extras/volume_id/volume_id/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 "volume_id.h"
  27 #include "logging.h"
  28 #include "util.h"
  29 #include "fat.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 struct vfat_super_block {
  40         uint8_t         boot_jump[3];
  41         uint8_t         sysid[8];
  42         uint16_t        sector_size;
  43         uint8_t         sectors_per_cluster;
  44         uint16_t        reserved;
  45         uint8_t         fats;
  46         uint16_t        dir_entries;
  47         uint16_t        sectors;
  48         uint8_t         media;
  49         uint16_t        fat_length;
  50         uint16_t        secs_track;
  51         uint16_t        heads;
  52         uint32_t        hidden;
  53         uint32_t        total_sect;
  54         union {
  55                 struct fat_super_block {
  56                         uint8_t         unknown[3];
  57                         uint8_t         serno[4];
  58                         uint8_t         label[11];
  59                         uint8_t         magic[8];
  60                         uint8_t         dummy2[192];
  61                         uint8_t         pmagic[2];
  62                 } __attribute__((__packed__)) fat;
  63                 struct fat32_super_block {
  64                         uint32_t        fat32_length;
  65                         uint16_t        flags;
  66                         uint8_t         version[2];
  67                         uint32_t        root_cluster;
  68                         uint16_t        insfo_sector;
  69                         uint16_t        backup_boot;
  70                         uint16_t        reserved2[6];
  71                         uint8_t         unknown[3];
  72                         uint8_t         serno[4];
  73                         uint8_t         label[11];
  74                         uint8_t         magic[8];
  75                         uint8_t         dummy2[164];
  76                         uint8_t         pmagic[2];
  77                 } __attribute__((__packed__)) fat32;
  78         } __attribute__((__packed__)) type;
  79 } __attribute__((__packed__));
  80
  81 struct vfat_dir_entry {
  82         uint8_t         name[11];
  83         uint8_t         attr;
  84         uint16_t        time_creat;
  85         uint16_t        date_creat;
  86         uint16_t        time_acc;
  87         uint16_t        date_acc;
  88         uint16_t        cluster_high;
  89         uint16_t        time_write;
  90         uint16_t        date_write;
  91         uint16_t        cluster_low;
  92         uint32_t        size;
  93 } __attribute__((__packed__));
  94
  95 static uint8_t *get_attr_volume_id(struct vfat_dir_entry *dir, unsigned int count)
  96 {
  97         unsigned int i;
  98
  99         for (i = 0; i < count; i++) {
 100                 /* end marker */
 101                 if (dir[i].name[0] == 0x00) {
 102                         dbg("end of dir");
 103                         break;
 104                 }
 105
 106                 /* empty entry */
 107                 if (dir[i].name[0] == FAT_ENTRY_FREE)
 108                         continue;
 109
 110                 /* long name */
 111                 if ((dir[i].attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
 112                         continue;
 113
 114                 if ((dir[i].attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
 115                         /* labels do not have file data */
 116                         if (dir[i].cluster_high != 0 || dir[i].cluster_low != 0)
 117                                 continue;
 118
 119                         dbg("found ATTR_VOLUME_ID id in root dir");
 120                         return dir[i].name;
 121                 }
 122
 123                 dbg("skip dir entry");
 124         }
 125
 126         return NULL;
 127 }
 128
 129 int volume_id_probe_vfat(struct volume_id *id, uint64_t off)
 130 {
 131         struct vfat_super_block *vs;
 132         struct vfat_dir_entry *dir;
 133         uint16_t sector_size;
 134         uint16_t dir_entries;
 135         uint32_t sect_count;
 136         uint16_t reserved;
 137         uint32_t fat_size;
 138         uint32_t root_cluster;
 139         uint32_t dir_size;
 140         uint32_t cluster_count;
 141         uint16_t fat_length;
 142         uint32_t fat32_length;
 143         uint64_t root_start;
 144         uint32_t start_data_sect;
 145         uint16_t root_dir_entries;
 146         uint8_t *buf;
 147         uint32_t buf_size;
 148         uint8_t *label = NULL;
 149         uint32_t next;
 150         int maxloop;
 151
 152         dbg("probing at offset 0x%llx", (unsigned long long) off);
 153
 154         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 155         if (vs == NULL)
 156                 return -1;
 157
 158         /* believe only that's fat, don't trust the version
 159          * the cluster_count will tell us
 160          */
 161         if (memcmp(vs->sysid, "NTFS", 4) == 0)
 162                 return -1;
 163
 164         if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
 165                 goto valid;
 166
 167         if (memcmp(vs->type.fat32.magic, "FAT32   ", 8) == 0)
 168                 goto valid;
 169
 170         if (memcmp(vs->type.fat.magic, "FAT16   ", 8) == 0)
 171                 goto valid;
 172
 173         if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
 174                 goto valid;
 175
 176         if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
 177                 goto valid;
 178
 179         /*
 180          * There are old floppies out there without a magic, so we check
 181          * for well known values and guess if it's a fat volume
 182          */
 183
 184         /* boot jump address check */
 185         if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
 186              vs->boot_jump[0] != 0xe9)
 187                 return -1;
 188
 189         /* heads check */
 190         if (vs->heads == 0)
 191                 return -1;
 192
 193         /* cluster size check*/
 194         if (vs->sectors_per_cluster == 0 ||
 195             (vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
 196                 return -1;
 197
 198         /* media check */
 199         if (vs->media < 0xf8 && vs->media != 0xf0)
 200                 return -1;
 201
 202         /* fat count*/
 203         if (vs->fats != 2)
 204                 return -1;
 205
 206 valid:
 207         /* sector size check */
 208         sector_size = le16_to_cpu(vs->sector_size);
 209         if (sector_size != 0x200 && sector_size != 0x400 &&
 210             sector_size != 0x800 && sector_size != 0x1000)
 211                 return -1;
 212
 213         dbg("sector_size 0x%x", sector_size);
 214         dbg("sectors_per_cluster 0x%x", vs->sectors_per_cluster);
 215
 216         dir_entries = le16_to_cpu(vs->dir_entries);
 217         reserved = le16_to_cpu(vs->reserved);
 218         dbg("reserved 0x%x", reserved);
 219
 220         sect_count = le16_to_cpu(vs->sectors);
 221         if (sect_count == 0)
 222                 sect_count = le32_to_cpu(vs->total_sect);
 223         dbg("sect_count 0x%x", sect_count);
 224
 225         fat_length = le16_to_cpu(vs->fat_length);
 226         dbg("fat_length 0x%x", fat_length);
 227         fat32_length = le32_to_cpu(vs->type.fat32.fat32_length);
 228         dbg("fat32_length 0x%x", fat32_length);
 229
 230         if (fat_length)
 231                 fat_size = fat_length * vs->fats;
 232         else if (fat32_length)
 233                 fat_size = fat32_length * vs->fats;
 234         else
 235                 return -1;
 236         dbg("fat_size 0x%x", fat_size);
 237
 238         dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
 239                         (sector_size-1)) / sector_size;
 240         dbg("dir_size 0x%x", dir_size);
 241
 242         cluster_count = sect_count - (reserved + fat_size + dir_size);
 243         cluster_count /= vs->sectors_per_cluster;
 244         dbg("cluster_count 0x%x", cluster_count);
 245
 246         /* must be FAT32 */
 247         if (!fat_length && fat32_length)
 248                 goto fat32;
 249
 250         /* cluster_count tells us the format */
 251         if (cluster_count < FAT12_MAX)
 252                 strcpy(id->type_version, "FAT12");
 253         else if (cluster_count < FAT16_MAX)
 254                 strcpy(id->type_version, "FAT16");
 255         else
 256                 goto fat32;
 257
 258         /* the label may be an attribute in the root directory */
 259         root_start = (reserved + fat_size) * sector_size;
 260         dbg("root dir start 0x%llx", (unsigned long long) root_start);
 261         root_dir_entries = le16_to_cpu(vs->dir_entries);
 262         dbg("expected entries 0x%x", root_dir_entries);
 263
 264         buf_size = root_dir_entries * sizeof(struct vfat_dir_entry);
 265         buf = volume_id_get_buffer(id, off + root_start, buf_size);
 266         if (buf == NULL)
 267                 goto found;
 268
 269         dir = (struct vfat_dir_entry*) buf;
 270
 271         label = get_attr_volume_id(dir, root_dir_entries);
 272
 273         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 274         if (vs == NULL)
 275                 return -1;
 276
 277         if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
 278                 volume_id_set_label_raw(id, label, 11);
 279                 volume_id_set_label_string(id, label, 11);
 280         } else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
 281                 volume_id_set_label_raw(id, vs->type.fat.label, 11);
 282                 volume_id_set_label_string(id, vs->type.fat.label, 11);
 283         }
 284         volume_id_set_uuid(id, vs->type.fat.serno, UUID_DOS);
 285         goto found;
 286
 287 fat32:
 288         strcpy(id->type_version, "FAT32");
 289
 290         /* FAT32 root dir is a cluster chain like any other directory */
 291         buf_size = vs->sectors_per_cluster * sector_size;
 292         root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
 293         dbg("root dir cluster %u", root_cluster);
 294         start_data_sect = reserved + fat_size;
 295
 296         next = root_cluster;
 297         maxloop = 100;
 298         while (--maxloop) {
 299                 uint32_t next_sect_off;
 300                 uint64_t next_off;
 301                 uint64_t fat_entry_off;
 302                 int count;
 303
 304                 dbg("next cluster %u", next);
 305                 next_sect_off = (next - 2) * vs->sectors_per_cluster;
 306                 next_off = (start_data_sect + next_sect_off) * sector_size;
 307                 dbg("cluster offset 0x%llx", (unsigned long long) next_off);
 308
 309                 /* get cluster */
 310                 buf = volume_id_get_buffer(id, off + next_off, buf_size);
 311                 if (buf == NULL)
 312                         goto found;
 313
 314                 dir = (struct vfat_dir_entry*) buf;
 315                 count = buf_size / sizeof(struct vfat_dir_entry);
 316                 dbg("expected entries 0x%x", count);
 317
 318                 label = get_attr_volume_id(dir, count);
 319                 if (label)
 320                         break;
 321
 322                 /* get FAT entry */
 323                 fat_entry_off = (reserved * sector_size) + (next * sizeof(uint32_t));
 324                 buf = volume_id_get_buffer(id, off + fat_entry_off, buf_size);
 325                 if (buf == NULL)
 326                         goto found;
 327
 328                 /* set next cluster */
 329                 next = le32_to_cpu(*((uint32_t *) buf) & 0x0fffffff);
 330                 if (next == 0)
 331                         break;
 332         }
 333         if (maxloop == 0)
 334                 dbg("reached maximum follow count of root cluster chain, give up");
 335
 336         vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
 337         if (vs == NULL)
 338                 return -1;
 339
 340         if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
 341                 volume_id_set_label_raw(id, label, 11);
 342                 volume_id_set_label_string(id, label, 11);
 343         } else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
 344                 volume_id_set_label_raw(id, vs->type.fat32.label, 11);
 345                 volume_id_set_label_string(id, vs->type.fat32.label, 11);
 346         }
 347         volume_id_set_uuid(id, vs->type.fat32.serno, UUID_DOS);
 348
 349 found:
 350         volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
 351         id->type = "vfat";
 352
 353         return 0;
 354 }