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 "libvolume_id-private.h"
  29 #include "util.h"
  30
  31 #define FAT12_MAX                       0xff5
  32 #define FAT16_MAX                       0xfff5
  33 #define FAT_ATTR_VOLUME_ID              0x08
  34 #define FAT_ATTR_DIR                    0x10
  35 #define FAT_ATTR_LONG_NAME              0x0f
  36 #define FAT_ATTR_MASK                   0x3f
  37 #define FAT_ENTRY_FREE                  0xe5
  38
  39 #define VFAT_LFN_SEQ_MASK               0x3f
  40 #define VFAT_LFN_SEQ_LAST               0x40
  41 #define VFAT_LFN_SEQ_MAX                20
  42 #define VFAT_LFN_CHARS_PER_ENTRY        (5 + 6 + 2)
  43 #define VFAT_LOWERCASE_NAME             0x10
  44 #define VFAT_LOWERCASE_EXT              0x08
  45
  46 struct vfat_super_block {
  47         uint8_t         boot_jump[3];
  48         uint8_t         sysid[8];
  49         uint16_t        sector_size;
  50         uint8_t         sectors_per_cluster;
  51         uint16_t        reserved;
  52         uint8_t         fats;
  53         uint16_t        dir_entries;
  54         uint16_t        sectors;
  55         uint8_t         media;
  56         uint16_t        fat_length;
  57         uint16_t        secs_track;
  58         uint16_t        heads;
  59         uint32_t        hidden;
  60         uint32_t        total_sect;
  61         union {
  62                 struct fat_super_block {
  63                         uint8_t         unknown[3];
  64                         uint8_t         serno[4];
  65                         uint8_t         label[11];
  66                         uint8_t         magic[8];
  67                         uint8_t         dummy2[192];
  68                         uint8_t         pmagic[2];
  69                 } PACKED fat;
  70                 struct fat32_super_block {
  71                         uint32_t        fat32_length;
  72                         uint16_t        flags;
  73                         uint8_t         version[2];
  74                         uint32_t        root_cluster;
  75                         uint16_t        fsinfo_sector;
  76                         uint16_t        backup_boot;
  77                         uint16_t        reserved2[6];
  78                         uint8_t         unknown[3];
  79                         uint8_t         serno[4];
  80                         uint8_t         label[11];
  81                         uint8_t         magic[8];
  82                         uint8_t         dummy2[164];
  83                         uint8_t         pmagic[2];
  84                 } PACKED fat32;
  85         } PACKED type;
  86 } PACKED;
  87
  88 struct fat32_fsinfo {
  89         uint8_t signature1[4];
  90         uint32_t reserved1[120];
  91         uint8_t signature2[4];
  92         uint32_t free_clusters;
  93         uint32_t next_cluster;
  94         uint32_t reserved2[4];
  95 } PACKED;
  96
  97 struct vfat_dir_entry {
  98         uint8_t         name[11];
  99         uint8_t         attr;
 100         uint8_t         lowercase;
 101         uint8_t         fine_time_creat;
 102         uint16_t        time_creat;
 103         uint16_t        date_creat;
 104         uint16_t        date_acc;
 105         uint16_t        cluster_high;
 106         uint16_t        time_write;
 107         uint16_t        date_write;
 108         uint16_t        cluster_low;
 109         uint32_t        size;
 110 } PACKED;
 111
 112
 113 struct vfat_lfn_entry {
 114         uint8_t         seq;
 115         uint16_t        name0[5];
 116         uint8_t         attr;
 117         uint8_t         reserved;
 118         uint8_t         cksum;
 119         uint16_t        name1[6];
 120         uint16_t        cluster;
 121         uint16_t        name2[2];
 122 } PACKED;
 123
 124 static uint8_t fat_lfn_checksum(const uint8_t name[11])
 125 {
 126         uint8_t cksum = 0;
 127         int i;
 128
 129         /* http://en.wikipedia.org/wiki/File_Allocation_Table */
 130         for (i = 0; i < 11; i++)
 131                 cksum = ((cksum & 1) ? 0x80 : 0) + (cksum >> 1) + name[i];
 132
 133         return cksum;
 134 }
 135
 136 static size_t fat_read_lfn(uint8_t *filename, size_t fnsize,
 137                            struct vfat_dir_entry *dir,
 138                            struct vfat_dir_entry *entry)
 139 {
 140         uint8_t buffer[VFAT_LFN_SEQ_MAX * VFAT_LFN_CHARS_PER_ENTRY * 2];
 141         uint8_t expected_seq = 1;
 142         uint8_t cksum;
 143         size_t len = 0;
 144         size_t fnlen = 0;
 145
 146         cksum = fat_lfn_checksum(entry->name);
 147
 148         while (--entry >= dir) {
 149                 struct vfat_lfn_entry *lfn = (struct vfat_lfn_entry *) entry;
 150
 151                 if (expected_seq > VFAT_LFN_SEQ_MAX)
 152                         break;
 153
 154                 if ((lfn->attr & FAT_ATTR_MASK) != FAT_ATTR_LONG_NAME)
 155                         break;
 156
 157                 if (lfn->cksum != cksum)
 158                         break;
 159
 160                 if ((lfn->seq & VFAT_LFN_SEQ_MASK) != expected_seq++)
 161                         break;
 162
 163                 if (lfn->cluster != 0)
 164                         break;
 165
 166                 /* extra paranoia -- should never happen */
 167                 if (len + sizeof(lfn->name0) + sizeof(lfn->name1) +
 168                     sizeof(lfn->name2) > sizeof(buffer))
 169                         break;
 170
 171                 memcpy (&buffer[len], lfn->name0, sizeof(lfn->name0));
 172                 len += sizeof(lfn->name0);
 173                 memcpy (&buffer[len], lfn->name1, sizeof(lfn->name1));
 174                 len += sizeof(lfn->name1);
 175                 memcpy (&buffer[len], lfn->name2, sizeof(lfn->name2));
 176                 len += sizeof(lfn->name2);
 177
 178                 if (lfn->seq & VFAT_LFN_SEQ_LAST) {
 179                         fnlen = volume_id_set_unicode16(filename, fnsize, buffer, LE, len);
 180                         break;
 181                 }
 182         }
 183
 184         return fnlen;
 185 }
 186
 187 static size_t fat_read_filename(uint8_t *filename, size_t fnsize,
 188                                 struct vfat_dir_entry *dir, struct vfat_dir_entry *entry)
 189 {
 190         size_t len;
 191         int i;
 192
 193         /* check if maybe we have LFN entries */
 194         len = fat_read_lfn(filename, fnsize, dir, entry);
 195         if (len > 0)
 196                 goto out;
 197
 198         /* else, read the normal 8.3 name */
 199         for (i = 0; i < 11; i++) {
 200                 if (entry->lowercase & ((i < 8) ? VFAT_LOWERCASE_NAME : VFAT_LOWERCASE_EXT))
 201                         filename[i] = tolower(entry->name[i]);
 202                 else
 203                         filename[i] = entry->name[i];
 204         }
 205         len = 11;
 206
 207 out:
 208         filename[len] = '\0';
 209         return len;
 210 }
 211
 212 /* fills filename, returns string length */
 213 static size_t get_fat_attr_volume_id(uint8_t *filename, size_t fnsize,
 214                                      struct vfat_dir_entry *dir, unsigned int count)
 215 {
 216         unsigned int i;
 217
 218         for (i = 0; i < count; i++) {
 219                 /* end marker */
 220                 if (dir[i].name[0] == 0x00) {
 221                         dbg("end of dir\n");
 222                         break;
 223                 }
 224
 225                 /* empty entry */
 226                 if (dir[i].name[0] == FAT_ENTRY_FREE)
 227                         continue;
 228
 229                 /* long name */
 230                 if ((dir[i].attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
 231                         continue;
 232
 233                 if ((dir[i].attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
 234                         /* labels do not have file data */
 235                         if (dir[i].cluster_high != 0 || dir[i].cluster_low != 0)
 236                                 continue;
 237
 238                         dbg("found ATTR_VOLUME_ID id in root dir\n");
 239                         return fat_read_filename(filename, fnsize, dir, &dir[i]);
 240                 }
 241
 242                 dbg("skip dir entry\n");
 243         }
 244
 245         return 0;
 246 }
 247
 248 int volume_id_probe_vfat(struct volume_id *id, uint64_t off, uint64_t size)
 249 {
 250         uint8_t filename[255 * 3];
 251         struct vfat_super_block *vs;
 252         struct vfat_dir_entry *dir;
 253         struct fat32_fsinfo *fsinfo;
 254         uint16_t sector_size;
 255         uint16_t dir_entries;
 256         uint32_t sect_count;
 257         uint16_t reserved;
 258         uint32_t fat_size;
 259         uint32_t root_cluster;
 260         uint32_t dir_size;
 261         uint32_t cluster_count;
 262         uint16_t fat_length;
 263         uint32_t fat32_length;
 264         uint64_t root_start;
 265         uint32_t start_data_sect;
 266         uint16_t root_dir_entries;
 267         uint16_t fsinfo_sect;
 268         uint8_t *buf;
 269         uint32_t buf_size;
 270         uint32_t next;
 271         int maxloop;
 272         size_t fnlen;
 273
 274         info("probing at offset 0x%llx\n", (unsigned long long) off);
 275
 276         buf = volume_id_get_buffer(id, off, 0x400);
 277         if (buf == NULL)
 278                 return -1;
 279
 280         /* check signature */
 281         if (buf[510] != 0x55 || buf[511] != 0xaa)
 282                 return -1;
 283
 284         vs = (struct vfat_super_block *) buf;
 285         if (memcmp(vs->sysid, "NTFS", 4) == 0)
 286                 return -1;
 287
 288         /* believe only that's fat, don't trust the version */
 289         if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
 290                 goto magic;
 291
 292         if (memcmp(vs->type.fat32.magic, "FAT32   ", 8) == 0)
 293                 goto magic;
 294
 295         if (memcmp(vs->type.fat.magic, "FAT16   ", 8) == 0)
 296                 goto magic;
 297
 298         if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
 299                 goto magic;
 300
 301         if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
 302                 goto magic;
 303
 304         /* some old floppies don't have a magic, expect the boot jump address to match */
 305         if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
 306              vs->boot_jump[0] != 0xe9)
 307                 return -1;
 308
 309 magic:
 310         /* reserverd sector count */
 311         if (!vs->reserved)
 312                 return -1;
 313
 314         /* fat count */
 315         if (!vs->fats)
 316                 return -1;
 317
 318         /* media check */
 319         if (vs->media < 0xf8 && vs->media != 0xf0)
 320                 return -1;
 321
 322         /* cluster size check */
 323         if (vs->sectors_per_cluster == 0 ||
 324             (vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
 325                 return -1;
 326
 327         /* sector size check */
 328         sector_size = le16_to_cpu(vs->sector_size);
 329         if (sector_size == 0 || ((sector_size & (sector_size-1)) != 0))
 330                 return -1;
 331
 332         dbg("sector_size 0x%x\n", sector_size);
 333         dbg("sectors_per_cluster 0x%x\n", vs->sectors_per_cluster);
 334
 335         dir_entries = le16_to_cpu(vs->dir_entries);
 336         reserved = le16_to_cpu(vs->reserved);
 337         dbg("reserved 0x%x\n", reserved);
 338
 339         sect_count = le16_to_cpu(vs->sectors);
 340         if (sect_count == 0)
 341                 sect_count = le32_to_cpu(vs->total_sect);
 342         dbg("sect_count 0x%x\n", sect_count);
 343
 344         fat_length = le16_to_cpu(vs->fat_length);
 345         dbg("fat_length 0x%x\n", fat_length);
 346         fat32_length = le32_to_cpu(vs->type.fat32.fat32_length);
 347         dbg("fat32_length 0x%x\n", fat32_length);
 348
 349         if (fat_length)
 350                 fat_size = fat_length * vs->fats;
 351         else if (fat32_length)
 352                 fat_size = fat32_length * vs->fats;
 353         else
 354                 return -1;
 355         dbg("fat_size 0x%x\n", fat_size);
 356
 357         dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
 358                         (sector_size-1)) / sector_size;
 359         dbg("dir_size 0x%x\n", dir_size);
 360
 361         cluster_count = sect_count - (reserved + fat_size + dir_size);
 362         cluster_count /= vs->sectors_per_cluster;
 363         dbg("cluster_count 0x%x\n", cluster_count);
 364
 365         /* must be FAT32 */
 366         if (!fat_length && fat32_length)
 367                 goto fat32;
 368
 369         /* cluster_count tells us the format */
 370         if (cluster_count < FAT12_MAX)
 371                 strcpy(id->type_version, "FAT12");
 372         else if (cluster_count < FAT16_MAX)
 373                 strcpy(id->type_version, "FAT16");
 374         else
 375                 goto fat32;
 376
 377         /* the label may be an attribute in the root directory */
 378         root_start = (reserved + fat_size) * sector_size;
 379         dbg("root dir start 0x%llx\n", (unsigned long long) root_start);
 380         root_dir_entries = le16_to_cpu(vs->dir_entries);
 381         dbg("expected entries 0x%x\n", root_dir_entries);
 382
 383         buf_size = root_dir_entries * sizeof(struct vfat_dir_entry);
 384         buf = volume_id_get_buffer(id, off + root_start, buf_size);
 385         if (buf == NULL)
 386                 goto found;
 387
 388         dir = (struct vfat_dir_entry*) buf;
 389
 390         fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, root_dir_entries);
 391
 392         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 393         if (vs == NULL)
 394                 return -1;
 395
 396         if (fnlen > 0 && memcmp(filename, "NO NAME    ", 11) != 0) {
 397                 volume_id_set_label_raw(id, filename, fnlen);
 398                 volume_id_set_label_string(id, filename, fnlen);
 399         } else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
 400                 volume_id_set_label_raw(id, vs->type.fat.label, 11);
 401                 volume_id_set_label_string(id, vs->type.fat.label, 11);
 402         }
 403         volume_id_set_uuid(id, vs->type.fat.serno, 0, UUID_DOS);
 404         goto found;
 405
 406 fat32:
 407         /* FAT32 should have a valid signature in the fsinfo block */
 408         fsinfo_sect = le16_to_cpu(vs->type.fat32.fsinfo_sector);
 409         buf = volume_id_get_buffer(id, off + (fsinfo_sect * sector_size), 0x200);
 410         if (buf == NULL)
 411                 return -1;
 412         fsinfo = (struct fat32_fsinfo *) buf;
 413         if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0)
 414                 return -1;
 415         if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0)
 416                 return -1 ;
 417
 418         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 419         if (vs == NULL)
 420                 return -1;
 421
 422         strcpy(id->type_version, "FAT32");
 423
 424         /* FAT32 root dir is a cluster chain like any other directory */
 425         buf_size = vs->sectors_per_cluster * sector_size;
 426         root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
 427         dbg("root dir cluster %u\n", root_cluster);
 428         start_data_sect = reserved + fat_size;
 429
 430         next = root_cluster;
 431         maxloop = 100;
 432         while (--maxloop) {
 433                 uint32_t next_sect_off;
 434                 uint64_t next_off;
 435                 uint64_t fat_entry_off;
 436                 int count;
 437
 438                 dbg("next cluster %u\n", next);
 439                 next_sect_off = (next - 2) * vs->sectors_per_cluster;
 440                 next_off = (start_data_sect + next_sect_off) * sector_size;
 441                 dbg("cluster offset 0x%llx\n", (unsigned long long) next_off);
 442
 443                 /* get cluster */
 444                 buf = volume_id_get_buffer(id, off + next_off, buf_size);
 445                 if (buf == NULL)
 446                         goto found;
 447
 448                 dir = (struct vfat_dir_entry*) buf;
 449                 count = buf_size / sizeof(struct vfat_dir_entry);
 450                 dbg("expected entries 0x%x\n", count);
 451
 452                 fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, count);
 453                 if (fnlen > 0)
 454                         break;
 455
 456                 /* get FAT entry */
 457                 fat_entry_off = (reserved * sector_size) + (next * sizeof(uint32_t));
 458                 buf = volume_id_get_buffer(id, off + fat_entry_off, buf_size);
 459                 if (buf == NULL)
 460                         goto found;
 461
 462                 /* set next cluster */
 463                 next = le32_to_cpu(*((uint32_t *) buf)) & 0x0fffffff;
 464                 if (next < 2 || next >= 0x0ffffff0)
 465                         break;
 466         }
 467         if (maxloop == 0)
 468                 dbg("reached maximum follow count of root cluster chain, give up\n");
 469
 470         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 471         if (vs == NULL)
 472                 return -1;
 473
 474         if (fnlen > 0 && memcmp(filename, "NO NAME    ", 11) != 0) {
 475                 volume_id_set_label_raw(id, filename, fnlen);
 476                 volume_id_set_label_string(id, filename, fnlen);
 477         } else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
 478                 volume_id_set_label_raw(id, vs->type.fat32.label, 11);
 479                 volume_id_set_label_string(id, vs->type.fat32.label, 11);
 480         }
 481         volume_id_set_uuid(id, vs->type.fat32.serno, 0, UUID_DOS);
 482
 483 found:
 484         volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
 485         id->type = "vfat";
 486
 487         return 0;
 488 }