arp.c revision 346476 
1/*	$NetBSD: arp.c,v 1.18 1997/07/07 15:52:49 drochner Exp $	*/
2
3/*
4 * Copyright (c) 1992 Regents of the University of California.
5 * All rights reserved.
6 *
7 * This software was developed by the Computer Systems Engineering group
8 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
9 * contributed to Berkeley.
10 *
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
13 * are met:
14 * 1. Redistributions of source code must retain the above copyright
15 *    notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 *    notice, this list of conditions and the following disclaimer in the
18 *    documentation and/or other materials provided with the distribution.
19 * 4. Neither the name of the University nor the names of its contributors
20 *    may be used to endorse or promote products derived from this software
21 *    without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 *
35 * @(#) Header: arp.c,v 1.5 93/07/15 05:52:26 leres Exp  (LBL)
36 */
37
38#include <sys/cdefs.h>
39__FBSDID("$FreeBSD: stable/11/stand/libsa/arp.c 346476 2019-04-21 03:36:05Z kevans $");
40
41#include <sys/types.h>
42#include <sys/socket.h>
43#include <net/if.h>
44#include <netinet/in.h>
45#include <netinet/if_ether.h>
46
47#include <netinet/in_systm.h>
48
49#include <string.h>
50
51#include "stand.h"
52#include "net.h"
53
54/* Cache stuff */
55#define ARP_NUM 8			/* need at most 3 arp entries */
56
57struct arp_list {
58	struct in_addr	addr;
59	u_char		ea[6];
60} arp_list[ARP_NUM] = {
61	/* XXX - net order `INADDR_BROADCAST' must be a constant */
62	{ {0xffffffff}, BA }
63};
64int arp_num = 1;
65
66/* Local forwards */
67static	ssize_t arpsend(struct iodesc *, void *, size_t);
68static	ssize_t arprecv(struct iodesc *, void **, void **, time_t, void *);
69
70/* Broadcast an ARP packet, asking who has addr on interface d */
71u_char *
72arpwhohas(struct iodesc *d, struct in_addr addr)
73{
74	int i;
75	struct ether_arp *ah;
76	struct arp_list *al;
77	void *pkt;
78	struct {
79		struct ether_header eh;
80		struct {
81			struct ether_arp arp;
82			u_char pad[18]; 	/* 60 - sizeof(...) */
83		} data;
84	} wbuf;
85
86	/* Try for cached answer first */
87	for (i = 0, al = arp_list; i < arp_num; ++i, ++al)
88		if (addr.s_addr == al->addr.s_addr)
89			return (al->ea);
90
91	/* Don't overflow cache */
92	if (arp_num > ARP_NUM - 1) {
93		arp_num = 1;	/* recycle */
94		printf("arpwhohas: overflowed arp_list!\n");
95	}
96
97#ifdef ARP_DEBUG
98 	if (debug)
99 	    printf("arpwhohas: send request for %s\n", inet_ntoa(addr));
100#endif
101
102	bzero((char*)&wbuf.data, sizeof(wbuf.data));
103	ah = &wbuf.data.arp;
104	ah->arp_hrd = htons(ARPHRD_ETHER);
105	ah->arp_pro = htons(ETHERTYPE_IP);
106	ah->arp_hln = sizeof(ah->arp_sha); /* hardware address length */
107	ah->arp_pln = sizeof(ah->arp_spa); /* protocol address length */
108	ah->arp_op = htons(ARPOP_REQUEST);
109	MACPY(d->myea, ah->arp_sha);
110	bcopy(&d->myip, ah->arp_spa, sizeof(ah->arp_spa));
111	/* Leave zeros in arp_tha */
112	bcopy(&addr, ah->arp_tpa, sizeof(ah->arp_tpa));
113
114	/* Store ip address in cache (incomplete entry). */
115	al->addr = addr;
116
117	pkt = NULL;
118	ah = NULL;
119	i = sendrecv(d,
120	    arpsend, &wbuf.data, sizeof(wbuf.data),
121	    arprecv, &pkt, (void **)&ah, NULL);
122	if (i == -1) {
123		panic("arp: no response for %s",
124			  inet_ntoa(addr));
125	}
126
127	/* Store ethernet address in cache */
128#ifdef ARP_DEBUG
129 	if (debug) {
130		struct ether_header *eh;
131
132		eh = (struct ether_header *)((uintptr_t)pkt + ETHER_ALIGN);
133		printf("arp: response from %s\n",
134		    ether_sprintf(eh->ether_shost));
135		printf("arp: cacheing %s --> %s\n",
136		    inet_ntoa(addr), ether_sprintf(ah->arp_sha));
137	}
138#endif
139	MACPY(ah->arp_sha, al->ea);
140	++arp_num;
141
142	free(pkt);
143	return (al->ea);
144}
145
146static ssize_t
147arpsend(struct iodesc *d, void *pkt, size_t len)
148{
149
150#ifdef ARP_DEBUG
151 	if (debug)
152		printf("arpsend: called\n");
153#endif
154
155	return (sendether(d, pkt, len, bcea, ETHERTYPE_ARP));
156}
157
158/*
159 * Returns 0 if this is the packet we're waiting for
160 * else -1 (and errno == 0)
161 */
162static ssize_t
163arprecv(struct iodesc *d, void **pkt, void **payload, time_t tleft, void *extra)
164{
165	ssize_t n;
166	struct ether_arp *ah;
167	uint16_t etype;	/* host order */
168	void *ptr;
169
170#ifdef ARP_DEBUG
171 	if (debug)
172		printf("arprecv: ");
173#endif
174
175	ptr = NULL;
176	n = readether(d, &ptr, (void **)&ah, tleft, &etype);
177	errno = 0;	/* XXX */
178	if (n == -1 || n < sizeof(struct ether_arp)) {
179#ifdef ARP_DEBUG
180		if (debug)
181			printf("bad len=%d\n", n);
182#endif
183		free(ptr);
184		return (-1);
185	}
186
187	if (etype != ETHERTYPE_ARP) {
188#ifdef ARP_DEBUG
189		if (debug)
190			printf("not arp type=%d\n", etype);
191#endif
192		free(ptr);
193		return (-1);
194	}
195
196	/* Ethernet address now checked in readether() */
197	if (ah->arp_hrd != htons(ARPHRD_ETHER) ||
198	    ah->arp_pro != htons(ETHERTYPE_IP) ||
199	    ah->arp_hln != sizeof(ah->arp_sha) ||
200	    ah->arp_pln != sizeof(ah->arp_spa) )
201	{
202#ifdef ARP_DEBUG
203		if (debug)
204			printf("bad hrd/pro/hln/pln\n");
205#endif
206		free(ptr);
207		return (-1);
208	}
209
210	if (ah->arp_op == htons(ARPOP_REQUEST)) {
211#ifdef ARP_DEBUG
212		if (debug)
213			printf("is request\n");
214#endif
215		arp_reply(d, ah);
216		free(ptr);
217		return (-1);
218	}
219
220	if (ah->arp_op != htons(ARPOP_REPLY)) {
221#ifdef ARP_DEBUG
222		if (debug)
223			printf("not ARP reply\n");
224#endif
225		free(ptr);
226		return (-1);
227	}
228
229	/* Is the reply from the source we want? */
230	if (bcmp(&arp_list[arp_num].addr,
231			 ah->arp_spa, sizeof(ah->arp_spa)))
232	{
233#ifdef ARP_DEBUG
234		if (debug)
235			printf("unwanted address\n");
236#endif
237		free(ptr);
238		return (-1);
239	}
240	/* We don't care who the reply was sent to. */
241
242	/* We have our answer. */
243#ifdef ARP_DEBUG
244 	if (debug)
245		printf("got it\n");
246#endif
247	*pkt = ptr;
248	*payload = ah;
249	return (n);
250}
251
252/*
253 * Convert an ARP request into a reply and send it.
254 * Notes:  Re-uses buffer.  Pad to length = 46.
255 */
256void
257arp_reply(struct iodesc *d, void *pkt)
258{
259	struct ether_arp *arp = pkt;
260
261	if (arp->arp_hrd != htons(ARPHRD_ETHER) ||
262	    arp->arp_pro != htons(ETHERTYPE_IP) ||
263	    arp->arp_hln != sizeof(arp->arp_sha) ||
264	    arp->arp_pln != sizeof(arp->arp_spa) )
265	{
266#ifdef ARP_DEBUG
267		if (debug)
268			printf("arp_reply: bad hrd/pro/hln/pln\n");
269#endif
270		return;
271	}
272
273	if (arp->arp_op != htons(ARPOP_REQUEST)) {
274#ifdef ARP_DEBUG
275		if (debug)
276			printf("arp_reply: not request!\n");
277#endif
278		return;
279	}
280
281	/* If we are not the target, ignore the request. */
282	if (bcmp(arp->arp_tpa, &d->myip, sizeof(arp->arp_tpa)))
283		return;
284
285#ifdef ARP_DEBUG
286	if (debug) {
287		printf("arp_reply: to %s\n", ether_sprintf(arp->arp_sha));
288	}
289#endif
290
291	arp->arp_op = htons(ARPOP_REPLY);
292	/* source becomes target */
293	bcopy(arp->arp_sha, arp->arp_tha, sizeof(arp->arp_tha));
294	bcopy(arp->arp_spa, arp->arp_tpa, sizeof(arp->arp_tpa));
295	/* here becomes source */
296	bcopy(d->myea,  arp->arp_sha, sizeof(arp->arp_sha));
297	bcopy(&d->myip, arp->arp_spa, sizeof(arp->arp_spa));
298
299	/*
300	 * No need to get fancy here.  If the send fails, the
301	 * requestor will just ask again.
302	 */
303	(void) sendether(d, pkt, sizeof(*arp) + 18,
304	                 arp->arp_tha, ETHERTYPE_ARP);
305}
306