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