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
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation, either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  19  */
  20
  21 #ifndef _GNU_SOURCE
  22 #define _GNU_SOURCE 1
  23 #endif
  24
  25 #include <stdio.h>
  26 #include <stdlib.h>
  27 #include <unistd.h>
  28 #include <string.h>
  29 #include <errno.h>
  30 #include <ctype.h>
  31
  32 #include "libvolume_id.h"
  33 #include "libvolume_id-private.h"
  34
  35 #define FAT12_MAX                       0xff5
  36 #define FAT16_MAX                       0xfff5
  37 #define FAT_ATTR_VOLUME_ID              0x08
  38 #define FAT_ATTR_DIR                    0x10
  39 #define FAT_ATTR_LONG_NAME              0x0f
  40 #define FAT_ATTR_MASK                   0x3f
  41 #define FAT_ENTRY_FREE                  0xe5
  42
  43 #define VFAT_LFN_SEQ_MASK               0x3f
  44 #define VFAT_LFN_SEQ_LAST               0x40
  45 #define VFAT_LFN_SEQ_MAX                20
  46 #define VFAT_LFN_CHARS_PER_ENTRY        (5 + 6 + 2)
  47 #define VFAT_LOWERCASE_NAME             0x10
  48 #define VFAT_LOWERCASE_EXT              0x08
  49
  50 struct vfat_super_block {
  51         uint8_t         boot_jump[3];
  52         uint8_t         sysid[8];
  53         uint16_t        sector_size;
  54         uint8_t         sectors_per_cluster;
  55         uint16_t        reserved;
  56         uint8_t         fats;
  57         uint16_t        dir_entries;
  58         uint16_t        sectors;
  59         uint8_t         media;
  60         uint16_t        fat_length;
  61         uint16_t        secs_track;
  62         uint16_t        heads;
  63         uint32_t        hidden;
  64         uint32_t        total_sect;
  65         union {
  66                 struct fat_super_block {
  67                         uint8_t         unknown[3];
  68                         uint8_t         serno[4];
  69                         uint8_t         label[11];
  70                         uint8_t         magic[8];
  71                         uint8_t         dummy2[192];
  72                         uint8_t         pmagic[2];
  73                 } PACKED fat;
  74                 struct fat32_super_block {
  75                         uint32_t        fat32_length;
  76                         uint16_t        flags;
  77                         uint8_t         version[2];
  78                         uint32_t        root_cluster;
  79                         uint16_t        fsinfo_sector;
  80                         uint16_t        backup_boot;
  81                         uint16_t        reserved2[6];
  82                         uint8_t         unknown[3];
  83                         uint8_t         serno[4];
  84                         uint8_t         label[11];
  85                         uint8_t         magic[8];
  86                         uint8_t         dummy2[164];
  87                         uint8_t         pmagic[2];
  88                 } PACKED fat32;
  89         } PACKED type;
  90 } PACKED;
  91
  92 struct fat32_fsinfo {
  93         uint8_t signature1[4];
  94         uint32_t reserved1[120];
  95         uint8_t signature2[4];
  96         uint32_t free_clusters;
  97         uint32_t next_cluster;
  98         uint32_t reserved2[4];
  99 } PACKED;
 100
 101 struct vfat_dir_entry {
 102         uint8_t         name[11];
 103         uint8_t         attr;
 104         uint8_t         lowercase;
 105         uint8_t         fine_time_creat;
 106         uint16_t        time_creat;
 107         uint16_t        date_creat;
 108         uint16_t        date_acc;
 109         uint16_t        cluster_high;
 110         uint16_t        time_write;
 111         uint16_t        date_write;
 112         uint16_t        cluster_low;
 113         uint32_t        size;
 114 } PACKED;
 115
 116
 117 struct vfat_lfn_entry {
 118         uint8_t         seq;
 119         uint16_t        name0[5];
 120         uint8_t         attr;
 121         uint8_t         reserved;
 122         uint8_t         cksum;
 123         uint16_t        name1[6];
 124         uint16_t        cluster;
 125         uint16_t        name2[2];
 126 } PACKED;
 127
 128 static uint8_t fat_lfn_checksum(const uint8_t name[11])
 129 {
 130         uint8_t cksum = 0;
 131         int i;
 132
 133         /* http://en.wikipedia.org/wiki/File_Allocation_Table */
 134         for (i = 0; i < 11; i++)
 135                 cksum = ((cksum & 1) ? 0x80 : 0) + (cksum >> 1) + name[i];
 136
 137         return cksum;
 138 }
 139
 140 static size_t fat_read_lfn(uint8_t *filename, size_t fnsize,
 141                            struct vfat_dir_entry *dir,
 142                            struct vfat_dir_entry *entry)
 143 {
 144         uint8_t buffer[VFAT_LFN_SEQ_MAX * VFAT_LFN_CHARS_PER_ENTRY * 2];
 145         uint8_t expected_seq = 1;
 146         uint8_t cksum;
 147         size_t len = 0;
 148         size_t fnlen = 0;
 149
 150         cksum = fat_lfn_checksum(entry->name);
 151
 152         while (--entry >= dir) {
 153                 struct vfat_lfn_entry *lfn = (struct vfat_lfn_entry *) entry;
 154
 155                 if (expected_seq > VFAT_LFN_SEQ_MAX)
 156                         break;
 157
 158                 if ((lfn->attr & FAT_ATTR_MASK) != FAT_ATTR_LONG_NAME)
 159                         break;
 160
 161                 if (lfn->cksum != cksum)
 162                         break;
 163
 164                 if ((lfn->seq & VFAT_LFN_SEQ_MASK) != expected_seq++)
 165                         break;
 166
 167                 if (lfn->cluster != 0)
 168                         break;
 169
 170                 /* extra paranoia -- should never happen */
 171                 if (len + sizeof(lfn->name0) + sizeof(lfn->name1) +
 172                     sizeof(lfn->name2) > sizeof(buffer))
 173                         break;
 174
 175                 memcpy (&buffer[len], lfn->name0, sizeof(lfn->name0));
 176                 len += sizeof(lfn->name0);
 177                 memcpy (&buffer[len], lfn->name1, sizeof(lfn->name1));
 178                 len += sizeof(lfn->name1);
 179                 memcpy (&buffer[len], lfn->name2, sizeof(lfn->name2));
 180                 len += sizeof(lfn->name2);
 181
 182                 if (lfn->seq & VFAT_LFN_SEQ_LAST) {
 183                         fnlen = volume_id_set_unicode16(filename, fnsize, buffer, LE, len);
 184                         break;
 185                 }
 186         }
 187
 188         return fnlen;
 189 }
 190
 191 static size_t fat_read_filename(uint8_t *filename, size_t fnsize,
 192                                 struct vfat_dir_entry *dir, struct vfat_dir_entry *entry)
 193 {
 194         size_t len;
 195         int i;
 196
 197         /* check if maybe we have LFN entries */
 198         len = fat_read_lfn(filename, fnsize, dir, entry);
 199         if (len > 0)
 200                 goto out;
 201
 202         /* else, read the normal 8.3 name */
 203         for (i = 0; i < 11; i++) {
 204                 if (entry->lowercase & ((i < 8) ? VFAT_LOWERCASE_NAME : VFAT_LOWERCASE_EXT))
 205                         filename[i] = tolower(entry->name[i]);
 206                 else
 207                         filename[i] = entry->name[i];
 208         }
 209         len = 11;
 210
 211 out:
 212         filename[len] = '\0';
 213         return len;
 214 }
 215
 216 /* fills filename, returns string length */
 217 static size_t get_fat_attr_volume_id(uint8_t *filename, size_t fnsize,
 218                                      struct vfat_dir_entry *dir, unsigned int count)
 219 {
 220         unsigned int i;
 221
 222         for (i = 0; i < count; i++) {
 223                 /* end marker */
 224                 if (dir[i].name[0] == 0x00) {
 225                         dbg("end of dir\n");
 226                         break;
 227                 }
 228
 229                 /* empty entry */
 230                 if (dir[i].name[0] == FAT_ENTRY_FREE)
 231                         continue;
 232
 233                 /* long name */
 234                 if ((dir[i].attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
 235                         continue;
 236
 237                 if ((dir[i].attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
 238                         /* labels do not have file data */
 239                         if (dir[i].cluster_high != 0 || dir[i].cluster_low != 0)
 240                                 continue;
 241
 242                         dbg("found ATTR_VOLUME_ID id in root dir\n");
 243                         return fat_read_filename(filename, fnsize, dir, &dir[i]);
 244                 }
 245
 246                 dbg("skip dir entry\n");
 247         }
 248
 249         return 0;
 250 }
 251
 252 int volume_id_probe_vfat(struct volume_id *id, uint64_t off, uint64_t size)
 253 {
 254         uint8_t filename[255 * 3];
 255         struct vfat_super_block *vs;
 256         struct vfat_dir_entry *dir;
 257         struct fat32_fsinfo *fsinfo;
 258         uint16_t sector_size;
 259         uint16_t dir_entries;
 260         uint32_t sect_count;
 261         uint16_t reserved;
 262         uint32_t fat_size;
 263         uint32_t root_cluster;
 264         uint32_t dir_size;
 265         uint32_t cluster_count;
 266         uint16_t fat_length;
 267         uint32_t fat32_length;
 268         uint64_t root_start;
 269         uint32_t start_data_sect;
 270         uint16_t root_dir_entries;
 271         uint16_t fsinfo_sect;
 272         uint8_t *buf;
 273         uint32_t buf_size;
 274         uint32_t next;
 275         int maxloop;
 276         size_t fnlen;
 277
 278         info("probing at offset 0x%" PRIx64 "\n", off);
 279
 280         buf = volume_id_get_buffer(id, off, 0x400);
 281         if (buf == NULL)
 282                 return -1;
 283
 284         /* check signature */
 285         if (buf[510] != 0x55 || buf[511] != 0xaa)
 286                 return -1;
 287
 288         vs = (struct vfat_super_block *) buf;
 289         if (memcmp(vs->sysid, "NTFS", 4) == 0)
 290                 return -1;
 291
 292         /* believe only that's fat, don't trust the version */
 293         if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
 294                 goto magic;
 295
 296         if (memcmp(vs->type.fat32.magic, "FAT32   ", 8) == 0)
 297                 goto magic;
 298
 299         if (memcmp(vs->type.fat.magic, "FAT16   ", 8) == 0)
 300                 goto magic;
 301
 302         if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
 303                 goto magic;
 304
 305         if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
 306                 goto magic;
 307
 308         /* some old floppies don't have a magic, expect the boot jump address to match */
 309         if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
 310              vs->boot_jump[0] != 0xe9)
 311                 return -1;
 312
 313 magic:
 314         info("magic found\n");
 315         /* reserverd sector count */
 316         if (!vs->reserved)
 317                 return -1;
 318
 319         /* fat count */
 320         if (!vs->fats)
 321                 return -1;
 322
 323         /* media check */
 324         if (vs->media < 0xf8 && vs->media != 0xf0)
 325                 return -1;
 326
 327         /* cluster size check */
 328         if (vs->sectors_per_cluster == 0 ||
 329             (vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
 330                 return -1;
 331
 332         /* sector size check */
 333         sector_size = le16_to_cpu(vs->sector_size);
 334         if (sector_size == 0 || ((sector_size & (sector_size-1)) != 0))
 335                 return -1;
 336
 337         info("checks passed\n");
 338         dbg("sector_size 0x%x\n", sector_size);
 339         dbg("sectors_per_cluster 0x%x\n", vs->sectors_per_cluster);
 340
 341         dir_entries = le16_to_cpu(vs->dir_entries);
 342         reserved = le16_to_cpu(vs->reserved);
 343         dbg("reserved 0x%x\n", reserved);
 344
 345         sect_count = le16_to_cpu(vs->sectors);
 346         if (sect_count == 0)
 347                 sect_count = le32_to_cpu(vs->total_sect);
 348         dbg("sect_count 0x%x\n", sect_count);
 349
 350         fat_length = le16_to_cpu(vs->fat_length);
 351         dbg("fat_length 0x%x\n", fat_length);
 352         fat32_length = le32_to_cpu(vs->type.fat32.fat32_length);
 353         dbg("fat32_length 0x%x\n", fat32_length);
 354
 355         if (fat_length)
 356                 fat_size = fat_length * vs->fats;
 357         else if (fat32_length)
 358                 fat_size = fat32_length * vs->fats;
 359         else
 360                 return -1;
 361         info("fat_size 0x%x\n", fat_size);
 362
 363         dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
 364                         (sector_size-1)) / sector_size;
 365         dbg("dir_size 0x%x\n", dir_size);
 366
 367         cluster_count = sect_count - (reserved + fat_size + dir_size);
 368         cluster_count /= vs->sectors_per_cluster;
 369         info("cluster_count 0x%x\n", cluster_count);
 370
 371         /* must be FAT32 */
 372         if (!fat_length && fat32_length)
 373                 goto fat32;
 374
 375         /* cluster_count tells us the format */
 376         if (cluster_count < FAT12_MAX)
 377                 strcpy(id->type_version, "FAT12");
 378         else if (cluster_count < FAT16_MAX)
 379                 strcpy(id->type_version, "FAT16");
 380         else
 381                 goto fat32;
 382
 383         /* the label may be an attribute in the root directory */
 384         root_start = (reserved + fat_size) * sector_size;
 385         dbg("root dir start 0x%" PRIx64 "\n", root_start);
 386         root_dir_entries = le16_to_cpu(vs->dir_entries);
 387         dbg("expected entries 0x%x\n", root_dir_entries);
 388
 389         buf_size = root_dir_entries * sizeof(struct vfat_dir_entry);
 390         buf = volume_id_get_buffer(id, off + root_start, buf_size);
 391         if (buf == NULL)
 392                 goto found;
 393
 394         dir = (struct vfat_dir_entry*) buf;
 395
 396         fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, root_dir_entries);
 397
 398         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 399         if (vs == NULL)
 400                 return -1;
 401
 402         if (fnlen > 0 && memcmp(filename, "NO NAME    ", 11) != 0) {
 403                 volume_id_set_label_raw(id, filename, fnlen);
 404                 volume_id_set_label_string(id, filename, fnlen);
 405         } else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
 406                 volume_id_set_label_raw(id, vs->type.fat.label, 11);
 407                 volume_id_set_label_string(id, vs->type.fat.label, 11);
 408         }
 409         volume_id_set_uuid(id, vs->type.fat.serno, 0, UUID_DOS);
 410         goto found;
 411
 412 fat32:
 413         info("looking for FAT32\n");
 414         /* FAT32 should have a valid signature in the fsinfo block */
 415         fsinfo_sect = le16_to_cpu(vs->type.fat32.fsinfo_sector);
 416         buf = volume_id_get_buffer(id, off + (fsinfo_sect * sector_size), 0x200);
 417         if (buf == NULL)
 418                 return -1;
 419         fsinfo = (struct fat32_fsinfo *) buf;
 420         info("signature1: 0x%02x%02x%02x%02x\n",
 421              fsinfo->signature1[0], fsinfo->signature1[1],
 422              fsinfo->signature1[2], fsinfo->signature1[3]);
 423         info("signature2: 0x%02x%02x%02x%02x\n",
 424              fsinfo->signature2[0], fsinfo->signature2[1],
 425              fsinfo->signature2[2], fsinfo->signature2[3]);
 426         if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0)
 427                 return -1;
 428         if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0)
 429                 return -1 ;
 430         info("FAT32 signatures match\n");
 431
 432         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 433         if (vs == NULL)
 434                 return -1;
 435
 436         strcpy(id->type_version, "FAT32");
 437
 438         /* FAT32 root dir is a cluster chain like any other directory */
 439         buf_size = vs->sectors_per_cluster * sector_size;
 440         root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
 441         dbg("root dir cluster %u\n", root_cluster);
 442         start_data_sect = reserved + fat_size;
 443
 444         next = root_cluster;
 445         maxloop = 100;
 446         while (--maxloop) {
 447                 uint32_t next_sect_off;
 448                 uint64_t next_off;
 449                 uint64_t fat_entry_off;
 450                 int count;
 451
 452                 dbg("next cluster %u\n", next);
 453                 next_sect_off = (next - 2) * vs->sectors_per_cluster;
 454                 next_off = (start_data_sect + next_sect_off) * sector_size;
 455                 dbg("cluster offset 0x%" PRIx64 "\n", next_off);
 456
 457                 /* get cluster */
 458                 buf = volume_id_get_buffer(id, off + next_off, buf_size);
 459                 if (buf == NULL)
 460                         goto found;
 461
 462                 dir = (struct vfat_dir_entry*) buf;
 463                 count = buf_size / sizeof(struct vfat_dir_entry);
 464                 dbg("expected entries 0x%x\n", count);
 465
 466                 fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, count);
 467                 if (fnlen > 0)
 468                         break;
 469
 470                 /* get FAT entry */
 471                 fat_entry_off = (reserved * sector_size) + (next * sizeof(uint32_t));
 472                 buf = volume_id_get_buffer(id, off + fat_entry_off, buf_size);
 473                 if (buf == NULL)
 474                         goto found;
 475
 476                 /* set next cluster */
 477                 next = le32_to_cpu(*((uint32_t *) buf)) & 0x0fffffff;
 478                 if (next < 2 || next >= 0x0ffffff0)
 479                         break;
 480         }
 481         if (maxloop == 0)
 482                 dbg("reached maximum follow count of root cluster chain, give up\n");
 483
 484         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 485         if (vs == NULL)
 486                 return -1;
 487
 488         if (fnlen > 0 && memcmp(filename, "NO NAME    ", 11) != 0) {
 489                 volume_id_set_label_raw(id, filename, fnlen);
 490                 volume_id_set_label_string(id, filename, fnlen);
 491         } else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
 492                 volume_id_set_label_raw(id, vs->type.fat32.label, 11);
 493                 volume_id_set_label_string(id, vs->type.fat32.label, 11);
 494         }
 495         volume_id_set_uuid(id, vs->type.fat32.serno, 0, UUID_DOS);
 496
 497 found:
 498         volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
 499         id->type = "vfat";
 500
 501         return 0;
 502 }