1 /* $NetBSD: fat.c,v 1.30 2019/06/04 00:08:00 christos Exp $ */ 2 3 /* 4 * Copyright (C) 1995, 1996, 1997 Wolfgang Solfrank 5 * Copyright (c) 1995 Martin Husemann 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28 29 #include <sys/cdefs.h> 30 #ifndef lint 31 __RCSID("$NetBSD: fat.c,v 1.30 2019/06/04 00:08:00 christos Exp $"); 32 #endif /* not lint */ 33 34 #include <stdlib.h> 35 #include <string.h> 36 #include <ctype.h> 37 #include <stdio.h> 38 #include <unistd.h> 39 40 #include "ext.h" 41 #include "fsutil.h" 42 43 static int checkclnum(struct bootblock *, u_int, cl_t, cl_t *); 44 static int clustdiffer(cl_t, cl_t *, cl_t *, u_int); 45 static int tryclear(struct bootblock *, struct fatEntry *, cl_t, cl_t *); 46 static int _readfat(int, struct bootblock *, u_int, u_char **); 47 48 /* 49 * Check a cluster number for valid value 50 */ 51 static int 52 checkclnum(struct bootblock *boot, u_int fat, cl_t cl, cl_t *next) 53 { 54 if (*next >= (CLUST_RSRVD&boot->ClustMask)) 55 *next |= ~boot->ClustMask; 56 if (*next == CLUST_FREE) { 57 boot->NumFree++; 58 return FSOK; 59 } 60 if (*next == CLUST_BAD) { 61 boot->NumBad++; 62 return FSOK; 63 } 64 if (*next < CLUST_FIRST 65 || (*next >= boot->NumClusters && *next < CLUST_EOFS)) { 66 pwarn("Cluster %u in FAT %u continues with %s cluster number %u\n", 67 cl, fat, 68 *next < CLUST_RSRVD ? "out of range" : "reserved", 69 *next&boot->ClustMask); 70 if (ask(0, "Truncate")) { 71 *next = CLUST_EOF; 72 return FSFATMOD; 73 } 74 return FSERROR; 75 } 76 return FSOK; 77 } 78 79 /* 80 * Read a FAT from disk. Returns 1 if successful, 0 otherwise. 81 */ 82 static int 83 _readfat(int fs, struct bootblock *boot, u_int no, u_char **buffer) 84 { 85 off_t off; 86 size_t len; 87 88 *buffer = malloc(len = boot->FATsecs * boot->BytesPerSec); 89 if (*buffer == NULL) { 90 perr("No space for FAT sectors (%zu)", len); 91 return 0; 92 } 93 94 off = boot->ResSectors + no * boot->FATsecs; 95 off *= boot->BytesPerSec; 96 97 if (lseek(fs, off, SEEK_SET) != off) { 98 perr("Unable to read FAT"); 99 goto err; 100 } 101 102 if ((size_t)read(fs, *buffer, boot->FATsecs * boot->BytesPerSec) 103 != boot->FATsecs * boot->BytesPerSec) { 104 perr("Unable to read FAT"); 105 goto err; 106 } 107 108 return 1; 109 110 err: 111 free(*buffer); 112 return 0; 113 } 114 115 /* 116 * Read a FAT and decode it into internal format 117 */ 118 int 119 readfat(int fs, struct bootblock *boot, u_int no, struct fatEntry **fp) 120 { 121 struct fatEntry *fat; 122 u_char *buffer, *p; 123 cl_t cl; 124 int ret = FSOK; 125 size_t len; 126 127 boot->NumFree = boot->NumBad = 0; 128 129 if (!_readfat(fs, boot, no, &buffer)) 130 return FSFATAL; 131 132 fat = malloc(len = boot->NumClusters * sizeof(struct fatEntry)); 133 if (fat == NULL) { 134 perr("No space for FAT clusters (%zu)", len); 135 free(buffer); 136 return FSFATAL; 137 } 138 (void)memset(fat, 0, len); 139 140 if (buffer[0] != boot->Media 141 || buffer[1] != 0xff || buffer[2] != 0xff 142 || (boot->ClustMask == CLUST16_MASK && buffer[3] != 0xff) 143 || (boot->ClustMask == CLUST32_MASK 144 && ((buffer[3]&0x0f) != 0x0f 145 || buffer[4] != 0xff || buffer[5] != 0xff 146 || buffer[6] != 0xff || (buffer[7]&0x0f) != 0x0f))) { 147 148 /* Windows 95 OSR2 (and possibly any later) changes 149 * the FAT signature to 0xXXffff7f for FAT16 and to 150 * 0xXXffff0fffffff07 for FAT32 upon boot, to know that the 151 * filesystem is dirty if it doesn't reboot cleanly. 152 * Check this special condition before errorring out. 153 */ 154 if (buffer[0] == boot->Media && buffer[1] == 0xff 155 && buffer[2] == 0xff 156 && ((boot->ClustMask == CLUST16_MASK && buffer[3] == 0x7f) 157 || (boot->ClustMask == CLUST32_MASK 158 && buffer[3] == 0x0f && buffer[4] == 0xff 159 && buffer[5] == 0xff && buffer[6] == 0xff 160 && buffer[7] == 0x07))) 161 ret |= FSDIRTY; 162 else { 163 /* just some odd byte sequence in FAT */ 164 165 switch (boot->ClustMask) { 166 case CLUST32_MASK: 167 pwarn("%s (%02x%02x%02x%02x%02x%02x%02x%02x)\n", 168 "FAT starts with odd byte sequence", 169 buffer[0], buffer[1], buffer[2], buffer[3], 170 buffer[4], buffer[5], buffer[6], buffer[7]); 171 break; 172 case CLUST16_MASK: 173 pwarn("%s (%02x%02x%02x%02x)\n", 174 "FAT starts with odd byte sequence", 175 buffer[0], buffer[1], buffer[2], buffer[3]); 176 break; 177 default: 178 pwarn("%s (%02x%02x%02x)\n", 179 "FAT starts with odd byte sequence", 180 buffer[0], buffer[1], buffer[2]); 181 break; 182 } 183 184 185 if (ask(1, "Correct")) 186 ret |= FSFIXFAT; 187 } 188 } 189 switch (boot->ClustMask) { 190 case CLUST32_MASK: 191 p = buffer + 8; 192 break; 193 case CLUST16_MASK: 194 p = buffer + 4; 195 break; 196 default: 197 p = buffer + 3; 198 break; 199 } 200 for (cl = CLUST_FIRST; cl < boot->NumClusters;) { 201 switch (boot->ClustMask) { 202 case CLUST32_MASK: 203 fat[cl].next = p[0] + (p[1] << 8) 204 + (p[2] << 16) + (p[3] << 24); 205 fat[cl].next &= boot->ClustMask; 206 ret |= checkclnum(boot, no, cl, &fat[cl].next); 207 cl++; 208 p += 4; 209 break; 210 case CLUST16_MASK: 211 fat[cl].next = p[0] + (p[1] << 8); 212 ret |= checkclnum(boot, no, cl, &fat[cl].next); 213 cl++; 214 p += 2; 215 break; 216 default: 217 fat[cl].next = (p[0] + (p[1] << 8)) & 0x0fff; 218 ret |= checkclnum(boot, no, cl, &fat[cl].next); 219 cl++; 220 if (cl >= boot->NumClusters) 221 break; 222 fat[cl].next = ((p[1] >> 4) + (p[2] << 4)) & 0x0fff; 223 ret |= checkclnum(boot, no, cl, &fat[cl].next); 224 cl++; 225 p += 3; 226 break; 227 } 228 } 229 230 free(buffer); 231 if (ret & FSFATAL) { 232 free(fat); 233 *fp = NULL; 234 } else 235 *fp = fat; 236 return ret; 237 } 238 239 /* 240 * Get type of reserved cluster 241 */ 242 const char * 243 rsrvdcltype(cl_t cl) 244 { 245 if (cl == CLUST_FREE) 246 return "free"; 247 if (cl < CLUST_BAD) 248 return "reserved"; 249 if (cl > CLUST_BAD) 250 return "as EOF"; 251 return "bad"; 252 } 253 254 static int 255 clustdiffer(cl_t cl, cl_t *cp1, cl_t *cp2, u_int fatnum) 256 { 257 if (*cp1 == CLUST_FREE || *cp1 >= CLUST_RSRVD) { 258 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) { 259 if ((*cp1 != CLUST_FREE && *cp1 < CLUST_BAD 260 && *cp2 != CLUST_FREE && *cp2 < CLUST_BAD) 261 || (*cp1 > CLUST_BAD && *cp2 > CLUST_BAD)) { 262 pwarn("Cluster %u is marked %s with different indicators, ", 263 cl, rsrvdcltype(*cp1)); 264 if (ask(1, "fix")) { 265 *cp2 = *cp1; 266 return FSFATMOD; 267 } 268 return FSFATAL; 269 } 270 pwarn("Cluster %u is marked %s in FAT 0, %s in FAT %u\n", 271 cl, rsrvdcltype(*cp1), rsrvdcltype(*cp2), fatnum); 272 if (ask(0, "use FAT 0's entry")) { 273 *cp2 = *cp1; 274 return FSFATMOD; 275 } 276 if (ask(0, "use FAT %u's entry", fatnum)) { 277 *cp1 = *cp2; 278 return FSFATMOD; 279 } 280 return FSFATAL; 281 } 282 pwarn("Cluster %u is marked %s in FAT 0, but continues with cluster %u in FAT %u\n", 283 cl, rsrvdcltype(*cp1), *cp2, fatnum); 284 if (ask(0, "Use continuation from FAT %u", fatnum)) { 285 *cp1 = *cp2; 286 return FSFATMOD; 287 } 288 if (ask(0, "Use mark from FAT 0")) { 289 *cp2 = *cp1; 290 return FSFATMOD; 291 } 292 return FSFATAL; 293 } 294 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) { 295 pwarn("Cluster %u continues with cluster %u in FAT 0, but is marked %s in FAT %u\n", 296 cl, *cp1, rsrvdcltype(*cp2), fatnum); 297 if (ask(0, "Use continuation from FAT 0")) { 298 *cp2 = *cp1; 299 return FSFATMOD; 300 } 301 if (ask(0, "Use mark from FAT %u", fatnum)) { 302 *cp1 = *cp2; 303 return FSFATMOD; 304 } 305 return FSERROR; 306 } 307 pwarn("Cluster %u continues with cluster %u in FAT 0, but with cluster %u in FAT %u\n", 308 cl, *cp1, *cp2, fatnum); 309 if (ask(0, "Use continuation from FAT 0")) { 310 *cp2 = *cp1; 311 return FSFATMOD; 312 } 313 if (ask(0, "Use continuation from FAT %u", fatnum)) { 314 *cp1 = *cp2; 315 return FSFATMOD; 316 } 317 return FSERROR; 318 } 319 320 /* 321 * Compare two FAT copies in memory. Resolve any conflicts and merge them 322 * into the first one. 323 */ 324 int 325 comparefat(struct bootblock *boot, struct fatEntry *first, 326 struct fatEntry *second, u_int fatnum) 327 { 328 cl_t cl; 329 int ret = FSOK; 330 331 for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) 332 if (first[cl].next != second[cl].next) 333 ret |= clustdiffer(cl, &first[cl].next, &second[cl].next, fatnum); 334 return ret; 335 } 336 337 void 338 clearchain(struct bootblock *boot, struct fatEntry *fat, cl_t head) 339 { 340 cl_t p, q; 341 342 for (p = head; p >= CLUST_FIRST && p < boot->NumClusters; p = q) { 343 if (fat[p].head != head) 344 break; 345 q = fat[p].next; 346 fat[p].next = fat[p].head = CLUST_FREE; 347 fat[p].length = 0; 348 } 349 } 350 351 int 352 tryclear(struct bootblock *boot, struct fatEntry *fat, cl_t head, cl_t *truncp) 353 { 354 if (ask(0, "Clear chain starting at %u", head)) { 355 clearchain(boot, fat, head); 356 return FSFATMOD; 357 } else if (ask(0, "Truncate")) { 358 uint32_t len; 359 cl_t p; 360 361 for (p = head, len = 0; 362 p >= CLUST_FIRST && p < boot->NumClusters; 363 p = fat[p].next, len++) 364 continue; 365 *truncp = CLUST_EOF; 366 fat[head].length = len; 367 return FSFATMOD; 368 } else 369 return FSERROR; 370 } 371 372 /* 373 * Check a complete FAT in-memory for crosslinks 374 */ 375 int 376 checkfat(struct bootblock *boot, struct fatEntry *fat) 377 { 378 cl_t head, p, h, n; 379 u_int len; 380 int ret = 0; 381 int conf; 382 383 /* 384 * pass 1: figure out the cluster chains. 385 */ 386 for (head = CLUST_FIRST; head < boot->NumClusters; head++) { 387 /* find next untravelled chain */ 388 if (fat[head].head != 0 /* cluster already belongs to some chain */ 389 || fat[head].next == CLUST_FREE 390 || fat[head].next == CLUST_BAD) 391 continue; /* skip it. */ 392 393 /* follow the chain and mark all clusters on the way */ 394 for (len = 0, p = head; 395 p >= CLUST_FIRST && p < boot->NumClusters && 396 fat[p].head != head; 397 p = fat[p].next) { 398 fat[p].head = head; 399 len++; 400 } 401 402 /* the head record gets the length */ 403 fat[head].length = fat[head].next == CLUST_FREE ? 0 : len; 404 } 405 406 /* 407 * pass 2: check for crosslinked chains (we couldn't do this in pass 1 because 408 * we didn't know the real start of the chain then - would have treated partial 409 * chains as interlinked with their main chain) 410 */ 411 for (head = CLUST_FIRST; head < boot->NumClusters; head++) { 412 /* find next untravelled chain */ 413 if (fat[head].head != head) 414 continue; 415 416 /* follow the chain to its end (hopefully) */ 417 for (len = fat[head].length, p = head; 418 (n = fat[p].next) >= CLUST_FIRST && n < boot->NumClusters; 419 p = n) 420 if (fat[n].head != head || len-- < 2) 421 break; 422 if (n >= CLUST_EOFS) 423 continue; 424 425 if (n == CLUST_FREE || n >= CLUST_RSRVD) { 426 pwarn("Cluster chain starting at %u ends with cluster marked %s\n", 427 head, rsrvdcltype(n)); 428 clear: 429 ret |= tryclear(boot, fat, head, &fat[p].next); 430 continue; 431 } 432 if (n < CLUST_FIRST || n >= boot->NumClusters) { 433 pwarn("Cluster chain starting at %u ends with cluster out of range (%u)\n", 434 head, n); 435 goto clear; 436 } 437 if (head == fat[n].head) { 438 pwarn("Cluster chain starting at %u loops at cluster %u\n", 439 440 head, p); 441 goto clear; 442 } 443 pwarn("Cluster chains starting at %u and %u are linked at cluster %u\n", 444 head, fat[n].head, n); 445 conf = tryclear(boot, fat, head, &fat[p].next); 446 if (ask(0, "Clear chain starting at %u", h = fat[n].head)) { 447 if (conf == FSERROR) { 448 /* 449 * Transfer the common chain to the one not cleared above. 450 */ 451 for (p = n; 452 p >= CLUST_FIRST && p < boot->NumClusters; 453 p = fat[p].next) { 454 if (h != fat[p].head) { 455 /* 456 * Have to reexamine this chain. 457 */ 458 head--; 459 break; 460 } 461 fat[p].head = head; 462 } 463 } 464 clearchain(boot, fat, h); 465 conf |= FSFATMOD; 466 } 467 ret |= conf; 468 } 469 470 return ret; 471 } 472 473 /* 474 * Write out FATs encoding them from the internal format 475 */ 476 int 477 writefat(int fs, struct bootblock *boot, struct fatEntry *fat, int correct_fat) 478 { 479 u_char *buffer, *p; 480 cl_t cl; 481 u_int i; 482 size_t fatsz; 483 off_t off; 484 int ret = FSOK; 485 486 buffer = malloc(fatsz = boot->FATsecs * boot->BytesPerSec); 487 if (buffer == NULL) { 488 perr("No space for FAT sectors (%zu)", fatsz); 489 return FSFATAL; 490 } 491 memset(buffer, 0, fatsz); 492 boot->NumFree = 0; 493 p = buffer; 494 if (correct_fat) { 495 *p++ = (u_char)boot->Media; 496 *p++ = 0xff; 497 *p++ = 0xff; 498 switch (boot->ClustMask) { 499 case CLUST16_MASK: 500 *p++ = 0xff; 501 break; 502 case CLUST32_MASK: 503 *p++ = 0x0f; 504 *p++ = 0xff; 505 *p++ = 0xff; 506 *p++ = 0xff; 507 *p++ = 0x0f; 508 break; 509 } 510 } else { 511 /* use same FAT signature as the old FAT has */ 512 int count; 513 u_char *old_fat; 514 515 switch (boot->ClustMask) { 516 case CLUST32_MASK: 517 count = 8; 518 break; 519 case CLUST16_MASK: 520 count = 4; 521 break; 522 default: 523 count = 3; 524 break; 525 } 526 527 if (!_readfat(fs, boot, boot->ValidFat >= 0 ? boot->ValidFat :0, 528 &old_fat)) { 529 free(buffer); 530 return FSFATAL; 531 } 532 533 memcpy(p, old_fat, count); 534 free(old_fat); 535 p += count; 536 } 537 538 for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) { 539 switch (boot->ClustMask) { 540 case CLUST32_MASK: 541 if (fat[cl].next == CLUST_FREE) 542 boot->NumFree++; 543 *p++ = (u_char)fat[cl].next; 544 *p++ = (u_char)(fat[cl].next >> 8); 545 *p++ = (u_char)(fat[cl].next >> 16); 546 *p &= 0xf0; 547 *p++ |= (fat[cl].next >> 24)&0x0f; 548 break; 549 case CLUST16_MASK: 550 if (fat[cl].next == CLUST_FREE) 551 boot->NumFree++; 552 *p++ = (u_char)fat[cl].next; 553 *p++ = (u_char)(fat[cl].next >> 8); 554 break; 555 default: 556 if (fat[cl].next == CLUST_FREE) 557 boot->NumFree++; 558 *p++ = (u_char)fat[cl].next; 559 *p = (u_char)((fat[cl].next >> 8) & 0xf); 560 cl++; 561 if (cl >= boot->NumClusters) 562 break; 563 if (fat[cl].next == CLUST_FREE) 564 boot->NumFree++; 565 *p++ |= (u_char)(fat[cl].next << 4); 566 *p++ = (u_char)(fat[cl].next >> 4); 567 break; 568 } 569 } 570 for (i = 0; i < boot->FATs; i++) { 571 off = boot->ResSectors + i * boot->FATsecs; 572 off *= boot->BytesPerSec; 573 if (lseek(fs, off, SEEK_SET) != off 574 || (size_t)write(fs, buffer, fatsz) != fatsz) { 575 perr("Unable to write FAT"); 576 ret = FSFATAL; /* Return immediately? XXX */ 577 } 578 } 579 free(buffer); 580 return ret; 581 } 582 583 /* 584 * Check a complete in-memory FAT for lost cluster chains 585 */ 586 int 587 checklost(int dosfs, struct bootblock *boot, struct fatEntry *fat) 588 { 589 cl_t head; 590 int mod = FSOK; 591 int ret; 592 593 for (head = CLUST_FIRST; head < boot->NumClusters; head++) { 594 /* find next untravelled chain */ 595 if (fat[head].head != head 596 || fat[head].next == CLUST_FREE 597 || (fat[head].next >= CLUST_RSRVD 598 && fat[head].next < CLUST_EOFS) 599 || (fat[head].flags & FAT_USED)) 600 continue; 601 602 pwarn("Lost cluster chain at cluster %u\n%d Cluster(s) lost\n", 603 head, fat[head].length); 604 mod |= ret = reconnect(dosfs, boot, fat, head); 605 if (mod & FSFATAL) 606 break; 607 if (ret == FSERROR && ask(0, "Clear")) { 608 clearchain(boot, fat, head); 609 mod |= FSFATMOD; 610 } 611 } 612 finishlf(); 613 614 if (boot->FSInfo) { 615 ret = 0; 616 if (boot->FSFree != 0xffffffffU && 617 boot->FSFree != boot->NumFree) { 618 pwarn("Free space in FSInfo block (%u) not correct (%u)\n", 619 boot->FSFree, boot->NumFree); 620 if (ask(1, "fix")) { 621 boot->FSFree = boot->NumFree; 622 ret = 1; 623 } 624 } 625 if (boot->FSNext != 0xffffffffU && 626 (boot->FSNext >= boot->NumClusters || 627 (boot->NumFree && fat[boot->FSNext].next != CLUST_FREE))) { 628 pwarn("Next free cluster in FSInfo block (%u) %s\n", 629 boot->FSNext, 630 (boot->FSNext >= boot->NumClusters) ? "invalid" : "not free"); 631 if (ask(1, "fix")) 632 for (head = CLUST_FIRST; head < boot->NumClusters; head++) 633 if (fat[head].next == CLUST_FREE) { 634 boot->FSNext = head; 635 ret = 1; 636 break; 637 } 638 } 639 if (ret) 640 mod |= writefsinfo(dosfs, boot); 641 } 642 643 return mod; 644 } 645
Indexes created Sun Sep 21 20:09:37 GMT 2025