extras/volume_id/lib/fat.c

   1 /*
   2  * volume_id - reads filesystem label and uuid
   3  *
   4  * Copyright (C) 2004-2007 Kay Sievers <kay.sievers@vrfy.org>
   5  * Copyright (C) 2007 Ryan Lortie <desrt@desrt.ca>
   6  *
   7  *      This program is free software; you can redistribute it and/or modify it
   8  *      under the terms of the GNU General Public License as published by the
   9  *      Free Software Foundation version 2 of the License.
  10  */
  11
  12 #ifndef _GNU_SOURCE
  13 #define _GNU_SOURCE 1
  14 #endif
  15
  16 #ifdef HAVE_CONFIG_H
  17 #  include <config.h>
  18 #endif
  19
  20 #include <stdio.h>
  21 #include <stdlib.h>
  22 #include <unistd.h>
  23 #include <string.h>
  24 #include <errno.h>
  25 #include <ctype.h>
  26
  27 #include "libvolume_id.h"
  28 #include "util.h"
  29
  30 #define FAT12_MAX                       0xff5
  31 #define FAT16_MAX                       0xfff5
  32 #define FAT_ATTR_VOLUME_ID              0x08
  33 #define FAT_ATTR_DIR                    0x10
  34 #define FAT_ATTR_LONG_NAME              0x0f
  35 #define FAT_ATTR_MASK                   0x3f
  36 #define FAT_ENTRY_FREE                  0xe5
  37
  38 #define VFAT_LFN_SEQ_MASK               0x3f
  39 #define VFAT_LFN_SEQ_LAST               0x40
  40 #define VFAT_LFN_SEQ_MAX                20
  41 #define VFAT_LFN_CHARS_PER_ENTRY        (5 + 6 + 2)
  42 #define VFAT_LOWERCASE_NAME             0x10
  43 #define VFAT_LOWERCASE_EXT              0x08
  44
  45 struct vfat_super_block {
  46         uint8_t         boot_jump[3];
  47         uint8_t         sysid[8];
  48         uint16_t        sector_size;
  49         uint8_t         sectors_per_cluster;
  50         uint16_t        reserved;
  51         uint8_t         fats;
  52         uint16_t        dir_entries;
  53         uint16_t        sectors;
  54         uint8_t         media;
  55         uint16_t        fat_length;
  56         uint16_t        secs_track;
  57         uint16_t        heads;
  58         uint32_t        hidden;
  59         uint32_t        total_sect;
  60         union {
  61                 struct fat_super_block {
  62                         uint8_t         unknown[3];
  63                         uint8_t         serno[4];
  64                         uint8_t         label[11];
  65                         uint8_t         magic[8];
  66                         uint8_t         dummy2[192];
  67                         uint8_t         pmagic[2];
  68                 } PACKED fat;
  69                 struct fat32_super_block {
  70                         uint32_t        fat32_length;
  71                         uint16_t        flags;
  72                         uint8_t         version[2];
  73                         uint32_t        root_cluster;
  74                         uint16_t        fsinfo_sector;
  75                         uint16_t        backup_boot;
  76                         uint16_t        reserved2[6];
  77                         uint8_t         unknown[3];
  78                         uint8_t         serno[4];
  79                         uint8_t         label[11];
  80                         uint8_t         magic[8];
  81                         uint8_t         dummy2[164];
  82                         uint8_t         pmagic[2];
  83                 } PACKED fat32;
  84         } PACKED type;
  85 } PACKED;
  86
  87 struct fat32_fsinfo {
  88         uint8_t signature1[4];
  89         uint32_t reserved1[120];
  90         uint8_t signature2[4];
  91         uint32_t free_clusters;
  92         uint32_t next_cluster;
  93         uint32_t reserved2[4];
  94 } PACKED;
  95
  96 struct vfat_dir_entry {
  97         uint8_t         name[11];
  98         uint8_t         attr;
  99         uint8_t         lowercase;
 100         uint8_t         fine_time_creat;
 101         uint16_t        time_creat;
 102         uint16_t        date_creat;
 103         uint16_t        date_acc;
 104         uint16_t        cluster_high;
 105         uint16_t        time_write;
 106         uint16_t        date_write;
 107         uint16_t        cluster_low;
 108         uint32_t        size;
 109 } PACKED;
 110
 111
 112 struct vfat_lfn_entry {
 113         uint8_t         seq;
 114         uint16_t        name0[5];
 115         uint8_t         attr;
 116         uint8_t         reserved;
 117         uint8_t         cksum;
 118         uint16_t        name1[6];
 119         uint16_t        cluster;
 120         uint16_t        name2[2];
 121 } PACKED;
 122
 123 static uint8_t fat_lfn_checksum(const uint8_t name[11])
 124 {
 125         uint8_t cksum = 0;
 126         int i;
 127
 128         /* http://en.wikipedia.org/wiki/File_Allocation_Table */
 129         for (i = 0; i < 11; i++)
 130                 cksum = ((cksum & 1) ? 0x80 : 0) + (cksum >> 1) + name[i];
 131
 132         return cksum;
 133 }
 134
 135 static size_t fat_read_lfn(uint8_t *filename, size_t fnsize,
 136                            struct vfat_dir_entry *dir,
 137                            struct vfat_dir_entry *entry)
 138 {
 139         uint8_t buffer[VFAT_LFN_SEQ_MAX * VFAT_LFN_CHARS_PER_ENTRY * 2];
 140         uint8_t expected_seq = 1;
 141         uint8_t cksum;
 142         size_t len = 0;
 143         size_t fnlen = 0;
 144
 145         cksum = fat_lfn_checksum(entry->name);
 146
 147         while (--entry >= dir) {
 148                 struct vfat_lfn_entry *lfn = (struct vfat_lfn_entry *) entry;
 149
 150                 if (expected_seq > VFAT_LFN_SEQ_MAX)
 151                         break;
 152
 153                 if ((lfn->attr & FAT_ATTR_MASK) != FAT_ATTR_LONG_NAME)
 154                         break;
 155
 156                 if (lfn->cksum != cksum)
 157                         break;
 158
 159                 if ((lfn->seq & VFAT_LFN_SEQ_MASK) != expected_seq++)
 160                         break;
 161
 162                 if (lfn->cluster != 0)
 163                         break;
 164
 165                 /* extra paranoia -- should never happen */
 166                 if (len + sizeof(lfn->name0) + sizeof(lfn->name1) +
 167                     sizeof(lfn->name2) > sizeof(buffer))
 168                         break;
 169
 170                 memcpy (&buffer[len], lfn->name0, sizeof(lfn->name0));
 171                 len += sizeof(lfn->name0);
 172                 memcpy (&buffer[len], lfn->name1, sizeof(lfn->name1));
 173                 len += sizeof(lfn->name1);
 174                 memcpy (&buffer[len], lfn->name2, sizeof(lfn->name2));
 175                 len += sizeof(lfn->name2);
 176
 177                 if (lfn->seq & VFAT_LFN_SEQ_LAST) {
 178                         fnlen = volume_id_set_unicode16(filename, fnsize, buffer, LE, len);
 179                         break;
 180                 }
 181         }
 182
 183         return fnlen;
 184 }
 185
 186 static size_t fat_read_filename(uint8_t *filename, size_t fnsize,
 187                                 struct vfat_dir_entry *dir, struct vfat_dir_entry *entry)
 188 {
 189         size_t len;
 190         int i;
 191
 192         /* check if maybe we have LFN entries */
 193         len = fat_read_lfn(filename, fnsize, dir, entry);
 194         if (len > 0)
 195                 goto out;
 196
 197         /* else, read the normal 8.3 name */
 198         for (i = 0; i < 11; i++) {
 199                 if (entry->lowercase & ((i < 8) ? VFAT_LOWERCASE_NAME : VFAT_LOWERCASE_EXT))
 200                         filename[i] = tolower(entry->name[i]);
 201                 else
 202                         filename[i] = entry->name[i];
 203         }
 204         len = 11;
 205
 206 out:
 207         filename[len] = '\0';
 208         return len;
 209 }
 210
 211 /* fills filename, returns string length */
 212 static size_t get_fat_attr_volume_id(uint8_t *filename, size_t fnsize,
 213                                      struct vfat_dir_entry *dir, unsigned int count)
 214 {
 215         unsigned int i;
 216
 217         for (i = 0; i < count; i++) {
 218                 /* end marker */
 219                 if (dir[i].name[0] == 0x00) {
 220                         dbg("end of dir");
 221                         break;
 222                 }
 223
 224                 /* empty entry */
 225                 if (dir[i].name[0] == FAT_ENTRY_FREE)
 226                         continue;
 227
 228                 /* long name */
 229                 if ((dir[i].attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
 230                         continue;
 231
 232                 if ((dir[i].attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
 233                         /* labels do not have file data */
 234                         if (dir[i].cluster_high != 0 || dir[i].cluster_low != 0)
 235                                 continue;
 236
 237                         dbg("found ATTR_VOLUME_ID id in root dir");
 238                         return fat_read_filename(filename, fnsize, dir, &dir[i]);
 239                 }
 240
 241                 dbg("skip dir entry");
 242         }
 243
 244         return 0;
 245 }
 246
 247 int volume_id_probe_vfat(struct volume_id *id, uint64_t off, uint64_t size)
 248 {
 249         uint8_t filename[255 * 3];
 250         struct vfat_super_block *vs;
 251         struct vfat_dir_entry *dir;
 252         struct fat32_fsinfo *fsinfo;
 253         uint16_t sector_size;
 254         uint16_t dir_entries;
 255         uint32_t sect_count;
 256         uint16_t reserved;
 257         uint32_t fat_size;
 258         uint32_t root_cluster;
 259         uint32_t dir_size;
 260         uint32_t cluster_count;
 261         uint16_t fat_length;
 262         uint32_t fat32_length;
 263         uint64_t root_start;
 264         uint32_t start_data_sect;
 265         uint16_t root_dir_entries;
 266         uint16_t fsinfo_sect;
 267         uint8_t *buf;
 268         uint32_t buf_size;
 269         uint32_t next;
 270         int maxloop;
 271         size_t fnlen;
 272
 273         info("probing at offset 0x%llx", (unsigned long long) off);
 274
 275         buf = volume_id_get_buffer(id, off, 0x400);
 276         if (buf == NULL)
 277                 return -1;
 278
 279         /* check signature */
 280         if (buf[510] != 0x55 || buf[511] != 0xaa)
 281                 return -1;
 282
 283         vs = (struct vfat_super_block *) buf;
 284         if (memcmp(vs->sysid, "NTFS", 4) == 0)
 285                 return -1;
 286
 287         /* believe only that's fat, don't trust the version */
 288         if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
 289                 goto magic;
 290
 291         if (memcmp(vs->type.fat32.magic, "FAT32   ", 8) == 0)
 292                 goto magic;
 293
 294         if (memcmp(vs->type.fat.magic, "FAT16   ", 8) == 0)
 295                 goto magic;
 296
 297         if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
 298                 goto magic;
 299
 300         if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
 301                 goto magic;
 302
 303         /* some old floppies don't have a magic, expect the boot jump address to match */
 304         if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
 305              vs->boot_jump[0] != 0xe9)
 306                 return -1;
 307
 308 magic:
 309         /* reserverd sector count */
 310         if (!vs->reserved)
 311                 return -1;
 312
 313         /* fat count */
 314         if (!vs->fats)
 315                 return -1;
 316
 317         /* media check */
 318         if (vs->media < 0xf8 && vs->media != 0xf0)
 319                 return -1;
 320
 321         /* cluster size check */
 322         if (vs->sectors_per_cluster == 0 ||
 323             (vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
 324                 return -1;
 325
 326         /* sector size check */
 327         sector_size = le16_to_cpu(vs->sector_size);
 328         if (sector_size == 0 || ((sector_size & (sector_size-1)) != 0))
 329                 return -1;
 330
 331         dbg("sector_size 0x%x", sector_size);
 332         dbg("sectors_per_cluster 0x%x", vs->sectors_per_cluster);
 333
 334         dir_entries = le16_to_cpu(vs->dir_entries);
 335         reserved = le16_to_cpu(vs->reserved);
 336         dbg("reserved 0x%x", reserved);
 337
 338         sect_count = le16_to_cpu(vs->sectors);
 339         if (sect_count == 0)
 340                 sect_count = le32_to_cpu(vs->total_sect);
 341         dbg("sect_count 0x%x", sect_count);
 342
 343         fat_length = le16_to_cpu(vs->fat_length);
 344         dbg("fat_length 0x%x", fat_length);
 345         fat32_length = le32_to_cpu(vs->type.fat32.fat32_length);
 346         dbg("fat32_length 0x%x", fat32_length);
 347
 348         if (fat_length)
 349                 fat_size = fat_length * vs->fats;
 350         else if (fat32_length)
 351                 fat_size = fat32_length * vs->fats;
 352         else
 353                 return -1;
 354         dbg("fat_size 0x%x", fat_size);
 355
 356         dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
 357                         (sector_size-1)) / sector_size;
 358         dbg("dir_size 0x%x", dir_size);
 359
 360         cluster_count = sect_count - (reserved + fat_size + dir_size);
 361         cluster_count /= vs->sectors_per_cluster;
 362         dbg("cluster_count 0x%x", cluster_count);
 363
 364         /* must be FAT32 */
 365         if (!fat_length && fat32_length)
 366                 goto fat32;
 367
 368         /* cluster_count tells us the format */
 369         if (cluster_count < FAT12_MAX)
 370                 strcpy(id->type_version, "FAT12");
 371         else if (cluster_count < FAT16_MAX)
 372                 strcpy(id->type_version, "FAT16");
 373         else
 374                 goto fat32;
 375
 376         /* the label may be an attribute in the root directory */
 377         root_start = (reserved + fat_size) * sector_size;
 378         dbg("root dir start 0x%llx", (unsigned long long) root_start);
 379         root_dir_entries = le16_to_cpu(vs->dir_entries);
 380         dbg("expected entries 0x%x", root_dir_entries);
 381
 382         buf_size = root_dir_entries * sizeof(struct vfat_dir_entry);
 383         buf = volume_id_get_buffer(id, off + root_start, buf_size);
 384         if (buf == NULL)
 385                 goto found;
 386
 387         dir = (struct vfat_dir_entry*) buf;
 388
 389         fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, root_dir_entries);
 390
 391         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 392         if (vs == NULL)
 393                 return -1;
 394
 395         if (fnlen > 0 && memcmp(filename, "NO NAME    ", 11) != 0) {
 396                 volume_id_set_label_raw(id, filename, fnlen);
 397                 volume_id_set_label_string(id, filename, fnlen);
 398         } else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
 399                 volume_id_set_label_raw(id, vs->type.fat.label, 11);
 400                 volume_id_set_label_string(id, vs->type.fat.label, 11);
 401         }
 402         volume_id_set_uuid(id, vs->type.fat.serno, 0, UUID_DOS);
 403         goto found;
 404
 405 fat32:
 406         /* FAT32 should have a valid signature in the fsinfo block */
 407         fsinfo_sect = le16_to_cpu(vs->type.fat32.fsinfo_sector);
 408         buf = volume_id_get_buffer(id, off + (fsinfo_sect * sector_size), 0x200);
 409         if (buf == NULL)
 410                 return -1;
 411         fsinfo = (struct fat32_fsinfo *) buf;
 412         if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0)
 413                 return -1;
 414         if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0)
 415                 return -1 ;
 416
 417         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 418         if (vs == NULL)
 419                 return -1;
 420
 421         strcpy(id->type_version, "FAT32");
 422
 423         /* FAT32 root dir is a cluster chain like any other directory */
 424         buf_size = vs->sectors_per_cluster * sector_size;
 425         root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
 426         dbg("root dir cluster %u", root_cluster);
 427         start_data_sect = reserved + fat_size;
 428
 429         next = root_cluster;
 430         maxloop = 100;
 431         while (--maxloop) {
 432                 uint32_t next_sect_off;
 433                 uint64_t next_off;
 434                 uint64_t fat_entry_off;
 435                 int count;
 436
 437                 dbg("next cluster %u", next);
 438                 next_sect_off = (next - 2) * vs->sectors_per_cluster;
 439                 next_off = (start_data_sect + next_sect_off) * sector_size;
 440                 dbg("cluster offset 0x%llx", (unsigned long long) next_off);
 441
 442                 /* get cluster */
 443                 buf = volume_id_get_buffer(id, off + next_off, buf_size);
 444                 if (buf == NULL)
 445                         goto found;
 446
 447                 dir = (struct vfat_dir_entry*) buf;
 448                 count = buf_size / sizeof(struct vfat_dir_entry);
 449                 dbg("expected entries 0x%x", count);
 450
 451                 fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, count);
 452                 if (fnlen > 0)
 453                         break;
 454
 455                 /* get FAT entry */
 456                 fat_entry_off = (reserved * sector_size) + (next * sizeof(uint32_t));
 457                 buf = volume_id_get_buffer(id, off + fat_entry_off, buf_size);
 458                 if (buf == NULL)
 459                         goto found;
 460
 461                 /* set next cluster */
 462                 next = le32_to_cpu(*((uint32_t *) buf)) & 0x0fffffff;
 463                 if (next < 2 || next >= 0x0ffffff0)
 464                         break;
 465         }
 466         if (maxloop == 0)
 467                 dbg("reached maximum follow count of root cluster chain, give up");
 468
 469         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 470         if (vs == NULL)
 471                 return -1;
 472
 473         if (fnlen > 0 && memcmp(filename, "NO NAME    ", 11) != 0) {
 474                 volume_id_set_label_raw(id, filename, fnlen);
 475                 volume_id_set_label_string(id, filename, fnlen);
 476         } else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
 477                 volume_id_set_label_raw(id, vs->type.fat32.label, 11);
 478                 volume_id_set_label_string(id, vs->type.fat32.label, 11);
 479         }
 480         volume_id_set_uuid(id, vs->type.fat32.serno, 0, UUID_DOS);
 481
 482 found:
 483         volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
 484         id->type = "vfat";
 485
 486         return 0;
 487 }