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                 *truncp = CLUST_EOF;
 350                 return FSFATMOD;
 351         } else
 352                 return FSERROR;
 353 }
 354
 355 /*
 356  * Check a complete FAT in-memory for crosslinks
 357  */
 358 int
 359 checkfat(struct bootblock *boot, struct fatEntry *fat)
 360 {
 361         cl_t head, p, h, n;
 362         u_int len;
 363         int ret = 0;
 364         int conf;
 365
 366         /*
 367          * pass 1: figure out the cluster chains.
 368          */
 369         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 370                 /* find next untravelled chain */
 371                 if (fat[head].head != 0         /* cluster already belongs to some chain */
 372                     || fat[head].next == CLUST_FREE
 373                     || fat[head].next == CLUST_BAD)
 374                         continue;               /* skip it. */
 375
 376                 /* follow the chain and mark all clusters on the way */
 377                 for (len = 0, p = head;
 378                      p >= CLUST_FIRST && p < boot->NumClusters;
 379                      p = fat[p].next) {
 380                         fat[p].head = head;
 381                         len++;
 382                 }
 383
 384                 /* the head record gets the length */
 385                 fat[head].length = fat[head].next == CLUST_FREE ? 0 : len;
 386         }
 387
 388         /*
 389          * pass 2: check for crosslinked chains (we couldn't do this in pass 1 because
 390          * we didn't know the real start of the chain then - would have treated partial
 391          * chains as interlinked with their main chain)
 392          */
 393         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 394                 /* find next untravelled chain */
 395                 if (fat[head].head != head)
 396                         continue;
 397
 398                 /* follow the chain to its end (hopefully) */
 399                 for (p = head;
 400                      (n = fat[p].next) >= CLUST_FIRST && n < boot->NumClusters;
 401                      p = n)
 402                         if (fat[n].head != head)
 403                                 break;
 404                 if (n >= CLUST_EOFS)
 405                         continue;
 406
 407                 if (n == CLUST_FREE || n >= CLUST_RSRVD) {
 408                         pwarn("Cluster chain starting at %u ends with cluster marked %s\n",
 409                               head, rsrvdcltype(n));
 410                         ret |= tryclear(boot, fat, head, &fat[p].next);
 411                         continue;
 412                 }
 413                 if (n < CLUST_FIRST || n >= boot->NumClusters) {
 414                         pwarn("Cluster chain starting at %u ends with cluster out of range (%u)\n",
 415                               head, n);
 416                         ret |= tryclear(boot, fat, head, &fat[p].next);
 417                         continue;
 418                 }
 419                 pwarn("Cluster chains starting at %u and %u are linked at cluster %u\n",
 420                       head, fat[n].head, n);
 421                 conf = tryclear(boot, fat, head, &fat[p].next);
 422                 if (ask(0, "Clear chain starting at %u", h = fat[n].head)) {
 423                         if (conf == FSERROR) {
 424                                 /*
 425                                  * Transfer the common chain to the one not cleared above.
 426                                  */
 427                                 for (p = n;
 428                                      p >= CLUST_FIRST && p < boot->NumClusters;
 429                                      p = fat[p].next) {
 430                                         if (h != fat[p].head) {
 431                                                 /*
 432                                                  * Have to reexamine this chain.
 433                                                  */
 434                                                 head--;
 435                                                 break;
 436                                         }
 437                                         fat[p].head = head;
 438                                 }
 439                         }
 440                         clearchain(boot, fat, h);
 441                         conf |= FSFATMOD;
 442                 }
 443                 ret |= conf;
 444         }
 445
 446         return ret;
 447 }
 448
 449 /*
 450  * Write out FATs encoding them from the internal format
 451  */
 452 int
 453 writefat(int fs, struct bootblock *boot, struct fatEntry *fat, int correct_fat)
 454 {
 455         u_char *buffer, *p;
 456         cl_t cl;
 457         u_int i;
 458         size_t fatsz;
 459         off_t off;
 460         int ret = FSOK;
 461
 462         fatsz = boot->FATsecs * boot->bpbBytesPerSec;
 463         buffer = calloc(boot->FATsecs, boot->bpbBytesPerSec);
 464         if (buffer == NULL) {
 465                 perr("No space for FAT sectors (%zu)",
 466                     (size_t)boot->FATsecs);
 467                 return FSFATAL;
 468         }
 469         boot->NumFree = 0;
 470         p = buffer;
 471         if (correct_fat) {
 472                 *p++ = (u_char)boot->bpbMedia;
 473                 *p++ = 0xff;
 474                 *p++ = 0xff;
 475                 switch (boot->ClustMask) {
 476                 case CLUST16_MASK:
 477                         *p++ = 0xff;
 478                         break;
 479                 case CLUST32_MASK:
 480                         *p++ = 0x0f;
 481                         *p++ = 0xff;
 482                         *p++ = 0xff;
 483                         *p++ = 0xff;
 484                         *p++ = 0x0f;
 485                         break;
 486                 }
 487         } else {
 488                 /* use same FAT signature as the old FAT has */
 489                 int count;
 490                 u_char *old_fat;
 491
 492                 switch (boot->ClustMask) {
 493                 case CLUST32_MASK:
 494                         count = 8;
 495                         break;
 496                 case CLUST16_MASK:
 497                         count = 4;
 498                         break;
 499                 default:
 500                         count = 3;
 501                         break;
 502                 }
 503
 504                 if (!_readfat(fs, boot, boot->ValidFat >= 0 ? boot->ValidFat :0,
 505                                          &old_fat)) {
 506                         free(buffer);
 507                         return FSFATAL;
 508                 }
 509
 510                 memcpy(p, old_fat, count);
 511                 free(old_fat);
 512                 p += count;
 513         }
 514
 515         for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) {
 516                 switch (boot->ClustMask) {
 517                 case CLUST32_MASK:
 518                         if (fat[cl].next == CLUST_FREE)
 519                                 boot->NumFree++;
 520                         *p++ = (u_char)fat[cl].next;
 521                         *p++ = (u_char)(fat[cl].next >> 8);
 522                         *p++ = (u_char)(fat[cl].next >> 16);
 523                         *p &= 0xf0;
 524                         *p++ |= (fat[cl].next >> 24)&0x0f;
 525                         break;
 526                 case CLUST16_MASK:
 527                         if (fat[cl].next == CLUST_FREE)
 528                                 boot->NumFree++;
 529                         *p++ = (u_char)fat[cl].next;
 530                         *p++ = (u_char)(fat[cl].next >> 8);
 531                         break;
 532                 default:
 533                         if (fat[cl].next == CLUST_FREE)
 534                                 boot->NumFree++;
 535                         if (cl + 1 < boot->NumClusters
 536                             && fat[cl + 1].next == CLUST_FREE)
 537                                 boot->NumFree++;
 538                         *p++ = (u_char)fat[cl].next;
 539                         *p++ = (u_char)((fat[cl].next >> 8) & 0xf)
 540                                |(u_char)(fat[cl+1].next << 4);
 541                         *p++ = (u_char)(fat[++cl].next >> 4);
 542                         break;
 543                 }
 544         }
 545         for (i = 0; i < boot->bpbFATs; i++) {
 546                 off = boot->bpbResSectors + i * boot->FATsecs;
 547                 off *= boot->bpbBytesPerSec;
 548                 if (lseek(fs, off, SEEK_SET) != off
 549                     || (size_t)write(fs, buffer, fatsz) != fatsz) {
 550                         perr("Unable to write FAT");
 551                         ret = FSFATAL; /* Return immediately?           XXX */
 552                 }
 553         }
 554         free(buffer);
 555         return ret;
 556 }
 557
 558 /*
 559  * Check a complete in-memory FAT for lost cluster chains
 560  */
 561 int
 562 checklost(int dosfs, struct bootblock *boot, struct fatEntry *fat)
 563 {
 564         cl_t head;
 565         int mod = FSOK;
 566         int ret;
 567
 568         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 569                 /* find next untravelled chain */
 570                 if (fat[head].head != head
 571                     || fat[head].next == CLUST_FREE
 572                     || (fat[head].next >= CLUST_RSRVD
 573                         && fat[head].next < CLUST_EOFS)
 574                     || (fat[head].flags & FAT_USED))
 575                         continue;
 576
 577                 pwarn("Lost cluster chain at cluster %u\n%d Cluster(s) lost\n",
 578                       head, fat[head].length);
 579                 mod |= ret = reconnect(dosfs, boot, fat, head);
 580                 if (mod & FSFATAL)
 581                         break;
 582                 if (ret == FSERROR && ask(0, "Clear")) {
 583                         clearchain(boot, fat, head);
 584                         mod |= FSFATMOD;
 585                 }
 586         }
 587         finishlf();
 588
 589         if (boot->bpbFSInfo) {
 590                 ret = 0;
 591                 if (boot->FSFree != boot->NumFree) {
 592                         pwarn("Free space in FSInfo block (%d) not correct (%d)\n",
 593                               boot->FSFree, boot->NumFree);
 594                         if (ask(1, "Fix")) {
 595                                 boot->FSFree = boot->NumFree;
 596                                 ret = 1;
 597                         }
 598                 }
 599                 if (ret)
 600                         mod |= writefsinfo(dosfs, boot);
 601         }
 602
 603         return mod;
 604 }