sbin/fsck_msdosfs/fat.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause
   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 #include <stdlib.h>
  29 #include <string.h>
  30 #include <ctype.h>
  31 #include <stdio.h>
  32 #include <unistd.h>
  33
  34 #include "ext.h"
  35 #include "fsutil.h"
  36
  37 static int checkclnum(struct bootblock *, u_int, cl_t, cl_t *);
  38 static int clustdiffer(cl_t, cl_t *, cl_t *, u_int);
  39 static int tryclear(struct bootblock *, struct fatEntry *, cl_t, cl_t *);
  40 static int _readfat(int, struct bootblock *, u_int, u_char **);
  41
  42 /*
  43  * Check a cluster number for valid value
  44  */
  45 static int
  46 checkclnum(struct bootblock *boot, u_int fat, cl_t cl, cl_t *next)
  47 {
  48         if (*next >= (CLUST_RSRVD&boot->ClustMask))
  49                 *next |= ~boot->ClustMask;
  50         if (*next == CLUST_FREE) {
  51                 boot->NumFree++;
  52                 return FSOK;
  53         }
  54         if (*next == CLUST_BAD) {
  55                 boot->NumBad++;
  56                 return FSOK;
  57         }
  58         if (*next < CLUST_FIRST
  59             || (*next >= boot->NumClusters && *next < CLUST_EOFS)) {
  60                 pwarn("Cluster %u in FAT %d continues with %s cluster number %u\n",
  61                       cl, fat,
  62                       *next < CLUST_RSRVD ? "out of range" : "reserved",
  63                       *next&boot->ClustMask);
  64                 if (ask(0, "Truncate")) {
  65                         *next = CLUST_EOF;
  66                         return FSFATMOD;
  67                 }
  68                 return FSERROR;
  69         }
  70         return FSOK;
  71 }
  72
  73 /*
  74  * Read a FAT from disk. Returns 1 if successful, 0 otherwise.
  75  */
  76 static int
  77 _readfat(int fs, struct bootblock *boot, u_int no, u_char **buffer)
  78 {
  79         off_t off;
  80
  81         *buffer = calloc(boot->FATsecs, boot->bpbBytesPerSec);
  82         if (*buffer == NULL) {
  83                 perr("No space for FAT sectors (%zu)",
  84                     (size_t)boot->FATsecs);
  85                 return 0;
  86         }
  87
  88         off = boot->bpbResSectors + no * boot->FATsecs;
  89         off *= boot->bpbBytesPerSec;
  90
  91         if (lseek(fs, off, SEEK_SET) != off) {
  92                 perr("Unable to read FAT");
  93                 goto err;
  94         }
  95
  96         if ((size_t)read(fs, *buffer, boot->FATsecs * boot->bpbBytesPerSec)
  97             != boot->FATsecs * boot->bpbBytesPerSec) {
  98                 perr("Unable to read FAT");
  99                 goto err;
 100         }
 101
 102         return 1;
 103
 104 err:
 105         free(*buffer);
 106         return 0;
 107 }
 108
 109 /*
 110  * Read a FAT and decode it into internal format
 111  */
 112 int
 113 readfat(int fs, struct bootblock *boot, u_int no, struct fatEntry **fp)
 114 {
 115         struct fatEntry *fat;
 116         u_char *buffer, *p;
 117         cl_t cl;
 118         int ret = FSOK;
 119
 120         boot->NumFree = boot->NumBad = 0;
 121
 122         if (!_readfat(fs, boot, no, &buffer))
 123                 return FSFATAL;
 124
 125         fat = calloc(boot->NumClusters, sizeof(struct fatEntry));
 126         if (fat == NULL) {
 127                 perr("No space for FAT clusters (%zu)",
 128                     (size_t)boot->NumClusters);
 129                 free(buffer);
 130                 return FSFATAL;
 131         }
 132
 133         if (buffer[0] != boot->bpbMedia
 134             || buffer[1] != 0xff || buffer[2] != 0xff
 135             || (boot->ClustMask == CLUST16_MASK && buffer[3] != 0xff)
 136             || (boot->ClustMask == CLUST32_MASK
 137                 && ((buffer[3]&0x0f) != 0x0f
 138                     || buffer[4] != 0xff || buffer[5] != 0xff
 139                     || buffer[6] != 0xff || (buffer[7]&0x0f) != 0x0f))) {
 140
 141                 /* Windows 95 OSR2 (and possibly any later) changes
 142                  * the FAT signature to 0xXXffff7f for FAT16 and to
 143                  * 0xXXffff0fffffff07 for FAT32 upon boot, to know that the
 144                  * file system is dirty if it doesn't reboot cleanly.
 145                  * Check this special condition before errorring out.
 146                  */
 147                 if (buffer[0] == boot->bpbMedia && buffer[1] == 0xff
 148                     && buffer[2] == 0xff
 149                     && ((boot->ClustMask == CLUST16_MASK && buffer[3] == 0x7f)
 150                         || (boot->ClustMask == CLUST32_MASK
 151                             && buffer[3] == 0x0f && buffer[4] == 0xff
 152                             && buffer[5] == 0xff && buffer[6] == 0xff
 153                             && buffer[7] == 0x07)))
 154                         ret |= FSDIRTY;
 155                 else {
 156                         /* just some odd byte sequence in FAT */
 157                         switch (boot->ClustMask) {
 158                         case CLUST32_MASK:
 159                                 pwarn("%s (%02x%02x%02x%02x%02x%02x%02x%02x)\n",
 160                                       "FAT starts with odd byte sequence",
 161                                       buffer[0], buffer[1], buffer[2], buffer[3],
 162                                       buffer[4], buffer[5], buffer[6], buffer[7]);
 163                                 break;
 164                         case CLUST16_MASK:
 165                                 pwarn("%s (%02x%02x%02x%02x)\n",
 166                                     "FAT starts with odd byte sequence",
 167                                     buffer[0], buffer[1], buffer[2], buffer[3]);
 168                                 break;
 169                         default:
 170                                 pwarn("%s (%02x%02x%02x)\n",
 171                                     "FAT starts with odd byte sequence",
 172                                     buffer[0], buffer[1], buffer[2]);
 173                                 break;
 174                         }
 175
 176                         if (ask(1, "Correct"))
 177                                 ret |= FSFIXFAT;
 178                 }
 179         }
 180         switch (boot->ClustMask) {
 181         case CLUST32_MASK:
 182                 p = buffer + 8;
 183                 break;
 184         case CLUST16_MASK:
 185                 p = buffer + 4;
 186                 break;
 187         default:
 188                 p = buffer + 3;
 189                 break;
 190         }
 191         for (cl = CLUST_FIRST; cl < boot->NumClusters;) {
 192                 switch (boot->ClustMask) {
 193                 case CLUST32_MASK:
 194                         fat[cl].next = p[0] + (p[1] << 8)
 195                                        + (p[2] << 16) + (p[3] << 24);
 196                         fat[cl].next &= boot->ClustMask;
 197                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 198                         cl++;
 199                         p += 4;
 200                         break;
 201                 case CLUST16_MASK:
 202                         fat[cl].next = p[0] + (p[1] << 8);
 203                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 204                         cl++;
 205                         p += 2;
 206                         break;
 207                 default:
 208                         fat[cl].next = (p[0] + (p[1] << 8)) & 0x0fff;
 209                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 210                         cl++;
 211                         if (cl >= boot->NumClusters)
 212                                 break;
 213                         fat[cl].next = ((p[1] >> 4) + (p[2] << 4)) & 0x0fff;
 214                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 215                         cl++;
 216                         p += 3;
 217                         break;
 218                 }
 219         }
 220
 221         free(buffer);
 222         if (ret & FSFATAL) {
 223                 free(fat);
 224                 *fp = NULL;
 225         } else
 226                 *fp = fat;
 227         return ret;
 228 }
 229
 230 /*
 231  * Get type of reserved cluster
 232  */
 233 const char *
 234 rsrvdcltype(cl_t cl)
 235 {
 236         if (cl == CLUST_FREE)
 237                 return "free";
 238         if (cl < CLUST_BAD)
 239                 return "reserved";
 240         if (cl > CLUST_BAD)
 241                 return "as EOF";
 242         return "bad";
 243 }
 244
 245 static int
 246 clustdiffer(cl_t cl, cl_t *cp1, cl_t *cp2, u_int fatnum)
 247 {
 248         if (*cp1 == CLUST_FREE || *cp1 >= CLUST_RSRVD) {
 249                 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
 250                         if ((*cp1 != CLUST_FREE && *cp1 < CLUST_BAD
 251                              && *cp2 != CLUST_FREE && *cp2 < CLUST_BAD)
 252                             || (*cp1 > CLUST_BAD && *cp2 > CLUST_BAD)) {
 253                                 pwarn("Cluster %u is marked %s with different indicators\n",
 254                                       cl, rsrvdcltype(*cp1));
 255                                 if (ask(1, "Fix")) {
 256                                         *cp2 = *cp1;
 257                                         return FSFATMOD;
 258                                 }
 259                                 return FSFATAL;
 260                         }
 261                         pwarn("Cluster %u is marked %s in FAT 0, %s in FAT %u\n",
 262                               cl, rsrvdcltype(*cp1), rsrvdcltype(*cp2), fatnum);
 263                         if (ask(0, "Use FAT 0's entry")) {
 264                                 *cp2 = *cp1;
 265                                 return FSFATMOD;
 266                         }
 267                         if (ask(0, "Use FAT %u's entry", fatnum)) {
 268                                 *cp1 = *cp2;
 269                                 return FSFATMOD;
 270                         }
 271                         return FSFATAL;
 272                 }
 273                 pwarn("Cluster %u is marked %s in FAT 0, but continues with cluster %u in FAT %d\n",
 274                       cl, rsrvdcltype(*cp1), *cp2, fatnum);
 275                 if (ask(0, "Use continuation from FAT %u", fatnum)) {
 276                         *cp1 = *cp2;
 277                         return FSFATMOD;
 278                 }
 279                 if (ask(0, "Use mark from FAT 0")) {
 280                         *cp2 = *cp1;
 281                         return FSFATMOD;
 282                 }
 283                 return FSFATAL;
 284         }
 285         if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
 286                 pwarn("Cluster %u continues with cluster %u in FAT 0, but is marked %s in FAT %u\n",
 287                       cl, *cp1, rsrvdcltype(*cp2), fatnum);
 288                 if (ask(0, "Use continuation from FAT 0")) {
 289                         *cp2 = *cp1;
 290                         return FSFATMOD;
 291                 }
 292                 if (ask(0, "Use mark from FAT %d", fatnum)) {
 293                         *cp1 = *cp2;
 294                         return FSFATMOD;
 295                 }
 296                 return FSERROR;
 297         }
 298         pwarn("Cluster %u continues with cluster %u in FAT 0, but with cluster %u in FAT %u\n",
 299               cl, *cp1, *cp2, fatnum);
 300         if (ask(0, "Use continuation from FAT 0")) {
 301                 *cp2 = *cp1;
 302                 return FSFATMOD;
 303         }
 304         if (ask(0, "Use continuation from FAT %u", fatnum)) {
 305                 *cp1 = *cp2;
 306                 return FSFATMOD;
 307         }
 308         return FSERROR;
 309 }
 310
 311 /*
 312  * Compare two FAT copies in memory. Resolve any conflicts and merge them
 313  * into the first one.
 314  */
 315 int
 316 comparefat(struct bootblock *boot, struct fatEntry *first,
 317     struct fatEntry *second, u_int fatnum)
 318 {
 319         cl_t cl;
 320         int ret = FSOK;
 321
 322         for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++)
 323                 if (first[cl].next != second[cl].next)
 324                         ret |= clustdiffer(cl, &first[cl].next, &second[cl].next, fatnum);
 325         return ret;
 326 }
 327
 328 void
 329 clearchain(struct bootblock *boot, struct fatEntry *fat, cl_t head)
 330 {
 331         cl_t p, q;
 332
 333         for (p = head; p >= CLUST_FIRST && p < boot->NumClusters; p = q) {
 334                 if (fat[p].head != head)
 335                         break;
 336                 q = fat[p].next;
 337                 fat[p].next = fat[p].head = CLUST_FREE;
 338                 fat[p].length = 0;
 339         }
 340 }
 341
 342 int
 343 tryclear(struct bootblock *boot, struct fatEntry *fat, cl_t head, cl_t *truncp)
 344 {
 345         if (ask(0, "Clear chain starting at %u", head)) {
 346                 clearchain(boot, fat, head);
 347                 return FSFATMOD;
 348         } else if (ask(0, "Truncate")) {
 349                 uint32_t len;
 350                 cl_t p;
 351
 352                 for (p = head, len = 0;
 353                     p >= CLUST_FIRST && p < boot->NumClusters;
 354                     p = fat[p].next, len++)
 355                         continue;
 356                 *truncp = CLUST_EOF;
 357                 fat[head].length = len;
 358                 return FSFATMOD;
 359         } else
 360                 return FSERROR;
 361 }
 362
 363 /*
 364  * Check a complete FAT in-memory for crosslinks
 365  */
 366 int
 367 checkfat(struct bootblock *boot, struct fatEntry *fat)
 368 {
 369         cl_t head, p, h, n;
 370         u_int len;
 371         int ret = 0;
 372         int conf;
 373
 374         /*
 375          * pass 1: figure out the cluster chains.
 376          */
 377         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 378                 /* find next untravelled chain */
 379                 if (fat[head].head != 0         /* cluster already belongs to some chain */
 380                     || fat[head].next == CLUST_FREE
 381                     || fat[head].next == CLUST_BAD)
 382                         continue;               /* skip it. */
 383
 384                 /* follow the chain and mark all clusters on the way */
 385                 for (len = 0, p = head;
 386                      p >= CLUST_FIRST && p < boot->NumClusters &&
 387                      fat[p].head != head;
 388                      p = fat[p].next) {
 389                         fat[p].head = head;
 390                         len++;
 391                 }
 392
 393                 /* the head record gets the length */
 394                 fat[head].length = fat[head].next == CLUST_FREE ? 0 : len;
 395         }
 396
 397         /*
 398          * pass 2: check for crosslinked chains (we couldn't do this in pass 1 because
 399          * we didn't know the real start of the chain then - would have treated partial
 400          * chains as interlinked with their main chain)
 401          */
 402         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 403                 /* find next untravelled chain */
 404                 if (fat[head].head != head)
 405                         continue;
 406
 407                 /* follow the chain to its end (hopefully) */
 408                 for (len = fat[head].length, p = head;
 409                      (n = fat[p].next) >= CLUST_FIRST && n < boot->NumClusters;
 410                      p = n)
 411                         if (fat[n].head != head || len-- < 2)
 412                                 break;
 413                 if (n >= CLUST_EOFS)
 414                         continue;
 415
 416                 if (n == CLUST_FREE || n >= CLUST_RSRVD) {
 417                         pwarn("Cluster chain starting at %u ends with cluster marked %s\n",
 418                               head, rsrvdcltype(n));
 419 clear:
 420                         ret |= tryclear(boot, fat, head, &fat[p].next);
 421                         continue;
 422                 }
 423                 if (n < CLUST_FIRST || n >= boot->NumClusters) {
 424                         pwarn("Cluster chain starting at %u ends with cluster out of range (%u)\n",
 425                             head, n);
 426                         goto clear;
 427                 }
 428                 if (head == fat[n].head) {
 429                         pwarn("Cluster chain starting at %u loops at cluster %u\n",
 430                             head, p);
 431                         goto clear;
 432                 }
 433                 pwarn("Cluster chains starting at %u and %u are linked at cluster %u\n",
 434                       head, fat[n].head, n);
 435                 conf = tryclear(boot, fat, head, &fat[p].next);
 436                 if (ask(0, "Clear chain starting at %u", h = fat[n].head)) {
 437                         if (conf == FSERROR) {
 438                                 /*
 439                                  * Transfer the common chain to the one not cleared above.
 440                                  */
 441                                 for (p = n;
 442                                      p >= CLUST_FIRST && p < boot->NumClusters;
 443                                      p = fat[p].next) {
 444                                         if (h != fat[p].head) {
 445                                                 /*
 446                                                  * Have to reexamine this chain.
 447                                                  */
 448                                                 head--;
 449                                                 break;
 450                                         }
 451                                         fat[p].head = head;
 452                                 }
 453                         }
 454                         clearchain(boot, fat, h);
 455                         conf |= FSFATMOD;
 456                 }
 457                 ret |= conf;
 458         }
 459
 460         return ret;
 461 }
 462
 463 /*
 464  * Write out FATs encoding them from the internal format
 465  */
 466 int
 467 writefat(int fs, struct bootblock *boot, struct fatEntry *fat, int correct_fat)
 468 {
 469         u_char *buffer, *p;
 470         cl_t cl;
 471         u_int i;
 472         size_t fatsz;
 473         off_t off;
 474         int ret = FSOK;
 475
 476         fatsz = boot->FATsecs * boot->bpbBytesPerSec;
 477         buffer = calloc(boot->FATsecs, boot->bpbBytesPerSec);
 478         if (buffer == NULL) {
 479                 perr("No space for FAT sectors (%zu)",
 480                     (size_t)boot->FATsecs);
 481                 return FSFATAL;
 482         }
 483         boot->NumFree = 0;
 484         p = buffer;
 485         if (correct_fat) {
 486                 *p++ = (u_char)boot->bpbMedia;
 487                 *p++ = 0xff;
 488                 *p++ = 0xff;
 489                 switch (boot->ClustMask) {
 490                 case CLUST16_MASK:
 491                         *p++ = 0xff;
 492                         break;
 493                 case CLUST32_MASK:
 494                         *p++ = 0x0f;
 495                         *p++ = 0xff;
 496                         *p++ = 0xff;
 497                         *p++ = 0xff;
 498                         *p++ = 0x0f;
 499                         break;
 500                 }
 501         } else {
 502                 /* use same FAT signature as the old FAT has */
 503                 int count;
 504                 u_char *old_fat;
 505
 506                 switch (boot->ClustMask) {
 507                 case CLUST32_MASK:
 508                         count = 8;
 509                         break;
 510                 case CLUST16_MASK:
 511                         count = 4;
 512                         break;
 513                 default:
 514                         count = 3;
 515                         break;
 516                 }
 517
 518                 if (!_readfat(fs, boot, boot->ValidFat >= 0 ? boot->ValidFat :0,
 519                                          &old_fat)) {
 520                         free(buffer);
 521                         return FSFATAL;
 522                 }
 523
 524                 memcpy(p, old_fat, count);
 525                 free(old_fat);
 526                 p += count;
 527         }
 528
 529         for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) {
 530                 switch (boot->ClustMask) {
 531                 case CLUST32_MASK:
 532                         if (fat[cl].next == CLUST_FREE)
 533                                 boot->NumFree++;
 534                         *p++ = (u_char)fat[cl].next;
 535                         *p++ = (u_char)(fat[cl].next >> 8);
 536                         *p++ = (u_char)(fat[cl].next >> 16);
 537                         *p &= 0xf0;
 538                         *p++ |= (fat[cl].next >> 24)&0x0f;
 539                         break;
 540                 case CLUST16_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                         break;
 546                 default:
 547                         if (fat[cl].next == CLUST_FREE)
 548                                 boot->NumFree++;
 549                         *p++ = (u_char)fat[cl].next;
 550                         *p = (u_char)((fat[cl].next >> 8) & 0xf);
 551                         cl++;
 552                         if (cl >= boot->NumClusters)
 553                                 break;
 554                         if (fat[cl].next == CLUST_FREE)
 555                                 boot->NumFree++;
 556                         *p++ |= (u_char)(fat[cl].next << 4);
 557                         *p++ = (u_char)(fat[cl].next >> 4);
 558                         break;
 559                 }
 560         }
 561         for (i = 0; i < boot->bpbFATs; i++) {
 562                 off = boot->bpbResSectors + i * boot->FATsecs;
 563                 off *= boot->bpbBytesPerSec;
 564                 if (lseek(fs, off, SEEK_SET) != off
 565                     || (size_t)write(fs, buffer, fatsz) != fatsz) {
 566                         perr("Unable to write FAT");
 567                         ret = FSFATAL; /* Return immediately?           XXX */
 568                 }
 569         }
 570         free(buffer);
 571         return ret;
 572 }
 573
 574 /*
 575  * Check a complete in-memory FAT for lost cluster chains
 576  */
 577 int
 578 checklost(int dosfs, struct bootblock *boot, struct fatEntry *fat)
 579 {
 580         cl_t head;
 581         int mod = FSOK;
 582         int ret;
 583
 584         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 585                 /* find next untravelled chain */
 586                 if (fat[head].head != head
 587                     || fat[head].next == CLUST_FREE
 588                     || (fat[head].next >= CLUST_RSRVD
 589                         && fat[head].next < CLUST_EOFS)
 590                     || (fat[head].flags & FAT_USED))
 591                         continue;
 592
 593                 pwarn("Lost cluster chain at cluster %u\n%d Cluster(s) lost\n",
 594                       head, fat[head].length);
 595                 mod |= ret = reconnect(dosfs, boot, fat, head);
 596                 if (mod & FSFATAL)
 597                         break;
 598                 if (ret == FSERROR && ask(0, "Clear")) {
 599                         clearchain(boot, fat, head);
 600                         mod |= FSFATMOD;
 601                 }
 602         }
 603         finishlf();
 604
 605         if (boot->bpbFSInfo) {
 606                 ret = 0;
 607                 if (boot->FSFree != boot->NumFree) {
 608                         pwarn("Free space in FSInfo block (%d) not correct (%d)\n",
 609                               boot->FSFree, boot->NumFree);
 610                         if (ask(1, "Fix")) {
 611                                 boot->FSFree = boot->NumFree;
 612                                 ret = 1;
 613                         }
 614                 }
 615                 if (ret)
 616                         mod |= writefsinfo(dosfs, boot);
 617         }
 618
 619         return mod;
 620 }