
	struct rtmsg *rtm;
	char buf[BUFSIZ];
	int s, n, na;

	c->v6 = -1;

	s = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
	if (s < 0) {
		perror("netlink socket");
		goto out;
	}

	if (bind(s, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
		perror("netlink bind");
		goto out;
	}

v6:
	if (send(s, &req, sizeof(req), 0) < 0) {
		perror("netlink send");
		goto out;
	}

	n = recv(s, &buf, sizeof(buf), 0);
	if (n < 0) {
		perror("netlink recv");
		goto out;
	}

	nlh = (struct nlmsghdr *)buf;
	for ( ; NLMSG_OK(nlh, n); nlh = NLMSG_NEXT(nlh, n)) {
		rtm = (struct rtmsg *)NLMSG_DATA(nlh);

		if (rtm->rtm_dst_len ||
		    (rtm->rtm_family != AF_INET && rtm->rtm_family != AF_INET6))
			continue;

		rta = (struct rtattr *)RTM_RTA(rtm);
		na = RTM_PAYLOAD(nlh);
		for ( ; RTA_OK(rta, na); rta = RTA_NEXT(rta, na)) {
			if (rta->rta_type == RTA_GATEWAY &&
			    rtm->rtm_family == AF_INET && !c->v4) {
				memcpy(&c->gw4, RTA_DATA(rta), sizeof(c->gw4));
				c->v4 = 1;
			}

			if (rta->rta_type == RTA_GATEWAY &&
			    rtm->rtm_family == AF_INET6 && !c->v6) {
				memcpy(&c->gw6, RTA_DATA(rta), sizeof(c->gw6));
				c->v6 = 1;
			}

			if (rta->rta_type == RTA_OIF && !*c->ifn) {
				if_indextoname(*(unsigned *)RTA_DATA(rta),
					       c->ifn);
			}
		}

		if (nlh->nlmsg_type == NLMSG_DONE)
			break;
	}

	if (c->v6 == -1) {
		c->v6 = 0;
		req.rtm.rtm_family = AF_INET6;
		req.nlh.nlmsg_seq++;
		recv(s, &buf, sizeof(buf), 0);
		goto v6;
	}

out:
	close(s);

	if (!(c->v4 || c->v6) || !*c->ifn) {
		fprintf(stderr, "No routing information\n");
		exit(EXIT_FAILURE);
	}
}

/**
 * get_addrs() - Fetch MAC, IP addresses, masks of external routable interface
 * @c:		Execution context
 */
static void get_addrs(struct ctx *c)
{
	struct ifreq ifr = {
		.ifr_addr.sa_family = AF_INET,
	};
	struct ifaddrs *ifaddr, *ifa;
	int s, v4 = 0, v6 = 0;

	if (getifaddrs(&ifaddr) == -1) {
		perror("getifaddrs");
		goto out;
	}

	for (ifa = ifaddr; ifa; ifa = ifa->ifa_next) {
		struct sockaddr_in *in_addr;
		struct sockaddr_in6 *in6_addr;

		if (strcmp(ifa->ifa_name, c->ifn))
			continue;

		if (!ifa->ifa_addr)
			continue;

		if (ifa->ifa_addr->sa_family == AF_INET && !v4) {
			in_addr = (struct sockaddr_in *)ifa->ifa_addr;
			c->addr4 = in_addr->sin_addr.s_addr;
			in_addr = (struct sockaddr_in *)ifa->ifa_netmask;
			c->mask4 = in_addr->sin_addr.s_addr;
			v4 = 1;
		} else if (ifa->ifa_addr->sa_family == AF_INET6 && !v6) {
			in6_addr = (struct sockaddr_in6 *)ifa->ifa_addr;
			memcpy(&c->addr6, &in6_addr->sin6_addr,
			       sizeof(c->addr6));
			v6 = 1;
		}

		if (v4 == c->v4 && v6 == c->v6)
			break;
	}

	freeifaddrs(ifaddr);

	if (v4 != c->v4 || v6 != c->v6)
		goto out;

	s = socket(AF_INET, SOCK_DGRAM, 0);
	if (s < 0) {
		perror("socket SIOCGIFHWADDR");
		goto out;
	}

	strncpy(ifr.ifr_name, c->ifn, IF_NAMESIZE);
	if (ioctl(s, SIOCGIFHWADDR, &ifr) < 0) {
		perror("SIOCGIFHWADDR");
		goto out;
	}

	close(s);
	memcpy(c->mac, ifr.ifr_hwaddr.sa_data, ETH_ALEN);

	return;
out:
	fprintf(stderr, "Couldn't get addresses for routable interface\n");
	exit(EXIT_FAILURE);
}

/**
 * get_dns() - Get nameserver addresses from local /etc/resolv.conf
 * @c:		Execution context
 */
static void get_dns(struct ctx *c)
{
	char buf[BUFSIZ], *p, *end;
	int dns4 = 0, dns6 = 0;
	FILE *r;

	r = fopen("/etc/resolv.conf", "r");
	while (fgets(buf, BUFSIZ, r) && !(dns4 && dns6)) {
		if (!strstr(buf, "nameserver "))
			continue;
		p = strrchr(buf, ' ');
		end = strpbrk(buf, "%\n");
		if (end)
			*end = 0;
		if (p && inet_pton(AF_INET, p + 1, &c->dns4))
			dns4 = 1;
		if (p && inet_pton(AF_INET6, p + 1, &c->dns6))
			dns6 = 1;
	}

	fclose(r);
	if (dns4 || dns6)
		return;

	fprintf(stderr, "Couldn't get any nameserver address\n");
	exit(EXIT_FAILURE);
}

/**
 * sock_l4() - Create and bind socket for given L4, add to epoll list
 * @c:		Execution context
 * @v:		IP protocol, 4 or 6
 * @proto:	Protocol number, network order
 * @port:	L4 port, network order
 *
 * Return: newly created socket, -1 on error
 */
static int sock_l4(struct ctx *c, int v, uint16_t proto, uint16_t port)
{
	struct sockaddr_in addr4 = {
		.sin_family = AF_INET,
		.sin_port = port,
		.sin_addr = { .s_addr = c->addr4 },
	};
	struct sockaddr_in6 addr6 = {
		.sin6_family = AF_INET6,
		.sin6_port = port,
		.sin6_addr = c->addr6,
	};
	struct epoll_event ev = { 0 };
	const struct sockaddr *sa;
	int fd, sl;

	fd = socket(v == 4 ? AF_INET : AF_INET6, SOCK_RAW, proto);
	if (fd < 0) {
		perror("L4 socket");
		return -1;
	}

	if (v == 4) {
		sa = (const struct sockaddr *)&addr4;
		sl = sizeof(addr4);
	} else {
		sa = (const struct sockaddr *)&addr6;
		sl = sizeof(addr6);
	}

	if (bind(fd, sa, sl) < 0) {
		perror("L4 bind");
		close(fd);
		return -1;
	}

	ev.events = EPOLLIN;
	ev.data.fd = fd;
	if (epoll_ctl(c->epollfd, EPOLL_CTL_ADD, fd, &ev) == -1) {
		perror("L4 epoll_ctl");
		return -1;
	}

	return fd;
}

/**
 * lookup4() - Look up entry from tap-sourced IPv4 packet, create if missing
 * @c:		Execution context
 * @eh:		Packet buffer, Ethernet header
 *
 * Return: -1 for unsupported or too many sockets, matching socket otherwise
 */
static int lookup4(struct ctx *c, const struct ethhdr *eh)
{
	struct iphdr *iph = (struct iphdr *)(eh + 1);
	struct tcphdr *th = (struct tcphdr *)((char *)iph + iph->ihl * 4);
	char buf_s[BUFSIZ], buf_d[BUFSIZ];
	struct ct4 *ct = c->map4;
	int i, one_icmp_fd = 0;

	if (iph->protocol != IPPROTO_ICMP && iph->protocol != IPPROTO_TCP &&
	    iph->protocol != IPPROTO_UDP)
		return -1;

	for (i = 0; i < CT_SIZE; i++) {
		if (ct[i].p == iph->protocol && ct[i].sa == iph->saddr &&
		    ((ct[i].p == IPPROTO_ICMP && ct[i].da == iph->daddr)
		     || ct[i].sp == th->source) &&
		    !memcmp(ct[i].hd, eh->h_dest, ETH_ALEN) &&
		    !memcmp(ct[i].hs, eh->h_source, ETH_ALEN)) {
			if (iph->protocol != IPPROTO_ICMP) {
				ct[i].da = iph->daddr;
				ct[i].dp = th->dest;
			}
			return ct[i].fd;
		}
	}

	for (i = 0; i < CT_SIZE && ct[i].p; i++) {
		if (iph->protocol == IPPROTO_ICMP && ct[i].p == IPPROTO_ICMP)
			one_icmp_fd = ct[i].fd;
	}

	if (i == CT_SIZE) {
		fprintf(stderr, "\nToo many sockets, aborting ");
	} else {
		if (iph->protocol == IPPROTO_ICMP) {
			if (one_icmp_fd)
				ct[i].fd = one_icmp_fd;
			else
				ct[i].fd = sock_l4(c, 4, iph->protocol, 0);
		} else {
			ct[i].fd = sock_l4(c, 4, iph->protocol, th->source);
		}

		fprintf(stderr, "\n(socket %i) New ", ct[i].fd);
		ct[i].p = iph->protocol;
		ct[i].sa = iph->saddr;
		ct[i].da = iph->daddr;
		if (iph->protocol != IPPROTO_ICMP) {
			ct[i].sp = th->source;
			ct[i].dp = th->dest;
		}
		memcpy(&ct[i].hd, eh->h_dest, ETH_ALEN);
		memcpy(&ct[i].hs, eh->h_source, ETH_ALEN);
	}

	if (iph->protocol == IPPROTO_ICMP) {
		fprintf(stderr, "icmp connection\n\tfrom %s to %s\n\n",
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)));
	} else {
		fprintf(stderr, "%s connection\n\tfrom %s:%i to %s:%i\n\n",
			getprotobynumber(iph->protocol)->p_name,
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			ntohs(th->source),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
			ntohs(th->dest));
	}

	return (i == CT_SIZE) ? -1 : ct[i].fd;
}

/**
 * lookup6() - Look up entry from tap-sourced IPv6 packet, create if missing
 * @c:		Execution context
 * @eh:		Packet buffer, Ethernet header
 *
 * Return: -1 for unsupported or too many sockets, matching socket otherwise
 */
static int lookup6(struct ctx *c, const struct ethhdr *eh)
{
	struct ipv6hdr *ip6h = (struct ipv6hdr *)(eh + 1);
	char buf_s[BUFSIZ], buf_d[BUFSIZ];
	struct ct6 *ct = c->map6;
	int i, one_icmp_fd = 0;
	struct tcphdr *th;
	uint8_t proto;

	th = (struct tcphdr *)ipv6_l4hdr(ip6h, &proto);
	if (!th)
		return -1;

	if (proto != IPPROTO_ICMPV6 && proto != IPPROTO_TCP &&
	    proto != IPPROTO_UDP)
		return -1;

	for (i = 0; i < CT_SIZE; i++) {
		if (ct[i].p != proto)
			continue;

		if (memcmp(ct[i].hd, eh->h_dest, ETH_ALEN) ||
		    memcmp(ct[i].hs, eh->h_source, ETH_ALEN) ||
		    memcmp(&ct[i].sa, &ip6h->saddr, sizeof(ct[i].sa)))
			continue;

		if (ct[i].p != IPPROTO_ICMPV6 &&
		    ct[i].sp != th->source)
			continue;

		if (ct[i].p == IPPROTO_ICMPV6 &&
		    memcmp(&ct[i].da, &ip6h->daddr, sizeof(ct[i].da)))
			continue;

		if (ct[i].p != IPPROTO_ICMPV6) {
			memcpy(&ct[i].da, &ip6h->daddr, sizeof(ct[i].da));
			ct[i].dp = th->dest;
		}

		return ct[i].fd;
	}

	for (i = 0; i < CT_SIZE && ct[i].p; i++) {
		if (proto == IPPROTO_ICMPV6 && ct[i].p == IPPROTO_ICMPV6)
			one_icmp_fd = ct[i].fd;
	}

	if (i == CT_SIZE) {
		fprintf(stderr, "\nToo many sockets, aborting ");
	} else {
		if (proto == IPPROTO_ICMPV6) {
			if (one_icmp_fd)
				ct[i].fd = one_icmp_fd;
			else
				ct[i].fd = sock_l4(c, 6, proto, 0);
		} else {
			ct[i].fd = sock_l4(c, 6, proto, th->source);
		}

		fprintf(stderr, "\n(socket %i) New ", ct[i].fd);
		ct[i].p = proto;
		memcpy(&ct[i].sa, &ip6h->saddr, sizeof(ct[i].sa));
		memcpy(&ct[i].da, &ip6h->daddr, sizeof(ct[i].da));
		if (ct[i].p != IPPROTO_ICMPV6) {
			ct[i].sp = th->source;
			ct[i].dp = th->dest;
		}
		memcpy(&ct[i].hd, eh->h_dest, ETH_ALEN);
		memcpy(&ct[i].hs, eh->h_source, ETH_ALEN);
	}

	if (proto == IPPROTO_ICMPV6) {
		fprintf(stderr, "icmpv6 connection\n\tfrom %s\n"
				"\tto %s\n\n",
			inet_ntop(AF_INET6, &ct[i].sa, buf_s, sizeof(buf_s)),
			inet_ntop(AF_INET6, &ct[i].da, buf_d, sizeof(buf_d)));
	} else {
		fprintf(stderr, "%s connection\n\tfrom [%s]:%i\n"
				"\tto [%s]:%i\n\n",
			getprotobynumber(proto)->p_name,
			inet_ntop(AF_INET6, &ct[i].sa, buf_s, sizeof(buf_s)),
			ntohs(th->source),
			inet_ntop(AF_INET6, &ct[i].da, buf_d, sizeof(buf_d)),
			ntohs(th->dest));
	}

	return (i == CT_SIZE) ? -1 : ct[i].fd;
}

/**
 * lookup_r4() - Reverse look up connection tracking entry for IPv4 packet
 * @ct:		Connection tracking table
 * @fd:		File descriptor that received the packet
 * @iph:	Packet buffer, IP header
 *
 * Return: matching entry if any, NULL otherwise
 */
struct ct4 *lookup_r4(struct ct4 *ct, int fd, struct iphdr *iph)
{
	struct tcphdr *th = (struct tcphdr *)((char *)iph + iph->ihl * 4);
	int i;

	for (i = 0; i < CT_SIZE; i++) {
		if (ct[i].fd == fd &&
		    iph->protocol == ct[i].p &&
		    iph->saddr == ct[i].da &&
		    (iph->protocol == IPPROTO_ICMP ||
		     (th->source == ct[i].dp && th->dest == ct[i].sp)))
			return &ct[i];
	}

	return NULL;
}

/**
 * lookup_r6() - Reverse look up connection tracking entry for IPv6 packet
 * @ct:		Connection tracking table
 * @fd:		File descriptor that received the packet
 *
 * Return: matching entry if any, NULL otherwise
 */
struct ct6 *lookup_r6(struct ct6 *ct, int fd, struct tcphdr *th)
{
	int i;

	for (i = 0; i < CT_SIZE; i++) {
		if (ct[i].fd != fd)
			continue;

		if (ct[i].p == IPPROTO_ICMPV6 ||
		    (ct[i].dp == th->source && ct[i].sp == th->dest))
			return &ct[i];
	}

	return NULL;
}

/**
 * nat4_in() - Perform incoming IPv4 address translation
 * @addr:	Original destination address to be used
 * @iph:	IP header
 */
static void nat_in(unsigned long addr, struct iphdr *iph)
{
	iph->daddr = addr;
}

/**
 * csum_ipv4() - Calculate TCP checksum for IPv4 and set in place
 * @iph:	Packet buffer, IP header
 */
static void csum_tcp4(struct iphdr *iph)
{
	struct tcphdr *th = (struct tcphdr *)((char *)iph + iph->ihl * 4);
	uint16_t tlen = ntohs(iph->tot_len) - iph->ihl * 4, *p = (uint16_t *)th;
	uint32_t sum = 0;

	sum += (iph->saddr >> 16) & 0xffff;
	sum += iph->saddr & 0xffff;
	sum += (iph->daddr >> 16) & 0xffff;
	sum += iph->daddr & 0xffff;

	sum += htons(IPPROTO_TCP);
	sum += htons(tlen);

	th->check = 0;
	while (tlen > 1) {
		sum += *p++;
		tlen -= 2;
	}

	if (tlen > 0) {
		sum += *p & htons(0xff00);
	}

	th->check = (uint16_t)~csum_fold(sum);
}

/**
 * tap4_handler() - IPv4 packet handler for tap file descriptor
 * @c:		Execution context
 * @len:	Total L2 packet length
 * @in:		Packet buffer, L2 headers
 */
static void tap4_handler(struct ctx *c, int len, char *in)
{
	struct ethhdr *eh = (struct ethhdr *)in;
	struct iphdr *iph = (struct iphdr *)(eh + 1);
	struct tcphdr *th = (struct tcphdr *)((char *)iph + iph->ihl * 4);
	struct udphdr *uh = (struct udphdr *)th;
	struct sockaddr_in addr = {
		.sin_family = AF_INET,
		.sin_port = th->dest,
		.sin_addr = { .s_addr = iph->daddr },
	};
	char buf_s[BUFSIZ], buf_d[BUFSIZ];
	int fd;

	if (arp(c, len, eh) || dhcp(c, len, eh))
		return;

	fd = lookup4(c, eh);
	if (fd == -1)
		return;

	if (iph->protocol == IPPROTO_ICMP) {
		fprintf(stderr, "icmp from tap: %s -> %s (socket %i)\n",
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
			fd);
	} else {
		fprintf(stderr, "%s from tap: %s:%i -> %s:%i (socket %i)\n",
			getprotobynumber(iph->protocol)->p_name,
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			ntohs(th->source),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
			ntohs(th->dest),
			fd);
	}

	if (iph->protocol == IPPROTO_TCP)
		csum_tcp4(iph);
	else if (iph->protocol == IPPROTO_UDP)
		uh->check = 0;
	else if (iph->protocol != IPPROTO_ICMP)
		return;

	if (sendto(fd, (void *)th, len - sizeof(*eh) - iph->ihl * 4, 0,
		   (struct sockaddr *)&addr, sizeof(addr)) < 0)
		perror("sendto");

}

/**
 * tap6_handler() - IPv6 packet handler for tap file descriptor
 * @c:		Execution context
 * @len:	Total L2 packet length
 * @in:		Packet buffer, L2 headers
 */
static void tap6_handler(struct ctx *c, int len, char *in)
{
	struct ethhdr *eh = (struct ethhdr *)in;
	struct ipv6hdr *ip6h = (struct ipv6hdr *)(eh + 1);
	struct tcphdr *th;
	struct udphdr *uh;
	struct icmp6hdr *ih;
	struct sockaddr_in6 addr = {
		.sin6_family = AF_INET6,
		.sin6_addr = ip6h->daddr,
	};
	char buf_s[BUFSIZ], buf_d[BUFSIZ];
	uint8_t proto;
	int fd;

	if (ndp(c, len, eh))
		return;

	fd = lookup6(c, eh);
	if (fd == -1)
		return;

	th = (struct tcphdr *)ipv6_l4hdr(ip6h, &proto);
	uh = (struct udphdr *)th;
	ih = (struct icmp6hdr *)th;

	if (proto == IPPROTO_ICMPV6) {
		fprintf(stderr, "icmpv6 from tap: %s ->\n\t%s (socket %i)\n",
			inet_ntop(AF_INET6, &ip6h->saddr, buf_s, sizeof(buf_s)),
			inet_ntop(AF_INET6, &ip6h->daddr, buf_d, sizeof(buf_d)),
			fd);
	} else {
		fprintf(stderr, "%s from tap: [%s]:%i\n"
				"\t-> [%s]:%i (socket %i)\n",
			getprotobynumber(proto)->p_name,
			inet_ntop(AF_INET6, &ip6h->saddr, buf_s, sizeof(buf_s)),
			ntohs(th->source),
			inet_ntop(AF_INET6, &ip6h->daddr, buf_d, sizeof(buf_d)),
			ntohs(th->dest),
			fd);
	}

	if (proto != IPPROTO_TCP && proto != IPPROTO_UDP &&
	    proto != IPPROTO_ICMPV6)
		return;

	ip6h->saddr = c->addr6;

	ip6h->hop_limit = proto;
	ip6h->version = 0;
	ip6h->nexthdr = 0;
	memset(ip6h->flow_lbl, 0, 3);

	if (proto == IPPROTO_TCP) {
		th->check = 0;
		th->check = csum_ip4(ip6h,
				     len - ((intptr_t)th - (intptr_t)eh) +
				     sizeof(*ip6h));
	} else if (proto == IPPROTO_UDP) {
		uh->check = 0;
		uh->check = csum_ip4(ip6h,
				     len - ((intptr_t)uh - (intptr_t)eh) +
				     sizeof(*ip6h));
	} else if (proto == IPPROTO_ICMPV6) {
		ih->icmp6_cksum = 0;
		ih->icmp6_cksum = csum_ip4(ip6h,
					   len - ((intptr_t)ih - (intptr_t)eh) +
					   sizeof(*ip6h));
	}

	ip6h->version = 6;
	ip6h->nexthdr = proto;
	ip6h->hop_limit = 255;

	if (sendto(fd, (void *)th, len - ((intptr_t)th - (intptr_t)eh), 0,
		   (struct sockaddr *)&addr, sizeof(addr)) < 0)
		perror("sendto");

}

static void tap_handler(struct ctx *c, int len, char *in)
{
	struct ethhdr *eh = (struct ethhdr *)in;

	if (eh->h_proto == ntohs(ETH_P_IP) || eh->h_proto == ntohs(ETH_P_ARP))
		tap4_handler(c, len, in);
	else if (eh->h_proto == ntohs(ETH_P_IPV6))
		tap6_handler(c, len, in);
}

/**
 * ext4_handler() - IPv4 packet handler for external routable interface
 * @c:		Execution context
 * @fd:		File descriptor that received the packet
 * @len:	Total L3 packet length
 * @in:		Packet buffer, L3 headers
 */
static void ext4_handler(struct ctx *c, int fd, int len, char *in)
{
	struct iphdr *iph = (struct iphdr *)in;
	struct tcphdr *th = (struct tcphdr *)((char *)iph + iph->ihl * 4);
	struct udphdr *uh = (struct udphdr *)th;
	char buf_s[BUFSIZ], buf_d[BUFSIZ], buf[ETH_MAX_MTU];
	struct ethhdr *eh = (struct ethhdr *)buf;
	struct ct4 *entry;

	entry = lookup_r4(c->map4, fd, iph);
	if (!entry)
		return;

	nat_in(entry->sa, iph);

	iph->check = 0;
	iph->check = csum_ip4(iph, iph->ihl * 4);

	if (iph->protocol == IPPROTO_TCP)
		csum_tcp4(iph);
	else if (iph->protocol == IPPROTO_UDP)
		uh->check = 0;

	memcpy(eh->h_dest, entry->hs, ETH_ALEN);
	memcpy(eh->h_source, entry->hd, ETH_ALEN);
	eh->h_proto = ntohs(ETH_P_IP);

	memcpy(eh + 1, in, len);

	if (iph->protocol == IPPROTO_ICMP) {
		fprintf(stderr, "icmp (socket %i) to tap: %s -> %s\n",
			entry->fd,
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)));
	} else {
		fprintf(stderr, "%s (socket %i) to tap: %s:%i -> %s:%i\n",
			getprotobynumber(iph->protocol)->p_name,
			entry->fd,
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			ntohs(th->source),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
			ntohs(th->dest));
	}

	if (send(c->fd_unix, buf, len + sizeof(*eh), 0) < 0)
		perror("send");
}

/**
 * ext6_handler() - IPv6 packet handler for external routable interface
 * @c:		Execution context
 * @fd:		File descriptor that received the packet
 * @len:	Total L4 packet length
 * @in:		Packet buffer, L4 headers
 */
static int ext6_handler(struct ctx *c, int fd, int len, char *in)
{
	struct tcphdr *th = (struct tcphdr *)in;
	struct udphdr *uh;
	struct icmp6hdr *ih;
	char buf_s[BUFSIZ], buf_d[BUFSIZ], buf[ETH_MAX_MTU] = { 0 };
	struct ethhdr *eh = (struct ethhdr *)buf;
	struct ipv6hdr *ip6h = (struct ipv6hdr *)(eh + 1);
	struct ct6 *entry;

	entry = lookup_r6(c->map6, fd, th);
	if (!entry)
		return 0;

	ip6h->daddr = entry->sa;
	ip6h->saddr = entry->da;
	memcpy(ip6h + 1, in, len);
	ip6h->payload_len = htons(len);

	th = (struct tcphdr *)(ip6h + 1);
	uh = (struct udphdr *)th;
	ih = (struct icmp6hdr *)th;
	ip6h->hop_limit = entry->p;

	if (entry->p == IPPROTO_TCP) {
		th->check = 0;
		th->check = csum_ip4(ip6h, len + sizeof(*ip6h));
	} else if (entry->p == IPPROTO_UDP) {
		uh->check = 0;
		uh->check = csum_ip4(ip6h, len + sizeof(*ip6h));
	} else if (entry->p == IPPROTO_ICMPV6) {
		ih->icmp6_cksum = 0;
		ih->icmp6_cksum = csum_ip4(ip6h, len + sizeof(*ip6h));
	}

	ip6h->version = 6;
	ip6h->nexthdr = entry->p;
	ip6h->hop_limit = 255;

	memcpy(eh->h_dest, entry->hs, ETH_ALEN);
	memcpy(eh->h_source, entry->hd, ETH_ALEN);
	eh->h_proto = ntohs(ETH_P_IPV6);

	if (entry->p == IPPROTO_ICMPV6) {
		fprintf(stderr, "icmpv6 (socket %i) to tap: %s\n\t-> %s\n",
			entry->fd,
			inet_ntop(AF_INET6, &ip6h->saddr, buf_s, sizeof(buf_s)),
			inet_ntop(AF_INET6, &ip6h->daddr, buf_d,
				  sizeof(buf_d)));
	} else {
		fprintf(stderr, "%s (socket %i) to tap: [%s]:%i\n"
				"\t-> [%s]:%i\n",
			getprotobynumber(entry->p)->p_name,
			entry->fd,
			inet_ntop(AF_INET6, &ip6h->saddr, buf_s, sizeof(buf_s)),
			ntohs(th->source),
			inet_ntop(AF_INET6, &ip6h->daddr, buf_d, sizeof(buf_d)),
			ntohs(th->dest));
	}

	if (send(c->fd_unix, buf, len + sizeof(*ip6h) + sizeof(*eh), 0) < 0)
		perror("send");

	return 1;
}

static void ext_handler(struct ctx *c, int fd, int len, char *in)
{
	if (!ext6_handler(c, fd, len, in))
		ext4_handler(c, fd, len, in);
}

/**
 * usage() - Print usage and exit
 * @name:	Executable name
 */
void usage(const char *name)
{
	fprintf(stderr, "Usage: %s\n", name);

	exit(EXIT_FAILURE);
}

/**
 * main() - Entry point and main loop
 * @argc:	Argument count
 * @argv:	Interface names
 *
 * Return: 0 once interrupted, non-zero on failure
 */
int main(int argc, char **argv)
{
	char buf6[3][sizeof("0123:4567:89ab:cdef:0123:4567:89ab:cdef")];
	char buf4[4][sizeof("255.255.255.255")];
	struct epoll_event events[EPOLL_EVENTS];
	struct epoll_event ev = { 0 };
	char buf[ETH_MAX_MTU];
	struct ctx c = { 0 };
	int nfds, i, len;
	int fd_unix;

	if (argc != 1)
		usage(argv[0]);

	get_routes(&c);
	get_addrs(&c);
	get_dns(&c);

	if (c.v4) {
		fprintf(stderr, "ARP:\n");
		fprintf(stderr, "\taddress: %02x:%02x:%02x:%02x:%02x:%02x "
			"from %s\n", c.mac[0], c.mac[1], c.mac[2],
				     c.mac[3], c.mac[4], c.mac[5], c.ifn);
		fprintf(stderr, "DHCP:\n");
		fprintf(stderr, "\tassign:\t%s\n\tnmask:\t%s\n"
				"\trouter:\t%s\n\tDNS:\t%s\n",
			inet_ntop(AF_INET, &c.addr4, buf4[0], sizeof(buf4[0])),
			inet_ntop(AF_INET, &c.mask4, buf4[1], sizeof(buf4[1])),
			inet_ntop(AF_INET, &c.gw4, buf4[2], sizeof(buf4[2])),
			inet_ntop(AF_INET, &c.dns4, buf4[3], sizeof(buf4[3])));
	}
	if (c.v6) {
		fprintf(stderr, "NDP:\n");
		fprintf(stderr, "\tassign:\t%s\n\trouter:\t%s\n\tDNS:\t%s\n",
			inet_ntop(AF_INET6, &c.addr6, buf6[0], sizeof(buf6[0])),
			inet_ntop(AF_INET6, &c.gw6, buf6[1], sizeof(buf6[1])),
			inet_ntop(AF_INET6, &c.dns6, buf6[2], sizeof(buf6[2])));
	}
	fprintf(stderr, "\n");

	c.epollfd = epoll_create1(0);
	if (c.epollfd == -1) {
		perror("epoll_create1");
		exit(EXIT_FAILURE);
	}

	fd_unix = sock_unix();
listen:
	listen(fd_unix, 1);
	fprintf(stderr,
		"You can now start qrap:\n\t"
		"./qrap 42 kvm ... -net tap,fd=42 -net nic,model=virtio\n\n");

	c.fd_unix = accept(fd_unix, NULL, NULL);
	ev.events = EPOLLIN;
	ev.data.fd = c.fd_unix;
	epoll_ctl(c.epollfd, EPOLL_CTL_ADD, c.fd_unix, &ev);

loop:
	nfds = epoll_wait(c.epollfd, events, EPOLL_EVENTS, -1);
	if (nfds == -1 && errno != EINTR) {
		perror("epoll_wait");
		exit(EXIT_FAILURE);
	}

	for (i = 0; i < nfds; i++) {
		len = recv(events[i].data.fd, buf, sizeof(buf), MSG_DONTWAIT);

		if (events[i].data.fd == c.fd_unix && len <= 0) {
			epoll_ctl(c.epollfd, EPOLL_CTL_DEL, c.fd_unix, &ev);
			close(c.fd_unix);
			goto listen;
		}

		if (len == 0 || (len < 0 && errno == EINTR))
			continue;

		if (len < 0) {
			if (errno == EAGAIN || errno == EWOULDBLOCK)
				break;
			goto out;
		}

		if (events[i].data.fd == c.fd_unix)
			tap_handler(&c, len, buf);
		else
			ext_handler(&c, events[i].data.fd, len, buf);
	}

	goto loop;

out:
	return 0;
}