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        insfo_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 vfat_dir_entry {
  80         uint8_t         name[11];
  81         uint8_t         attr;
  82         uint16_t        time_creat;
  83         uint16_t        date_creat;
  84         uint16_t        time_acc;
  85         uint16_t        date_acc;
  86         uint16_t        cluster_high;
  87         uint16_t        time_write;
  88         uint16_t        date_write;
  89         uint16_t        cluster_low;
  90         uint32_t        size;
  91 } PACKED;
  92
  93 static uint8_t *get_attr_volume_id(struct vfat_dir_entry *dir, unsigned int count)
  94 {
  95         unsigned int i;
  96
  97         for (i = 0; i < count; i++) {
  98                 /* end marker */
  99                 if (dir[i].name[0] == 0x00) {
 100                         dbg("end of dir");
 101                         break;
 102                 }
 103
 104                 /* empty entry */
 105                 if (dir[i].name[0] == FAT_ENTRY_FREE)
 106                         continue;
 107
 108                 /* long name */
 109                 if ((dir[i].attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
 110                         continue;
 111
 112                 if ((dir[i].attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
 113                         /* labels do not have file data */
 114                         if (dir[i].cluster_high != 0 || dir[i].cluster_low != 0)
 115                                 continue;
 116
 117                         dbg("found ATTR_VOLUME_ID id in root dir");
 118                         return dir[i].name;
 119                 }
 120
 121                 dbg("skip dir entry");
 122         }
 123
 124         return NULL;
 125 }
 126
 127 int volume_id_probe_vfat(struct volume_id *id, uint64_t off)
 128 {
 129         struct vfat_super_block *vs;
 130         struct vfat_dir_entry *dir;
 131         uint16_t sector_size;
 132         uint16_t dir_entries;
 133         uint32_t sect_count;
 134         uint16_t reserved;
 135         uint32_t fat_size;
 136         uint32_t root_cluster;
 137         uint32_t dir_size;
 138         uint32_t cluster_count;
 139         uint16_t fat_length;
 140         uint32_t fat32_length;
 141         uint64_t root_start;
 142         uint32_t start_data_sect;
 143         uint16_t root_dir_entries;
 144         uint8_t *buf;
 145         uint32_t buf_size;
 146         uint8_t *label = NULL;
 147         uint32_t next;
 148         int maxloop;
 149
 150         dbg("probing at offset 0x%llx", (unsigned long long) off);
 151
 152         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 153         if (vs == NULL)
 154                 return -1;
 155
 156         /* believe only that's fat, don't trust the version
 157          * the cluster_count will tell us
 158          */
 159         if (memcmp(vs->sysid, "NTFS", 4) == 0)
 160                 return -1;
 161
 162         if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
 163                 goto magic;
 164
 165         if (memcmp(vs->type.fat32.magic, "FAT32   ", 8) == 0)
 166                 goto magic;
 167
 168         if (memcmp(vs->type.fat.magic, "FAT16   ", 8) == 0)
 169                 goto magic;
 170
 171         if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
 172                 goto magic;
 173
 174         if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
 175                 goto magic;
 176
 177         /* some old floppies don't have a magic, so we expect the boot code to match */
 178
 179         /* boot jump address check */
 180         if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
 181              vs->boot_jump[0] != 0xe9)
 182                 return -1;
 183
 184 magic:
 185         /* reserverd sector count */
 186         if (!vs->reserved)
 187                 return -1;
 188
 189         /* fat count*/
 190         if (!vs->fats)
 191                 return -1;
 192
 193         /* media check */
 194         if (vs->media < 0xf8 && vs->media != 0xf0)
 195                 return -1;
 196
 197         /* cluster size check*/
 198         if (vs->sectors_per_cluster == 0 ||
 199             (vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
 200                 return -1;
 201
 202         /* sector size check */
 203         sector_size = le16_to_cpu(vs->sector_size);
 204         if (sector_size != 0x200 && sector_size != 0x400 &&
 205             sector_size != 0x800 && sector_size != 0x1000)
 206                 return -1;
 207
 208         dbg("sector_size 0x%x", sector_size);
 209         dbg("sectors_per_cluster 0x%x", vs->sectors_per_cluster);
 210
 211         dir_entries = le16_to_cpu(vs->dir_entries);
 212         reserved = le16_to_cpu(vs->reserved);
 213         dbg("reserved 0x%x", reserved);
 214
 215         sect_count = le16_to_cpu(vs->sectors);
 216         if (sect_count == 0)
 217                 sect_count = le32_to_cpu(vs->total_sect);
 218         dbg("sect_count 0x%x", sect_count);
 219
 220         fat_length = le16_to_cpu(vs->fat_length);
 221         dbg("fat_length 0x%x", fat_length);
 222         fat32_length = le32_to_cpu(vs->type.fat32.fat32_length);
 223         dbg("fat32_length 0x%x", fat32_length);
 224
 225         if (fat_length)
 226                 fat_size = fat_length * vs->fats;
 227         else if (fat32_length)
 228                 fat_size = fat32_length * vs->fats;
 229         else
 230                 return -1;
 231         dbg("fat_size 0x%x", fat_size);
 232
 233         dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
 234                         (sector_size-1)) / sector_size;
 235         dbg("dir_size 0x%x", dir_size);
 236
 237         cluster_count = sect_count - (reserved + fat_size + dir_size);
 238         cluster_count /= vs->sectors_per_cluster;
 239         dbg("cluster_count 0x%x", cluster_count);
 240
 241         /* must be FAT32 */
 242         if (!fat_length && fat32_length)
 243                 goto fat32;
 244
 245         /* cluster_count tells us the format */
 246         if (cluster_count < FAT12_MAX)
 247                 strcpy(id->type_version, "FAT12");
 248         else if (cluster_count < FAT16_MAX)
 249                 strcpy(id->type_version, "FAT16");
 250         else
 251                 goto fat32;
 252
 253         /* the label may be an attribute in the root directory */
 254         root_start = (reserved + fat_size) * sector_size;
 255         dbg("root dir start 0x%llx", (unsigned long long) root_start);
 256         root_dir_entries = le16_to_cpu(vs->dir_entries);
 257         dbg("expected entries 0x%x", root_dir_entries);
 258
 259         buf_size = root_dir_entries * sizeof(struct vfat_dir_entry);
 260         buf = volume_id_get_buffer(id, off + root_start, buf_size);
 261         if (buf == NULL)
 262                 goto found;
 263
 264         dir = (struct vfat_dir_entry*) buf;
 265
 266         label = get_attr_volume_id(dir, root_dir_entries);
 267
 268         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 269         if (vs == NULL)
 270                 return -1;
 271
 272         if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
 273                 volume_id_set_label_raw(id, label, 11);
 274                 volume_id_set_label_string(id, label, 11);
 275         } else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
 276                 volume_id_set_label_raw(id, vs->type.fat.label, 11);
 277                 volume_id_set_label_string(id, vs->type.fat.label, 11);
 278         }
 279         volume_id_set_uuid(id, vs->type.fat.serno, UUID_DOS);
 280         goto found;
 281
 282 fat32:
 283         strcpy(id->type_version, "FAT32");
 284
 285         /* FAT32 root dir is a cluster chain like any other directory */
 286         buf_size = vs->sectors_per_cluster * sector_size;
 287         root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
 288         dbg("root dir cluster %u", root_cluster);
 289         start_data_sect = reserved + fat_size;
 290
 291         next = root_cluster;
 292         maxloop = 100;
 293         while (--maxloop) {
 294                 uint32_t next_sect_off;
 295                 uint64_t next_off;
 296                 uint64_t fat_entry_off;
 297                 int count;
 298
 299                 dbg("next cluster %u", next);
 300                 next_sect_off = (next - 2) * vs->sectors_per_cluster;
 301                 next_off = (start_data_sect + next_sect_off) * sector_size;
 302                 dbg("cluster offset 0x%llx", (unsigned long long) next_off);
 303
 304                 /* get cluster */
 305                 buf = volume_id_get_buffer(id, off + next_off, buf_size);
 306                 if (buf == NULL)
 307                         goto found;
 308
 309                 dir = (struct vfat_dir_entry*) buf;
 310                 count = buf_size / sizeof(struct vfat_dir_entry);
 311                 dbg("expected entries 0x%x", count);
 312
 313                 label = get_attr_volume_id(dir, count);
 314                 if (label)
 315                         break;
 316
 317                 /* get FAT entry */
 318                 fat_entry_off = (reserved * sector_size) + (next * sizeof(uint32_t));
 319                 buf = volume_id_get_buffer(id, off + fat_entry_off, buf_size);
 320                 if (buf == NULL)
 321                         goto found;
 322
 323                 /* set next cluster */
 324                 next = le32_to_cpu(*((uint32_t *) buf) & 0x0fffffff);
 325                 if (next == 0)
 326                         break;
 327         }
 328         if (maxloop == 0)
 329                 dbg("reached maximum follow count of root cluster chain, give up");
 330
 331         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 332         if (vs == NULL)
 333                 return -1;
 334
 335         if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
 336                 volume_id_set_label_raw(id, label, 11);
 337                 volume_id_set_label_string(id, label, 11);
 338         } else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
 339                 volume_id_set_label_raw(id, vs->type.fat32.label, 11);
 340                 volume_id_set_label_string(id, vs->type.fat32.label, 11);
 341         }
 342         volume_id_set_uuid(id, vs->type.fat32.serno, UUID_DOS);
 343
 344 found:
 345         volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
 346         id->type = "vfat";
 347
 348         return 0;
 349 }