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         cnt = (tcp->th_off << 2) - sizeof(*tcp);
 139         optp = (const u_int8_t *)((const char *)tcp + sizeof(*tcp));
 140         for (; cnt > 0; cnt -= optlen, optp += optlen) {
 141                 if (*optp == TCPOPT_EOL)
 142                         break;
 143
 144                 fp.fp_optcnt++;
 145                 if (*optp == TCPOPT_NOP) {
 146                         fp.fp_tcpopts = (fp.fp_tcpopts << PF_OSFP_TCPOPT_BITS) |
 147                             PF_OSFP_TCPOPT_NOP;
 148                         optlen = 1;
 149                 } else {
 150                         if (cnt < 2)
 151                                 return (NULL);
 152                         optlen = optp[1];
 153                         if (optlen > cnt || optlen < 2)
 154                                 return (NULL);
 155                         switch (*optp) {
 156                         case TCPOPT_MAXSEG:
 157                                 if (optlen >= TCPOLEN_MAXSEG)
 158                                         memcpy(&fp.fp_mss, &optp[2],
 159                                             sizeof(fp.fp_mss));
 160                                 fp.fp_tcpopts = (fp.fp_tcpopts <<
 161                                     PF_OSFP_TCPOPT_BITS) | PF_OSFP_TCPOPT_MSS;
 162                                 NTOHS(fp.fp_mss);
 163                                 break;
 164                         case TCPOPT_WINDOW:
 165                                 if (optlen >= TCPOLEN_WINDOW)
 166                                         memcpy(&fp.fp_wscale, &optp[2],
 167                                             sizeof(fp.fp_wscale));
 168                                 NTOHS(fp.fp_wscale);
 169                                 fp.fp_tcpopts = (fp.fp_tcpopts <<
 170                                     PF_OSFP_TCPOPT_BITS) |
 171                                     PF_OSFP_TCPOPT_WSCALE;
 172                                 break;
 173                         case TCPOPT_SACK_PERMITTED:
 174                                 fp.fp_tcpopts = (fp.fp_tcpopts <<
 175                                     PF_OSFP_TCPOPT_BITS) | PF_OSFP_TCPOPT_SACK;
 176                                 break;
 177                         case TCPOPT_TIMESTAMP:
 178                                 if (optlen >= TCPOLEN_TIMESTAMP) {
 179                                         u_int32_t ts;
 180                                         memcpy(&ts, &optp[2], sizeof(ts));
 181                                         if (ts == 0)
 182                                                 fp.fp_flags |= PF_OSFP_TS0;
 183                                 }
 184                                 fp.fp_tcpopts = (fp.fp_tcpopts <<
 185                                     PF_OSFP_TCPOPT_BITS) | PF_OSFP_TCPOPT_TS;
 186                                 break;
 187                         default:
 188                                 return (NULL);
 189                         }
 190                 }
 191                 optlen = MAX(optlen, 1);        /* paranoia */
 192         }
 193
 194         DPFPRINTF("fingerprinted %s:%d  %d:%d:%d:%d:%llx (%d) "
 195             "(TS=%s,M=%s%d,W=%s%d)\n",
 196             srcname, ntohs(tcp->th_sport),
 197             fp.fp_wsize, fp.fp_ttl, (fp.fp_flags & PF_OSFP_DF) != 0,
 198             fp.fp_psize, (long long int)fp.fp_tcpopts, fp.fp_optcnt,
 199             (fp.fp_flags & PF_OSFP_TS0) ? "0" : "",
 200             (fp.fp_flags & PF_OSFP_MSS_MOD) ? "%" :
 201             (fp.fp_flags & PF_OSFP_MSS_DC) ? "*" : "",
 202             fp.fp_mss,
 203             (fp.fp_flags & PF_OSFP_WSCALE_MOD) ? "%" :
 204             (fp.fp_flags & PF_OSFP_WSCALE_DC) ? "*" : "",
 205             fp.fp_wscale);
 206
 207         if ((fpresult = pf_osfp_find(&V_pf_osfp_list, &fp,
 208             PF_OSFP_MAXTTL_OFFSET)))
 209                 return (&fpresult->fp_oses);
 210         return (NULL);
 211 }
 212
 213 /* Match a fingerprint ID against a list of OSes */
 214 int
 215 pf_osfp_match(struct pf_osfp_enlist *list, pf_osfp_t os)
 216 {
 217         struct pf_osfp_entry *entry;
 218         int os_class, os_version, os_subtype;
 219         int en_class, en_version, en_subtype;
 220
 221         if (os == PF_OSFP_ANY)
 222                 return (1);
 223         if (list == NULL) {
 224                 DPFPRINTF("osfp no match against %x\n", os);
 225                 return (os == PF_OSFP_UNKNOWN);
 226         }
 227         PF_OSFP_UNPACK(os, os_class, os_version, os_subtype);
 228         SLIST_FOREACH(entry, list, fp_entry) {
 229                 PF_OSFP_UNPACK(entry->fp_os, en_class, en_version, en_subtype);
 230                 if ((os_class == PF_OSFP_ANY || en_class == os_class) &&
 231                     (os_version == PF_OSFP_ANY || en_version == os_version) &&
 232                     (os_subtype == PF_OSFP_ANY || en_subtype == os_subtype)) {
 233                         DPFPRINTF("osfp matched %s %s %s  %x==%x\n",
 234                             entry->fp_class_nm, entry->fp_version_nm,
 235                             entry->fp_subtype_nm, os, entry->fp_os);
 236                         return (1);
 237                 }
 238         }
 239         DPFPRINTF("fingerprint 0x%x didn't match\n", os);
 240         return (0);
 241 }
 242
 243 /* Flush the fingerprint list */
 244 void
 245 pf_osfp_flush(void)
 246 {
 247         struct pf_os_fingerprint *fp;
 248         struct pf_osfp_entry *entry;
 249
 250         while ((fp = SLIST_FIRST(&V_pf_osfp_list))) {
 251                 SLIST_REMOVE_HEAD(&V_pf_osfp_list, fp_next);
 252                 while ((entry = SLIST_FIRST(&fp->fp_oses))) {
 253                         SLIST_REMOVE_HEAD(&fp->fp_oses, fp_entry);
 254                         free(entry, M_PFOSFP);
 255                 }
 256                 free(fp, M_PFOSFP);
 257         }
 258 }
 259
 260 /* Add a fingerprint */
 261 int
 262 pf_osfp_add(struct pf_osfp_ioctl *fpioc)
 263 {
 264         struct pf_os_fingerprint *fp, fpadd;
 265         struct pf_osfp_entry *entry;
 266
 267         PF_RULES_WASSERT();
 268
 269         memset(&fpadd, 0, sizeof(fpadd));
 270         fpadd.fp_tcpopts = fpioc->fp_tcpopts;
 271         fpadd.fp_wsize = fpioc->fp_wsize;
 272         fpadd.fp_psize = fpioc->fp_psize;
 273         fpadd.fp_mss = fpioc->fp_mss;
 274         fpadd.fp_flags = fpioc->fp_flags;
 275         fpadd.fp_optcnt = fpioc->fp_optcnt;
 276         fpadd.fp_wscale = fpioc->fp_wscale;
 277         fpadd.fp_ttl = fpioc->fp_ttl;
 278
 279 #if 0   /* XXX RYAN wants to fix logging */
 280         DPFPRINTF("adding osfp %s %s %s = %s%d:%d:%d:%s%d:0x%llx %d "
 281             "(TS=%s,M=%s%d,W=%s%d) %x\n",
 282             fpioc->fp_os.fp_class_nm, fpioc->fp_os.fp_version_nm,
 283             fpioc->fp_os.fp_subtype_nm,
 284             (fpadd.fp_flags & PF_OSFP_WSIZE_MOD) ? "%" :
 285             (fpadd.fp_flags & PF_OSFP_WSIZE_MSS) ? "S" :
 286             (fpadd.fp_flags & PF_OSFP_WSIZE_MTU) ? "T" :
 287             (fpadd.fp_flags & PF_OSFP_WSIZE_DC) ? "*" : "",
 288             fpadd.fp_wsize,
 289             fpadd.fp_ttl,
 290             (fpadd.fp_flags & PF_OSFP_DF) ? 1 : 0,
 291             (fpadd.fp_flags & PF_OSFP_PSIZE_MOD) ? "%" :
 292             (fpadd.fp_flags & PF_OSFP_PSIZE_DC) ? "*" : "",
 293             fpadd.fp_psize,
 294             (long long int)fpadd.fp_tcpopts, fpadd.fp_optcnt,
 295             (fpadd.fp_flags & PF_OSFP_TS0) ? "0" : "",
 296             (fpadd.fp_flags & PF_OSFP_MSS_MOD) ? "%" :
 297             (fpadd.fp_flags & PF_OSFP_MSS_DC) ? "*" : "",
 298             fpadd.fp_mss,
 299             (fpadd.fp_flags & PF_OSFP_WSCALE_MOD) ? "%" :
 300             (fpadd.fp_flags & PF_OSFP_WSCALE_DC) ? "*" : "",
 301             fpadd.fp_wscale,
 302             fpioc->fp_os.fp_os);
 303 #endif
 304
 305         if ((fp = pf_osfp_find_exact(&V_pf_osfp_list, &fpadd))) {
 306                  SLIST_FOREACH(entry, &fp->fp_oses, fp_entry) {
 307                         if (PF_OSFP_ENTRY_EQ(entry, &fpioc->fp_os))
 308                                 return (EEXIST);
 309                 }
 310                 if ((entry = malloc(sizeof(*entry), M_PFOSFP, M_NOWAIT))
 311                     == NULL)
 312                         return (ENOMEM);
 313         } else {
 314                 if ((fp = malloc(sizeof(*fp), M_PFOSFP, M_ZERO | M_NOWAIT))
 315                     == NULL)
 316                         return (ENOMEM);
 317                 fp->fp_tcpopts = fpioc->fp_tcpopts;
 318                 fp->fp_wsize = fpioc->fp_wsize;
 319                 fp->fp_psize = fpioc->fp_psize;
 320                 fp->fp_mss = fpioc->fp_mss;
 321                 fp->fp_flags = fpioc->fp_flags;
 322                 fp->fp_optcnt = fpioc->fp_optcnt;
 323                 fp->fp_wscale = fpioc->fp_wscale;
 324                 fp->fp_ttl = fpioc->fp_ttl;
 325                 SLIST_INIT(&fp->fp_oses);
 326                 if ((entry = malloc(sizeof(*entry), M_PFOSFP, M_NOWAIT))
 327                     == NULL) {
 328                         free(fp, M_PFOSFP);
 329                         return (ENOMEM);
 330                 }
 331                 pf_osfp_insert(&V_pf_osfp_list, fp);
 332         }
 333         memcpy(entry, &fpioc->fp_os, sizeof(*entry));
 334
 335         /* Make sure the strings are NUL terminated */
 336         entry->fp_class_nm[sizeof(entry->fp_class_nm)-1] = '\0';
 337         entry->fp_version_nm[sizeof(entry->fp_version_nm)-1] = '\0';
 338         entry->fp_subtype_nm[sizeof(entry->fp_subtype_nm)-1] = '\0';
 339
 340         SLIST_INSERT_HEAD(&fp->fp_oses, entry, fp_entry);
 341
 342 #ifdef PFDEBUG
 343         if ((fp = pf_osfp_validate()))
 344                 printf("Invalid fingerprint list\n");
 345 #endif /* PFDEBUG */
 346         return (0);
 347 }
 348
 349 /* Find a fingerprint in the list */
 350 static struct pf_os_fingerprint *
 351 pf_osfp_find(struct pf_osfp_list *list, struct pf_os_fingerprint *find,
 352     u_int8_t ttldiff)
 353 {
 354         struct pf_os_fingerprint *f;
 355
 356 #define MATCH_INT(_MOD, _DC, _field)                                    \
 357         if ((f->fp_flags & _DC) == 0) {                                 \
 358                 if ((f->fp_flags & _MOD) == 0) {                        \
 359                         if (f->_field != find->_field)                  \
 360                                 continue;                               \
 361                 } else {                                                \
 362                         if (f->_field == 0 || find->_field % f->_field) \
 363                                 continue;                               \
 364                 }                                                       \
 365         }
 366
 367         SLIST_FOREACH(f, list, fp_next) {
 368                 if (f->fp_tcpopts != find->fp_tcpopts ||
 369                     f->fp_optcnt != find->fp_optcnt ||
 370                     f->fp_ttl < find->fp_ttl ||
 371                     f->fp_ttl - find->fp_ttl > ttldiff ||
 372                     (f->fp_flags & (PF_OSFP_DF|PF_OSFP_TS0)) !=
 373                     (find->fp_flags & (PF_OSFP_DF|PF_OSFP_TS0)))
 374                         continue;
 375
 376                 MATCH_INT(PF_OSFP_PSIZE_MOD, PF_OSFP_PSIZE_DC, fp_psize)
 377                 MATCH_INT(PF_OSFP_MSS_MOD, PF_OSFP_MSS_DC, fp_mss)
 378                 MATCH_INT(PF_OSFP_WSCALE_MOD, PF_OSFP_WSCALE_DC, fp_wscale)
 379                 if ((f->fp_flags & PF_OSFP_WSIZE_DC) == 0) {
 380                         if (f->fp_flags & PF_OSFP_WSIZE_MSS) {
 381                                 if (find->fp_mss == 0)
 382                                         continue;
 383
 384 /*
 385  * Some "smart" NAT devices and DSL routers will tweak the MSS size and
 386  * will set it to whatever is suitable for the link type.
 387  */
 388 #define SMART_MSS       1460
 389                                 if ((find->fp_wsize % find->fp_mss ||
 390                                     find->fp_wsize / find->fp_mss !=
 391                                     f->fp_wsize) &&
 392                                     (find->fp_wsize % SMART_MSS ||
 393                                     find->fp_wsize / SMART_MSS !=
 394                                     f->fp_wsize))
 395                                         continue;
 396                         } else if (f->fp_flags & PF_OSFP_WSIZE_MTU) {
 397                                 if (find->fp_mss == 0)
 398                                         continue;
 399
 400 #define MTUOFF          (sizeof(struct ip) + sizeof(struct tcphdr))
 401 #define SMART_MTU       (SMART_MSS + MTUOFF)
 402                                 if ((find->fp_wsize % (find->fp_mss + MTUOFF) ||
 403                                     find->fp_wsize / (find->fp_mss + MTUOFF) !=
 404                                     f->fp_wsize) &&
 405                                     (find->fp_wsize % SMART_MTU ||
 406                                     find->fp_wsize / SMART_MTU !=
 407                                     f->fp_wsize))
 408                                         continue;
 409                         } else if (f->fp_flags & PF_OSFP_WSIZE_MOD) {
 410                                 if (f->fp_wsize == 0 || find->fp_wsize %
 411                                     f->fp_wsize)
 412                                         continue;
 413                         } else {
 414                                 if (f->fp_wsize != find->fp_wsize)
 415                                         continue;
 416                         }
 417                 }
 418                 return (f);
 419         }
 420
 421         return (NULL);
 422 }
 423
 424 /* Find an exact fingerprint in the list */
 425 static struct pf_os_fingerprint *
 426 pf_osfp_find_exact(struct pf_osfp_list *list, struct pf_os_fingerprint *find)
 427 {
 428         struct pf_os_fingerprint *f;
 429
 430         SLIST_FOREACH(f, list, fp_next) {
 431                 if (f->fp_tcpopts == find->fp_tcpopts &&
 432                     f->fp_wsize == find->fp_wsize &&
 433                     f->fp_psize == find->fp_psize &&
 434                     f->fp_mss == find->fp_mss &&
 435                     f->fp_flags == find->fp_flags &&
 436                     f->fp_optcnt == find->fp_optcnt &&
 437                     f->fp_wscale == find->fp_wscale &&
 438                     f->fp_ttl == find->fp_ttl)
 439                         return (f);
 440         }
 441
 442         return (NULL);
 443 }
 444
 445 /* Insert a fingerprint into the list */
 446 static void
 447 pf_osfp_insert(struct pf_osfp_list *list, struct pf_os_fingerprint *ins)
 448 {
 449         struct pf_os_fingerprint *f, *prev = NULL;
 450
 451         /* XXX need to go semi tree based.  can key on tcp options */
 452
 453         SLIST_FOREACH(f, list, fp_next)
 454                 prev = f;
 455         if (prev)
 456                 SLIST_INSERT_AFTER(prev, ins, fp_next);
 457         else
 458                 SLIST_INSERT_HEAD(list, ins, fp_next);
 459 }
 460
 461 /* Fill a fingerprint by its number (from an ioctl) */
 462 int
 463 pf_osfp_get(struct pf_osfp_ioctl *fpioc)
 464 {
 465         struct pf_os_fingerprint *fp;
 466         struct pf_osfp_entry *entry;
 467         int num = fpioc->fp_getnum;
 468         int i = 0;
 469
 470         memset(fpioc, 0, sizeof(*fpioc));
 471         SLIST_FOREACH(fp, &V_pf_osfp_list, fp_next) {
 472                 SLIST_FOREACH(entry, &fp->fp_oses, fp_entry) {
 473                         if (i++ == num) {
 474                                 fpioc->fp_mss = fp->fp_mss;
 475                                 fpioc->fp_wsize = fp->fp_wsize;
 476                                 fpioc->fp_flags = fp->fp_flags;
 477                                 fpioc->fp_psize = fp->fp_psize;
 478                                 fpioc->fp_ttl = fp->fp_ttl;
 479                                 fpioc->fp_wscale = fp->fp_wscale;
 480                                 fpioc->fp_getnum = num;
 481                                 memcpy(&fpioc->fp_os, entry,
 482                                     sizeof(fpioc->fp_os));
 483                                 return (0);
 484                         }
 485                 }
 486         }
 487
 488         return (EBUSY);
 489 }
 490
 491 #ifdef PFDEBUG
 492 /* Validate that each signature is reachable */
 493 static struct pf_os_fingerprint *
 494 pf_osfp_validate(void)
 495 {
 496         struct pf_os_fingerprint *f, *f2, find;
 497
 498         SLIST_FOREACH(f, &V_pf_osfp_list, fp_next) {
 499                 memcpy(&find, f, sizeof(find));
 500
 501                 /* We do a few MSS/th_win percolations to make things unique */
 502                 if (find.fp_mss == 0)
 503                         find.fp_mss = 128;
 504                 if (f->fp_flags & PF_OSFP_WSIZE_MSS)
 505                         find.fp_wsize *= find.fp_mss;
 506                 else if (f->fp_flags & PF_OSFP_WSIZE_MTU)
 507                         find.fp_wsize *= (find.fp_mss + 40);
 508                 else if (f->fp_flags & PF_OSFP_WSIZE_MOD)
 509                         find.fp_wsize *= 2;
 510                 if (f != (f2 = pf_osfp_find(&V_pf_osfp_list, &find, 0))) {
 511                         if (f2)
 512                                 printf("Found \"%s %s %s\" instead of "
 513                                     "\"%s %s %s\"\n",
 514                                     SLIST_FIRST(&f2->fp_oses)->fp_class_nm,
 515                                     SLIST_FIRST(&f2->fp_oses)->fp_version_nm,
 516                                     SLIST_FIRST(&f2->fp_oses)->fp_subtype_nm,
 517                                     SLIST_FIRST(&f->fp_oses)->fp_class_nm,
 518                                     SLIST_FIRST(&f->fp_oses)->fp_version_nm,
 519                                     SLIST_FIRST(&f->fp_oses)->fp_subtype_nm);
 520                         else
 521                                 printf("Couldn't find \"%s %s %s\"\n",
 522                                     SLIST_FIRST(&f->fp_oses)->fp_class_nm,
 523                                     SLIST_FIRST(&f->fp_oses)->fp_version_nm,
 524                                     SLIST_FIRST(&f->fp_oses)->fp_subtype_nm);
 525                         return (f);
 526                 }
 527         }
 528         return (NULL);
 529 }
 530 #endif /* PFDEBUG */