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