path: root/fw/src/ether.c

/*
 * fw, the ethernet side.
 *
 * To filter a real machine, fw has to be the wire: the card cannot
 * stay attached to the IP stack, or packets reach it whatever we
 * decide.  So fw opens /net/etherN itself and the protected stack gets
 * a pkt interface instead - a fake card with fw on the other end.
 *
 *	ether0 ---- fw ---- pkt ---- the stack ---- programs
 *
 * The stack no longer has ethernet, so nobody is doing ARP for it any
 * more, and fw has to: answer requests for the address we are
 * protecting, and resolve the next hop for anything we send.  That is
 * all the ethernet fw knows about; everything else it treats as an IP
 * packet and hands to the rules.
 *
 * An ether "bypass" connection looks like it should serve instead, but
 * it only intercepts the stack's transmissions - etheriq drops what
 * arrives from the wire while bypass is set - so it cannot filter
 * inbound at all.
 */
#include <u.h>
#include <libc.h>
#include <bio.h>
#include <ndb.h>
#include <ip.h>
#include "rules.h"

extern int etherdebug;

enum
{
	Eaddrlen	= 6,
	Ehdrlen		= 14,
	Etip4		= 0x0800,
	Etarp		= 0x0806,
	Etip6		= 0x86DD,

	Arplen		= 28,
	Eminlen		= 60,		/* ethernet minimum frame, devether enforces it */
	Maxframe	= Ehdrlen + 16*1024,
	Arpreq		= 1,
	Arpreply	= 2,

	Narp		= 64,
	Arplife		= 300,
};

typedef struct Arpent Arpent;
struct Arpent
{
	uchar	ip[IPaddrlen];
	uchar	mac[Eaddrlen];
	long	when;
};

static Arpent	arptab[Narp];
static Lock	arplock;

static uchar	ourmac[Eaddrlen];
static uchar	ouraddr[IPaddrlen];
static uchar	gateway[IPaddrlen];
static int	haveg;
static int	efd = -1;

static uchar bcast[Eaddrlen] = { 0xff,0xff,0xff,0xff,0xff,0xff };

/*
 * Open a card for raw frames of every type.  Promiscuous because we
 * are answering for an address the card does not believe is its own
 * once the stack has let go of it.
 */
int
etheropen(char *dev, uchar *mac)
{
	char path[128], buf[64];
	int cfd, dfd, n, conn;

	snprint(path, sizeof path, "%s/clone", dev);
	if((cfd = open(path, ORDWR)) < 0)
		sysfatal("open %s: %r", path);
	if((n = read(cfd, buf, sizeof buf - 1)) <= 0)
		sysfatal("read %s: %r", path);
	buf[n] = '\0';
	conn = atoi(buf);

	if(fprint(cfd, "connect -1") < 0)
		sysfatal("%s: connect -1: %r", dev);
	if(fprint(cfd, "promiscuous") < 0)
		sysfatal("%s: promiscuous: %r", dev);

	snprint(path, sizeof path, "%s/%d/data", dev, conn);
	if((dfd = open(path, ORDWR)) < 0)
		sysfatal("open %s: %r", path);

	/* the card's own address, which we answer with */
	snprint(path, sizeof path, "%s/addr", dev);
	if((n = open(path, OREAD)) < 0)
		sysfatal("open %s: %r", path);
	if(read(n, buf, 12) != 12)
		sysfatal("read %s: %r", path);
	close(n);
	buf[12] = '\0';
	if(parseether(mac, buf) < 0)
		sysfatal("%s: unparseable address %s", dev, buf);

	efd = dfd;
	memmove(ourmac, mac, Eaddrlen);
	return dfd;
}

void
ethersetaddr(uchar *ip, uchar *gw, int haveit)
{
	ipmove(ouraddr, ip);
	if(haveit)
		ipmove(gateway, gw);
	haveg = haveit;
}

static void
arpput(uchar *ip, uchar *mac)
{
	Arpent *a, *old;
	long now;
	int i;

	now = time(0);
	lock(&arplock);
	old = &arptab[0];
	for(i = 0; i < Narp; i++){
		a = &arptab[i];
		if(a->when != 0 && ipcmp(a->ip, ip) == 0){
			memmove(a->mac, mac, Eaddrlen);
			a->when = now;
			unlock(&arplock);
			return;
		}
		if(a->when < old->when)
			old = a;
	}
	ipmove(old->ip, ip);
	memmove(old->mac, mac, Eaddrlen);
	old->when = now;
	unlock(&arplock);
}

static int
arpget(uchar *ip, uchar *mac)
{
	Arpent *a;
	long now;
	int i, r;

	r = 0;
	now = time(0);
	lock(&arplock);
	for(i = 0; i < Narp; i++){
		a = &arptab[i];
		if(a->when != 0 && ipcmp(a->ip, ip) == 0){
			if(now - a->when <= Arplife){
				memmove(mac, a->mac, Eaddrlen);
				r = 1;
			}
			break;
		}
	}
	unlock(&arplock);
	return r;
}

/*
 * Broadcast and multicast are not resolved, they are addressed by rule.
 * Without this a DHCP renewal, which goes to 255.255.255.255, would be
 * sent to whatever the gateway's ethernet address happened to be, and
 * the lease would quietly never renew.
 */
static int
groupmac(uchar *dst, uchar *mask, uchar *mac)
{
	uchar net[IPaddrlen], all[IPaddrlen];
	int i;

	if(isv4(dst)){
		/* 255.255.255.255 */
		for(i = IPv4off; i < IPaddrlen; i++)
			if(dst[i] != 0xff)
				break;
		if(i == IPaddrlen){
			memmove(mac, bcast, Eaddrlen);
			return 1;
		}
		/* the broadcast address of our own network */
		maskip(ouraddr, mask, net);
		for(i = 0; i < IPaddrlen; i++)
			all[i] = net[i] | ~mask[i];
		if(ipcmp(dst, all) == 0){
			memmove(mac, bcast, Eaddrlen);
			return 1;
		}
		/* 224.0.0.0/4 */
		if(dst[IPv4off] >= 224 && dst[IPv4off] < 240){
			mac[0] = 0x01;
			mac[1] = 0x00;
			mac[2] = 0x5e;
			mac[3] = dst[IPv4off+1] & 0x7f;
			mac[4] = dst[IPv4off+2];
			mac[5] = dst[IPv4off+3];
			return 1;
		}
		return 0;
	}
	/* ff00::/8 */
	if(dst[0] == 0xff){
		mac[0] = 0x33;
		mac[1] = 0x33;
		memmove(mac+2, dst+12, 4);
		return 1;
	}
	return 0;
}

static void
puthdr(uchar *f, uchar *dst, int type)
{
	memmove(f, dst, Eaddrlen);
	memmove(f + Eaddrlen, ourmac, Eaddrlen);
	f[12] = type >> 8;
	f[13] = type;
}

/* ask who has ip; the answer arrives later and goes in the cache */
static void
arpask(uchar *ip)
{
	uchar f[Eminlen];

	if(!isv4(ip))
		return;
	memset(f, 0, sizeof f);
	puthdr(f, bcast, Etarp);
	hnputs(f + 14, 1);		/* ethernet */
	hnputs(f + 16, Etip4);
	f[18] = Eaddrlen;
	f[19] = 4;
	hnputs(f + 20, Arpreq);
	memmove(f + 22, ourmac, Eaddrlen);
	memmove(f + 28, ouraddr + IPv4off, 4);
	memmove(f + 38, ip + IPv4off, 4);
	if(etherdebug)
		fprint(2, "arp: who has %I? (asking)\n", ip);
	if(write(efd, f, sizeof f) != sizeof f)
		fprint(2, "arp: write failed: %r\n");
}

/*
 * An arp frame from the wire.  Learn from it either way, and answer a
 * request for the address we are standing in for.
 */
static void
arpin(uchar *f, int n)
{
	uchar sip[IPaddrlen], tip[IPaddrlen], r[Eminlen];
	int op;

	if(n < Ehdrlen + Arplen)
		return;
	if(nhgets(f + 16) != Etip4 || f[18] != Eaddrlen || f[19] != 4)
		return;
	op = nhgets(f + 20);
	v4tov6(sip, f + 28);
	v4tov6(tip, f + 38);

	if(ipcmp(sip, IPnoaddr) != 0){
		arpput(sip, f + 22);
		if(etherdebug)
			fprint(2, "arp: learned %I is %E (op %d)\n", sip, f+22, op);
	}
	if(op != Arpreq || ipcmp(tip, ouraddr) != 0)
		return;

	memset(r, 0, sizeof r);
	puthdr(r, f + 22, Etarp);
	hnputs(r + 14, 1);
	hnputs(r + 16, Etip4);
	r[18] = Eaddrlen;
	r[19] = 4;
	hnputs(r + 20, Arpreply);
	memmove(r + 22, ourmac, Eaddrlen);
	memmove(r + 28, ouraddr + IPv4off, 4);
	memmove(r + 32, f + 22, Eaddrlen);
	memmove(r + 38, f + 28, 4);
	write(efd, r, sizeof r);
}

int
etherisarp(uchar *f, int n)
{
	if(n < Ehdrlen)
		return 0;
	if(nhgets(f + 12) != Etarp)
		return 0;
	arpin(f, n);
	return 1;
}

int
etherisip(uchar *f, int n)
{
	int t;

	if(n < Ehdrlen)
		return 0;
	t = nhgets(f + 12);
	return t == Etip4 || t == Etip6;
}

/*
 * Send an IP packet out the card.  The next hop is the destination if
 * it is on our own network, otherwise the gateway.  If we do not know
 * its ethernet address yet we ask and drop this one; the sender will
 * try again, which is what every other stack does too.
 */
int
etherwriteip(uchar *p, int n, uchar *mask)
{
	/*
	 * On a proc stack, which libthread keeps small: 64K here
	 * overran it and corrupted the data segment.  pktmedium's maxtu
	 * is 4096, so this is already generous.
	 */
	uchar f[Maxframe], dst[IPaddrlen], hop[IPaddrlen];
	uchar net[IPaddrlen], ournet[IPaddrlen], mac[Eaddrlen];
	int type, len;

	if(n < 20 || n > Maxframe - Ehdrlen)
		return -1;
	switch(p[0] >> 4){
	case 4:
		type = Etip4;
		v4tov6(dst, p + 16);
		break;
	case 6:
		type = Etip6;
		ipmove(dst, p + 24);
		break;
	default:
		return -1;
	}

	if(groupmac(dst, mask, mac))
		goto Send;

	maskip(dst, mask, net);
	maskip(ouraddr, mask, ournet);
	if(ipcmp(net, ournet) == 0)
		ipmove(hop, dst);
	else if(haveg)
		ipmove(hop, gateway);
	else
		ipmove(hop, dst);

	if(!arpget(hop, mac)){
		/*
		 * v6 has no ARP; resolving a neighbour needs ICMPv6
		 * solicitation, which is not implemented.  Say so once,
		 * rather than dropping every v6 unicast in silence.
		 */
		if(!isv4(hop)){
			static int said;

			if(!said++)
				fprint(2, "fw: cannot resolve %I: "
					"IPv6 neighbour discovery is not implemented, "
					"so v6 unicast is dropped\n", hop);
			return -1;
		}
		if(etherdebug)
			fprint(2, "arp: no entry for %I, dropping and asking\n", hop);
		arpask(hop);
		return 0;
	}
Send:
	puthdr(f, mac, type);
	memmove(f + Ehdrlen, p, n);
	len = Ehdrlen + n;
	if(len < Eminlen){
		memset(f + len, 0, Eminlen - len);
		len = Eminlen;
	}
	if((len = write(efd, f, len)) < 0)
		fprint(2, "ether: write failed: %r\n");
	return len;
}