| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * Report MTU on path to specified host |
| 4 | * |
| 5 | * (c) 2008 Straylight/Edgeware |
| 6 | */ |
| 7 | |
| 8 | /*----- Licensing notice --------------------------------------------------* |
| 9 | * |
| 10 | * This file is part of Trivial IP Encryption (TrIPE). |
| 11 | * |
| 12 | * TrIPE is free software; you can redistribute it and/or modify |
| 13 | * it under the terms of the GNU General Public License as published by |
| 14 | * the Free Software Foundation; either version 2 of the License, or |
| 15 | * (at your option) any later version. |
| 16 | * |
| 17 | * TrIPE is distributed in the hope that it will be useful, |
| 18 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 20 | * GNU General Public License for more details. |
| 21 | * |
| 22 | * You should have received a copy of the GNU General Public License |
| 23 | * along with TrIPE; if not, write to the Free Software Foundation, |
| 24 | * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
| 25 | */ |
| 26 | |
| 27 | /*----- Header files ------------------------------------------------------*/ |
| 28 | |
| 29 | #if defined(linux) |
| 30 | # define _BSD_SOURCE |
| 31 | #endif |
| 32 | |
| 33 | #include "config.h" |
| 34 | |
| 35 | #include <assert.h> |
| 36 | #include <errno.h> |
| 37 | #include <stddef.h> |
| 38 | #include <stdio.h> |
| 39 | #include <stdlib.h> |
| 40 | #include <string.h> |
| 41 | #include <time.h> |
| 42 | |
| 43 | #include <sys/types.h> |
| 44 | #include <sys/time.h> |
| 45 | #include <unistd.h> |
| 46 | |
| 47 | #include <sys/socket.h> |
| 48 | #include <netinet/in.h> |
| 49 | #include <arpa/inet.h> |
| 50 | #include <netdb.h> |
| 51 | |
| 52 | #include <netinet/in_systm.h> |
| 53 | #include <netinet/ip.h> |
| 54 | #include <netinet/ip_icmp.h> |
| 55 | #include <netinet/udp.h> |
| 56 | |
| 57 | #include <net/if.h> |
| 58 | #include <ifaddrs.h> |
| 59 | #include <sys/ioctl.h> |
| 60 | |
| 61 | #include <mLib/alloc.h> |
| 62 | #include <mLib/bits.h> |
| 63 | #include <mLib/dstr.h> |
| 64 | #include <mLib/hex.h> |
| 65 | #include <mLib/mdwopt.h> |
| 66 | #include <mLib/quis.h> |
| 67 | #include <mLib/report.h> |
| 68 | #include <mLib/tv.h> |
| 69 | |
| 70 | /*----- Static variables --------------------------------------------------*/ |
| 71 | |
| 72 | static unsigned char buf[65536]; |
| 73 | |
| 74 | #define POLY 0x1002d |
| 75 | |
| 76 | /*----- Utility functions -------------------------------------------------*/ |
| 77 | |
| 78 | /* Step a value according to a simple LFSR. */ |
| 79 | #define STEP(q) \ |
| 80 | do (q) = ((q) & 0x8000) ? ((q) << 1) ^ POLY : ((q) << 1); while (0) |
| 81 | |
| 82 | /* Fill buffer with a constant but pseudorandom string. Uses a simple |
| 83 | * LFSR. |
| 84 | */ |
| 85 | static void fillbuffer(unsigned char *p, size_t sz) |
| 86 | { |
| 87 | unsigned int y = 0xbc20; |
| 88 | const unsigned char *l = p + sz; |
| 89 | int i; |
| 90 | |
| 91 | while (p < l) { |
| 92 | *p++ = y & 0xff; |
| 93 | for (i = 0; i < 8; i++) STEP(y); |
| 94 | } |
| 95 | } |
| 96 | |
| 97 | /* Convert a string to floating point. */ |
| 98 | static double s2f(const char *s, const char *what) |
| 99 | { |
| 100 | double f; |
| 101 | char *q; |
| 102 | |
| 103 | errno = 0; |
| 104 | f = strtod(s, &q); |
| 105 | if (errno || *q) die(EXIT_FAILURE, "bad %s", what); |
| 106 | return (f); |
| 107 | } |
| 108 | |
| 109 | /* Convert a floating-point value into a struct timeval. */ |
| 110 | static void f2tv(struct timeval *tv, double t) |
| 111 | { tv->tv_sec = t; tv->tv_usec = (t - tv->tv_sec)*MILLION; } |
| 112 | |
| 113 | /*----- Main algorithm skeleton -------------------------------------------*/ |
| 114 | |
| 115 | struct param { |
| 116 | unsigned f; /* Various flags */ |
| 117 | #define F_VERBOSE 1u /* Give a running commentary */ |
| 118 | double retx; /* Initial retransmit interval */ |
| 119 | double regr; /* Retransmit growth factor */ |
| 120 | double timeout; /* Retransmission timeout */ |
| 121 | int seqoff; /* Offset to write sequence number */ |
| 122 | const struct probe_ops *pops; /* Probe algorithm description */ |
| 123 | struct sockaddr_in sin; /* Destination address */ |
| 124 | }; |
| 125 | |
| 126 | struct probestate { |
| 127 | const struct param *pp; |
| 128 | unsigned q; |
| 129 | }; |
| 130 | |
| 131 | struct probe_ops { |
| 132 | const char *name; |
| 133 | const struct probe_ops *next; |
| 134 | size_t statesz; |
| 135 | int (*setup)(void *, int, const struct param *); |
| 136 | void (*finish)(void *); |
| 137 | void (*selprep)(void *, int *, fd_set *); |
| 138 | int (*xmit)(void *, int); |
| 139 | int (*selproc)(void *, fd_set *, struct probestate *); |
| 140 | }; |
| 141 | |
| 142 | #define OPS_CHAIN 0 |
| 143 | |
| 144 | enum { |
| 145 | RC_FAIL = -99, |
| 146 | RC_OK = 0, |
| 147 | RC_LOWER = -1, |
| 148 | RC_HIGHER = -2, |
| 149 | RC_NOREPLY = -3 |
| 150 | /* or a positive MTU upper-bound */ |
| 151 | }; |
| 152 | |
| 153 | /* Add a file descriptor FD to the set `fd_in', updating `*maxfd'. */ |
| 154 | #define ADDFD(fd) \ |
| 155 | do { FD_SET(fd, fd_in); if (*maxfd < fd) *maxfd = fd; } while (0) |
| 156 | |
| 157 | /* Check whether a buffer contains a packet from our current probe. */ |
| 158 | static int mypacketp(struct probestate *ps, |
| 159 | const unsigned char *p, size_t sz) |
| 160 | { |
| 161 | const struct param *pp = ps->pp; |
| 162 | |
| 163 | return (sz >= pp->seqoff + 2 && LOAD16(p + pp->seqoff) == ps->q); |
| 164 | } |
| 165 | |
| 166 | /* See whether MTU is an acceptable MTU value. Return an appropriate |
| 167 | * RC_... code or a new suggested MTU. |
| 168 | */ |
| 169 | static int probe(struct probestate *ps, void *st, int mtu) |
| 170 | { |
| 171 | const struct param *pp = ps->pp; |
| 172 | fd_set fd_in; |
| 173 | struct timeval tv, now, when, done; |
| 174 | double timer = pp->retx; |
| 175 | int rc, maxfd; |
| 176 | |
| 177 | /* Set up the first retransmit and give-up timers. */ |
| 178 | gettimeofday(&now, 0); |
| 179 | f2tv(&tv, pp->timeout); TV_ADD(&done, &now, &tv); |
| 180 | f2tv(&tv, timer); TV_ADD(&when, &now, &tv); |
| 181 | if (TV_CMP(&when, >, &done)) when = done; |
| 182 | |
| 183 | /* Send the initial probe. */ |
| 184 | if (pp->f & F_VERBOSE) |
| 185 | moan("sending probe of size %d (seq = %04x)", mtu, ps->q); |
| 186 | STEP(ps->q); |
| 187 | STORE16(buf + pp->seqoff, ps->q); |
| 188 | if ((rc = pp->pops->xmit(st, mtu)) != RC_OK) return (rc); |
| 189 | |
| 190 | for (;;) { |
| 191 | |
| 192 | /* Wait for something interesting to happen. */ |
| 193 | maxfd = 0; FD_ZERO(&fd_in); |
| 194 | pp->pops->selprep(st, &maxfd, &fd_in); |
| 195 | TV_SUB(&tv, &when, &now); |
| 196 | if (select(maxfd + 1, &fd_in, 0, 0, &tv) < 0) return (RC_FAIL); |
| 197 | gettimeofday(&now, 0); |
| 198 | |
| 199 | /* See whether the probe method has any answers for us. */ |
| 200 | if ((rc = pp->pops->selproc(st, &fd_in, ps)) != RC_OK) return (rc); |
| 201 | |
| 202 | /* If we've waited too long, give up. If we should retransmit, do |
| 203 | * that. |
| 204 | */ |
| 205 | if (TV_CMP(&now, >, &done)) |
| 206 | return (RC_NOREPLY); |
| 207 | else if (TV_CMP(&now, >, &when)) { |
| 208 | if (pp->f & F_VERBOSE) moan("re-sending probe of size %d", mtu); |
| 209 | if ((rc = pp->pops->xmit(st, mtu)) != RC_OK) return (rc); |
| 210 | do { |
| 211 | timer *= pp->regr; f2tv(&tv, timer); TV_ADD(&when, &when, &tv); |
| 212 | } while (TV_CMP(&when, <, &now)); |
| 213 | if (TV_CMP(&when, >, &done)) when = done; |
| 214 | } |
| 215 | } |
| 216 | } |
| 217 | |
| 218 | /* Discover the path MTU to the destination address. */ |
| 219 | static int pathmtu(const struct param *pp) |
| 220 | { |
| 221 | int sk; |
| 222 | int mtu, lo, hi; |
| 223 | int rc, droppy = -1; |
| 224 | void *st; |
| 225 | struct probestate ps; |
| 226 | |
| 227 | /* Build and connect a UDP socket. We'll need this to know the local port |
| 228 | * number to use if nothing else. Set other stuff up. |
| 229 | */ |
| 230 | if ((sk = socket(PF_INET, SOCK_DGRAM, 0)) < 0) goto fail_0; |
| 231 | if (connect(sk, (struct sockaddr *)&pp->sin, sizeof(pp->sin))) goto fail_1; |
| 232 | st = xmalloc(pp->pops->statesz); |
| 233 | if ((mtu = pp->pops->setup(st, sk, pp)) < 0) goto fail_2; |
| 234 | ps.pp = pp; ps.q = rand() & 0xffff; |
| 235 | lo = 576; hi = mtu; |
| 236 | |
| 237 | /* And now we do a thing which is sort of like a binary search, except that |
| 238 | * we also take explicit clues as establishing a new upper bound, and we |
| 239 | * try to hug that initially. |
| 240 | */ |
| 241 | for (;;) { |
| 242 | assert(lo <= mtu && mtu <= hi); |
| 243 | if (pp->f & F_VERBOSE) moan("probe: %d <= %d <= %d", lo, mtu, hi); |
| 244 | rc = probe(&ps, st, mtu); |
| 245 | switch (rc) { |
| 246 | |
| 247 | case RC_FAIL: |
| 248 | if (pp->f & F_VERBOSE) moan("probe failed"); |
| 249 | goto fail_3; |
| 250 | |
| 251 | case RC_NOREPLY: |
| 252 | /* If we've not seen a dropped packet before then we don't know what |
| 253 | * this means yet -- in particular, we don't know which bit of the |
| 254 | * network is swallowing packets. Send a minimum-size probe. If |
| 255 | * that doesn't come back then assume that the remote host is |
| 256 | * swallowing our packets. If it does, then we assume that dropped |
| 257 | * packets are a result of ICMP fragmentation-needed reports being |
| 258 | * lost or suppressed. |
| 259 | */ |
| 260 | if (pp->f & F_VERBOSE) moan("gave up: black hole detected"); |
| 261 | if (droppy == -1) { |
| 262 | if (pp->f & F_VERBOSE) moan("sending minimum-size probe"); |
| 263 | switch (probe(&ps, st, lo)) { |
| 264 | case RC_FAIL: |
| 265 | goto fail_3; |
| 266 | case RC_NOREPLY: |
| 267 | if (pp->f & F_VERBOSE) { |
| 268 | moan("no reply from min-size probe: " |
| 269 | "assume black hole at target"); |
| 270 | } |
| 271 | droppy = 1; |
| 272 | break; |
| 273 | case RC_HIGHER: |
| 274 | if (pp->f & F_VERBOSE) { |
| 275 | moan("reply from min-size probe OK: " |
| 276 | "assume black hole in network"); |
| 277 | } |
| 278 | droppy = 0; |
| 279 | break; |
| 280 | default: |
| 281 | if (pp->f & F_VERBOSE) |
| 282 | moan("unexpected return code from probe"); |
| 283 | errno = ENOTCONN; |
| 284 | goto fail_3; |
| 285 | } |
| 286 | } |
| 287 | |
| 288 | if (droppy) goto higher; else goto lower; |
| 289 | |
| 290 | case RC_HIGHER: |
| 291 | higher: |
| 292 | if (droppy == -1) { |
| 293 | if (pp->f & F_VERBOSE) |
| 294 | moan("probe returned: remote host is not a black hole"); |
| 295 | droppy = 0; |
| 296 | } |
| 297 | if (mtu == hi) { |
| 298 | if (pp->f & F_VERBOSE) moan("probe returned: found correct MTU"); |
| 299 | goto done; |
| 300 | } |
| 301 | lo = mtu; |
| 302 | |
| 303 | /* Now we must make a new guess, between lo and hi. We know that lo |
| 304 | * is good; but we're not so sure about hi here. We know that hi > |
| 305 | * lo, so this will find an approximate midpoint, greater than lo and |
| 306 | * no more than hi. |
| 307 | */ |
| 308 | if (pp->f & F_VERBOSE) moan("probe returned: guessing higher"); |
| 309 | mtu += (hi - lo + 1)/2; |
| 310 | break; |
| 311 | |
| 312 | case RC_LOWER: |
| 313 | lower: |
| 314 | /* If this didn't work, and we're already at the bottom of our |
| 315 | * possible range, then something has gone horribly wrong. |
| 316 | */ |
| 317 | assert(lo < mtu); |
| 318 | hi = mtu - 1; |
| 319 | if (lo == hi) { |
| 320 | if (pp->f & F_VERBOSE) moan("error returned: found correct MTU"); |
| 321 | mtu = lo; |
| 322 | goto done; |
| 323 | } |
| 324 | |
| 325 | /* We must make a new guess, between lo and hi. We're probably |
| 326 | * fairly sure that lo will succeed, since either it's the minimum |
| 327 | * MTU or we've tested it already; but we're not quite sure about hi, |
| 328 | * so we want to aim high. |
| 329 | */ |
| 330 | if (pp->f & F_VERBOSE) moan("error returned: guessing lower"); |
| 331 | mtu -= (hi - lo + 1)/2; |
| 332 | break; |
| 333 | |
| 334 | default: |
| 335 | if (pp->f & F_VERBOSE) moan("error returned with new MTU estimate"); |
| 336 | mtu = hi = rc; |
| 337 | break; |
| 338 | } |
| 339 | } |
| 340 | |
| 341 | done: |
| 342 | /* Clean up and return our result. */ |
| 343 | pp->pops->finish(st); |
| 344 | xfree(st); |
| 345 | close(sk); |
| 346 | return (mtu); |
| 347 | |
| 348 | fail_3: |
| 349 | pp->pops->finish(st); |
| 350 | fail_2: |
| 351 | xfree(st); |
| 352 | fail_1: |
| 353 | close(sk); |
| 354 | fail_0: |
| 355 | return (-1); |
| 356 | } |
| 357 | |
| 358 | /*----- Doing it the hard way ---------------------------------------------*/ |
| 359 | |
| 360 | #if defined(linux) || defined(__OpenBSD__) |
| 361 | #define IPHDR_SANE |
| 362 | #endif |
| 363 | |
| 364 | #ifdef IPHDR_SANE |
| 365 | # define sane_htons htons |
| 366 | # define sane_htonl htonl |
| 367 | #else |
| 368 | # define sane_htons |
| 369 | # define sane_htonl |
| 370 | #endif |
| 371 | |
| 372 | static int rawicmp = -1, rawudp = -1, rawerr = 0; |
| 373 | |
| 374 | #define IPCK_INIT 0xffff |
| 375 | |
| 376 | /* Compute an IP checksum over some data. This is a restartable interface: |
| 377 | * initialize A to `IPCK_INIT' for the first call. |
| 378 | */ |
| 379 | static unsigned ipcksum(const void *buf, size_t n, unsigned a) |
| 380 | { |
| 381 | unsigned long aa = a ^ 0xffff; |
| 382 | const unsigned char *p = buf, *l = p + n; |
| 383 | |
| 384 | while (p < l - 1) { aa += LOAD16_B(p); p += 2; } |
| 385 | if (p < l) { aa += (unsigned)(*p) << 8; } |
| 386 | do aa = (aa & 0xffff) + (aa >> 16); while (aa >= 0x10000); |
| 387 | return (aa == 0xffff ? aa : aa ^ 0xffff); |
| 388 | } |
| 389 | |
| 390 | /* TCP/UDP pseudoheader structure. */ |
| 391 | struct phdr { |
| 392 | struct in_addr ph_src, ph_dst; |
| 393 | u_char ph_z, ph_p; |
| 394 | u_short ph_len; |
| 395 | }; |
| 396 | |
| 397 | struct raw_state { |
| 398 | struct sockaddr_in me, sin; |
| 399 | int sk, rawicmp, rawudp; |
| 400 | unsigned q; |
| 401 | }; |
| 402 | |
| 403 | static int raw_setup(void *stv, int sk, const struct param *pp) |
| 404 | { |
| 405 | struct raw_state *st = stv; |
| 406 | size_t sz; |
| 407 | int i, mtu = -1; |
| 408 | struct ifaddrs *ifa, *ifaa, *ifap; |
| 409 | struct ifreq ifr; |
| 410 | |
| 411 | /* If we couldn't acquire raw sockets, we fail here. */ |
| 412 | if (rawerr) { errno = rawerr; goto fail_0; } |
| 413 | st->rawicmp = rawicmp; st->rawudp = rawudp; st->sk = sk; |
| 414 | |
| 415 | /* Initialize the sequence number. */ |
| 416 | st->q = rand() & 0xffff; |
| 417 | |
| 418 | /* Snaffle the local and remote address and port number. */ |
| 419 | st->sin = pp->sin; |
| 420 | sz = sizeof(st->me); |
| 421 | if (getsockname(sk, (struct sockaddr *)&st->me, &sz)) |
| 422 | goto fail_0; |
| 423 | |
| 424 | /* There isn't a portable way to force the DF flag onto a packet through |
| 425 | * UDP, or even through raw IP, unless we write the entire IP header |
| 426 | * ourselves. This is somewhat annoying, especially since we have an |
| 427 | * uphill struggle keeping track of which systems randomly expect which |
| 428 | * header fields to be presented in host byte order. Oh, well. |
| 429 | */ |
| 430 | i = 1; |
| 431 | if (setsockopt(rawudp, IPPROTO_IP, IP_HDRINCL, &i, sizeof(i))) goto fail_0; |
| 432 | |
| 433 | /* Find an upper bound on the MTU. Do two passes over the interface |
| 434 | * list. If we can find matches for our local address then use the |
| 435 | * highest one of those; otherwise do a second pass and simply take the |
| 436 | * highest MTU of any network interface. |
| 437 | */ |
| 438 | if (getifaddrs(&ifaa)) goto fail_0; |
| 439 | for (i = 0; i < 2; i++) { |
| 440 | for (ifap = 0, ifa = ifaa; ifa; ifa = ifa->ifa_next) { |
| 441 | if (!(ifa->ifa_flags & IFF_UP) || !ifa->ifa_addr || |
| 442 | ifa->ifa_addr->sa_family != AF_INET || |
| 443 | (i == 0 && |
| 444 | ((struct sockaddr_in *)ifa->ifa_addr)->sin_addr.s_addr != |
| 445 | st->me.sin_addr.s_addr) || |
| 446 | (i == 1 && ifap && strcmp(ifap->ifa_name, ifa->ifa_name) == 0) || |
| 447 | strlen(ifa->ifa_name) >= sizeof(ifr.ifr_name)) |
| 448 | continue; |
| 449 | ifap = ifa; |
| 450 | strcpy(ifr.ifr_name, ifa->ifa_name); |
| 451 | if (ioctl(sk, SIOCGIFMTU, &ifr)) goto fail_1; |
| 452 | if (mtu < ifr.ifr_mtu) mtu = ifr.ifr_mtu; |
| 453 | } |
| 454 | if (mtu > 0) break; |
| 455 | } |
| 456 | if (mtu < 0) { errno = ENOTCONN; goto fail_1; } |
| 457 | freeifaddrs(ifaa); |
| 458 | |
| 459 | /* Done. */ |
| 460 | return (mtu); |
| 461 | |
| 462 | fail_1: |
| 463 | freeifaddrs(ifaa); |
| 464 | fail_0: |
| 465 | return (-1); |
| 466 | } |
| 467 | |
| 468 | static void raw_finish(void *stv) { ; } |
| 469 | |
| 470 | static void raw_selprep(void *stv, int *maxfd, fd_set *fd_in) |
| 471 | { struct raw_state *st = stv; ADDFD(st->sk); ADDFD(st->rawicmp); } |
| 472 | |
| 473 | static int raw_xmit(void *stv, int mtu) |
| 474 | { |
| 475 | struct raw_state *st = stv; |
| 476 | unsigned char b[65536], *p; |
| 477 | struct ip *ip; |
| 478 | struct udphdr *udp; |
| 479 | struct phdr ph; |
| 480 | unsigned ck; |
| 481 | |
| 482 | /* Build the IP header. */ |
| 483 | ip = (struct ip *)b; |
| 484 | ip->ip_v = 4; |
| 485 | ip->ip_hl = sizeof(*ip)/4; |
| 486 | ip->ip_tos = IPTOS_RELIABILITY; |
| 487 | ip->ip_len = sane_htons(mtu); |
| 488 | STEP(st->q); ip->ip_id = htons(st->q); |
| 489 | ip->ip_off = sane_htons(0 | IP_DF); |
| 490 | ip->ip_ttl = 64; |
| 491 | ip->ip_p = IPPROTO_UDP; |
| 492 | ip->ip_sum = 0; |
| 493 | ip->ip_src = st->me.sin_addr; |
| 494 | ip->ip_dst = st->sin.sin_addr; |
| 495 | |
| 496 | /* Build a UDP packet in the output buffer. */ |
| 497 | udp = (struct udphdr *)(ip + 1); |
| 498 | udp->uh_sport = st->me.sin_port; |
| 499 | udp->uh_dport = st->sin.sin_port; |
| 500 | udp->uh_ulen = htons(mtu - sizeof(*ip)); |
| 501 | udp->uh_sum = 0; |
| 502 | |
| 503 | /* Copy the payload. */ |
| 504 | p = (unsigned char *)(udp + 1); |
| 505 | memcpy(p, buf, mtu - (p - b)); |
| 506 | |
| 507 | /* Calculate the UDP checksum. */ |
| 508 | ph.ph_src = ip->ip_src; |
| 509 | ph.ph_dst = ip->ip_dst; |
| 510 | ph.ph_z = 0; |
| 511 | ph.ph_p = IPPROTO_UDP; |
| 512 | ph.ph_len = udp->uh_ulen; |
| 513 | ck = IPCK_INIT; |
| 514 | ck = ipcksum(&ph, sizeof(ph), ck); |
| 515 | ck = ipcksum(udp, mtu - sizeof(*ip), ck); |
| 516 | udp->uh_sum = htons(ck); |
| 517 | |
| 518 | /* Send the whole thing off. If we're too big for the interface then we |
| 519 | * might need to trim immediately. |
| 520 | */ |
| 521 | if (sendto(st->rawudp, b, mtu, 0, |
| 522 | (struct sockaddr *)&st->sin, sizeof(st->sin)) < 0) { |
| 523 | if (errno == EMSGSIZE) return (RC_LOWER); |
| 524 | else goto fail_0; |
| 525 | } |
| 526 | |
| 527 | /* Done. */ |
| 528 | return (RC_OK); |
| 529 | |
| 530 | fail_0: |
| 531 | return (RC_FAIL); |
| 532 | } |
| 533 | |
| 534 | static int raw_selproc(void *stv, fd_set *fd_in, struct probestate *ps) |
| 535 | { |
| 536 | struct raw_state *st = stv; |
| 537 | unsigned char b[65536]; |
| 538 | struct ip *ip; |
| 539 | struct icmp *icmp; |
| 540 | struct udphdr *udp; |
| 541 | ssize_t n; |
| 542 | |
| 543 | /* An ICMP packet: see what's inside. */ |
| 544 | if (FD_ISSET(st->rawicmp, fd_in)) { |
| 545 | if ((n = read(st->rawicmp, b, sizeof(b))) < 0) goto fail_0; |
| 546 | |
| 547 | ip = (struct ip *)b; |
| 548 | if (n < sizeof(*ip) || n < sizeof(4*ip->ip_hl) || |
| 549 | ip->ip_v != 4 || ip->ip_p != IPPROTO_ICMP) |
| 550 | goto skip_icmp; |
| 551 | n -= sizeof(4*ip->ip_hl); |
| 552 | |
| 553 | icmp = (struct icmp *)(b + 4*ip->ip_hl); |
| 554 | if (n < sizeof(*icmp) || icmp->icmp_type != ICMP_UNREACH) |
| 555 | goto skip_icmp; |
| 556 | n -= offsetof(struct icmp, icmp_ip); |
| 557 | |
| 558 | ip = &icmp->icmp_ip; |
| 559 | if (n < sizeof(*ip) || |
| 560 | ip->ip_p != IPPROTO_UDP || ip->ip_hl != sizeof(*ip)/4 || |
| 561 | ip->ip_id != htons(st->q) || |
| 562 | ip->ip_src.s_addr != st->me.sin_addr.s_addr || |
| 563 | ip->ip_dst.s_addr != st->sin.sin_addr.s_addr) |
| 564 | goto skip_icmp; |
| 565 | n -= sizeof(*ip); |
| 566 | |
| 567 | udp = (struct udphdr *)(ip + 1); |
| 568 | if (n < sizeof(udp) || udp->uh_sport != st->me.sin_port || |
| 569 | udp->uh_dport != st->sin.sin_port) |
| 570 | goto skip_icmp; |
| 571 | n -= sizeof(*udp); |
| 572 | |
| 573 | if (icmp->icmp_code == ICMP_UNREACH_PORT) return (RC_HIGHER); |
| 574 | else if (icmp->icmp_code != ICMP_UNREACH_NEEDFRAG) goto skip_icmp; |
| 575 | else if (icmp->icmp_nextmtu) return (htons(icmp->icmp_nextmtu)); |
| 576 | else return (RC_LOWER); |
| 577 | } |
| 578 | skip_icmp:; |
| 579 | |
| 580 | /* If we got a reply to the current probe then we're good. If we got an |
| 581 | * error, or the packet's sequence number is wrong, then ignore it. |
| 582 | */ |
| 583 | if (FD_ISSET(st->sk, fd_in)) { |
| 584 | if ((n = read(st->sk, b, sizeof(b))) < 0) return (RC_OK); |
| 585 | else if (mypacketp(ps, b, n)) return (RC_HIGHER); |
| 586 | else return (RC_OK); |
| 587 | } |
| 588 | |
| 589 | return (RC_OK); |
| 590 | |
| 591 | fail_0: |
| 592 | return (RC_FAIL); |
| 593 | } |
| 594 | |
| 595 | static const struct probe_ops raw_ops = { |
| 596 | "raw", OPS_CHAIN, sizeof(struct raw_state), |
| 597 | raw_setup, raw_finish, |
| 598 | raw_selprep, raw_xmit, raw_selproc |
| 599 | }; |
| 600 | |
| 601 | #undef OPS_CHAIN |
| 602 | #define OPS_CHAIN &raw_ops |
| 603 | |
| 604 | /*----- Doing the job on Linux --------------------------------------------*/ |
| 605 | |
| 606 | #if defined(linux) |
| 607 | |
| 608 | #ifndef IP_MTU |
| 609 | # define IP_MTU 14 /* Blech! */ |
| 610 | #endif |
| 611 | |
| 612 | struct linux_state { |
| 613 | int sk; |
| 614 | }; |
| 615 | |
| 616 | static int linux_setup(void *stv, int sk, const struct param *pp) |
| 617 | { |
| 618 | struct linux_state *st = stv; |
| 619 | int i, mtu; |
| 620 | size_t sz; |
| 621 | |
| 622 | /* Snaffle the UDP socket. */ |
| 623 | st->sk = sk; |
| 624 | |
| 625 | /* Turn on kernel path-MTU discovery and force DF on. */ |
| 626 | i = IP_PMTUDISC_PROBE; |
| 627 | if (setsockopt(st->sk, IPPROTO_IP, IP_MTU_DISCOVER, &i, sizeof(i))) |
| 628 | return (-1); |
| 629 | |
| 630 | /* Read the initial MTU guess back and report it. */ |
| 631 | sz = sizeof(mtu); |
| 632 | if (getsockopt(st->sk, IPPROTO_IP, IP_MTU, &mtu, &sz)) |
| 633 | return (-1); |
| 634 | |
| 635 | /* Done. */ |
| 636 | return (mtu); |
| 637 | } |
| 638 | |
| 639 | static void linux_finish(void *stv) { ; } |
| 640 | |
| 641 | static void linux_selprep(void *stv, int *maxfd, fd_set *fd_in) |
| 642 | { struct linux_state *st = stv; ADDFD(st->sk); } |
| 643 | |
| 644 | static int linux_xmit(void *stv, int mtu) |
| 645 | { |
| 646 | struct linux_state *st = stv; |
| 647 | |
| 648 | /* Write the packet. */ |
| 649 | if (write(st->sk, buf, mtu - 28) >= 0) return (RC_OK); |
| 650 | else if (errno == EMSGSIZE) return (RC_LOWER); |
| 651 | else return (RC_FAIL); |
| 652 | } |
| 653 | |
| 654 | static int linux_selproc(void *stv, fd_set *fd_in, struct probestate *ps) |
| 655 | { |
| 656 | struct linux_state *st = stv; |
| 657 | int mtu; |
| 658 | size_t sz; |
| 659 | ssize_t n; |
| 660 | unsigned char b[65536]; |
| 661 | |
| 662 | /* Read an answer. If it looks like the right kind of error then report a |
| 663 | * success. This is potentially wrong, since we can't tell whether an |
| 664 | * error was delayed from an earlier probe. However, we never return |
| 665 | * RC_LOWER from this method, so the packet sizes ought to be monotonically |
| 666 | * decreasing and this won't cause trouble. Otherwise update from the |
| 667 | * kernel's idea of the right MTU. |
| 668 | */ |
| 669 | if (FD_ISSET(st->sk, fd_in)) { |
| 670 | n = read(st->sk, &buf, sizeof(buf)); |
| 671 | if (n >= 0 ? |
| 672 | mypacketp(ps, b, n) : |
| 673 | errno == ECONNREFUSED || errno == EHOSTUNREACH) |
| 674 | return (RC_HIGHER); |
| 675 | sz = sizeof(mtu); |
| 676 | if (getsockopt(st->sk, IPPROTO_IP, IP_MTU, &mtu, &sz)) |
| 677 | return (RC_FAIL); |
| 678 | return (mtu); |
| 679 | } |
| 680 | return (RC_OK); |
| 681 | } |
| 682 | |
| 683 | static const struct probe_ops linux_ops = { |
| 684 | "linux", OPS_CHAIN, sizeof(struct linux_state), |
| 685 | linux_setup, linux_finish, |
| 686 | linux_selprep, linux_xmit, linux_selproc |
| 687 | }; |
| 688 | |
| 689 | #undef OPS_CHAIN |
| 690 | #define OPS_CHAIN &linux_ops |
| 691 | |
| 692 | #endif |
| 693 | |
| 694 | /*----- Help options ------------------------------------------------------*/ |
| 695 | |
| 696 | static const struct probe_ops *probe_ops = OPS_CHAIN; |
| 697 | |
| 698 | static void version(FILE *fp) |
| 699 | { pquis(fp, "$, TrIPE version " VERSION "\n"); } |
| 700 | |
| 701 | static void usage(FILE *fp) |
| 702 | { |
| 703 | pquis(fp, "Usage: $ [-H HEADER] [-m METHOD]\n\ |
| 704 | [-r SECS] [-g FACTOR] [-t SECS] HOST [PORT]\n"); |
| 705 | } |
| 706 | |
| 707 | static void help(FILE *fp) |
| 708 | { |
| 709 | const struct probe_ops *ops; |
| 710 | |
| 711 | version(fp); |
| 712 | fputc('\n', fp); |
| 713 | usage(fp); |
| 714 | fputs("\ |
| 715 | \n\ |
| 716 | Options in full:\n\ |
| 717 | \n\ |
| 718 | -h, --help Show this help text.\n\ |
| 719 | -v, --version Show version number.\n\ |
| 720 | -u, --usage Show brief usage message.\n\ |
| 721 | \n\ |
| 722 | -g, --growth=FACTOR Growth factor for retransmit interval.\n\ |
| 723 | -m, --method=METHOD Use METHOD to probe for MTU.\n\ |
| 724 | -r, --retransmit=SECS Retransmit if no reply after SEC.\n\ |
| 725 | -t, --timeout=SECS Give up expecting a reply after SECS.\n\ |
| 726 | -H, --header=HEX Packet header, in hexadecimal.\n\ |
| 727 | \n\ |
| 728 | Probe methods:\n\ |
| 729 | ", fp); |
| 730 | for (ops = probe_ops; ops; ops = ops->next) |
| 731 | printf("\t%s\n", ops->name); |
| 732 | } |
| 733 | |
| 734 | /*----- Main code ---------------------------------------------------------*/ |
| 735 | |
| 736 | int main(int argc, char *argv[]) |
| 737 | { |
| 738 | struct param pp = { 0, 0.333, 3.0, 8.0, 0, OPS_CHAIN }; |
| 739 | hex_ctx hc; |
| 740 | dstr d = DSTR_INIT; |
| 741 | size_t sz; |
| 742 | int i; |
| 743 | unsigned long u; |
| 744 | char *q; |
| 745 | struct hostent *h; |
| 746 | struct servent *s; |
| 747 | unsigned f = 0; |
| 748 | |
| 749 | #define f_bogus 1u |
| 750 | |
| 751 | if ((rawicmp = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP)) < 0 || |
| 752 | (rawudp = socket(PF_INET, SOCK_RAW, IPPROTO_UDP)) < 0) |
| 753 | rawerr = errno; |
| 754 | if (setuid(getuid())) |
| 755 | abort(); |
| 756 | |
| 757 | ego(argv[0]); |
| 758 | fillbuffer(buf, sizeof(buf)); |
| 759 | pp.sin.sin_port = htons(7); |
| 760 | |
| 761 | for (;;) { |
| 762 | static const struct option opts[] = { |
| 763 | { "help", 0, 0, 'h' }, |
| 764 | { "version", 0, 0, 'V' }, |
| 765 | { "usage", 0, 0, 'u' }, |
| 766 | { "header", OPTF_ARGREQ, 0, 'H' }, |
| 767 | { "growth", OPTF_ARGREQ, 0, 'g' }, |
| 768 | { "method", OPTF_ARGREQ, 0, 'm' }, |
| 769 | { "retransmit", OPTF_ARGREQ, 0, 'r' }, |
| 770 | { "timeout", OPTF_ARGREQ, 0, 't' }, |
| 771 | { "verbose", 0, 0, 'v' }, |
| 772 | { 0, 0, 0, 0 } |
| 773 | }; |
| 774 | |
| 775 | i = mdwopt(argc, argv, "hVu" "H:g:m:r:t:v", opts, 0, 0, 0); |
| 776 | if (i < 0) break; |
| 777 | switch (i) { |
| 778 | case 'h': help(stdout); exit(0); |
| 779 | case 'V': version(stdout); exit(0); |
| 780 | case 'u': usage(stdout); exit(0); |
| 781 | |
| 782 | case 'H': |
| 783 | DRESET(&d); |
| 784 | hex_init(&hc); |
| 785 | hex_decode(&hc, optarg, strlen(optarg), &d); |
| 786 | hex_decode(&hc, 0, 0, &d); |
| 787 | sz = d.len < 532 ? d.len : 532; |
| 788 | memcpy(buf, d.buf, sz); |
| 789 | pp.seqoff = sz; |
| 790 | break; |
| 791 | |
| 792 | case 'g': pp.regr = s2f(optarg, "retransmit growth factor"); break; |
| 793 | case 'r': pp.retx = s2f(optarg, "retransmit interval"); break; |
| 794 | case 't': pp.timeout = s2f(optarg, "timeout"); break; |
| 795 | |
| 796 | case 'm': |
| 797 | for (pp.pops = OPS_CHAIN; pp.pops; pp.pops = pp.pops->next) |
| 798 | if (strcmp(pp.pops->name, optarg) == 0) goto found_alg; |
| 799 | die(EXIT_FAILURE, "unknown probe algorithm `%s'", optarg); |
| 800 | found_alg: |
| 801 | break; |
| 802 | |
| 803 | case 'v': pp.f |= F_VERBOSE; break; |
| 804 | |
| 805 | default: |
| 806 | f |= f_bogus; |
| 807 | break; |
| 808 | } |
| 809 | } |
| 810 | argv += optind; argc -= optind; |
| 811 | if ((f & f_bogus) || 1 > argc || argc > 2) { |
| 812 | usage(stderr); |
| 813 | exit(EXIT_FAILURE); |
| 814 | } |
| 815 | |
| 816 | if ((h = gethostbyname(*argv)) == 0) |
| 817 | die(EXIT_FAILURE, "unknown host `%s': %s", *argv, hstrerror(h_errno)); |
| 818 | if (h->h_addrtype != AF_INET) |
| 819 | die(EXIT_FAILURE, "unsupported address family for host `%s'", *argv); |
| 820 | memcpy(&pp.sin.sin_addr, h->h_addr, sizeof(struct in_addr)); |
| 821 | argv++; argc--; |
| 822 | |
| 823 | if (*argv) { |
| 824 | errno = 0; |
| 825 | u = strtoul(*argv, &q, 0); |
| 826 | if (!errno && !*q) |
| 827 | pp.sin.sin_port = htons(u); |
| 828 | else if ((s = getservbyname(*argv, "udp")) == 0) |
| 829 | die(EXIT_FAILURE, "unknown UDP service `%s'", *argv); |
| 830 | else |
| 831 | pp.sin.sin_port = s->s_port; |
| 832 | } |
| 833 | |
| 834 | pp.sin.sin_family = AF_INET; |
| 835 | i = pathmtu(&pp); |
| 836 | if (i < 0) |
| 837 | die(EXIT_FAILURE, "failed to discover MTU: %s", strerror(errno)); |
| 838 | printf("%d\n", i); |
| 839 | if (ferror(stdout) || fflush(stdout) || fclose(stdout)) |
| 840 | die(EXIT_FAILURE, "failed to write result: %s", strerror(errno)); |
| 841 | return (0); |
| 842 | } |
| 843 | |
| 844 | /*----- That's all, folks -------------------------------------------------*/ |