dhcpd.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include <u.h>
#include <libc.h>
#include <ip.h>
#include <bio.h>
#include <ndb.h>
#include "dat.h"

//
//	ala rfc2131
//

typedef struct Req Req;
struct Req
{
	int	fd;			/* for reply */
	Bootp	*bp;
	OUdphdr	*up;
	uchar	*e;			/* end of received message */
	uchar	*p;			/* options pointer */
	uchar	*max;			/* max end of reply */

	/* expanded to v6 */
	uchar	ciaddr[IPaddrlen];
	uchar	giaddr[IPaddrlen];

	/* parsed options */
	int	p9request;		/* true if this is a bootp with plan9 options */
	int	genrequest;		/* true if this is a bootp with generic options */
	int	dhcptype;		/* dhcp message type */
	int	leasetime;		/* dhcp lease */
	uchar	ip[IPaddrlen];		/* requested address */
	uchar	server[IPaddrlen];	/* server address */
	char	msg[ERRMAX];		/* error message */
	char	vci[32];		/* vendor class id */
	char	*id;			/* client id */
	uchar	requested[32];		/* requested params */
	uchar	vendorclass[32];
	char	cputype[32-3];

	Info	gii;			/* about target network */
	Info	ii;			/* about target system */
	int	staticbinding;

	uchar buf[2*1024];		/* message buffer */
};

#define TFTP "/lib/tftpd"
char	*blog = "ipboot";
char	mysysname[64];
Ipifc	*ipifcs;
int	debug;
int	nobootp;
long	now;
int	slowstat, slowdyn;
char	net[256];

int	pptponly;	// only answer request that came from the pptp server
int	mute, mutestat;
int	minlease = MinLease;

ulong	start;

/* option magic */
char plan9opt[4] = { 'p', '9', ' ', ' ' };
char genericopt[4] = { 0x63, 0x82, 0x53, 0x63 };

/* well known addresses */
uchar zeros[Maxhwlen];

/* option debug buffer */
char optbuf[1024];
char *op;
char *oe = optbuf + sizeof(optbuf);

char *optname[256] =
{
[OBend]			"end",
[OBpad]			"pad",
[OBmask]		"mask",
[OBtimeoff]		"timeoff",
[OBrouter]		"router",
[OBtimeserver]		"time",
[OBnameserver]		"name",
[OBdnserver]		"dns",
[OBlogserver]		"log",
[OBcookieserver]	"cookie",
[OBlprserver]		"lpr",
[OBimpressserver]	"impress",
[OBrlserver]		"rl",
[OBhostname]		"host",
[OBbflen]		"bflen",
[OBdumpfile]		"dumpfile",
[OBdomainname]		"dom",
[OBswapserver]		"swap",
[OBrootpath]		"rootpath",
[OBextpath]		"extpath",
[OBipforward]		"ipforward",
[OBnonlocal]		"nonlocal",
[OBpolicyfilter]	"policyfilter",
[OBmaxdatagram]		"maxdatagram",
[OBttl]			"ttl",
[OBpathtimeout]		"pathtimeout",
[OBpathplateau]		"pathplateau",
[OBmtu]			"mtu",
[OBsubnetslocal]	"subnetslocal",
[OBbaddr]		"baddr",
[OBdiscovermask]	"discovermask",
[OBsupplymask]		"supplymask",
[OBdiscoverrouter]	"discoverrouter",
[OBrsserver]		"rsserver",
[OBstaticroutes]	"staticroutes",
[OBtrailerencap]	"trailerencap",
[OBarptimeout]		"arptimeout",
[OBetherencap]		"etherencap",
[OBtcpttl]		"tcpttl",
[OBtcpka]		"tcpka",
[OBtcpkag]		"tcpkag",
[OBnisdomain]		"nisdomain",
[OBniserver]		"niserver",
[OBntpserver]		"ntpserver",
[OBvendorinfo]		"vendorinfo",
[OBnetbiosns]		"NBns",
[OBnetbiosdds]		"NBdds",
[OBnetbiostype]		"NBtype",
[OBnetbiosscope]	"NBscope",
[OBxfontserver]		"xfont",
[OBxdispmanager]	"xdisp",
[OBnisplusdomain]	"NPdomain",
[OBnisplusserver]	"NP",
[OBhomeagent]		"homeagent",
[OBsmtpserver]		"smtp",
[OBpop3server]		"pop3",
[OBnntpserver]		"nntp",
[OBwwwserver]		"www",
[OBfingerserver]	"finger",
[OBircserver]		"ircserver",
[OBstserver]		"stserver",
[OBstdaserver]		"stdaserver",

/* dhcp options */
[ODipaddr]		"ip",
[ODlease]		"leas",
[ODoverload]		"overload",
[ODtype]		"typ",
[ODserverid]		"sid",
[ODparams]		"params",
[ODmessage]		"message",
[ODmaxmsg]		"maxmsg",
[ODrenewaltime]		"renewaltime",
[ODrebindingtime]	"rebindingtime",
[ODvendorclass]		"vendorclass",
[ODclientid]		"cid",
[ODtftpserver]		"tftpserver",
[ODbootfile]		"bf",
};

void	addropt(Req*, int, uchar*);
void	addrsopt(Req*, int, uchar**, int);
void	arpenter(uchar*, uchar*);
void	bootp(Req*);
void	byteopt(Req*, int, uchar);
void	dhcp(Req*);
void	fatal(int, char*, ...);
void	hexopt(Req*, int, char*);
void	longopt(Req*, int, long);
void	maskopt(Req*, int, uchar*);
void	miscoptions(Req*, uchar*);
int	openlisten(char *net);
void	parseoptions(Req*);
void	proto(Req*, int);
void	rcvdecline(Req*);
void	rcvdiscover(Req*);
void	rcvinform(Req*);
void	rcvrelease(Req*);
void	rcvrequest(Req*);
char*	readsysname(void);
void	remrequested(Req*, int);
void	sendack(Req*, uchar*, int, int);
void	sendnak(Req*, char*);
void	sendoffer(Req*, uchar*, int);
void	stringopt(Req*, int, char*);
void	termopt(Req*);
int	validip(uchar*);
void	vectoropt(Req*, int, uchar*, int);
void	warning(int, char*, ...);
void	logdhcp(Req*);
void	logdhcpout(Req *, char *);
int	readlast(int, uchar*, int);

void
timestamp(char *tag)
{
	ulong t;

	t = nsec()/1000;
	syslog(0, blog, "%s %lud", tag, t - start);
}

void
usage(void)
{
	fprint(2, "usage: dhcp [-dmsnp] [-f directory] [-x netmtpt] [-M minlease] addr n [addr n ...]\n");
	exits("usage");
}

void
main(int argc, char **argv)
{
	int i, n, fd;
	char *p;
	uchar ip[IPaddrlen];
	Req r;

	setnetmtpt(net, sizeof(net), nil);

	fmtinstall('E', eipfmt);
	fmtinstall('I', eipfmt);
	fmtinstall('V', eipfmt);
	fmtinstall('M', eipfmt);
	ARGBEGIN {
	case 'm':
		mute = 1;
		break;
	case 'd':
		debug = 1;
		break;
	case 'f':
		p = ARGF();
		if(p == nil)
			usage();
		ndbfile = p;
		break;
	case 's':
		slowstat = 1;
		break;
	case 'S':
		slowdyn = 1;
		break;
	case 'n':
		nobootp = 1;
		break;
	case 'p':
		pptponly = 1;
		break;
	case 'r':
		mutestat = 1;
		break;
	case 'x':
		p = ARGF();
		if(p == nil)
			usage();
		setnetmtpt(net, sizeof(net), p);
		break;
	case 'M':
		p = ARGF();
		if(p == nil)
			usage();
		minlease = atoi(p);
		if(minlease <= 0)
			minlease = MinLease;
		break;
	} ARGEND;

	while(argc > 1){
		parseip(ip, argv[0]);
		if(!validip(ip))
			usage();
		n = atoi(argv[1]);
		if(n <= 0)
			usage();
		initbinding(ip, n);
		argc -= 2;
		argv += 2;
	}

	/* for debugging */
	for(i = 0; i < 256; i++)
		if(optname[i] == 0)
			optname[i] = smprint("%d", i);

	/* what is my name? */
	p = readsysname();
	strcpy(mysysname, p);

	/* put process in background */
	if(!debug) switch(rfork(RFNOTEG|RFPROC|RFFDG)) {
	case -1:
		fatal(1, "fork");
	case 0:
		break;
	default:
		exits(0);
	}

	chdir(TFTP);
	fd = openlisten(net);

	for(;;){
		memset(&r, 0, sizeof(r));
		r.fd = fd;
		n = readlast(r.fd, r.buf, sizeof(r.buf));
		if(n < OUdphdrsize)
			fatal(1, "error reading requests");
		start = nsec()/1000;
		op = optbuf;
		*op = 0;
		proto(&r, n);
		if(r.id != nil)
			free(r.id);
	}
}

void
proto(Req *rp, int n)
{
	uchar relip[IPaddrlen];
	char buf[64];

	now = time(0);

	rp->e = rp->buf + n;
	rp->bp = (Bootp*)rp->buf;
	rp->up = (OUdphdr*)rp->buf;
	rp->max = rp->buf + OUdphdrsize + MINSUPPORTED - IPUDPHDRSIZE;
	rp->p = rp->bp->optdata;
	v4tov6(rp->giaddr, rp->bp->giaddr);
	v4tov6(rp->ciaddr, rp->bp->ciaddr);

	if(pptponly && rp->bp->htype != 0)
		return;

	ipifcs = readipifc(net, ipifcs, -1);
	if(validip(rp->giaddr))
		ipmove(relip, rp->giaddr);
	else if(validip(rp->up->raddr))
		ipmove(relip, rp->up->raddr);
	else
		ipmove(relip, rp->up->laddr);
	if(rp->e < (uchar*)rp->bp->sname){
		warning(0, "packet too short");
		return;
	}
	if(rp->bp->op != Bootrequest){
		warning(0, "not bootrequest");
		return;
	}

	if(rp->e >= rp->bp->optdata){
		if(memcmp(rp->bp->optmagic, plan9opt, sizeof(rp->bp->optmagic)) == 0)
			rp->p9request = 1;
		if(memcmp(rp->bp->optmagic, genericopt, sizeof(rp->bp->optmagic)) == 0) {
			rp->genrequest = 1;
			parseoptions(rp);
		}
	}
	rp->p = rp->bp->optdata;

	/*  If no id is specified, make one from the hardware address
	 *  of the target.  We assume all zeros is not a hardware address
	 *  which could be a mistake.
	 */
	if(rp->id == nil){
		if(rp->bp->hlen > Maxhwlen){
			warning(0, "hlen %d", rp->bp->hlen);
			return;
		}
		if(memcmp(zeros, rp->bp->chaddr, rp->bp->hlen) == 0){
			warning(0, "no chaddr");
			return;
		}
		sprint(buf, "hwa%2.2ux_", rp->bp->htype);
		rp->id = tohex(buf, rp->bp->chaddr, rp->bp->hlen);
	}

	/* info about gateway */
	if(lookupip(relip, &rp->gii, 1) < 0){
		warning(0, "lookupip failed");
		return;
	}

	/* info about target system */
	if(lookup(rp->bp, &rp->ii, &rp->gii) == 0)
		if(rp->ii.indb && rp->ii.dhcpgroup[0] == 0)
			rp->staticbinding = 1;

	if(rp->dhcptype)
		dhcp(rp);
	else
		bootp(rp);
timestamp("done");
}

static void
slowdelay(Req *rp)
{
	if(slowstat && rp->staticbinding || slowdyn && !rp->staticbinding)
		sleep(2000);
}

void
dhcp(Req *rp)
{
	logdhcp(rp);

	switch(rp->dhcptype){
	case Discover:
		slowdelay(rp);
		rcvdiscover(rp);
		break;
	case Request:
		rcvrequest(rp);
		break;
	case Decline:
		rcvdecline(rp);
		break;
	case Release:
		rcvrelease(rp);
		break;
	case Inform:
		rcvinform(rp);
		break;
	}
}

void
rcvdiscover(Req *rp)
{
	Binding *b, *nb;

	if(rp->staticbinding){
		sendoffer(rp, rp->ii.ipaddr, (StaticLease > minlease ? StaticLease : minlease));
		return;
	}

	/*
	 *  first look for an outstanding offer
	 */
	b = idtooffer(rp->id, &rp->gii);

	/*
	 * rfc2131 says:
	 *   If an address is available, the new address
	 *   SHOULD be chosen as follows:
	 *
	 *      o The client's current address as recorded in the client's current
	 *        binding, ELSE
	 *
	 *      o The client's previous address as recorded in the client's (now
	 *        expired or released) binding, if that address is in the server's
	 *        pool of available addresses and not already allocated, ELSE
	 *
	 *      o The address requested in the 'Requested IP Address' option, if that
	 *        address is valid and not already allocated, ELSE
	 *
	 *      o A new address allocated from the server's pool of available
	 *        addresses; the address is selected based on the subnet from which
	 *        the message was received (if 'giaddr' is 0) or on the address of
	 *        the relay agent that forwarded the message ('giaddr' when not 0).
	 */
	if(b == nil){
		b = idtobinding(rp->id, &rp->gii, 1);
		if(b && b->boundto && strcmp(b->boundto, rp->id) != 0)
		if(validip(rp->ip) && samenet(rp->ip, &rp->gii)){
			nb = iptobinding(rp->ip, 0);
			if(nb && nb->lease < now)
				b = nb;
		}
	}
	if(b == nil){
		warning(0, "!Discover(%s via %I): no binding %I",
			rp->id, rp->gii.ipaddr, rp->ip);
		return;
	}
	mkoffer(b, rp->id, rp->leasetime);
	sendoffer(rp, b->ip, b->offer);
}

void
rcvrequest(Req *rp)
{
	Binding *b;

	if(validip(rp->server)){
		/* this is a reply to an offer - SELECTING */

		/* check for hard assignment */
		if(rp->staticbinding){
			if(forme(rp->server))
				sendack(rp, rp->ii.ipaddr, (StaticLease > minlease ? StaticLease : minlease), 1);
			else
				warning(0, "!Request(%s via %I): for server %I not me",
					rp->id, rp->gii.ipaddr, rp->server);
			return;
		}

		b = idtooffer(rp->id, &rp->gii);

		/* if we don't have an offer, nak */
		if(b == nil){
			warning(0, "!Request(%s via %I): no offer",
				rp->id, rp->gii.ipaddr);
			if(forme(rp->server))
				sendnak(rp, "no offer for you");
			return;
		}

		/* if not for me, retract offer */
		if(!forme(rp->server)){
			b->expoffer = 0;
			warning(0, "!Request(%s via %I): for server %I not me",
				rp->id, rp->gii.ipaddr, rp->server);
			return;
		}

		/*
		 *  if the client is confused about what we offered, nak.
		 *  client really shouldn't be specifying this when selecting
		 */
		if(validip(rp->ip) && ipcmp(rp->ip, b->ip) != 0){
			warning(0, "!Request(%s via %I): requests %I, not %I",
				rp->id, rp->gii.ipaddr, rp->ip, b->ip);
			sendnak(rp, "bad ip address option");
			return;
		}
		if(commitbinding(b) < 0){
			warning(0, "!Request(%s via %I): can't commit %I",
				rp->id, rp->gii.ipaddr, b->ip);
			sendnak(rp, "can't commit binding");
			return;
		}
		sendack(rp, b->ip, b->offer, 1);
	} else if(validip(rp->ip)){
		/*
		 *  checking address/net - INIT-REBOOT
		 *
		 *  This is a rebooting client that remembers its old
		 *  address.
		 */