xref: /freebsd/sys/netpfil/pf/pf_osfp.c (revision 38f0b757fd84d17d0fc24739a7cda160c4516d81) 
1 /*-
2  * Copyright (c) 2003 Mike Frantzen <frantzen@w4g.org>
3  *
4  * Permission to use, copy, modify, and distribute this software for any
5  * purpose with or without fee is hereby granted, provided that the above
6  * copyright notice and this permission notice appear in all copies.
7  *
8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15  *
16  *	$OpenBSD: pf_osfp.c,v 1.14 2008/06/12 18:17:01 henning Exp $
17  */
18 
19 #include <sys/cdefs.h>
20 __FBSDID("$FreeBSD$");
21 
22 #include <sys/param.h>
23 #include <sys/kernel.h>
24 #include <sys/lock.h>
25 #include <sys/mbuf.h>
26 #include <sys/rwlock.h>
27 #include <sys/socket.h>
28 
29 #include <netinet/in.h>
30 #include <netinet/ip.h>
31 #include <netinet/tcp.h>
32 
33 #include <net/if.h>
34 #include <net/vnet.h>
35 #include <net/pfvar.h>
36 
37 #include <netinet/ip6.h>
38 
39 static MALLOC_DEFINE(M_PFOSFP, "pf_osfp", "pf(4) operating system fingerprints");
40 #define	DPFPRINTF(format, x...)		\
41 	if (V_pf_status.debug >= PF_DEBUG_NOISY)	\
42 		printf(format , ##x)
43 
44 SLIST_HEAD(pf_osfp_list, pf_os_fingerprint);
45 static VNET_DEFINE(struct pf_osfp_list,	pf_osfp_list) =
46 	SLIST_HEAD_INITIALIZER();
47 #define	V_pf_osfp_list			VNET(pf_osfp_list)
48 
49 static struct pf_osfp_enlist	*pf_osfp_fingerprint_hdr(const struct ip *,
50 				    const struct ip6_hdr *,
51 				    const struct tcphdr *);
52 static struct pf_os_fingerprint	*pf_osfp_find(struct pf_osfp_list *,
53 				    struct pf_os_fingerprint *, u_int8_t);
54 static struct pf_os_fingerprint	*pf_osfp_find_exact(struct pf_osfp_list *,
55 				    struct pf_os_fingerprint *);
56 static void			 pf_osfp_insert(struct pf_osfp_list *,
57 				    struct pf_os_fingerprint *);
58 #ifdef PFDEBUG
59 static struct pf_os_fingerprint	*pf_osfp_validate(void);
60 #endif
61 
62 /*
63  * Passively fingerprint the OS of the host (IPv4 TCP SYN packets only)
64  * Returns the list of possible OSes.
65  */
66 struct pf_osfp_enlist *
67 pf_osfp_fingerprint(struct pf_pdesc *pd, struct mbuf *m, int off,
68     const struct tcphdr *tcp)
69 {
70 	struct ip *ip;
71 	struct ip6_hdr *ip6;
72 	char hdr[60];
73 
74 	if ((pd->af != PF_INET && pd->af != PF_INET6) ||
75 	    pd->proto != IPPROTO_TCP || (tcp->th_off << 2) < sizeof(*tcp))
76 		return (NULL);
77 
78 	if (pd->af == PF_INET) {
79 		ip = mtod(m, struct ip *);
80 		ip6 = (struct ip6_hdr *)NULL;
81 	} else {
82 		ip = (struct ip *)NULL;
83 		ip6 = mtod(m, struct ip6_hdr *);
84 	}
85 	if (!pf_pull_hdr(m, off, hdr, tcp->th_off << 2, NULL, NULL,
86 	    pd->af)) return (NULL);
87 
88 	return (pf_osfp_fingerprint_hdr(ip, ip6, (struct tcphdr *)hdr));
89 }
90 
91 static struct pf_osfp_enlist *
92 pf_osfp_fingerprint_hdr(const struct ip *ip, const struct ip6_hdr *ip6, const struct tcphdr *tcp)
93 {
94 	struct pf_os_fingerprint fp, *fpresult;
95 	int cnt, optlen = 0;
96 	const u_int8_t *optp;
97 	char srcname[128];
98 
99 	if ((tcp->th_flags & (TH_SYN|TH_ACK)) != TH_SYN)
100 		return (NULL);
101 	if (ip) {
102 		if ((ip->ip_off & htons(IP_OFFMASK)) != 0)
103 			return (NULL);
104 	}
105 
106 	memset(&fp, 0, sizeof(fp));
107 
108 	if (ip) {
109 		fp.fp_psize = ntohs(ip->ip_len);
110 		fp.fp_ttl = ip->ip_ttl;
111 		if (ip->ip_off & htons(IP_DF))
112 			fp.fp_flags |= PF_OSFP_DF;
113 		strlcpy(srcname, inet_ntoa(ip->ip_src), sizeof(srcname));
114 	}
115 #ifdef INET6
116 	else if (ip6) {
117 		/* jumbo payload? */
118 		fp.fp_psize = sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen);
119 		fp.fp_ttl = ip6->ip6_hlim;
120 		fp.fp_flags |= PF_OSFP_DF;
121 		fp.fp_flags |= PF_OSFP_INET6;
122 		strlcpy(srcname, ip6_sprintf((struct in6_addr *)&ip6->ip6_src),
123 		    sizeof(srcname));
124 	}
125 #endif
126 	else
127 		return (NULL);
128 	fp.fp_wsize = ntohs(tcp->th_win);
129 
130 
131 	cnt = (tcp->th_off << 2) - sizeof(*tcp);
132 	optp = (const u_int8_t *)((const char *)tcp + sizeof(*tcp));
133 	for (; cnt > 0; cnt -= optlen, optp += optlen) {
134 		if (*optp == TCPOPT_EOL)
135 			break;
136 
137 		fp.fp_optcnt++;
138 		if (*optp == TCPOPT_NOP) {
139 			fp.fp_tcpopts = (fp.fp_tcpopts << PF_OSFP_TCPOPT_BITS) |
140 			    PF_OSFP_TCPOPT_NOP;
141 			optlen = 1;
142 		} else {
143 			if (cnt < 2)
144 				return (NULL);
145 			optlen = optp[1];
146 			if (optlen > cnt || optlen < 2)
147 				return (NULL);
148 			switch (*optp) {
149 			case TCPOPT_MAXSEG:
150 				if (optlen >= TCPOLEN_MAXSEG)
151 					memcpy(&fp.fp_mss, &optp[2],
152 					    sizeof(fp.fp_mss));
153 				fp.fp_tcpopts = (fp.fp_tcpopts <<
154 				    PF_OSFP_TCPOPT_BITS) | PF_OSFP_TCPOPT_MSS;
155 				NTOHS(fp.fp_mss);
156 				break;
157 			case TCPOPT_WINDOW:
158 				if (optlen >= TCPOLEN_WINDOW)
159 					memcpy(&fp.fp_wscale, &optp[2],
160 					    sizeof(fp.fp_wscale));
161 				NTOHS(fp.fp_wscale);
162 				fp.fp_tcpopts = (fp.fp_tcpopts <<
163 				    PF_OSFP_TCPOPT_BITS) |
164 				    PF_OSFP_TCPOPT_WSCALE;
165 				break;
166 			case TCPOPT_SACK_PERMITTED:
167 				fp.fp_tcpopts = (fp.fp_tcpopts <<
168 				    PF_OSFP_TCPOPT_BITS) | PF_OSFP_TCPOPT_SACK;
169 				break;
170 			case TCPOPT_TIMESTAMP:
171 				if (optlen >= TCPOLEN_TIMESTAMP) {
172 					u_int32_t ts;
173 					memcpy(&ts, &optp[2], sizeof(ts));
174 					if (ts == 0)
175 						fp.fp_flags |= PF_OSFP_TS0;
176 
177 				}
178 				fp.fp_tcpopts = (fp.fp_tcpopts <<
179 				    PF_OSFP_TCPOPT_BITS) | PF_OSFP_TCPOPT_TS;
180 				break;
181 			default:
182 				return (NULL);
183 			}
184 		}
185 		optlen = MAX(optlen, 1);	/* paranoia */
186 	}
187 
188 	DPFPRINTF("fingerprinted %s:%d  %d:%d:%d:%d:%llx (%d) "
189 	    "(TS=%s,M=%s%d,W=%s%d)\n",
190 	    srcname, ntohs(tcp->th_sport),
191 	    fp.fp_wsize, fp.fp_ttl, (fp.fp_flags & PF_OSFP_DF) != 0,
192 	    fp.fp_psize, (long long int)fp.fp_tcpopts, fp.fp_optcnt,
193 	    (fp.fp_flags & PF_OSFP_TS0) ? "0" : "",
194 	    (fp.fp_flags & PF_OSFP_MSS_MOD) ? "%" :
195 	    (fp.fp_flags & PF_OSFP_MSS_DC) ? "*" : "",
196 	    fp.fp_mss,
197 	    (fp.fp_flags & PF_OSFP_WSCALE_MOD) ? "%" :
198 	    (fp.fp_flags & PF_OSFP_WSCALE_DC) ? "*" : "",
199 	    fp.fp_wscale);
200 
201 	if ((fpresult = pf_osfp_find(&V_pf_osfp_list, &fp,
202 	    PF_OSFP_MAXTTL_OFFSET)))
203 		return (&fpresult->fp_oses);
204 	return (NULL);
205 }
206 
207 /* Match a fingerprint ID against a list of OSes */
208 int
209 pf_osfp_match(struct pf_osfp_enlist *list, pf_osfp_t os)
210 {
211 	struct pf_osfp_entry *entry;
212 	int os_class, os_version, os_subtype;
213 	int en_class, en_version, en_subtype;
214 
215 	if (os == PF_OSFP_ANY)
216 		return (1);
217 	if (list == NULL) {
218 		DPFPRINTF("osfp no match against %x\n", os);
219 		return (os == PF_OSFP_UNKNOWN);
220 	}
221 	PF_OSFP_UNPACK(os, os_class, os_version, os_subtype);
222 	SLIST_FOREACH(entry, list, fp_entry) {
223 		PF_OSFP_UNPACK(entry->fp_os, en_class, en_version, en_subtype);
224 		if ((os_class == PF_OSFP_ANY || en_class == os_class) &&
225 		    (os_version == PF_OSFP_ANY || en_version == os_version) &&
226 		    (os_subtype == PF_OSFP_ANY || en_subtype == os_subtype)) {
227 			DPFPRINTF("osfp matched %s %s %s  %x==%x\n",
228 			    entry->fp_class_nm, entry->fp_version_nm,
229 			    entry->fp_subtype_nm, os, entry->fp_os);
230 			return (1);
231 		}
232 	}
233 	DPFPRINTF("fingerprint 0x%x didn't match\n", os);
234 	return (0);
235 }
236 
237 /* Flush the fingerprint list */
238 void
239 pf_osfp_flush(void)
240 {
241 	struct pf_os_fingerprint *fp;
242 	struct pf_osfp_entry *entry;
243 
244 	while ((fp = SLIST_FIRST(&V_pf_osfp_list))) {
245 		SLIST_REMOVE_HEAD(&V_pf_osfp_list, fp_next);
246 		while ((entry = SLIST_FIRST(&fp->fp_oses))) {
247 			SLIST_REMOVE_HEAD(&fp->fp_oses, fp_entry);
248 			free(entry, M_PFOSFP);
249 		}
250 		free(fp, M_PFOSFP);
251 	}
252 }
253 
254 
255 /* Add a fingerprint */
256 int
257 pf_osfp_add(struct pf_osfp_ioctl *fpioc)
258 {
259 	struct pf_os_fingerprint *fp, fpadd;
260 	struct pf_osfp_entry *entry;
261 
262 	PF_RULES_WASSERT();
263 
264 	memset(&fpadd, 0, sizeof(fpadd));
265 	fpadd.fp_tcpopts = fpioc->fp_tcpopts;
266 	fpadd.fp_wsize = fpioc->fp_wsize;
267 	fpadd.fp_psize = fpioc->fp_psize;
268 	fpadd.fp_mss = fpioc->fp_mss;
269 	fpadd.fp_flags = fpioc->fp_flags;
270 	fpadd.fp_optcnt = fpioc->fp_optcnt;
271 	fpadd.fp_wscale = fpioc->fp_wscale;
272 	fpadd.fp_ttl = fpioc->fp_ttl;
273 
274 #if 0	/* XXX RYAN wants to fix logging */
275 	DPFPRINTF("adding osfp %s %s %s = %s%d:%d:%d:%s%d:0x%llx %d "
276 	    "(TS=%s,M=%s%d,W=%s%d) %x\n",
277 	    fpioc->fp_os.fp_class_nm, fpioc->fp_os.fp_version_nm,
278 	    fpioc->fp_os.fp_subtype_nm,
279 	    (fpadd.fp_flags & PF_OSFP_WSIZE_MOD) ? "%" :
280 	    (fpadd.fp_flags & PF_OSFP_WSIZE_MSS) ? "S" :
281 	    (fpadd.fp_flags & PF_OSFP_WSIZE_MTU) ? "T" :
282 	    (fpadd.fp_flags & PF_OSFP_WSIZE_DC) ? "*" : "",
283 	    fpadd.fp_wsize,
284 	    fpadd.fp_ttl,
285 	    (fpadd.fp_flags & PF_OSFP_DF) ? 1 : 0,
286 	    (fpadd.fp_flags & PF_OSFP_PSIZE_MOD) ? "%" :
287 	    (fpadd.fp_flags & PF_OSFP_PSIZE_DC) ? "*" : "",
288 	    fpadd.fp_psize,
289 	    (long long int)fpadd.fp_tcpopts, fpadd.fp_optcnt,
290 	    (fpadd.fp_flags & PF_OSFP_TS0) ? "0" : "",
291 	    (fpadd.fp_flags & PF_OSFP_MSS_MOD) ? "%" :
292 	    (fpadd.fp_flags & PF_OSFP_MSS_DC) ? "*" : "",
293 	    fpadd.fp_mss,
294 	    (fpadd.fp_flags & PF_OSFP_WSCALE_MOD) ? "%" :
295 	    (fpadd.fp_flags & PF_OSFP_WSCALE_DC) ? "*" : "",
296 	    fpadd.fp_wscale,
297 	    fpioc->fp_os.fp_os);
298 #endif
299 
300 	if ((fp = pf_osfp_find_exact(&V_pf_osfp_list, &fpadd))) {
301 		 SLIST_FOREACH(entry, &fp->fp_oses, fp_entry) {
302 			if (PF_OSFP_ENTRY_EQ(entry, &fpioc->fp_os))
303 				return (EEXIST);
304 		}
305 		if ((entry = malloc(sizeof(*entry), M_PFOSFP, M_NOWAIT))
306 		    == NULL)
307 			return (ENOMEM);
308 	} else {
309 		if ((fp = malloc(sizeof(*fp), M_PFOSFP, M_ZERO | M_NOWAIT))
310 		    == NULL)
311 			return (ENOMEM);
312 		fp->fp_tcpopts = fpioc->fp_tcpopts;
313 		fp->fp_wsize = fpioc->fp_wsize;
314 		fp->fp_psize = fpioc->fp_psize;
315 		fp->fp_mss = fpioc->fp_mss;
316 		fp->fp_flags = fpioc->fp_flags;
317 		fp->fp_optcnt = fpioc->fp_optcnt;
318 		fp->fp_wscale = fpioc->fp_wscale;
319 		fp->fp_ttl = fpioc->fp_ttl;
320 		SLIST_INIT(&fp->fp_oses);
321 		if ((entry = malloc(sizeof(*entry), M_PFOSFP, M_NOWAIT))
322 		    == NULL) {
323 			free(fp, M_PFOSFP);
324 			return (ENOMEM);
325 		}
326 		pf_osfp_insert(&V_pf_osfp_list, fp);
327 	}
328 	memcpy(entry, &fpioc->fp_os, sizeof(*entry));
329 
330 	/* Make sure the strings are NUL terminated */
331 	entry->fp_class_nm[sizeof(entry->fp_class_nm)-1] = '\0';
332 	entry->fp_version_nm[sizeof(entry->fp_version_nm)-1] = '\0';
333 	entry->fp_subtype_nm[sizeof(entry->fp_subtype_nm)-1] = '\0';
334 
335 	SLIST_INSERT_HEAD(&fp->fp_oses, entry, fp_entry);
336 
337 #ifdef PFDEBUG
338 	if ((fp = pf_osfp_validate()))
339 		printf("Invalid fingerprint list\n");
340 #endif /* PFDEBUG */
341 	return (0);
342 }
343 
344 
345 /* Find a fingerprint in the list */
346 static struct pf_os_fingerprint *
347 pf_osfp_find(struct pf_osfp_list *list, struct pf_os_fingerprint *find,
348     u_int8_t ttldiff)
349 {
350 	struct pf_os_fingerprint *f;
351 
352 #define	MATCH_INT(_MOD, _DC, _field)					\
353 	if ((f->fp_flags & _DC) == 0) {					\
354 		if ((f->fp_flags & _MOD) == 0) {			\
355 			if (f->_field != find->_field)			\
356 				continue;				\
357 		} else {						\
358 			if (f->_field == 0 || find->_field % f->_field)	\
359 				continue;				\
360 		}							\
361 	}
362 
363 	SLIST_FOREACH(f, list, fp_next) {
364 		if (f->fp_tcpopts != find->fp_tcpopts ||
365 		    f->fp_optcnt != find->fp_optcnt ||
366 		    f->fp_ttl < find->fp_ttl ||
367 		    f->fp_ttl - find->fp_ttl > ttldiff ||
368 		    (f->fp_flags & (PF_OSFP_DF|PF_OSFP_TS0)) !=
369 		    (find->fp_flags & (PF_OSFP_DF|PF_OSFP_TS0)))
370 			continue;
371 
372 		MATCH_INT(PF_OSFP_PSIZE_MOD, PF_OSFP_PSIZE_DC, fp_psize)
373 		MATCH_INT(PF_OSFP_MSS_MOD, PF_OSFP_MSS_DC, fp_mss)
374 		MATCH_INT(PF_OSFP_WSCALE_MOD, PF_OSFP_WSCALE_DC, fp_wscale)
375 		if ((f->fp_flags & PF_OSFP_WSIZE_DC) == 0) {
376 			if (f->fp_flags & PF_OSFP_WSIZE_MSS) {
377 				if (find->fp_mss == 0)
378 					continue;
379 
380 /*
381  * Some "smart" NAT devices and DSL routers will tweak the MSS size and
382  * will set it to whatever is suitable for the link type.
383  */
384 #define	SMART_MSS	1460
385 				if ((find->fp_wsize % find->fp_mss ||
386 				    find->fp_wsize / find->fp_mss !=
387 				    f->fp_wsize) &&
388 				    (find->fp_wsize % SMART_MSS ||
389 				    find->fp_wsize / SMART_MSS !=
390 				    f->fp_wsize))
391 					continue;
392 			} else if (f->fp_flags & PF_OSFP_WSIZE_MTU) {
393 				if (find->fp_mss == 0)
394 					continue;
395 
396 #define	MTUOFF		(sizeof(struct ip) + sizeof(struct tcphdr))
397 #define	SMART_MTU	(SMART_MSS + MTUOFF)
398 				if ((find->fp_wsize % (find->fp_mss + MTUOFF) ||
399 				    find->fp_wsize / (find->fp_mss + MTUOFF) !=
400 				    f->fp_wsize) &&
401 				    (find->fp_wsize % SMART_MTU ||
402 				    find->fp_wsize / SMART_MTU !=
403 				    f->fp_wsize))
404 					continue;
405 			} else if (f->fp_flags & PF_OSFP_WSIZE_MOD) {
406 				if (f->fp_wsize == 0 || find->fp_wsize %
407 				    f->fp_wsize)
408 					continue;
409 			} else {
410 				if (f->fp_wsize != find->fp_wsize)
411 					continue;
412 			}
413 		}
414 		return (f);
415 	}
416 
417 	return (NULL);
418 }
419 
420 /* Find an exact fingerprint in the list */
421 static struct pf_os_fingerprint *
422 pf_osfp_find_exact(struct pf_osfp_list *list, struct pf_os_fingerprint *find)
423 {
424 	struct pf_os_fingerprint *f;
425 
426 	SLIST_FOREACH(f, list, fp_next) {
427 		if (f->fp_tcpopts == find->fp_tcpopts &&
428 		    f->fp_wsize == find->fp_wsize &&
429 		    f->fp_psize == find->fp_psize &&
430 		    f->fp_mss == find->fp_mss &&
431 		    f->fp_flags == find->fp_flags &&
432 		    f->fp_optcnt == find->fp_optcnt &&
433 		    f->fp_wscale == find->fp_wscale &&
434 		    f->fp_ttl == find->fp_ttl)
435 			return (f);
436 	}
437 
438 	return (NULL);
439 }
440 
441 /* Insert a fingerprint into the list */
442 static void
443 pf_osfp_insert(struct pf_osfp_list *list, struct pf_os_fingerprint *ins)
444 {
445 	struct pf_os_fingerprint *f, *prev = NULL;
446 
447 	/* XXX need to go semi tree based.  can key on tcp options */
448 
449 	SLIST_FOREACH(f, list, fp_next)
450 		prev = f;
451 	if (prev)
452 		SLIST_INSERT_AFTER(prev, ins, fp_next);
453 	else
454 		SLIST_INSERT_HEAD(list, ins, fp_next);
455 }
456 
457 /* Fill a fingerprint by its number (from an ioctl) */
458 int
459 pf_osfp_get(struct pf_osfp_ioctl *fpioc)
460 {
461 	struct pf_os_fingerprint *fp;
462 	struct pf_osfp_entry *entry;
463 	int num = fpioc->fp_getnum;
464 	int i = 0;
465 
466 
467 	memset(fpioc, 0, sizeof(*fpioc));
468 	SLIST_FOREACH(fp, &V_pf_osfp_list, fp_next) {
469 		SLIST_FOREACH(entry, &fp->fp_oses, fp_entry) {
470 			if (i++ == num) {
471 				fpioc->fp_mss = fp->fp_mss;
472 				fpioc->fp_wsize = fp->fp_wsize;
473 				fpioc->fp_flags = fp->fp_flags;
474 				fpioc->fp_psize = fp->fp_psize;
475 				fpioc->fp_ttl = fp->fp_ttl;
476 				fpioc->fp_wscale = fp->fp_wscale;
477 				fpioc->fp_getnum = num;
478 				memcpy(&fpioc->fp_os, entry,
479 				    sizeof(fpioc->fp_os));
480 				return (0);
481 			}
482 		}
483 	}
484 
485 	return (EBUSY);
486 }
487 
488 
489 #ifdef PFDEBUG
490 /* Validate that each signature is reachable */
491 static struct pf_os_fingerprint *
492 pf_osfp_validate(void)
493 {
494 	struct pf_os_fingerprint *f, *f2, find;
495 
496 	SLIST_FOREACH(f, &V_pf_osfp_list, fp_next) {
497 		memcpy(&find, f, sizeof(find));
498 
499 		/* We do a few MSS/th_win percolations to make things unique */
500 		if (find.fp_mss == 0)
501 			find.fp_mss = 128;
502 		if (f->fp_flags & PF_OSFP_WSIZE_MSS)
503 			find.fp_wsize *= find.fp_mss;
504 		else if (f->fp_flags & PF_OSFP_WSIZE_MTU)
505 			find.fp_wsize *= (find.fp_mss + 40);
506 		else if (f->fp_flags & PF_OSFP_WSIZE_MOD)
507 			find.fp_wsize *= 2;
508 		if (f != (f2 = pf_osfp_find(&V_pf_osfp_list, &find, 0))) {
509 			if (f2)
510 				printf("Found \"%s %s %s\" instead of "
511 				    "\"%s %s %s\"\n",
512 				    SLIST_FIRST(&f2->fp_oses)->fp_class_nm,
513 				    SLIST_FIRST(&f2->fp_oses)->fp_version_nm,
514 				    SLIST_FIRST(&f2->fp_oses)->fp_subtype_nm,
515 				    SLIST_FIRST(&f->fp_oses)->fp_class_nm,
516 				    SLIST_FIRST(&f->fp_oses)->fp_version_nm,
517 				    SLIST_FIRST(&f->fp_oses)->fp_subtype_nm);
518 			else
519 				printf("Couldn't find \"%s %s %s\"\n",
520 				    SLIST_FIRST(&f->fp_oses)->fp_class_nm,
521 				    SLIST_FIRST(&f->fp_oses)->fp_version_nm,
522 				    SLIST_FIRST(&f->fp_oses)->fp_subtype_nm);
523 			return (f);
524 		}
525 	}
526 	return (NULL);
527 }
528 #endif /* PFDEBUG */
529