extras/volume_id/lib/fat.c

   1 /*
   2  * volume_id - reads filesystem label and uuid
   3  *
   4  * Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>
   5  *
   6  *      This program is free software; you can redistribute it and/or modify it
   7  *      under the terms of the GNU General Public License as published by the
   8  *      Free Software Foundation version 2 of the License.
   9  */
  10
  11 #ifndef _GNU_SOURCE
  12 #define _GNU_SOURCE 1
  13 #endif
  14
  15 #ifdef HAVE_CONFIG_H
  16 #  include <config.h>
  17 #endif
  18
  19 #include <stdio.h>
  20 #include <stdlib.h>
  21 #include <unistd.h>
  22 #include <string.h>
  23 #include <errno.h>
  24 #include <ctype.h>
  25
  26 #include "libvolume_id.h"
  27 #include "util.h"
  28
  29 #define FAT12_MAX                       0xff5
  30 #define FAT16_MAX                       0xfff5
  31 #define FAT_ATTR_VOLUME_ID              0x08
  32 #define FAT_ATTR_DIR                    0x10
  33 #define FAT_ATTR_LONG_NAME              0x0f
  34 #define FAT_ATTR_MASK                   0x3f
  35 #define FAT_ENTRY_FREE                  0xe5
  36
  37 struct vfat_super_block {
  38         uint8_t         boot_jump[3];
  39         uint8_t         sysid[8];
  40         uint16_t        sector_size;
  41         uint8_t         sectors_per_cluster;
  42         uint16_t        reserved;
  43         uint8_t         fats;
  44         uint16_t        dir_entries;
  45         uint16_t        sectors;
  46         uint8_t         media;
  47         uint16_t        fat_length;
  48         uint16_t        secs_track;
  49         uint16_t        heads;
  50         uint32_t        hidden;
  51         uint32_t        total_sect;
  52         union {
  53                 struct fat_super_block {
  54                         uint8_t         unknown[3];
  55                         uint8_t         serno[4];
  56                         uint8_t         label[11];
  57                         uint8_t         magic[8];
  58                         uint8_t         dummy2[192];
  59                         uint8_t         pmagic[2];
  60                 } PACKED fat;
  61                 struct fat32_super_block {
  62                         uint32_t        fat32_length;
  63                         uint16_t        flags;
  64                         uint8_t         version[2];
  65                         uint32_t        root_cluster;
  66                         uint16_t        fsinfo_sector;
  67                         uint16_t        backup_boot;
  68                         uint16_t        reserved2[6];
  69                         uint8_t         unknown[3];
  70                         uint8_t         serno[4];
  71                         uint8_t         label[11];
  72                         uint8_t         magic[8];
  73                         uint8_t         dummy2[164];
  74                         uint8_t         pmagic[2];
  75                 } PACKED fat32;
  76         } PACKED type;
  77 } PACKED;
  78
  79 struct fat32_fsinfo {
  80         uint8_t signature1[4];
  81         uint32_t reserved1[120];
  82         uint8_t signature2[4];
  83         uint32_t free_clusters;
  84         uint32_t next_cluster;
  85         uint32_t reserved2[4];
  86 } PACKED;
  87
  88 struct vfat_dir_entry {
  89         uint8_t         name[11];
  90         uint8_t         attr;
  91         uint16_t        time_creat;
  92         uint16_t        date_creat;
  93         uint16_t        time_acc;
  94         uint16_t        date_acc;
  95         uint16_t        cluster_high;
  96         uint16_t        time_write;
  97         uint16_t        date_write;
  98         uint16_t        cluster_low;
  99         uint32_t        size;
 100 } PACKED;
 101
 102 static uint8_t *get_attr_volume_id(struct vfat_dir_entry *dir, unsigned int count)
 103 {
 104         unsigned int i;
 105
 106         for (i = 0; i < count; i++) {
 107                 /* end marker */
 108                 if (dir[i].name[0] == 0x00) {
 109                         dbg("end of dir");
 110                         break;
 111                 }
 112
 113                 /* empty entry */
 114                 if (dir[i].name[0] == FAT_ENTRY_FREE)
 115                         continue;
 116
 117                 /* long name */
 118                 if ((dir[i].attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
 119                         continue;
 120
 121                 if ((dir[i].attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
 122                         /* labels do not have file data */
 123                         if (dir[i].cluster_high != 0 || dir[i].cluster_low != 0)
 124                                 continue;
 125
 126                         dbg("found ATTR_VOLUME_ID id in root dir");
 127                         return dir[i].name;
 128                 }
 129
 130                 dbg("skip dir entry");
 131         }
 132
 133         return NULL;
 134 }
 135
 136 int volume_id_probe_vfat(struct volume_id *id, uint64_t off, uint64_t size)
 137 {
 138         struct vfat_super_block *vs;
 139         struct vfat_dir_entry *dir;
 140         struct fat32_fsinfo *fsinfo;
 141         uint16_t sector_size;
 142         uint16_t dir_entries;
 143         uint32_t sect_count;
 144         uint16_t reserved;
 145         uint32_t fat_size;
 146         uint32_t root_cluster;
 147         uint32_t dir_size;
 148         uint32_t cluster_count;
 149         uint16_t fat_length;
 150         uint32_t fat32_length;
 151         uint64_t root_start;
 152         uint32_t start_data_sect;
 153         uint16_t root_dir_entries;
 154         uint16_t fsinfo_sect;
 155         uint8_t *buf;
 156         uint32_t buf_size;
 157         uint8_t *label = NULL;
 158         uint32_t next;
 159         int maxloop;
 160
 161         info("probing at offset 0x%llx", (unsigned long long) off);
 162
 163         buf = volume_id_get_buffer(id, off, 0x400);
 164         if (buf == NULL)
 165                 return -1;
 166
 167         /* check signature */
 168         if (buf[510] != 0x55 || buf[511] != 0xaa)
 169                 return -1;
 170
 171         vs = (struct vfat_super_block *) buf;
 172         if (memcmp(vs->sysid, "NTFS", 4) == 0)
 173                 return -1;
 174
 175         /* believe only that's fat, don't trust the version */
 176         if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
 177                 goto magic;
 178
 179         if (memcmp(vs->type.fat32.magic, "FAT32   ", 8) == 0)
 180                 goto magic;
 181
 182         if (memcmp(vs->type.fat.magic, "FAT16   ", 8) == 0)
 183                 goto magic;
 184
 185         if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
 186                 goto magic;
 187
 188         if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
 189                 goto magic;
 190
 191         /* some old floppies don't have a magic, expect the boot jump address to match */
 192         if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
 193              vs->boot_jump[0] != 0xe9)
 194                 return -1;
 195
 196 magic:
 197         /* reserverd sector count */
 198         if (!vs->reserved)
 199                 return -1;
 200
 201         /* fat count*/
 202         if (!vs->fats)
 203                 return -1;
 204
 205         /* media check */
 206         if (vs->media < 0xf8 && vs->media != 0xf0)
 207                 return -1;
 208
 209         /* cluster size check*/
 210         if (vs->sectors_per_cluster == 0 ||
 211             (vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
 212                 return -1;
 213
 214         /* sector size check */
 215         sector_size = le16_to_cpu(vs->sector_size);
 216         if (sector_size != 0x200 && sector_size != 0x400 &&
 217             sector_size != 0x800 && sector_size != 0x1000)
 218                 return -1;
 219
 220         dbg("sector_size 0x%x", sector_size);
 221         dbg("sectors_per_cluster 0x%x", vs->sectors_per_cluster);
 222
 223         dir_entries = le16_to_cpu(vs->dir_entries);
 224         reserved = le16_to_cpu(vs->reserved);
 225         dbg("reserved 0x%x", reserved);
 226
 227         sect_count = le16_to_cpu(vs->sectors);
 228         if (sect_count == 0)
 229                 sect_count = le32_to_cpu(vs->total_sect);
 230         dbg("sect_count 0x%x", sect_count);
 231
 232         fat_length = le16_to_cpu(vs->fat_length);
 233         dbg("fat_length 0x%x", fat_length);
 234         fat32_length = le32_to_cpu(vs->type.fat32.fat32_length);
 235         dbg("fat32_length 0x%x", fat32_length);
 236
 237         if (fat_length)
 238                 fat_size = fat_length * vs->fats;
 239         else if (fat32_length)
 240                 fat_size = fat32_length * vs->fats;
 241         else
 242                 return -1;
 243         dbg("fat_size 0x%x", fat_size);
 244
 245         dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
 246                         (sector_size-1)) / sector_size;
 247         dbg("dir_size 0x%x", dir_size);
 248
 249         cluster_count = sect_count - (reserved + fat_size + dir_size);
 250         cluster_count /= vs->sectors_per_cluster;
 251         dbg("cluster_count 0x%x", cluster_count);
 252
 253         /* must be FAT32 */
 254         if (!fat_length && fat32_length)
 255                 goto fat32;
 256
 257         /* cluster_count tells us the format */
 258         if (cluster_count < FAT12_MAX)
 259                 strcpy(id->type_version, "FAT12");
 260         else if (cluster_count < FAT16_MAX)
 261                 strcpy(id->type_version, "FAT16");
 262         else
 263                 goto fat32;
 264
 265         /* the label may be an attribute in the root directory */
 266         root_start = (reserved + fat_size) * sector_size;
 267         dbg("root dir start 0x%llx", (unsigned long long) root_start);
 268         root_dir_entries = le16_to_cpu(vs->dir_entries);
 269         dbg("expected entries 0x%x", root_dir_entries);
 270
 271         buf_size = root_dir_entries * sizeof(struct vfat_dir_entry);
 272         buf = volume_id_get_buffer(id, off + root_start, buf_size);
 273         if (buf == NULL)
 274                 goto found;
 275
 276         dir = (struct vfat_dir_entry*) buf;
 277
 278         label = get_attr_volume_id(dir, root_dir_entries);
 279
 280         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 281         if (vs == NULL)
 282                 return -1;
 283
 284         if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
 285                 volume_id_set_label_raw(id, label, 11);
 286                 volume_id_set_label_string(id, label, 11);
 287         } else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
 288                 volume_id_set_label_raw(id, vs->type.fat.label, 11);
 289                 volume_id_set_label_string(id, vs->type.fat.label, 11);
 290         }
 291         volume_id_set_uuid(id, vs->type.fat.serno, 0, UUID_DOS);
 292         goto found;
 293
 294 fat32:
 295         /* FAT32 should have a valid signature in the fsinfo block */
 296         fsinfo_sect = le16_to_cpu(vs->type.fat32.fsinfo_sector);
 297         buf = volume_id_get_buffer(id, off + (fsinfo_sect * sector_size), 0x200);
 298         if (buf == NULL)
 299                 return -1;
 300         fsinfo = (struct fat32_fsinfo *) buf;
 301         if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0)
 302                 return -1;
 303         if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0)
 304                 return -1 ;
 305
 306         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 307         if (vs == NULL)
 308                 return -1;
 309
 310         strcpy(id->type_version, "FAT32");
 311
 312         /* FAT32 root dir is a cluster chain like any other directory */
 313         buf_size = vs->sectors_per_cluster * sector_size;
 314         root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
 315         dbg("root dir cluster %u", root_cluster);
 316         start_data_sect = reserved + fat_size;
 317
 318         next = root_cluster;
 319         maxloop = 100;
 320         while (--maxloop) {
 321                 uint32_t next_sect_off;
 322                 uint64_t next_off;
 323                 uint64_t fat_entry_off;
 324                 int count;
 325
 326                 dbg("next cluster %u", next);
 327                 next_sect_off = (next - 2) * vs->sectors_per_cluster;
 328                 next_off = (start_data_sect + next_sect_off) * sector_size;
 329                 dbg("cluster offset 0x%llx", (unsigned long long) next_off);
 330
 331                 /* get cluster */
 332                 buf = volume_id_get_buffer(id, off + next_off, buf_size);
 333                 if (buf == NULL)
 334                         goto found;
 335
 336                 dir = (struct vfat_dir_entry*) buf;
 337                 count = buf_size / sizeof(struct vfat_dir_entry);
 338                 dbg("expected entries 0x%x", count);
 339
 340                 label = get_attr_volume_id(dir, count);
 341                 if (label)
 342                         break;
 343
 344                 /* get FAT entry */
 345                 fat_entry_off = (reserved * sector_size) + (next * sizeof(uint32_t));
 346                 buf = volume_id_get_buffer(id, off + fat_entry_off, buf_size);
 347                 if (buf == NULL)
 348                         goto found;
 349
 350                 /* set next cluster */
 351                 next = le32_to_cpu(*((uint32_t *) buf)) & 0x0fffffff;
 352                 if (next < 2 || next >= 0x0ffffff0)
 353                         break;
 354         }
 355         if (maxloop == 0)
 356                 dbg("reached maximum follow count of root cluster chain, give up");
 357
 358         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 359         if (vs == NULL)
 360                 return -1;
 361
 362         if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
 363                 volume_id_set_label_raw(id, label, 11);
 364                 volume_id_set_label_string(id, label, 11);
 365         } else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
 366                 volume_id_set_label_raw(id, vs->type.fat32.label, 11);
 367                 volume_id_set_label_string(id, vs->type.fat32.label, 11);
 368         }
 369         volume_id_set_uuid(id, vs->type.fat32.serno, 0, UUID_DOS);
 370
 371 found:
 372         volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
 373         id->type = "vfat";
 374
 375         return 0;
 376 }