sys/netpfil/pf/pf_osfp.c

   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 */