sys/netpfil/pf/pf_osfp.c

   1 /*-
   2  * SPDX-License-Identifier: ISC
   3  *
   4  * Copyright (c) 2003 Mike Frantzen <frantzen@w4g.org>
   5  *
   6  * Permission to use, copy, modify, and distribute this software for any
   7  * purpose with or without fee is hereby granted, provided that the above
   8  * copyright notice and this permission notice appear in all copies.
   9  *
  10  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  11  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  12  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  13  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  14  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  15  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  16  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  17  *
  18  *      $OpenBSD: pf_osfp.c,v 1.14 2008/06/12 18:17:01 henning Exp $
  19  */
  20
  21 #include <sys/cdefs.h>
  22 __FBSDID("$FreeBSD$");
  23
  24 #include "opt_inet6.h"
  25
  26 #include <sys/param.h>
  27 #include <sys/kernel.h>
  28 #include <sys/lock.h>
  29 #include <sys/mbuf.h>
  30 #include <sys/rwlock.h>
  31 #include <sys/socket.h>
  32
  33 #include <netinet/in.h>
  34 #include <netinet/ip.h>
  35 #include <netinet/tcp.h>
  36
  37 #include <net/if.h>
  38 #include <net/vnet.h>
  39 #include <net/pfvar.h>
  40
  41 #ifdef INET6
  42 #include <netinet/ip6.h>
  43 #endif
  44
  45 static MALLOC_DEFINE(M_PFOSFP, "pf_osfp", "pf(4) operating system fingerprints");
  46 #define DPFPRINTF(format, x...)         \
  47         if (V_pf_status.debug >= PF_DEBUG_NOISY)        \
  48                 printf(format , ##x)
  49
  50 SLIST_HEAD(pf_osfp_list, pf_os_fingerprint);
  51 static VNET_DEFINE(struct pf_osfp_list, pf_osfp_list) =
  52         SLIST_HEAD_INITIALIZER();
  53 #define V_pf_osfp_list                  VNET(pf_osfp_list)
  54
  55 static struct pf_osfp_enlist    *pf_osfp_fingerprint_hdr(const struct ip *,
  56                                     const struct ip6_hdr *,
  57                                     const struct tcphdr *);
  58 static struct pf_os_fingerprint *pf_osfp_find(struct pf_osfp_list *,
  59                                     struct pf_os_fingerprint *, u_int8_t);
  60 static struct pf_os_fingerprint *pf_osfp_find_exact(struct pf_osfp_list *,
  61                                     struct pf_os_fingerprint *);
  62 static void                      pf_osfp_insert(struct pf_osfp_list *,
  63                                     struct pf_os_fingerprint *);
  64 #ifdef PFDEBUG
  65 static struct pf_os_fingerprint *pf_osfp_validate(void);
  66 #endif
  67
  68 /*
  69  * Passively fingerprint the OS of the host (IPv4 TCP SYN packets only)
  70  * Returns the list of possible OSes.
  71  */
  72 struct pf_osfp_enlist *
  73 pf_osfp_fingerprint(struct pf_pdesc *pd, struct mbuf *m, int off,
  74     const struct tcphdr *tcp)
  75 {
  76         struct ip *ip;
  77         struct ip6_hdr *ip6;
  78         char hdr[60];
  79
  80         if ((pd->af != PF_INET && pd->af != PF_INET6) ||
  81             pd->proto != IPPROTO_TCP || (tcp->th_off << 2) < sizeof(*tcp))
  82                 return (NULL);
  83
  84         if (pd->af == PF_INET) {
  85                 ip = mtod(m, struct ip *);
  86                 ip6 = (struct ip6_hdr *)NULL;
  87         } else {
  88                 ip = (struct ip *)NULL;
  89                 ip6 = mtod(m, struct ip6_hdr *);
  90         }
  91         if (!pf_pull_hdr(m, off, hdr, tcp->th_off << 2, NULL, NULL,
  92             pd->af)) return (NULL);
  93
  94         return (pf_osfp_fingerprint_hdr(ip, ip6, (struct tcphdr *)hdr));
  95 }
  96
  97 static struct pf_osfp_enlist *
  98 pf_osfp_fingerprint_hdr(const struct ip *ip, const struct ip6_hdr *ip6, const struct tcphdr *tcp)
  99 {
 100         struct pf_os_fingerprint fp, *fpresult;
 101         int cnt, optlen = 0;
 102         const u_int8_t *optp;
 103 #ifdef INET6
 104         char srcname[INET6_ADDRSTRLEN];
 105 #else
 106         char srcname[INET_ADDRSTRLEN];
 107 #endif
 108
 109         if ((tcp->th_flags & (TH_SYN|TH_ACK)) != TH_SYN)
 110                 return (NULL);
 111         if (ip) {
 112                 if ((ip->ip_off & htons(IP_OFFMASK)) != 0)
 113                         return (NULL);
 114         }
 115
 116         memset(&fp, 0, sizeof(fp));
 117
 118         if (ip) {
 119                 fp.fp_psize = ntohs(ip->ip_len);
 120                 fp.fp_ttl = ip->ip_ttl;
 121                 if (ip->ip_off & htons(IP_DF))
 122                         fp.fp_flags |= PF_OSFP_DF;
 123                 inet_ntoa_r(ip->ip_src, srcname);
 124         }
 125 #ifdef INET6
 126         else if (ip6) {
 127                 /* jumbo payload? */
 128                 fp.fp_psize = sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen);
 129                 fp.fp_ttl = ip6->ip6_hlim;
 130                 fp.fp_flags |= PF_OSFP_DF;
 131                 fp.fp_flags |= PF_OSFP_INET6;
 132                 ip6_sprintf(srcname, (const struct in6_addr *)&ip6->ip6_src);
 133         }
 134 #endif
 135         else
 136                 return (NULL);
 137         fp.fp_wsize = ntohs(tcp->th_win);
 138
 139
 140         cnt = (tcp->th_off << 2) - sizeof(*tcp);
 141         optp = (const u_int8_t *)((const char *)tcp + sizeof(*tcp));
 142         for (; cnt > 0; cnt -= optlen, optp += optlen) {
 143                 if (*optp == TCPOPT_EOL)
 144                         break;
 145
 146                 fp.fp_optcnt++;
 147                 if (*optp == TCPOPT_NOP) {
 148                         fp.fp_tcpopts = (fp.fp_tcpopts << PF_OSFP_TCPOPT_BITS) |
 149                             PF_OSFP_TCPOPT_NOP;
 150                         optlen = 1;
 151                 } else {
 152                         if (cnt < 2)
 153                                 return (NULL);
 154                         optlen = optp[1];
 155                         if (optlen > cnt || optlen < 2)
 156                                 return (NULL);
 157                         switch (*optp) {
 158                         case TCPOPT_MAXSEG:
 159                                 if (optlen >= TCPOLEN_MAXSEG)
 160                                         memcpy(&fp.fp_mss, &optp[2],
 161                                             sizeof(fp.fp_mss));
 162                                 fp.fp_tcpopts = (fp.fp_tcpopts <<
 163                                     PF_OSFP_TCPOPT_BITS) | PF_OSFP_TCPOPT_MSS;
 164                                 NTOHS(fp.fp_mss);
 165                                 break;
 166                         case TCPOPT_WINDOW:
 167                                 if (optlen >= TCPOLEN_WINDOW)
 168                                         memcpy(&fp.fp_wscale, &optp[2],
 169                                             sizeof(fp.fp_wscale));
 170                                 NTOHS(fp.fp_wscale);
 171                                 fp.fp_tcpopts = (fp.fp_tcpopts <<
 172                                     PF_OSFP_TCPOPT_BITS) |
 173                                     PF_OSFP_TCPOPT_WSCALE;
 174                                 break;
 175                         case TCPOPT_SACK_PERMITTED:
 176                                 fp.fp_tcpopts = (fp.fp_tcpopts <<
 177                                     PF_OSFP_TCPOPT_BITS) | PF_OSFP_TCPOPT_SACK;
 178                                 break;
 179                         case TCPOPT_TIMESTAMP:
 180                                 if (optlen >= TCPOLEN_TIMESTAMP) {
 181                                         u_int32_t ts;
 182                                         memcpy(&ts, &optp[2], sizeof(ts));
 183                                         if (ts == 0)
 184                                                 fp.fp_flags |= PF_OSFP_TS0;
 185
 186                                 }
 187                                 fp.fp_tcpopts = (fp.fp_tcpopts <<
 188                                     PF_OSFP_TCPOPT_BITS) | PF_OSFP_TCPOPT_TS;
 189                                 break;
 190                         default:
 191                                 return (NULL);
 192                         }
 193                 }
 194                 optlen = MAX(optlen, 1);        /* paranoia */
 195         }
 196
 197         DPFPRINTF("fingerprinted %s:%d  %d:%d:%d:%d:%llx (%d) "
 198             "(TS=%s,M=%s%d,W=%s%d)\n",
 199             srcname, ntohs(tcp->th_sport),
 200             fp.fp_wsize, fp.fp_ttl, (fp.fp_flags & PF_OSFP_DF) != 0,
 201             fp.fp_psize, (long long int)fp.fp_tcpopts, fp.fp_optcnt,
 202             (fp.fp_flags & PF_OSFP_TS0) ? "0" : "",
 203             (fp.fp_flags & PF_OSFP_MSS_MOD) ? "%" :
 204             (fp.fp_flags & PF_OSFP_MSS_DC) ? "*" : "",
 205             fp.fp_mss,
 206             (fp.fp_flags & PF_OSFP_WSCALE_MOD) ? "%" :
 207             (fp.fp_flags & PF_OSFP_WSCALE_DC) ? "*" : "",
 208             fp.fp_wscale);
 209
 210         if ((fpresult = pf_osfp_find(&V_pf_osfp_list, &fp,
 211             PF_OSFP_MAXTTL_OFFSET)))
 212                 return (&fpresult->fp_oses);
 213         return (NULL);
 214 }
 215
 216 /* Match a fingerprint ID against a list of OSes */
 217 int
 218 pf_osfp_match(struct pf_osfp_enlist *list, pf_osfp_t os)
 219 {
 220         struct pf_osfp_entry *entry;
 221         int os_class, os_version, os_subtype;
 222         int en_class, en_version, en_subtype;
 223
 224         if (os == PF_OSFP_ANY)
 225                 return (1);
 226         if (list == NULL) {
 227                 DPFPRINTF("osfp no match against %x\n", os);
 228                 return (os == PF_OSFP_UNKNOWN);
 229         }
 230         PF_OSFP_UNPACK(os, os_class, os_version, os_subtype);
 231         SLIST_FOREACH(entry, list, fp_entry) {
 232                 PF_OSFP_UNPACK(entry->fp_os, en_class, en_version, en_subtype);
 233                 if ((os_class == PF_OSFP_ANY || en_class == os_class) &&
 234                     (os_version == PF_OSFP_ANY || en_version == os_version) &&
 235                     (os_subtype == PF_OSFP_ANY || en_subtype == os_subtype)) {
 236                         DPFPRINTF("osfp matched %s %s %s  %x==%x\n",
 237                             entry->fp_class_nm, entry->fp_version_nm,
 238                             entry->fp_subtype_nm, os, entry->fp_os);
 239                         return (1);
 240                 }
 241         }
 242         DPFPRINTF("fingerprint 0x%x didn't match\n", os);
 243         return (0);
 244 }
 245
 246 /* Flush the fingerprint list */
 247 void
 248 pf_osfp_flush(void)
 249 {
 250         struct pf_os_fingerprint *fp;
 251         struct pf_osfp_entry *entry;
 252
 253         while ((fp = SLIST_FIRST(&V_pf_osfp_list))) {
 254                 SLIST_REMOVE_HEAD(&V_pf_osfp_list, fp_next);
 255                 while ((entry = SLIST_FIRST(&fp->fp_oses))) {
 256                         SLIST_REMOVE_HEAD(&fp->fp_oses, fp_entry);
 257                         free(entry, M_PFOSFP);
 258                 }
 259                 free(fp, M_PFOSFP);
 260         }
 261 }
 262
 263
 264 /* Add a fingerprint */
 265 int
 266 pf_osfp_add(struct pf_osfp_ioctl *fpioc)
 267 {
 268         struct pf_os_fingerprint *fp, fpadd;
 269         struct pf_osfp_entry *entry;
 270
 271         PF_RULES_WASSERT();
 272
 273         memset(&fpadd, 0, sizeof(fpadd));
 274         fpadd.fp_tcpopts = fpioc->fp_tcpopts;
 275         fpadd.fp_wsize = fpioc->fp_wsize;
 276         fpadd.fp_psize = fpioc->fp_psize;
 277         fpadd.fp_mss = fpioc->fp_mss;
 278         fpadd.fp_flags = fpioc->fp_flags;
 279         fpadd.fp_optcnt = fpioc->fp_optcnt;
 280         fpadd.fp_wscale = fpioc->fp_wscale;
 281         fpadd.fp_ttl = fpioc->fp_ttl;
 282
 283 #if 0   /* XXX RYAN wants to fix logging */
 284         DPFPRINTF("adding osfp %s %s %s = %s%d:%d:%d:%s%d:0x%llx %d "
 285             "(TS=%s,M=%s%d,W=%s%d) %x\n",
 286             fpioc->fp_os.fp_class_nm, fpioc->fp_os.fp_version_nm,
 287             fpioc->fp_os.fp_subtype_nm,
 288             (fpadd.fp_flags & PF_OSFP_WSIZE_MOD) ? "%" :
 289             (fpadd.fp_flags & PF_OSFP_WSIZE_MSS) ? "S" :
 290             (fpadd.fp_flags & PF_OSFP_WSIZE_MTU) ? "T" :
 291             (fpadd.fp_flags & PF_OSFP_WSIZE_DC) ? "*" : "",
 292             fpadd.fp_wsize,
 293             fpadd.fp_ttl,
 294             (fpadd.fp_flags & PF_OSFP_DF) ? 1 : 0,
 295             (fpadd.fp_flags & PF_OSFP_PSIZE_MOD) ? "%" :
 296             (fpadd.fp_flags & PF_OSFP_PSIZE_DC) ? "*" : "",
 297             fpadd.fp_psize,
 298             (long long int)fpadd.fp_tcpopts, fpadd.fp_optcnt,
 299             (fpadd.fp_flags & PF_OSFP_TS0) ? "0" : "",
 300             (fpadd.fp_flags & PF_OSFP_MSS_MOD) ? "%" :
 301             (fpadd.fp_flags & PF_OSFP_MSS_DC) ? "*" : "",
 302             fpadd.fp_mss,
 303             (fpadd.fp_flags & PF_OSFP_WSCALE_MOD) ? "%" :
 304             (fpadd.fp_flags & PF_OSFP_WSCALE_DC) ? "*" : "",
 305             fpadd.fp_wscale,
 306             fpioc->fp_os.fp_os);
 307 #endif
 308
 309         if ((fp = pf_osfp_find_exact(&V_pf_osfp_list, &fpadd))) {
 310                  SLIST_FOREACH(entry, &fp->fp_oses, fp_entry) {
 311                         if (PF_OSFP_ENTRY_EQ(entry, &fpioc->fp_os))
 312                                 return (EEXIST);
 313                 }
 314                 if ((entry = malloc(sizeof(*entry), M_PFOSFP, M_NOWAIT))
 315                     == NULL)
 316                         return (ENOMEM);
 317         } else {
 318                 if ((fp = malloc(sizeof(*fp), M_PFOSFP, M_ZERO | M_NOWAIT))
 319                     == NULL)
 320                         return (ENOMEM);
 321                 fp->fp_tcpopts = fpioc->fp_tcpopts;
 322                 fp->fp_wsize = fpioc->fp_wsize;
 323                 fp->fp_psize = fpioc->fp_psize;
 324                 fp->fp_mss = fpioc->fp_mss;
 325                 fp->fp_flags = fpioc->fp_flags;
 326                 fp->fp_optcnt = fpioc->fp_optcnt;
 327                 fp->fp_wscale = fpioc->fp_wscale;
 328                 fp->fp_ttl = fpioc->fp_ttl;
 329                 SLIST_INIT(&fp->fp_oses);
 330                 if ((entry = malloc(sizeof(*entry), M_PFOSFP, M_NOWAIT))
 331                     == NULL) {
 332                         free(fp, M_PFOSFP);
 333                         return (ENOMEM);
 334                 }
 335                 pf_osfp_insert(&V_pf_osfp_list, fp);
 336         }
 337         memcpy(entry, &fpioc->fp_os, sizeof(*entry));
 338
 339         /* Make sure the strings are NUL terminated */
 340         entry->fp_class_nm[sizeof(entry->fp_class_nm)-1] = '\0';
 341         entry->fp_version_nm[sizeof(entry->fp_version_nm)-1] = '\0';
 342         entry->fp_subtype_nm[sizeof(entry->fp_subtype_nm)-1] = '\0';
 343
 344         SLIST_INSERT_HEAD(&fp->fp_oses, entry, fp_entry);
 345
 346 #ifdef PFDEBUG
 347         if ((fp = pf_osfp_validate()))
 348                 printf("Invalid fingerprint list\n");
 349 #endif /* PFDEBUG */
 350         return (0);
 351 }
 352
 353
 354 /* Find a fingerprint in the list */
 355 static struct pf_os_fingerprint *
 356 pf_osfp_find(struct pf_osfp_list *list, struct pf_os_fingerprint *find,
 357     u_int8_t ttldiff)
 358 {
 359         struct pf_os_fingerprint *f;
 360
 361 #define MATCH_INT(_MOD, _DC, _field)                                    \
 362         if ((f->fp_flags & _DC) == 0) {                                 \
 363                 if ((f->fp_flags & _MOD) == 0) {                        \
 364                         if (f->_field != find->_field)                  \
 365                                 continue;                               \
 366                 } else {                                                \
 367                         if (f->_field == 0 || find->_field % f->_field) \
 368                                 continue;                               \
 369                 }                                                       \
 370         }
 371
 372         SLIST_FOREACH(f, list, fp_next) {
 373                 if (f->fp_tcpopts != find->fp_tcpopts ||
 374                     f->fp_optcnt != find->fp_optcnt ||
 375                     f->fp_ttl < find->fp_ttl ||
 376                     f->fp_ttl - find->fp_ttl > ttldiff ||
 377                     (f->fp_flags & (PF_OSFP_DF|PF_OSFP_TS0)) !=
 378                     (find->fp_flags & (PF_OSFP_DF|PF_OSFP_TS0)))
 379                         continue;
 380
 381                 MATCH_INT(PF_OSFP_PSIZE_MOD, PF_OSFP_PSIZE_DC, fp_psize)
 382                 MATCH_INT(PF_OSFP_MSS_MOD, PF_OSFP_MSS_DC, fp_mss)
 383                 MATCH_INT(PF_OSFP_WSCALE_MOD, PF_OSFP_WSCALE_DC, fp_wscale)
 384                 if ((f->fp_flags & PF_OSFP_WSIZE_DC) == 0) {
 385                         if (f->fp_flags & PF_OSFP_WSIZE_MSS) {
 386                                 if (find->fp_mss == 0)
 387                                         continue;
 388
 389 /*
 390  * Some "smart" NAT devices and DSL routers will tweak the MSS size and
 391  * will set it to whatever is suitable for the link type.
 392  */
 393 #define SMART_MSS       1460
 394                                 if ((find->fp_wsize % find->fp_mss ||
 395                                     find->fp_wsize / find->fp_mss !=
 396                                     f->fp_wsize) &&
 397                                     (find->fp_wsize % SMART_MSS ||
 398                                     find->fp_wsize / SMART_MSS !=
 399                                     f->fp_wsize))
 400                                         continue;
 401                         } else if (f->fp_flags & PF_OSFP_WSIZE_MTU) {
 402                                 if (find->fp_mss == 0)
 403                                         continue;
 404
 405 #define MTUOFF          (sizeof(struct ip) + sizeof(struct tcphdr))
 406 #define SMART_MTU       (SMART_MSS + MTUOFF)
 407                                 if ((find->fp_wsize % (find->fp_mss + MTUOFF) ||
 408                                     find->fp_wsize / (find->fp_mss + MTUOFF) !=
 409                                     f->fp_wsize) &&
 410                                     (find->fp_wsize % SMART_MTU ||
 411                                     find->fp_wsize / SMART_MTU !=
 412                                     f->fp_wsize))
 413                                         continue;
 414                         } else if (f->fp_flags & PF_OSFP_WSIZE_MOD) {
 415                                 if (f->fp_wsize == 0 || find->fp_wsize %
 416                                     f->fp_wsize)
 417                                         continue;
 418                         } else {
 419                                 if (f->fp_wsize != find->fp_wsize)
 420                                         continue;
 421                         }
 422                 }
 423                 return (f);
 424         }
 425
 426         return (NULL);
 427 }
 428
 429 /* Find an exact fingerprint in the list */
 430 static struct pf_os_fingerprint *
 431 pf_osfp_find_exact(struct pf_osfp_list *list, struct pf_os_fingerprint *find)
 432 {
 433         struct pf_os_fingerprint *f;
 434
 435         SLIST_FOREACH(f, list, fp_next) {
 436                 if (f->fp_tcpopts == find->fp_tcpopts &&
 437                     f->fp_wsize == find->fp_wsize &&
 438                     f->fp_psize == find->fp_psize &&
 439                     f->fp_mss == find->fp_mss &&
 440                     f->fp_flags == find->fp_flags &&
 441                     f->fp_optcnt == find->fp_optcnt &&
 442                     f->fp_wscale == find->fp_wscale &&
 443                     f->fp_ttl == find->fp_ttl)
 444                         return (f);
 445         }
 446
 447         return (NULL);
 448 }
 449
 450 /* Insert a fingerprint into the list */
 451 static void
 452 pf_osfp_insert(struct pf_osfp_list *list, struct pf_os_fingerprint *ins)
 453 {
 454         struct pf_os_fingerprint *f, *prev = NULL;
 455
 456         /* XXX need to go semi tree based.  can key on tcp options */
 457
 458         SLIST_FOREACH(f, list, fp_next)
 459                 prev = f;
 460         if (prev)
 461                 SLIST_INSERT_AFTER(prev, ins, fp_next);
 462         else
 463                 SLIST_INSERT_HEAD(list, ins, fp_next);
 464 }
 465
 466 /* Fill a fingerprint by its number (from an ioctl) */
 467 int
 468 pf_osfp_get(struct pf_osfp_ioctl *fpioc)
 469 {
 470         struct pf_os_fingerprint *fp;
 471         struct pf_osfp_entry *entry;
 472         int num = fpioc->fp_getnum;
 473         int i = 0;
 474
 475
 476         memset(fpioc, 0, sizeof(*fpioc));
 477         SLIST_FOREACH(fp, &V_pf_osfp_list, fp_next) {
 478                 SLIST_FOREACH(entry, &fp->fp_oses, fp_entry) {
 479                         if (i++ == num) {
 480                                 fpioc->fp_mss = fp->fp_mss;
 481                                 fpioc->fp_wsize = fp->fp_wsize;
 482                                 fpioc->fp_flags = fp->fp_flags;
 483                                 fpioc->fp_psize = fp->fp_psize;
 484                                 fpioc->fp_ttl = fp->fp_ttl;
 485                                 fpioc->fp_wscale = fp->fp_wscale;
 486                                 fpioc->fp_getnum = num;
 487                                 memcpy(&fpioc->fp_os, entry,
 488                                     sizeof(fpioc->fp_os));
 489                                 return (0);
 490                         }
 491                 }
 492         }
 493
 494         return (EBUSY);
 495 }
 496
 497
 498 #ifdef PFDEBUG
 499 /* Validate that each signature is reachable */
 500 static struct pf_os_fingerprint *
 501 pf_osfp_validate(void)
 502 {
 503         struct pf_os_fingerprint *f, *f2, find;
 504
 505         SLIST_FOREACH(f, &V_pf_osfp_list, fp_next) {
 506                 memcpy(&find, f, sizeof(find));
 507
 508                 /* We do a few MSS/th_win percolations to make things unique */
 509                 if (find.fp_mss == 0)
 510                         find.fp_mss = 128;
 511                 if (f->fp_flags & PF_OSFP_WSIZE_MSS)
 512                         find.fp_wsize *= find.fp_mss;
 513                 else if (f->fp_flags & PF_OSFP_WSIZE_MTU)
 514                         find.fp_wsize *= (find.fp_mss + 40);
 515                 else if (f->fp_flags & PF_OSFP_WSIZE_MOD)
 516                         find.fp_wsize *= 2;
 517                 if (f != (f2 = pf_osfp_find(&V_pf_osfp_list, &find, 0))) {
 518                         if (f2)
 519                                 printf("Found \"%s %s %s\" instead of "
 520                                     "\"%s %s %s\"\n",
 521                                     SLIST_FIRST(&f2->fp_oses)->fp_class_nm,
 522                                     SLIST_FIRST(&f2->fp_oses)->fp_version_nm,
 523                                     SLIST_FIRST(&f2->fp_oses)->fp_subtype_nm,
 524                                     SLIST_FIRST(&f->fp_oses)->fp_class_nm,
 525                                     SLIST_FIRST(&f->fp_oses)->fp_version_nm,
 526                                     SLIST_FIRST(&f->fp_oses)->fp_subtype_nm);
 527                         else
 528                                 printf("Couldn't find \"%s %s %s\"\n",
 529                                     SLIST_FIRST(&f->fp_oses)->fp_class_nm,
 530                                     SLIST_FIRST(&f->fp_oses)->fp_version_nm,
 531                                     SLIST_FIRST(&f->fp_oses)->fp_subtype_nm);
 532                         return (f);
 533                 }
 534         }
 535         return (NULL);
 536 }
 537 #endif /* PFDEBUG */