ip_input.c@ 532

Last change on this file since 532 was 530, checked in by vboxsync, 18 years ago
Hack for running slirp (NAT) on 64-bit hosts.
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1	/*
2	* Copyright (c) 1982, 1986, 1988, 1993
3	* The Regents of the University of California. All rights reserved.
4	*
5	* Redistribution and use in source and binary forms, with or without
6	* modification, are permitted provided that the following conditions
7	* are met:
8	* 1. Redistributions of source code must retain the above copyright
9	* notice, this list of conditions and the following disclaimer.
10	* 2. Redistributions in binary form must reproduce the above copyright
11	* notice, this list of conditions and the following disclaimer in the
12	* documentation and/or other materials provided with the distribution.
13	* 3. All advertising materials mentioning features or use of this software
14	* must display the following acknowledgement:
15	* This product includes software developed by the University of
16	* California, Berkeley and its contributors.
17	* 4. Neither the name of the University nor the names of its contributors
18	* may be used to endorse or promote products derived from this software
19	* without specific prior written permission.
20	*
21	* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24	* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31	* SUCH DAMAGE.
32	*
33	* @(#)ip_input.c 8.2 (Berkeley) 1/4/94
34	* ip_input.c,v 1.11 1994/11/16 10:17:08 jkh Exp
35	*/
36
37	/*
38	* Changes and additions relating to SLiRP are
39	* Copyright (c) 1995 Danny Gasparovski.
40	*
41	* Please read the file COPYRIGHT for the
42	* terms and conditions of the copyright.
43	*/
44
45	#include <slirp.h>
46	#include "ip_icmp.h"
47
48	int ip_defttl;
49	struct ipstat ipstat;
50	struct ipq ipq;
51
52	/*
53	* IP initialization: fill in IP protocol switch table.
54	* All protocols not implemented in kernel go to raw IP protocol handler.
55	*/
56	void
57	ip_init()
58	{
59	ipq.next = ipq.prev = ptr_to_u32(&ipq);
60	ip_id = tt.tv_sec & 0xffff;
61	udp_init();
62	tcp_init();
63	ip_defttl = IPDEFTTL;
64	}
65
66	/*
67	* Ip input routine. Checksum and byte swap header. If fragmented
68	* try to reassemble. Process options. Pass to next level.
69	*/
70	void
71	ip_input(m)
72	struct mbuf *m;
73	{
74	register struct ip *ip;
75	int hlen;
76
77	DEBUG_CALL("ip_input");
78	DEBUG_ARG("m = %lx", (long)m);
79	DEBUG_ARG("m_len = %d", m->m_len);
80
81	ipstat.ips_total++;
82
83	if (m->m_len < sizeof (struct ip)) {
84	ipstat.ips_toosmall++;
85	return;
86	}
87
88	ip = mtod(m, struct ip *);
89
90	if (ip->ip_v != IPVERSION) {
91	ipstat.ips_badvers++;
92	goto bad;
93	}
94
95	hlen = ip->ip_hl << 2;
96	if (hlen<sizeof(struct ip ) \|\| hlen>m->m_len) {/* min header length */
97	ipstat.ips_badhlen++; /* or packet too short */
98	goto bad;
99	}
100
101	/* keep ip header intact for ICMP reply
102	* ip->ip_sum = cksum(m, hlen);
103	* if (ip->ip_sum) {
104	*/
105	if(cksum(m,hlen)) {
106	ipstat.ips_badsum++;
107	goto bad;
108	}
109
110	/*
111	* Convert fields to host representation.
112	*/
113	NTOHS(ip->ip_len);
114	if (ip->ip_len < hlen) {
115	ipstat.ips_badlen++;
116	goto bad;
117	}
118	NTOHS(ip->ip_id);
119	NTOHS(ip->ip_off);
120
121	/*
122	* Check that the amount of data in the buffers
123	* is as at least much as the IP header would have us expect.
124	* Trim mbufs if longer than we expect.
125	* Drop packet if shorter than we expect.
126	*/
127	if (m->m_len < ip->ip_len) {
128	ipstat.ips_tooshort++;
129	goto bad;
130	}
131	/* Should drop packet if mbuf too long? hmmm... */
132	if (m->m_len > ip->ip_len)
133	m_adj(m, ip->ip_len - m->m_len);
134
135	/* check ip_ttl for a correct ICMP reply */
136	if(ip->ip_ttl==0 \|\| ip->ip_ttl==1) {
137	icmp_error(m, ICMP_TIMXCEED,ICMP_TIMXCEED_INTRANS, 0,"ttl");
138	goto bad;
139	}
140
141	/*
142	* Process options and, if not destined for us,
143	* ship it on. ip_dooptions returns 1 when an
144	* error was detected (causing an icmp message
145	* to be sent and the original packet to be freed).
146	*/
147	/* We do no IP options */
148	/* if (hlen > sizeof (struct ip) && ip_dooptions(m))
149	* goto next;
150	*/
151	/*
152	* If offset or IP_MF are set, must reassemble.
153	* Otherwise, nothing need be done.
154	* (We could look in the reassembly queue to see
155	* if the packet was previously fragmented,
156	* but it's not worth the time; just let them time out.)
157	*
158	* XXX This should fail, don't fragment yet
159	*/
160	if (ip->ip_off &~ IP_DF) {
161	register struct ipq *fp;
162	/*
163	* Look for queue of fragments
164	* of this datagram.
165	*/
166	for (fp = u32_to_ptr(ipq.next, struct ipq *); fp != &ipq;
167	fp = u32_to_ptr(fp->next, struct ipq *))
168	if (ip->ip_id == fp->ipq_id &&
169	ip->ip_src.s_addr == fp->ipq_src.s_addr &&
170	ip->ip_dst.s_addr == fp->ipq_dst.s_addr &&
171	ip->ip_p == fp->ipq_p)
172	goto found;
173	fp = 0;
174	found:
175
176	/*
177	* Adjust ip_len to not reflect header,
178	* set ip_mff if more fragments are expected,
179	* convert offset of this to bytes.
180	*/
181	ip->ip_len -= hlen;
182	if (ip->ip_off & IP_MF)
183	((struct ipasfrag *)ip)->ipf_mff \|= 1;
184	else
185	((struct ipasfrag *)ip)->ipf_mff &= ~1;
186
187	ip->ip_off <<= 3;
188
189	/*
190	* If datagram marked as having more fragments
191	* or if this is not the first fragment,
192	* attempt reassembly; if it succeeds, proceed.
193	*/
194	if (((struct ipasfrag *)ip)->ipf_mff & 1 \|\| ip->ip_off) {
195	ipstat.ips_fragments++;
196	ip = ip_reass((struct ipasfrag *)ip, fp);
197	if (ip == 0)
198	return;
199	ipstat.ips_reassembled++;
200	m = dtom(ip);
201	} else
202	if (fp)
203	ip_freef(fp);
204
205	} else
206	ip->ip_len -= hlen;
207
208	/*
209	* Switch out to protocol's input routine.
210	*/
211	ipstat.ips_delivered++;
212	switch (ip->ip_p) {
213	case IPPROTO_TCP:
214	tcp_input(m, hlen, (struct socket *)NULL);
215	break;
216	case IPPROTO_UDP:
217	udp_input(m, hlen);
218	break;
219	case IPPROTO_ICMP:
220	icmp_input(m, hlen);
221	break;
222	default:
223	ipstat.ips_noproto++;
224	m_free(m);
225	}
226	return;
227	bad:
228	m_freem(m);
229	return;
230	}
231
232	/*
233	* Take incoming datagram fragment and try to
234	* reassemble it into whole datagram. If a chain for
235	* reassembly of this datagram already exists, then it
236	* is given as fp; otherwise have to make a chain.
237	*/
238	struct ip *
239	ip_reass(ip, fp)
240	register struct ipasfrag *ip;
241	register struct ipq *fp;
242	{
243	register struct mbuf *m = dtom(ip);
244	register struct ipasfrag *q;
245	int hlen = ip->ip_hl << 2;
246	int i, next;
247
248	DEBUG_CALL("ip_reass");
249	DEBUG_ARG("ip = %lx", (long)ip);
250	DEBUG_ARG("fp = %lx", (long)fp);
251	DEBUG_ARG("m = %lx", (long)m);
252
253	/*
254	* Presence of header sizes in mbufs
255	* would confuse code below.
256	* Fragment m_data is concatenated.
257	*/
258	m->m_data += hlen;
259	m->m_len -= hlen;
260
261	/*
262	* If first fragment to arrive, create a reassembly queue.
263	*/
264	if (fp == 0) {
265	struct mbuf *t;
266	if ((t = m_get()) == NULL) goto dropfrag;
267	fp = mtod(t, struct ipq *);
268	insque_32(fp, &ipq);
269	fp->ipq_ttl = IPFRAGTTL;
270	fp->ipq_p = ip->ip_p;
271	fp->ipq_id = ip->ip_id;
272	fp->ipq_next = fp->ipq_prev = ptr_to_u32((struct ipasfrag *)fp);
273	fp->ipq_src = ((struct ip *)ip)->ip_src;
274	fp->ipq_dst = ((struct ip *)ip)->ip_dst;
275	q = (struct ipasfrag *)fp;
276	goto insert;
277	}
278
279	/*
280	* Find a segment which begins after this one does.
281	*/
282	for (q = u32_to_ptr(fp->ipq_next, struct ipasfrag ); q != (struct ipasfrag )fp;
283	q = u32_to_ptr(q->ipf_next, struct ipasfrag *))
284	if (q->ip_off > ip->ip_off)
285	break;
286
287	/*
288	* If there is a preceding segment, it may provide some of
289	* our data already. If so, drop the data from the incoming
290	* segment. If it provides all of our data, drop us.
291	*/
292	if (u32_to_ptr(q->ipf_prev, struct ipq *) != fp) {
293	i = (u32_to_ptr(q->ipf_prev, struct ipasfrag *))->ip_off +
294	(u32_to_ptr(q->ipf_prev, struct ipasfrag *))->ip_len - ip->ip_off;
295	if (i > 0) {
296	if (i >= ip->ip_len)
297	goto dropfrag;
298	m_adj(dtom(ip), i);
299	ip->ip_off += i;
300	ip->ip_len -= i;
301	}
302	}
303
304	/*
305	* While we overlap succeeding segments trim them or,
306	* if they are completely covered, dequeue them.
307	*/
308	while (q != (struct ipasfrag *)fp && ip->ip_off + ip->ip_len > q->ip_off) {
309	i = (ip->ip_off + ip->ip_len) - q->ip_off;
310	if (i < q->ip_len) {
311	q->ip_len -= i;
312	q->ip_off += i;
313	m_adj(dtom(q), i);
314	break;
315	}
316	q = u32_to_ptr(q->ipf_next, struct ipasfrag *);
317	m_freem(dtom(u32_to_ptr(q->ipf_prev, struct ipasfrag *)));
318	ip_deq(u32_to_ptr(q->ipf_prev, struct ipasfrag *));
319	}
320
321	insert:
322	/*
323	* Stick new segment in its place;
324	* check for complete reassembly.
325	*/
326	ip_enq(ip, u32_to_ptr(q->ipf_prev, struct ipasfrag *));
327	next = 0;
328	for (q = u32_to_ptr(fp->ipq_next, struct ipasfrag ); q != (struct ipasfrag )fp;
329	q = u32_to_ptr(q->ipf_next, struct ipasfrag *)) {
330	if (q->ip_off != next)
331	return (0);
332	next += q->ip_len;
333	}
334	if (u32_to_ptr(q->ipf_prev, struct ipasfrag *)->ipf_mff & 1)
335	return (0);
336
337	/*
338	* Reassembly is complete; concatenate fragments.
339	*/
340	q = u32_to_ptr(fp->ipq_next, struct ipasfrag *);
341	m = dtom(q);
342
343	q = u32_to_ptr(q->ipf_next, struct ipasfrag *);
344	while (q != (struct ipasfrag *)fp) {
345	struct mbuf *t;
346	t = dtom(q);
347	q = u32_to_ptr(q->ipf_next, struct ipasfrag *);
348	m_cat(m, t);
349	}
350
351	/*
352	* Create header for new ip packet by
353	* modifying header of first packet;
354	* dequeue and discard fragment reassembly header.
355	* Make header visible.
356	*/
357	ip = u32_to_ptr(fp->ipq_next, struct ipasfrag *);
358
359	/*
360	* If the fragments concatenated to an mbuf that's
361	* bigger than the total size of the fragment, then and
362	* m_ext buffer was alloced. But fp->ipq_next points to
363	* the old buffer (in the mbuf), so we must point ip
364	* into the new buffer.
365	*/
366	if (m->m_flags & M_EXT) {
367	int delta;
368	delta = (char *)ip - m->m_dat;
369	ip = (struct ipasfrag *)(m->m_ext + delta);
370	}
371
372	/* DEBUG_ARG("ip = %lx", (long)ip);
373	* ip=(struct ipasfrag )m->m_data; /
374
375	ip->ip_len = next;
376	ip->ipf_mff &= ~1;
377	((struct ip *)ip)->ip_src = fp->ipq_src;
378	((struct ip *)ip)->ip_dst = fp->ipq_dst;
379	remque_32(fp);
380	(void) m_free(dtom(fp));
381	m = dtom(ip);
382	m->m_len += (ip->ip_hl << 2);
383	m->m_data -= (ip->ip_hl << 2);
384
385	return ((struct ip *)ip);
386
387	dropfrag:
388	ipstat.ips_fragdropped++;
389	m_freem(m);
390	return (0);
391	}
392
393	/*
394	* Free a fragment reassembly header and all
395	* associated datagrams.
396	*/
397	void
398	ip_freef(fp)
399	struct ipq *fp;
400	{
401	register struct ipasfrag q, p;
402
403	for (q = u32_to_ptr(fp->ipq_next, struct ipasfrag ); q != (struct ipasfrag )fp;
404	q = p) {
405	p = u32_to_ptr(q->ipf_next, struct ipasfrag *);
406	ip_deq(q);
407	m_freem(dtom(q));
408	}
409	remque_32(fp);
410	(void) m_free(dtom(fp));
411	}
412
413	/*
414	* Put an ip fragment on a reassembly chain.
415	* Like insque, but pointers in middle of structure.
416	*/
417	void
418	ip_enq(p, prev)
419	register struct ipasfrag p, prev;
420	{
421	DEBUG_CALL("ip_enq");
422	DEBUG_ARG("prev = %lx", (long)prev);
423	p->ipf_prev = ptr_to_u32(prev);
424	p->ipf_next = prev->ipf_next;
425	u32_to_ptr(prev->ipf_next, struct ipasfrag *)->ipf_prev = ptr_to_u32(p);
426	prev->ipf_next = ptr_to_u32(p);
427	}
428
429	/*
430	* To ip_enq as remque is to insque.
431	*/
432	void
433	ip_deq(p)
434	register struct ipasfrag *p;
435	{
436	struct ipasfrag prev = u32_to_ptr(p->ipf_prev, struct ipasfrag );
437	struct ipasfrag next = u32_to_ptr(p->ipf_next, struct ipasfrag );
438	u32ptr_done(prev->ipf_next, p);
439	prev->ipf_next = p->ipf_next;
440	next->ipf_prev = p->ipf_prev;
441	}
442
443	/*
444	* IP timer processing;
445	* if a timer expires on a reassembly
446	* queue, discard it.
447	*/
448	void
449	ip_slowtimo()
450	{
451	register struct ipq *fp;
452
453	DEBUG_CALL("ip_slowtimo");
454
455	fp = u32_to_ptr(ipq.next, struct ipq *);
456	if (fp == 0)
457	return;
458
459	while (fp != &ipq) {
460	--fp->ipq_ttl;
461	fp = u32_to_ptr(fp->next, struct ipq *);
462	if (u32_to_ptr(fp->prev, struct ipq *)->ipq_ttl == 0) {
463	ipstat.ips_fragtimeout++;
464	ip_freef(u32_to_ptr(fp->prev, struct ipq *));
465	}
466	}
467	}
468
469	/*
470	* Do option processing on a datagram,
471	* possibly discarding it if bad options are encountered,
472	* or forwarding it if source-routed.
473	* Returns 1 if packet has been forwarded/freed,
474	* 0 if the packet should be processed further.
475	*/
476
477	#ifdef notdef
478
479	int
480	ip_dooptions(m)
481	struct mbuf *m;
482	{
483	register struct ip ip = mtod(m, struct ip );
484	register u_char *cp;
485	register struct ip_timestamp *ipt;
486	register struct in_ifaddr *ia;
487	/* int opt, optlen, cnt, off, code, type = ICMP_PARAMPROB, forward = 0; */
488	int opt, optlen, cnt, off, code, type, forward = 0;
489	struct in_addr *sin, dst;
490	typedef u_int32_t n_time;
491	n_time ntime;
492
493	dst = ip->ip_dst;
494	cp = (u_char *)(ip + 1);
495	cnt = (ip->ip_hl << 2) - sizeof (struct ip);
496	for (; cnt > 0; cnt -= optlen, cp += optlen) {
497	opt = cp[IPOPT_OPTVAL];
498	if (opt == IPOPT_EOL)
499	break;
500	if (opt == IPOPT_NOP)
501	optlen = 1;
502	else {
503	optlen = cp[IPOPT_OLEN];
504	if (optlen <= 0 \|\| optlen > cnt) {
505	code = &cp[IPOPT_OLEN] - (u_char *)ip;
506	goto bad;
507	}
508	}
509	switch (opt) {
510
511	default:
512	break;
513
514	/*
515	* Source routing with record.
516	* Find interface with current destination address.
517	* If none on this machine then drop if strictly routed,
518	* or do nothing if loosely routed.
519	* Record interface address and bring up next address
520	* component. If strictly routed make sure next
521	* address is on directly accessible net.
522	*/
523	case IPOPT_LSRR:
524	case IPOPT_SSRR:
525	if ((off = cp[IPOPT_OFFSET]) < IPOPT_MINOFF) {
526	code = &cp[IPOPT_OFFSET] - (u_char *)ip;
527	goto bad;
528	}
529	ipaddr.sin_addr = ip->ip_dst;
530	ia = (struct in_ifaddr *)
531	ifa_ifwithaddr((struct sockaddr *)&ipaddr);
532	if (ia == 0) {
533	if (opt == IPOPT_SSRR) {
534	type = ICMP_UNREACH;
535	code = ICMP_UNREACH_SRCFAIL;
536	goto bad;
537	}
538	/*
539	* Loose routing, and not at next destination
540	* yet; nothing to do except forward.
541	*/
542	break;
543	}
544	off--; / * 0 origin * /
545	if (off > optlen - sizeof(struct in_addr)) {
546	/*
547	* End of source route. Should be for us.
548	*/
549	save_rte(cp, ip->ip_src);
550	break;
551	}
552	/*
553	* locate outgoing interface
554	*/
555	bcopy((caddr_t)(cp + off), (caddr_t)&ipaddr.sin_addr,
556	sizeof(ipaddr.sin_addr));
557	if (opt == IPOPT_SSRR) {
558	#define INA struct in_ifaddr *
559	#define SA struct sockaddr *
560	if ((ia = (INA)ifa_ifwithdstaddr((SA)&ipaddr)) == 0)
561	ia = (INA)ifa_ifwithnet((SA)&ipaddr);
562	} else
563	ia = ip_rtaddr(ipaddr.sin_addr);
564	if (ia == 0) {
565	type = ICMP_UNREACH;
566	code = ICMP_UNREACH_SRCFAIL;
567	goto bad;
568	}
569	ip->ip_dst = ipaddr.sin_addr;
570	bcopy((caddr_t)&(IA_SIN(ia)->sin_addr),
571	(caddr_t)(cp + off), sizeof(struct in_addr));
572	cp[IPOPT_OFFSET] += sizeof(struct in_addr);
573	/*
574	* Let ip_intr's mcast routing check handle mcast pkts
575	*/
576	forward = !IN_MULTICAST(ntohl(ip->ip_dst.s_addr));
577	break;
578
579	case IPOPT_RR:
580	if ((off = cp[IPOPT_OFFSET]) < IPOPT_MINOFF) {
581	code = &cp[IPOPT_OFFSET] - (u_char *)ip;
582	goto bad;
583	}
584	/*
585	* If no space remains, ignore.
586	*/
587	off--; * 0 origin *
588	if (off > optlen - sizeof(struct in_addr))
589	break;
590	bcopy((caddr_t)(&ip->ip_dst), (caddr_t)&ipaddr.sin_addr,
591	sizeof(ipaddr.sin_addr));
592	/*
593	* locate outgoing interface; if we're the destination,
594	* use the incoming interface (should be same).
595	*/
596	if ((ia = (INA)ifa_ifwithaddr((SA)&ipaddr)) == 0 &&
597	(ia = ip_rtaddr(ipaddr.sin_addr)) == 0) {
598	type = ICMP_UNREACH;
599	code = ICMP_UNREACH_HOST;
600	goto bad;
601	}
602	bcopy((caddr_t)&(IA_SIN(ia)->sin_addr),
603	(caddr_t)(cp + off), sizeof(struct in_addr));
604	cp[IPOPT_OFFSET] += sizeof(struct in_addr);
605	break;
606
607	case IPOPT_TS:
608	code = cp - (u_char *)ip;
609	ipt = (struct ip_timestamp *)cp;
610	if (ipt->ipt_len < 5)
611	goto bad;
612	if (ipt->ipt_ptr > ipt->ipt_len - sizeof (int32_t)) {
613	if (++ipt->ipt_oflw == 0)
614	goto bad;
615	break;
616	}
617	sin = (struct in_addr *)(cp + ipt->ipt_ptr - 1);
618	switch (ipt->ipt_flg) {
619
620	case IPOPT_TS_TSONLY:
621	break;
622
623	case IPOPT_TS_TSANDADDR:
624	if (ipt->ipt_ptr + sizeof(n_time) +
625	sizeof(struct in_addr) > ipt->ipt_len)
626	goto bad;
627	ipaddr.sin_addr = dst;
628	ia = (INA)ifaof_ i f p foraddr((SA)&ipaddr,
629	m->m_pkthdr.rcvif);
630	if (ia == 0)
631	continue;
632	bcopy((caddr_t)&IA_SIN(ia)->sin_addr,
633	(caddr_t)sin, sizeof(struct in_addr));
634	ipt->ipt_ptr += sizeof(struct in_addr);
635	break;
636
637	case IPOPT_TS_PRESPEC:
638	if (ipt->ipt_ptr + sizeof(n_time) +
639	sizeof(struct in_addr) > ipt->ipt_len)
640	goto bad;
641	bcopy((caddr_t)sin, (caddr_t)&ipaddr.sin_addr,
642	sizeof(struct in_addr));
643	if (ifa_ifwithaddr((SA)&ipaddr) == 0)
644	continue;
645	ipt->ipt_ptr += sizeof(struct in_addr);
646	break;
647
648	default:
649	goto bad;
650	}
651	ntime = iptime();
652	bcopy((caddr_t)&ntime, (caddr_t)cp + ipt->ipt_ptr - 1,
653	sizeof(n_time));
654	ipt->ipt_ptr += sizeof(n_time);
655	}
656	}
657	if (forward) {
658	ip_forward(m, 1);
659	return (1);
660	}
661	}
662	}
663	return (0);
664	bad:
665	/* ip->ip_len -= ip->ip_hl << 2; XXX icmp_error adds in hdr length */
666
667	/* Not yet */
668	icmp_error(m, type, code, 0, 0);
669
670	ipstat.ips_badoptions++;
671	return (1);
672	}
673
674	#endif /* notdef */
675
676	/*
677	* Strip out IP options, at higher
678	* level protocol in the kernel.
679	* Second argument is buffer to which options
680	* will be moved, and return value is their length.
681	* (XXX) should be deleted; last arg currently ignored.
682	*/
683	void
684	ip_stripoptions(m, mopt)
685	register struct mbuf *m;
686	struct mbuf *mopt;
687	{
688	register int i;
689	struct ip ip = mtod(m, struct ip );
690	register caddr_t opts;
691	int olen;
692
693	olen = (ip->ip_hl<<2) - sizeof (struct ip);
694	opts = (caddr_t)(ip + 1);
695	i = m->m_len - (sizeof (struct ip) + olen);
696	memcpy(opts, opts + olen, (unsigned)i);
697	m->m_len -= olen;
698
699	ip->ip_hl = sizeof(struct ip) >> 2;
700	}

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source: vbox/trunk/src/VBox/Devices/Network/slirp/ip_input.c@ 532

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