xref: /freebsd/sys/netinet/ip_icmp.c (revision 3a3af6b2a160bea72509a9d5ef84e25906b0478a)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 1982, 1986, 1988, 1993
5  *	The Regents of the University of California.  All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  * 3. Neither the name of the University nor the names of its contributors
16  *    may be used to endorse or promote products derived from this software
17  *    without specific prior written permission.
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29  * SUCH DAMAGE.
30  *
31  *	@(#)ip_icmp.c	8.2 (Berkeley) 1/4/94
32  */
33 
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
36 
37 #include "opt_inet.h"
38 
39 #include <sys/param.h>
40 #include <sys/systm.h>
41 #include <sys/mbuf.h>
42 #include <sys/protosw.h>
43 #include <sys/socket.h>
44 #include <sys/time.h>
45 #include <sys/kernel.h>
46 #include <sys/lock.h>
47 #include <sys/sysctl.h>
48 #include <sys/syslog.h>
49 
50 #include <net/if.h>
51 #include <net/if_var.h>
52 #include <net/if_types.h>
53 #include <net/route.h>
54 #include <net/route/route_ctl.h>
55 #include <net/route/nhop.h>
56 #include <net/vnet.h>
57 
58 #include <netinet/in.h>
59 #include <netinet/in_fib.h>
60 #include <netinet/in_pcb.h>
61 #include <netinet/in_systm.h>
62 #include <netinet/in_var.h>
63 #include <netinet/ip.h>
64 #include <netinet/ip_icmp.h>
65 #include <netinet/ip_var.h>
66 #include <netinet/ip_options.h>
67 #include <netinet/sctp.h>
68 #include <netinet/tcp.h>
69 #include <netinet/tcp_var.h>
70 #include <netinet/tcpip.h>
71 #include <netinet/icmp_var.h>
72 
73 #ifdef INET
74 
75 #include <machine/in_cksum.h>
76 
77 #include <security/mac/mac_framework.h>
78 #endif /* INET */
79 
80 /*
81  * ICMP routines: error generation, receive packet processing, and
82  * routines to turnaround packets back to the originator, and
83  * host table maintenance routines.
84  */
85 VNET_DEFINE_STATIC(int, icmplim) = 200;
86 #define	V_icmplim			VNET(icmplim)
87 SYSCTL_INT(_net_inet_icmp, ICMPCTL_ICMPLIM, icmplim, CTLFLAG_VNET | CTLFLAG_RW,
88 	&VNET_NAME(icmplim), 0,
89 	"Maximum number of ICMP responses per second");
90 
91 VNET_DEFINE_STATIC(int, icmplim_curr_jitter) = 0;
92 #define V_icmplim_curr_jitter		VNET(icmplim_curr_jitter)
93 VNET_DEFINE_STATIC(int, icmplim_jitter) = 16;
94 #define	V_icmplim_jitter		VNET(icmplim_jitter)
95 SYSCTL_INT(_net_inet_icmp, OID_AUTO, icmplim_jitter, CTLFLAG_VNET | CTLFLAG_RW,
96 	&VNET_NAME(icmplim_jitter), 0,
97 	"Random icmplim jitter adjustment limit");
98 
99 VNET_DEFINE_STATIC(int, icmplim_output) = 1;
100 #define	V_icmplim_output		VNET(icmplim_output)
101 SYSCTL_INT(_net_inet_icmp, OID_AUTO, icmplim_output, CTLFLAG_VNET | CTLFLAG_RW,
102 	&VNET_NAME(icmplim_output), 0,
103 	"Enable logging of ICMP response rate limiting");
104 
105 #ifdef INET
106 VNET_PCPUSTAT_DEFINE(struct icmpstat, icmpstat);
107 VNET_PCPUSTAT_SYSINIT(icmpstat);
108 SYSCTL_VNET_PCPUSTAT(_net_inet_icmp, ICMPCTL_STATS, stats, struct icmpstat,
109     icmpstat, "ICMP statistics (struct icmpstat, netinet/icmp_var.h)");
110 
111 #ifdef VIMAGE
112 VNET_PCPUSTAT_SYSUNINIT(icmpstat);
113 #endif /* VIMAGE */
114 
115 VNET_DEFINE_STATIC(int, icmpmaskrepl) = 0;
116 #define	V_icmpmaskrepl			VNET(icmpmaskrepl)
117 SYSCTL_INT(_net_inet_icmp, ICMPCTL_MASKREPL, maskrepl, CTLFLAG_VNET | CTLFLAG_RW,
118 	&VNET_NAME(icmpmaskrepl), 0,
119 	"Reply to ICMP Address Mask Request packets");
120 
121 VNET_DEFINE_STATIC(u_int, icmpmaskfake) = 0;
122 #define	V_icmpmaskfake			VNET(icmpmaskfake)
123 SYSCTL_UINT(_net_inet_icmp, OID_AUTO, maskfake, CTLFLAG_VNET | CTLFLAG_RW,
124 	&VNET_NAME(icmpmaskfake), 0,
125 	"Fake reply to ICMP Address Mask Request packets");
126 
127 VNET_DEFINE(int, drop_redirect) = 0;
128 #define	V_drop_redirect			VNET(drop_redirect)
129 SYSCTL_INT(_net_inet_icmp, OID_AUTO, drop_redirect, CTLFLAG_VNET | CTLFLAG_RW,
130 	&VNET_NAME(drop_redirect), 0,
131 	"Ignore ICMP redirects");
132 
133 VNET_DEFINE_STATIC(int, log_redirect) = 0;
134 #define	V_log_redirect			VNET(log_redirect)
135 SYSCTL_INT(_net_inet_icmp, OID_AUTO, log_redirect, CTLFLAG_VNET | CTLFLAG_RW,
136 	&VNET_NAME(log_redirect), 0,
137 	"Log ICMP redirects to the console");
138 
139 VNET_DEFINE_STATIC(int, redirtimeout) = 60 * 10; /* 10 minutes */
140 #define	V_redirtimeout			VNET(redirtimeout)
141 SYSCTL_INT(_net_inet_icmp, OID_AUTO, redirtimeout, CTLFLAG_VNET | CTLFLAG_RW,
142 	&VNET_NAME(redirtimeout), 0,
143 	"Delay in seconds before expiring redirect route");
144 
145 VNET_DEFINE_STATIC(char, reply_src[IFNAMSIZ]);
146 #define	V_reply_src			VNET(reply_src)
147 SYSCTL_STRING(_net_inet_icmp, OID_AUTO, reply_src, CTLFLAG_VNET | CTLFLAG_RW,
148 	&VNET_NAME(reply_src), IFNAMSIZ,
149 	"ICMP reply source for non-local packets");
150 
151 VNET_DEFINE_STATIC(int, icmp_rfi) = 0;
152 #define	V_icmp_rfi			VNET(icmp_rfi)
153 SYSCTL_INT(_net_inet_icmp, OID_AUTO, reply_from_interface, CTLFLAG_VNET | CTLFLAG_RW,
154 	&VNET_NAME(icmp_rfi), 0,
155 	"ICMP reply from incoming interface for non-local packets");
156 /* Router requirements RFC 1812 section 4.3.2.3 requires 576 - 28. */
157 VNET_DEFINE_STATIC(int, icmp_quotelen) = 548;
158 #define	V_icmp_quotelen			VNET(icmp_quotelen)
159 SYSCTL_INT(_net_inet_icmp, OID_AUTO, quotelen, CTLFLAG_VNET | CTLFLAG_RW,
160 	&VNET_NAME(icmp_quotelen), 0,
161 	"Number of bytes from original packet to quote in ICMP reply");
162 
163 VNET_DEFINE_STATIC(int, icmpbmcastecho) = 0;
164 #define	V_icmpbmcastecho		VNET(icmpbmcastecho)
165 SYSCTL_INT(_net_inet_icmp, OID_AUTO, bmcastecho, CTLFLAG_VNET | CTLFLAG_RW,
166 	&VNET_NAME(icmpbmcastecho), 0,
167 	"Reply to multicast ICMP Echo Request and Timestamp packets");
168 
169 VNET_DEFINE_STATIC(int, icmptstamprepl) = 1;
170 #define	V_icmptstamprepl		VNET(icmptstamprepl)
171 SYSCTL_INT(_net_inet_icmp, OID_AUTO, tstamprepl, CTLFLAG_VNET | CTLFLAG_RW,
172 	&VNET_NAME(icmptstamprepl), 0,
173 	"Respond to ICMP Timestamp packets");
174 
175 VNET_DEFINE_STATIC(int, error_keeptags) = 0;
176 #define	V_error_keeptags		VNET(error_keeptags)
177 SYSCTL_INT(_net_inet_icmp, OID_AUTO, error_keeptags, CTLFLAG_VNET | CTLFLAG_RW,
178 	&VNET_NAME(error_keeptags), 0,
179 	"ICMP error response keeps copy of mbuf_tags of original packet");
180 
181 #ifdef ICMPPRINTFS
182 int	icmpprintfs = 0;
183 #endif
184 
185 static void	icmp_reflect(struct mbuf *);
186 static void	icmp_send(struct mbuf *, struct mbuf *);
187 static int	icmp_verify_redirect_gateway(struct sockaddr_in *,
188     struct sockaddr_in *, struct sockaddr_in *, u_int);
189 
190 extern	struct protosw inetsw[];
191 
192 /*
193  * Kernel module interface for updating icmpstat.  The argument is an index
194  * into icmpstat treated as an array of u_long.  While this encodes the
195  * general layout of icmpstat into the caller, it doesn't encode its
196  * location, so that future changes to add, for example, per-CPU stats
197  * support won't cause binary compatibility problems for kernel modules.
198  */
199 void
200 kmod_icmpstat_inc(int statnum)
201 {
202 
203 	counter_u64_add(VNET(icmpstat)[statnum], 1);
204 }
205 
206 /*
207  * Generate an error packet of type error
208  * in response to bad packet ip.
209  */
210 void
211 icmp_error(struct mbuf *n, int type, int code, uint32_t dest, int mtu)
212 {
213 	struct ip *oip, *nip;
214 	struct icmp *icp;
215 	struct mbuf *m;
216 	unsigned icmplen, icmpelen, nlen, oiphlen;
217 
218 	KASSERT((u_int)type <= ICMP_MAXTYPE, ("%s: illegal ICMP type",
219 	    __func__));
220 
221 	if (type != ICMP_REDIRECT)
222 		ICMPSTAT_INC(icps_error);
223 	/*
224 	 * Don't send error:
225 	 *  if the original packet was encrypted.
226 	 *  if not the first fragment of message.
227 	 *  in response to a multicast or broadcast packet.
228 	 *  if the old packet protocol was an ICMP error message.
229 	 */
230 	if (n->m_flags & M_DECRYPTED)
231 		goto freeit;
232 	if (n->m_flags & (M_BCAST|M_MCAST))
233 		goto freeit;
234 
235 	/* Drop if IP header plus 8 bytes is not contiguous in first mbuf. */
236 	if (n->m_len < sizeof(struct ip) + ICMP_MINLEN)
237 		goto freeit;
238 	oip = mtod(n, struct ip *);
239 	oiphlen = oip->ip_hl << 2;
240 	if (n->m_len < oiphlen + ICMP_MINLEN)
241 		goto freeit;
242 #ifdef ICMPPRINTFS
243 	if (icmpprintfs)
244 		printf("icmp_error(%p, %x, %d)\n", oip, type, code);
245 #endif
246 	if (oip->ip_off & htons(~(IP_MF|IP_DF)))
247 		goto freeit;
248 	if (oip->ip_p == IPPROTO_ICMP && type != ICMP_REDIRECT &&
249 	    !ICMP_INFOTYPE(((struct icmp *)((caddr_t)oip +
250 		oiphlen))->icmp_type)) {
251 		ICMPSTAT_INC(icps_oldicmp);
252 		goto freeit;
253 	}
254 	/*
255 	 * Calculate length to quote from original packet and
256 	 * prevent the ICMP mbuf from overflowing.
257 	 * Unfortunately this is non-trivial since ip_forward()
258 	 * sends us truncated packets.
259 	 */
260 	nlen = m_length(n, NULL);
261 	if (oip->ip_p == IPPROTO_TCP) {
262 		struct tcphdr *th;
263 		int tcphlen;
264 
265 		if (oiphlen + sizeof(struct tcphdr) > n->m_len &&
266 		    n->m_next == NULL)
267 			goto stdreply;
268 		if (n->m_len < oiphlen + sizeof(struct tcphdr) &&
269 		    (n = m_pullup(n, oiphlen + sizeof(struct tcphdr))) == NULL)
270 			goto freeit;
271 		oip = mtod(n, struct ip *);
272 		th = mtodo(n, oiphlen);
273 		tcphlen = th->th_off << 2;
274 		if (tcphlen < sizeof(struct tcphdr))
275 			goto freeit;
276 		if (ntohs(oip->ip_len) < oiphlen + tcphlen)
277 			goto freeit;
278 		if (oiphlen + tcphlen > n->m_len && n->m_next == NULL)
279 			goto stdreply;
280 		if (n->m_len < oiphlen + tcphlen &&
281 		    (n = m_pullup(n, oiphlen + tcphlen)) == NULL)
282 			goto freeit;
283 		oip = mtod(n, struct ip *);
284 		icmpelen = max(tcphlen, min(V_icmp_quotelen,
285 		    ntohs(oip->ip_len) - oiphlen));
286 	} else if (oip->ip_p == IPPROTO_SCTP) {
287 		struct sctphdr *sh;
288 		struct sctp_chunkhdr *ch;
289 
290 		if (ntohs(oip->ip_len) < oiphlen + sizeof(struct sctphdr))
291 			goto stdreply;
292 		if (oiphlen + sizeof(struct sctphdr) > n->m_len &&
293 		    n->m_next == NULL)
294 			goto stdreply;
295 		if (n->m_len < oiphlen + sizeof(struct sctphdr) &&
296 		    (n = m_pullup(n, oiphlen + sizeof(struct sctphdr))) == NULL)
297 			goto freeit;
298 		oip = mtod(n, struct ip *);
299 		icmpelen = max(sizeof(struct sctphdr),
300 		    min(V_icmp_quotelen, ntohs(oip->ip_len) - oiphlen));
301 		sh = mtodo(n, oiphlen);
302 		if (ntohl(sh->v_tag) == 0 &&
303 		    ntohs(oip->ip_len) >= oiphlen +
304 		    sizeof(struct sctphdr) + 8 &&
305 		    (n->m_len >= oiphlen + sizeof(struct sctphdr) + 8 ||
306 		     n->m_next != NULL)) {
307 			if (n->m_len < oiphlen + sizeof(struct sctphdr) + 8 &&
308 			    (n = m_pullup(n, oiphlen +
309 			    sizeof(struct sctphdr) + 8)) == NULL)
310 				goto freeit;
311 			oip = mtod(n, struct ip *);
312 			sh = mtodo(n, oiphlen);
313 			ch = (struct sctp_chunkhdr *)(sh + 1);
314 			if (ch->chunk_type == SCTP_INITIATION) {
315 				icmpelen = max(sizeof(struct sctphdr) + 8,
316 				    min(V_icmp_quotelen, ntohs(oip->ip_len) -
317 				    oiphlen));
318 			}
319 		}
320 	} else
321 stdreply:	icmpelen = max(8, min(V_icmp_quotelen, ntohs(oip->ip_len) -
322 		    oiphlen));
323 
324 	icmplen = min(oiphlen + icmpelen, nlen);
325 	if (icmplen < sizeof(struct ip))
326 		goto freeit;
327 
328 	if (MHLEN > sizeof(struct ip) + ICMP_MINLEN + icmplen)
329 		m = m_gethdr(M_NOWAIT, MT_DATA);
330 	else
331 		m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
332 	if (m == NULL)
333 		goto freeit;
334 #ifdef MAC
335 	mac_netinet_icmp_reply(n, m);
336 #endif
337 	icmplen = min(icmplen, M_TRAILINGSPACE(m) -
338 	    sizeof(struct ip) - ICMP_MINLEN);
339 	m_align(m, sizeof(struct ip) + ICMP_MINLEN + icmplen);
340 	m->m_data += sizeof(struct ip);
341 	m->m_len = ICMP_MINLEN + icmplen;
342 
343 	/* XXX MRT  make the outgoing packet use the same FIB
344 	 * that was associated with the incoming packet
345 	 */
346 	M_SETFIB(m, M_GETFIB(n));
347 	icp = mtod(m, struct icmp *);
348 	ICMPSTAT_INC(icps_outhist[type]);
349 	icp->icmp_type = type;
350 	if (type == ICMP_REDIRECT)
351 		icp->icmp_gwaddr.s_addr = dest;
352 	else {
353 		icp->icmp_void = 0;
354 		/*
355 		 * The following assignments assume an overlay with the
356 		 * just zeroed icmp_void field.
357 		 */
358 		if (type == ICMP_PARAMPROB) {
359 			icp->icmp_pptr = code;
360 			code = 0;
361 		} else if (type == ICMP_UNREACH &&
362 			code == ICMP_UNREACH_NEEDFRAG && mtu) {
363 			icp->icmp_nextmtu = htons(mtu);
364 		}
365 	}
366 	icp->icmp_code = code;
367 
368 	/*
369 	 * Copy the quotation into ICMP message and
370 	 * convert quoted IP header back to network representation.
371 	 */
372 	m_copydata(n, 0, icmplen, (caddr_t)&icp->icmp_ip);
373 	nip = &icp->icmp_ip;
374 
375 	/*
376 	 * Set up ICMP message mbuf and copy old IP header (without options
377 	 * in front of ICMP message.
378 	 * If the original mbuf was meant to bypass the firewall, the error
379 	 * reply should bypass as well.
380 	 */
381 	m->m_flags |= n->m_flags & M_SKIP_FIREWALL;
382 	KASSERT(M_LEADINGSPACE(m) >= sizeof(struct ip),
383 	    ("insufficient space for ip header"));
384 	m->m_data -= sizeof(struct ip);
385 	m->m_len += sizeof(struct ip);
386 	m->m_pkthdr.len = m->m_len;
387 	m->m_pkthdr.rcvif = n->m_pkthdr.rcvif;
388 	nip = mtod(m, struct ip *);
389 	bcopy((caddr_t)oip, (caddr_t)nip, sizeof(struct ip));
390 	nip->ip_len = htons(m->m_len);
391 	nip->ip_v = IPVERSION;
392 	nip->ip_hl = 5;
393 	nip->ip_p = IPPROTO_ICMP;
394 	nip->ip_tos = 0;
395 	nip->ip_off = 0;
396 
397 	if (V_error_keeptags)
398 		m_tag_copy_chain(m, n, M_NOWAIT);
399 
400 	icmp_reflect(m);
401 
402 freeit:
403 	m_freem(n);
404 }
405 
406 /*
407  * Process a received ICMP message.
408  */
409 int
410 icmp_input(struct mbuf **mp, int *offp, int proto)
411 {
412 	struct icmp *icp;
413 	struct in_ifaddr *ia;
414 	struct mbuf *m = *mp;
415 	struct ip *ip = mtod(m, struct ip *);
416 	struct sockaddr_in icmpsrc, icmpdst, icmpgw;
417 	int hlen = *offp;
418 	int icmplen = ntohs(ip->ip_len) - *offp;
419 	int i, code;
420 	void (*ctlfunc)(int, struct sockaddr *, void *);
421 	int fibnum;
422 
423 	NET_EPOCH_ASSERT();
424 
425 	*mp = NULL;
426 
427 	/*
428 	 * Locate icmp structure in mbuf, and check
429 	 * that not corrupted and of at least minimum length.
430 	 */
431 #ifdef ICMPPRINTFS
432 	if (icmpprintfs) {
433 		char srcbuf[INET_ADDRSTRLEN];
434 		char dstbuf[INET_ADDRSTRLEN];
435 
436 		printf("icmp_input from %s to %s, len %d\n",
437 		    inet_ntoa_r(ip->ip_src, srcbuf),
438 		    inet_ntoa_r(ip->ip_dst, dstbuf), icmplen);
439 	}
440 #endif
441 	if (icmplen < ICMP_MINLEN) {
442 		ICMPSTAT_INC(icps_tooshort);
443 		goto freeit;
444 	}
445 	i = hlen + min(icmplen, ICMP_ADVLENMIN);
446 	if (m->m_len < i && (m = m_pullup(m, i)) == NULL)  {
447 		ICMPSTAT_INC(icps_tooshort);
448 		return (IPPROTO_DONE);
449 	}
450 	ip = mtod(m, struct ip *);
451 	m->m_len -= hlen;
452 	m->m_data += hlen;
453 	icp = mtod(m, struct icmp *);
454 	if (in_cksum(m, icmplen)) {
455 		ICMPSTAT_INC(icps_checksum);
456 		goto freeit;
457 	}
458 	m->m_len += hlen;
459 	m->m_data -= hlen;
460 
461 #ifdef ICMPPRINTFS
462 	if (icmpprintfs)
463 		printf("icmp_input, type %d code %d\n", icp->icmp_type,
464 		    icp->icmp_code);
465 #endif
466 
467 	/*
468 	 * Message type specific processing.
469 	 */
470 	if (icp->icmp_type > ICMP_MAXTYPE)
471 		goto raw;
472 
473 	/* Initialize */
474 	bzero(&icmpsrc, sizeof(icmpsrc));
475 	icmpsrc.sin_len = sizeof(struct sockaddr_in);
476 	icmpsrc.sin_family = AF_INET;
477 	bzero(&icmpdst, sizeof(icmpdst));
478 	icmpdst.sin_len = sizeof(struct sockaddr_in);
479 	icmpdst.sin_family = AF_INET;
480 	bzero(&icmpgw, sizeof(icmpgw));
481 	icmpgw.sin_len = sizeof(struct sockaddr_in);
482 	icmpgw.sin_family = AF_INET;
483 
484 	ICMPSTAT_INC(icps_inhist[icp->icmp_type]);
485 	code = icp->icmp_code;
486 	switch (icp->icmp_type) {
487 	case ICMP_UNREACH:
488 		switch (code) {
489 			case ICMP_UNREACH_NET:
490 			case ICMP_UNREACH_HOST:
491 			case ICMP_UNREACH_SRCFAIL:
492 			case ICMP_UNREACH_NET_UNKNOWN:
493 			case ICMP_UNREACH_HOST_UNKNOWN:
494 			case ICMP_UNREACH_ISOLATED:
495 			case ICMP_UNREACH_TOSNET:
496 			case ICMP_UNREACH_TOSHOST:
497 			case ICMP_UNREACH_HOST_PRECEDENCE:
498 			case ICMP_UNREACH_PRECEDENCE_CUTOFF:
499 				code = PRC_UNREACH_NET;
500 				break;
501 
502 			case ICMP_UNREACH_NEEDFRAG:
503 				code = PRC_MSGSIZE;
504 				break;
505 
506 			/*
507 			 * RFC 1122, Sections 3.2.2.1 and 4.2.3.9.
508 			 * Treat subcodes 2,3 as immediate RST
509 			 */
510 			case ICMP_UNREACH_PROTOCOL:
511 				code = PRC_UNREACH_PROTOCOL;
512 				break;
513 			case ICMP_UNREACH_PORT:
514 				code = PRC_UNREACH_PORT;
515 				break;
516 
517 			case ICMP_UNREACH_NET_PROHIB:
518 			case ICMP_UNREACH_HOST_PROHIB:
519 			case ICMP_UNREACH_FILTER_PROHIB:
520 				code = PRC_UNREACH_ADMIN_PROHIB;
521 				break;
522 
523 			default:
524 				goto badcode;
525 		}
526 		goto deliver;
527 
528 	case ICMP_TIMXCEED:
529 		if (code > 1)
530 			goto badcode;
531 		code += PRC_TIMXCEED_INTRANS;
532 		goto deliver;
533 
534 	case ICMP_PARAMPROB:
535 		if (code > 1)
536 			goto badcode;
537 		code = PRC_PARAMPROB;
538 	deliver:
539 		/*
540 		 * Problem with datagram; advise higher level routines.
541 		 */
542 		if (icmplen < ICMP_ADVLENMIN || icmplen < ICMP_ADVLEN(icp) ||
543 		    icp->icmp_ip.ip_hl < (sizeof(struct ip) >> 2)) {
544 			ICMPSTAT_INC(icps_badlen);
545 			goto freeit;
546 		}
547 		/* Discard ICMP's in response to multicast packets */
548 		if (IN_MULTICAST(ntohl(icp->icmp_ip.ip_dst.s_addr)))
549 			goto badcode;
550 #ifdef ICMPPRINTFS
551 		if (icmpprintfs)
552 			printf("deliver to protocol %d\n", icp->icmp_ip.ip_p);
553 #endif
554 		icmpsrc.sin_addr = icp->icmp_ip.ip_dst;
555 		/*
556 		 * XXX if the packet contains [IPv4 AH TCP], we can't make a
557 		 * notification to TCP layer.
558 		 */
559 		i = sizeof(struct ip) + min(icmplen, ICMP_ADVLENPREF(icp));
560 		ip_stripoptions(m);
561 		if (m->m_len < i && (m = m_pullup(m, i)) == NULL) {
562 			/* This should actually not happen */
563 			ICMPSTAT_INC(icps_tooshort);
564 			return (IPPROTO_DONE);
565 		}
566 		ip = mtod(m, struct ip *);
567 		icp = (struct icmp *)(ip + 1);
568 		/*
569 		 * The upper layer handler can rely on:
570 		 * - The outer IP header has no options.
571 		 * - The outer IP header, the ICMP header, the inner IP header,
572 		 *   and the first n bytes of the inner payload are contiguous.
573 		 *   n is at least 8, but might be larger based on
574 		 *   ICMP_ADVLENPREF. See its definition in ip_icmp.h.
575 		 */
576 		ctlfunc = inetsw[ip_protox[icp->icmp_ip.ip_p]].pr_ctlinput;
577 		if (ctlfunc)
578 			(*ctlfunc)(code, (struct sockaddr *)&icmpsrc,
579 				   (void *)&icp->icmp_ip);
580 		break;
581 
582 	badcode:
583 		ICMPSTAT_INC(icps_badcode);
584 		break;
585 
586 	case ICMP_ECHO:
587 		if (!V_icmpbmcastecho
588 		    && (m->m_flags & (M_MCAST | M_BCAST)) != 0) {
589 			ICMPSTAT_INC(icps_bmcastecho);
590 			break;
591 		}
592 		if (badport_bandlim(BANDLIM_ICMP_ECHO) < 0)
593 			goto freeit;
594 		icp->icmp_type = ICMP_ECHOREPLY;
595 		goto reflect;
596 
597 	case ICMP_TSTAMP:
598 		if (V_icmptstamprepl == 0)
599 			break;
600 		if (!V_icmpbmcastecho
601 		    && (m->m_flags & (M_MCAST | M_BCAST)) != 0) {
602 			ICMPSTAT_INC(icps_bmcasttstamp);
603 			break;
604 		}
605 		if (icmplen < ICMP_TSLEN) {
606 			ICMPSTAT_INC(icps_badlen);
607 			break;
608 		}
609 		if (badport_bandlim(BANDLIM_ICMP_TSTAMP) < 0)
610 			goto freeit;
611 		icp->icmp_type = ICMP_TSTAMPREPLY;
612 		icp->icmp_rtime = iptime();
613 		icp->icmp_ttime = icp->icmp_rtime;	/* bogus, do later! */
614 		goto reflect;
615 
616 	case ICMP_MASKREQ:
617 		if (V_icmpmaskrepl == 0)
618 			break;
619 		/*
620 		 * We are not able to respond with all ones broadcast
621 		 * unless we receive it over a point-to-point interface.
622 		 */
623 		if (icmplen < ICMP_MASKLEN)
624 			break;
625 		switch (ip->ip_dst.s_addr) {
626 		case INADDR_BROADCAST:
627 		case INADDR_ANY:
628 			icmpdst.sin_addr = ip->ip_src;
629 			break;
630 
631 		default:
632 			icmpdst.sin_addr = ip->ip_dst;
633 		}
634 		ia = (struct in_ifaddr *)ifaof_ifpforaddr(
635 			    (struct sockaddr *)&icmpdst, m->m_pkthdr.rcvif);
636 		if (ia == NULL)
637 			break;
638 		if (ia->ia_ifp == NULL)
639 			break;
640 		icp->icmp_type = ICMP_MASKREPLY;
641 		if (V_icmpmaskfake == 0)
642 			icp->icmp_mask = ia->ia_sockmask.sin_addr.s_addr;
643 		else
644 			icp->icmp_mask = V_icmpmaskfake;
645 		if (ip->ip_src.s_addr == 0) {
646 			if (ia->ia_ifp->if_flags & IFF_BROADCAST)
647 			    ip->ip_src = satosin(&ia->ia_broadaddr)->sin_addr;
648 			else if (ia->ia_ifp->if_flags & IFF_POINTOPOINT)
649 			    ip->ip_src = satosin(&ia->ia_dstaddr)->sin_addr;
650 		}
651 reflect:
652 		ICMPSTAT_INC(icps_reflect);
653 		ICMPSTAT_INC(icps_outhist[icp->icmp_type]);
654 		icmp_reflect(m);
655 		return (IPPROTO_DONE);
656 
657 	case ICMP_REDIRECT:
658 		if (V_log_redirect) {
659 			u_long src, dst, gw;
660 
661 			src = ntohl(ip->ip_src.s_addr);
662 			dst = ntohl(icp->icmp_ip.ip_dst.s_addr);
663 			gw = ntohl(icp->icmp_gwaddr.s_addr);
664 			printf("icmp redirect from %d.%d.%d.%d: "
665 			       "%d.%d.%d.%d => %d.%d.%d.%d\n",
666 			       (int)(src >> 24), (int)((src >> 16) & 0xff),
667 			       (int)((src >> 8) & 0xff), (int)(src & 0xff),
668 			       (int)(dst >> 24), (int)((dst >> 16) & 0xff),
669 			       (int)((dst >> 8) & 0xff), (int)(dst & 0xff),
670 			       (int)(gw >> 24), (int)((gw >> 16) & 0xff),
671 			       (int)((gw >> 8) & 0xff), (int)(gw & 0xff));
672 		}
673 		/*
674 		 * RFC1812 says we must ignore ICMP redirects if we
675 		 * are acting as router.
676 		 */
677 		if (V_drop_redirect || V_ipforwarding)
678 			break;
679 		if (code > 3)
680 			goto badcode;
681 		if (icmplen < ICMP_ADVLENMIN || icmplen < ICMP_ADVLEN(icp) ||
682 		    icp->icmp_ip.ip_hl < (sizeof(struct ip) >> 2)) {
683 			ICMPSTAT_INC(icps_badlen);
684 			break;
685 		}
686 		/*
687 		 * Short circuit routing redirects to force
688 		 * immediate change in the kernel's routing
689 		 * tables.  The message is also handed to anyone
690 		 * listening on a raw socket (e.g. the routing
691 		 * daemon for use in updating its tables).
692 		 */
693 		icmpgw.sin_addr = ip->ip_src;
694 		icmpdst.sin_addr = icp->icmp_gwaddr;
695 #ifdef	ICMPPRINTFS
696 		if (icmpprintfs) {
697 			char dstbuf[INET_ADDRSTRLEN];
698 			char gwbuf[INET_ADDRSTRLEN];
699 
700 			printf("redirect dst %s to %s\n",
701 			       inet_ntoa_r(icp->icmp_ip.ip_dst, dstbuf),
702 			       inet_ntoa_r(icp->icmp_gwaddr, gwbuf));
703 		}
704 #endif
705 		icmpsrc.sin_addr = icp->icmp_ip.ip_dst;
706 
707 		/*
708 		 * RFC 1122 says network (code 0,2) redirects SHOULD
709 		 * be treated identically to the host redirects.
710 		 * Given that, ignore network masks.
711 		 */
712 
713 		/*
714 		 * Variable values:
715 		 * icmpsrc: route destination
716 		 * icmpdst: route gateway
717 		 * icmpgw: message source
718 		 */
719 
720 		if (icmp_verify_redirect_gateway(&icmpgw, &icmpsrc, &icmpdst,
721 		    M_GETFIB(m)) != 0) {
722 			/* TODO: increment bad redirects here */
723 			break;
724 		}
725 
726 		for ( fibnum = 0; fibnum < rt_numfibs; fibnum++) {
727 			rib_add_redirect(fibnum, (struct sockaddr *)&icmpsrc,
728 			    (struct sockaddr *)&icmpdst,
729 			    (struct sockaddr *)&icmpgw, m->m_pkthdr.rcvif,
730 			    RTF_GATEWAY, V_redirtimeout);
731 		}
732 		break;
733 
734 	/*
735 	 * No kernel processing for the following;
736 	 * just fall through to send to raw listener.
737 	 */
738 	case ICMP_ECHOREPLY:
739 	case ICMP_ROUTERADVERT:
740 	case ICMP_ROUTERSOLICIT:
741 	case ICMP_TSTAMPREPLY:
742 	case ICMP_IREQREPLY:
743 	case ICMP_MASKREPLY:
744 	case ICMP_SOURCEQUENCH:
745 	default:
746 		break;
747 	}
748 
749 raw:
750 	*mp = m;
751 	rip_input(mp, offp, proto);
752 	return (IPPROTO_DONE);
753 
754 freeit:
755 	m_freem(m);
756 	return (IPPROTO_DONE);
757 }
758 
759 /*
760  * Reflect the ip packet back to the source
761  */
762 static void
763 icmp_reflect(struct mbuf *m)
764 {
765 	struct ip *ip = mtod(m, struct ip *);
766 	struct ifaddr *ifa;
767 	struct ifnet *ifp;
768 	struct in_ifaddr *ia;
769 	struct in_addr t;
770 	struct nhop_object *nh;
771 	struct mbuf *opts = NULL;
772 	int optlen = (ip->ip_hl << 2) - sizeof(struct ip);
773 
774 	NET_EPOCH_ASSERT();
775 
776 	if (IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
777 	    (IN_EXPERIMENTAL(ntohl(ip->ip_src.s_addr)) && !V_ip_allow_net240) ||
778 	    (IN_ZERONET(ntohl(ip->ip_src.s_addr)) && !V_ip_allow_net0) ) {
779 		m_freem(m);	/* Bad return address */
780 		ICMPSTAT_INC(icps_badaddr);
781 		goto done;	/* Ip_output() will check for broadcast */
782 	}
783 
784 	t = ip->ip_dst;
785 	ip->ip_dst = ip->ip_src;
786 
787 	/*
788 	 * Source selection for ICMP replies:
789 	 *
790 	 * If the incoming packet was addressed directly to one of our
791 	 * own addresses, use dst as the src for the reply.
792 	 */
793 	CK_LIST_FOREACH(ia, INADDR_HASH(t.s_addr), ia_hash) {
794 		if (t.s_addr == IA_SIN(ia)->sin_addr.s_addr) {
795 			t = IA_SIN(ia)->sin_addr;
796 			goto match;
797 		}
798 	}
799 
800 	/*
801 	 * If the incoming packet was addressed to one of our broadcast
802 	 * addresses, use the first non-broadcast address which corresponds
803 	 * to the incoming interface.
804 	 */
805 	ifp = m->m_pkthdr.rcvif;
806 	if (ifp != NULL && ifp->if_flags & IFF_BROADCAST) {
807 		CK_STAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link) {
808 			if (ifa->ifa_addr->sa_family != AF_INET)
809 				continue;
810 			ia = ifatoia(ifa);
811 			if (satosin(&ia->ia_broadaddr)->sin_addr.s_addr ==
812 			    t.s_addr) {
813 				t = IA_SIN(ia)->sin_addr;
814 				goto match;
815 			}
816 		}
817 	}
818 	/*
819 	 * If the packet was transiting through us, use the address of
820 	 * the interface the packet came through in.  If that interface
821 	 * doesn't have a suitable IP address, the normal selection
822 	 * criteria apply.
823 	 */
824 	if (V_icmp_rfi && ifp != NULL) {
825 		CK_STAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link) {
826 			if (ifa->ifa_addr->sa_family != AF_INET)
827 				continue;
828 			ia = ifatoia(ifa);
829 			t = IA_SIN(ia)->sin_addr;
830 			goto match;
831 		}
832 	}
833 	/*
834 	 * If the incoming packet was not addressed directly to us, use
835 	 * designated interface for icmp replies specified by sysctl
836 	 * net.inet.icmp.reply_src (default not set). Otherwise continue
837 	 * with normal source selection.
838 	 */
839 	if (V_reply_src[0] != '\0' && (ifp = ifunit(V_reply_src))) {
840 		CK_STAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link) {
841 			if (ifa->ifa_addr->sa_family != AF_INET)
842 				continue;
843 			ia = ifatoia(ifa);
844 			t = IA_SIN(ia)->sin_addr;
845 			goto match;
846 		}
847 	}
848 	/*
849 	 * If the packet was transiting through us, use the address of
850 	 * the interface that is the closest to the packet source.
851 	 * When we don't have a route back to the packet source, stop here
852 	 * and drop the packet.
853 	 */
854 	nh = fib4_lookup(M_GETFIB(m), ip->ip_dst, 0, NHR_NONE, 0);
855 	if (nh == NULL) {
856 		m_freem(m);
857 		ICMPSTAT_INC(icps_noroute);
858 		goto done;
859 	}
860 	t = IA_SIN(ifatoia(nh->nh_ifa))->sin_addr;
861 match:
862 #ifdef MAC
863 	mac_netinet_icmp_replyinplace(m);
864 #endif
865 	ip->ip_src = t;
866 	ip->ip_ttl = V_ip_defttl;
867 
868 	if (optlen > 0) {
869 		u_char *cp;
870 		int opt, cnt;
871 		u_int len;
872 
873 		/*
874 		 * Retrieve any source routing from the incoming packet;
875 		 * add on any record-route or timestamp options.
876 		 */
877 		cp = (u_char *) (ip + 1);
878 		if ((opts = ip_srcroute(m)) == NULL &&
879 		    (opts = m_gethdr(M_NOWAIT, MT_DATA))) {
880 			opts->m_len = sizeof(struct in_addr);
881 			mtod(opts, struct in_addr *)->s_addr = 0;
882 		}
883 		if (opts) {
884 #ifdef ICMPPRINTFS
885 		    if (icmpprintfs)
886 			    printf("icmp_reflect optlen %d rt %d => ",
887 				optlen, opts->m_len);
888 #endif
889 		    for (cnt = optlen; cnt > 0; cnt -= len, cp += len) {
890 			    opt = cp[IPOPT_OPTVAL];
891 			    if (opt == IPOPT_EOL)
892 				    break;
893 			    if (opt == IPOPT_NOP)
894 				    len = 1;
895 			    else {
896 				    if (cnt < IPOPT_OLEN + sizeof(*cp))
897 					    break;
898 				    len = cp[IPOPT_OLEN];
899 				    if (len < IPOPT_OLEN + sizeof(*cp) ||
900 				        len > cnt)
901 					    break;
902 			    }
903 			    /*
904 			     * Should check for overflow, but it "can't happen"
905 			     */
906 			    if (opt == IPOPT_RR || opt == IPOPT_TS ||
907 				opt == IPOPT_SECURITY) {
908 				    bcopy((caddr_t)cp,
909 					mtod(opts, caddr_t) + opts->m_len, len);
910 				    opts->m_len += len;
911 			    }
912 		    }
913 		    /* Terminate & pad, if necessary */
914 		    cnt = opts->m_len % 4;
915 		    if (cnt) {
916 			    for (; cnt < 4; cnt++) {
917 				    *(mtod(opts, caddr_t) + opts->m_len) =
918 					IPOPT_EOL;
919 				    opts->m_len++;
920 			    }
921 		    }
922 #ifdef ICMPPRINTFS
923 		    if (icmpprintfs)
924 			    printf("%d\n", opts->m_len);
925 #endif
926 		}
927 		ip_stripoptions(m);
928 	}
929 	m_tag_delete_nonpersistent(m);
930 	m->m_flags &= ~(M_BCAST|M_MCAST);
931 	icmp_send(m, opts);
932 done:
933 	if (opts)
934 		(void)m_free(opts);
935 }
936 
937 /*
938  * Verifies if redirect message is valid, according to RFC 1122
939  *
940  * @src: sockaddr with address of redirect originator
941  * @dst: sockaddr with destination in question
942  * @gateway: new proposed gateway
943  *
944  * Returns 0 on success.
945  */
946 static int
947 icmp_verify_redirect_gateway(struct sockaddr_in *src, struct sockaddr_in *dst,
948     struct sockaddr_in *gateway, u_int fibnum)
949 {
950 	struct nhop_object *nh;
951 	struct ifaddr *ifa;
952 
953 	NET_EPOCH_ASSERT();
954 
955 	/* Verify the gateway is directly reachable. */
956 	if ((ifa = ifa_ifwithnet((struct sockaddr *)gateway, 0, fibnum))==NULL)
957 		return (ENETUNREACH);
958 
959 	/* TODO: fib-aware. */
960 	if (ifa_ifwithaddr_check((struct sockaddr *)gateway))
961 		return (EHOSTUNREACH);
962 
963 	nh = fib4_lookup(fibnum, dst->sin_addr, 0, NHR_NONE, 0);
964 	if (nh == NULL)
965 		return (EINVAL);
966 
967 	/*
968 	 * If the redirect isn't from our current router for this dst,
969 	 * it's either old or wrong.  If it redirects us to ourselves,
970 	 * we have a routing loop, perhaps as a result of an interface
971 	 * going down recently.
972 	 */
973 	if (!sa_equal((struct sockaddr *)src, &nh->gw_sa))
974 		return (EINVAL);
975 	if (nh->nh_ifa != ifa && ifa->ifa_addr->sa_family != AF_LINK)
976 		return (EINVAL);
977 
978 	/* If host route already exists, ignore redirect. */
979 	if (nh->nh_flags & NHF_HOST)
980 		return (EEXIST);
981 
982 	/* If the prefix is directly reachable, ignore redirect. */
983 	if (!(nh->nh_flags & NHF_GATEWAY))
984 		return (EEXIST);
985 
986 	return (0);
987 }
988 
989 /*
990  * Send an icmp packet back to the ip level,
991  * after supplying a checksum.
992  */
993 static void
994 icmp_send(struct mbuf *m, struct mbuf *opts)
995 {
996 	struct ip *ip = mtod(m, struct ip *);
997 	int hlen;
998 	struct icmp *icp;
999 
1000 	hlen = ip->ip_hl << 2;
1001 	m->m_data += hlen;
1002 	m->m_len -= hlen;
1003 	icp = mtod(m, struct icmp *);
1004 	icp->icmp_cksum = 0;
1005 	icp->icmp_cksum = in_cksum(m, ntohs(ip->ip_len) - hlen);
1006 	m->m_data -= hlen;
1007 	m->m_len += hlen;
1008 	m->m_pkthdr.rcvif = (struct ifnet *)0;
1009 #ifdef ICMPPRINTFS
1010 	if (icmpprintfs) {
1011 		char dstbuf[INET_ADDRSTRLEN];
1012 		char srcbuf[INET_ADDRSTRLEN];
1013 
1014 		printf("icmp_send dst %s src %s\n",
1015 		    inet_ntoa_r(ip->ip_dst, dstbuf),
1016 		    inet_ntoa_r(ip->ip_src, srcbuf));
1017 	}
1018 #endif
1019 	(void) ip_output(m, opts, NULL, 0, NULL, NULL);
1020 }
1021 
1022 /*
1023  * Return milliseconds since 00:00 UTC in network format.
1024  */
1025 uint32_t
1026 iptime(void)
1027 {
1028 	struct timeval atv;
1029 	u_long t;
1030 
1031 	getmicrotime(&atv);
1032 	t = (atv.tv_sec % (24*60*60)) * 1000 + atv.tv_usec / 1000;
1033 	return (htonl(t));
1034 }
1035 
1036 /*
1037  * Return the next larger or smaller MTU plateau (table from RFC 1191)
1038  * given current value MTU.  If DIR is less than zero, a larger plateau
1039  * is returned; otherwise, a smaller value is returned.
1040  */
1041 int
1042 ip_next_mtu(int mtu, int dir)
1043 {
1044 	static int mtutab[] = {
1045 		65535, 32000, 17914, 8166, 4352, 2002, 1492, 1280, 1006, 508,
1046 		296, 68, 0
1047 	};
1048 	int i, size;
1049 
1050 	size = (sizeof mtutab) / (sizeof mtutab[0]);
1051 	if (dir >= 0) {
1052 		for (i = 0; i < size; i++)
1053 			if (mtu > mtutab[i])
1054 				return mtutab[i];
1055 	} else {
1056 		for (i = size - 1; i >= 0; i--)
1057 			if (mtu < mtutab[i])
1058 				return mtutab[i];
1059 		if (mtu == mtutab[0])
1060 			return mtutab[0];
1061 	}
1062 	return 0;
1063 }
1064 #endif /* INET */
1065 
1066 /*
1067  * badport_bandlim() - check for ICMP bandwidth limit
1068  *
1069  *	Return 0 if it is ok to send an ICMP error response, -1 if we have
1070  *	hit our bandwidth limit and it is not ok.
1071  *
1072  *	If icmplim is <= 0, the feature is disabled and 0 is returned.
1073  *
1074  *	For now we separate the TCP and UDP subsystems w/ different 'which'
1075  *	values.  We may eventually remove this separation (and simplify the
1076  *	code further).
1077  *
1078  *	Note that the printing of the error message is delayed so we can
1079  *	properly print the icmp error rate that the system was trying to do
1080  *	(i.e. 22000/100 pps, etc...).  This can cause long delays in printing
1081  *	the 'final' error, but it doesn't make sense to solve the printing
1082  *	delay with more complex code.
1083  */
1084 struct icmp_rate {
1085 	const char *descr;
1086 	struct counter_rate cr;
1087 };
1088 VNET_DEFINE_STATIC(struct icmp_rate, icmp_rates[BANDLIM_MAX]) = {
1089 	{ "icmp unreach response" },
1090 	{ "icmp ping response" },
1091 	{ "icmp tstamp response" },
1092 	{ "closed port RST response" },
1093 	{ "open port RST response" },
1094 	{ "icmp6 unreach response" },
1095 	{ "sctp ootb response" }
1096 };
1097 #define	V_icmp_rates	VNET(icmp_rates)
1098 
1099 static void
1100 icmp_bandlimit_init(void)
1101 {
1102 
1103 	for (int i = 0; i < BANDLIM_MAX; i++) {
1104 		V_icmp_rates[i].cr.cr_rate = counter_u64_alloc(M_WAITOK);
1105 		V_icmp_rates[i].cr.cr_ticks = ticks;
1106 	}
1107 }
1108 VNET_SYSINIT(icmp_bandlimit, SI_SUB_PROTO_DOMAIN, SI_ORDER_ANY,
1109     icmp_bandlimit_init, NULL);
1110 
1111 static void
1112 icmp_bandlimit_uninit(void)
1113 {
1114 
1115 	for (int i = 0; i < BANDLIM_MAX; i++)
1116 		counter_u64_free(V_icmp_rates[i].cr.cr_rate);
1117 }
1118 VNET_SYSUNINIT(icmp_bandlimit, SI_SUB_PROTO_DOMAIN, SI_ORDER_THIRD,
1119     icmp_bandlimit_uninit, NULL);
1120 
1121 int
1122 badport_bandlim(int which)
1123 {
1124 	int64_t pps;
1125 
1126 	if (V_icmplim == 0 || which == BANDLIM_UNLIMITED)
1127 		return (0);
1128 
1129 	KASSERT(which >= 0 && which < BANDLIM_MAX,
1130 	    ("%s: which %d", __func__, which));
1131 
1132 	if ((V_icmplim + V_icmplim_curr_jitter) <= 0)
1133 		V_icmplim_curr_jitter = -V_icmplim + 1;
1134 
1135 	pps = counter_ratecheck(&V_icmp_rates[which].cr, V_icmplim +
1136 	    V_icmplim_curr_jitter);
1137 	if (pps > 0) {
1138 		/*
1139 		 * Adjust limit +/- to jitter the measurement to deny a
1140 		 * side-channel port scan as in CVE-2020-25705
1141 		 */
1142 		if (V_icmplim_jitter > 0) {
1143 			int32_t inc =
1144 			    arc4random_uniform(V_icmplim_jitter * 2 +1)
1145 			    - V_icmplim_jitter;
1146 
1147 			V_icmplim_curr_jitter = inc;
1148 		}
1149 	}
1150 	if (pps == -1)
1151 		return (-1);
1152 	if (pps > 0 && V_icmplim_output)
1153 		log(LOG_NOTICE, "Limiting %s from %jd to %d packets/sec\n",
1154 		    V_icmp_rates[which].descr, (intmax_t )pps, V_icmplim +
1155 		    V_icmplim_curr_jitter);
1156 	return (0);
1157 }
1158