libblkid-tiny/vfat.c

   1 /*
   2  * Copyright (C) 1999 by Andries Brouwer
   3  * Copyright (C) 1999, 2000, 2003 by Theodore Ts'o
   4  * Copyright (C) 2001 by Andreas Dilger
   5  * Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>
   6  * Copyright (C) 2008 Karel Zak <kzak@redhat.com>
   7  *
   8  * This file may be redistributed under the terms of the
   9  * GNU Lesser General Public License.
  10  */
  11 #include <stdio.h>
  12 #include <stdlib.h>
  13 #include <unistd.h>
  14 #include <string.h>
  15 #include <errno.h>
  16 #include <ctype.h>
  17 #include <stdint.h>
  18
  19 #include "superblocks.h"
  20
  21 /* Yucky misaligned values */
  22 struct vfat_super_block {
  23 /* 00*/ unsigned char   vs_ignored[3];
  24 /* 03*/ unsigned char   vs_sysid[8];
  25 /* 0b*/ unsigned char   vs_sector_size[2];
  26 /* 0d*/ uint8_t         vs_cluster_size;
  27 /* 0e*/ uint16_t        vs_reserved;
  28 /* 10*/ uint8_t         vs_fats;
  29 /* 11*/ unsigned char   vs_dir_entries[2];
  30 /* 13*/ unsigned char   vs_sectors[2];
  31 /* 15*/ unsigned char   vs_media;
  32 /* 16*/ uint16_t        vs_fat_length;
  33 /* 18*/ uint16_t        vs_secs_track;
  34 /* 1a*/ uint16_t        vs_heads;
  35 /* 1c*/ uint32_t        vs_hidden;
  36 /* 20*/ uint32_t        vs_total_sect;
  37 /* 24*/ uint32_t        vs_fat32_length;
  38 /* 28*/ uint16_t        vs_flags;
  39 /* 2a*/ uint8_t         vs_version[2];
  40 /* 2c*/ uint32_t        vs_root_cluster;
  41 /* 30*/ uint16_t        vs_fsinfo_sector;
  42 /* 32*/ uint16_t        vs_backup_boot;
  43 /* 34*/ uint16_t        vs_reserved2[6];
  44 /* 40*/ unsigned char   vs_unknown[3];
  45 /* 43*/ unsigned char   vs_serno[4];
  46 /* 47*/ unsigned char   vs_label[11];
  47 /* 52*/ unsigned char   vs_magic[8];
  48 /* 5a*/ unsigned char   vs_dummy2[0x1fe - 0x5a];
  49 /*1fe*/ unsigned char   vs_pmagic[2];
  50 } __attribute__((packed));
  51
  52 /* Yucky misaligned values */
  53 struct msdos_super_block {
  54 /* 00*/ unsigned char   ms_ignored[3];
  55 /* 03*/ unsigned char   ms_sysid[8];
  56 /* 0b*/ unsigned char   ms_sector_size[2];
  57 /* 0d*/ uint8_t         ms_cluster_size;
  58 /* 0e*/ uint16_t        ms_reserved;
  59 /* 10*/ uint8_t         ms_fats;
  60 /* 11*/ unsigned char   ms_dir_entries[2];
  61 /* 13*/ unsigned char   ms_sectors[2]; /* =0 iff V3 or later */
  62 /* 15*/ unsigned char   ms_media;
  63 /* 16*/ uint16_t        ms_fat_length; /* Sectors per FAT */
  64 /* 18*/ uint16_t        ms_secs_track;
  65 /* 1a*/ uint16_t        ms_heads;
  66 /* 1c*/ uint32_t        ms_hidden;
  67 /* V3 BPB */
  68 /* 20*/ uint32_t        ms_total_sect; /* iff ms_sectors == 0 */
  69 /* V4 BPB */
  70 /* 24*/ unsigned char   ms_unknown[3]; /* Phys drive no., resvd, V4 sig (0x29) */
  71 /* 27*/ unsigned char   ms_serno[4];
  72 /* 2b*/ unsigned char   ms_label[11];
  73 /* 36*/ unsigned char   ms_magic[8];
  74 /* 3e*/ unsigned char   ms_dummy2[0x1fe - 0x3e];
  75 /*1fe*/ unsigned char   ms_pmagic[2];
  76 } __attribute__((packed));
  77
  78 struct vfat_dir_entry {
  79         uint8_t         name[11];
  80         uint8_t         attr;
  81         uint16_t        time_creat;
  82         uint16_t        date_creat;
  83         uint16_t        time_acc;
  84         uint16_t        date_acc;
  85         uint16_t        cluster_high;
  86         uint16_t        time_write;
  87         uint16_t        date_write;
  88         uint16_t        cluster_low;
  89         uint32_t        size;
  90 } __attribute__((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 } __attribute__((packed));
 100
 101 /* maximum number of clusters */
 102 #define FAT12_MAX 0xFF4
 103 #define FAT16_MAX 0xFFF4
 104 #define FAT32_MAX 0x0FFFFFF6
 105
 106 #define FAT_ATTR_VOLUME_ID              0x08
 107 #define FAT_ATTR_DIR                    0x10
 108 #define FAT_ATTR_LONG_NAME              0x0f
 109 #define FAT_ATTR_MASK                   0x3f
 110 #define FAT_ENTRY_FREE                  0xe5
 111
 112 static const char *no_name = "NO NAME    ";
 113
 114 #define unaligned_le16(x) \
 115                 (((unsigned char *) x)[0] + (((unsigned char *) x)[1] << 8))
 116
 117 /*
 118  * Look for LABEL (name) in the FAT root directory.
 119  */
 120 static unsigned char *search_fat_label(blkid_probe pr,
 121                                 uint64_t offset, uint32_t entries)
 122 {
 123         struct vfat_dir_entry *ent, *dir = NULL;
 124         uint32_t i;
 125
 126         DBG(DEBUG_LOWPROBE,
 127                 printf("\tlook for label in root-dir "
 128                         "(entries: %d, offset: %jd)\n", entries, offset));
 129
 130         if (!blkid_probe_is_tiny(pr)) {
 131                 /* large disk, read whole root directory */
 132                 dir = (struct vfat_dir_entry *)
 133                         blkid_probe_get_buffer(pr,
 134                                         offset,
 135                                         (blkid_loff_t) entries *
 136                                                 sizeof(struct vfat_dir_entry));
 137                 if (!dir)
 138                         return NULL;
 139         }
 140
 141         for (i = 0; i < entries; i++) {
 142                 /*
 143                  * The root directory could be relatively large (4-16kB).
 144                  * Fortunately, the LABEL is usually the first entry in the
 145                  * directory. On tiny disks we call read() per entry.
 146                  */
 147                 if (!dir)
 148                         ent = (struct vfat_dir_entry *)
 149                                 blkid_probe_get_buffer(pr,
 150                                         (blkid_loff_t) offset + (i *
 151                                                 sizeof(struct vfat_dir_entry)),
 152                                         sizeof(struct vfat_dir_entry));
 153                 else
 154                         ent = &dir[i];
 155
 156                 if (!ent || ent->name[0] == 0x00)
 157                         break;
 158
 159                 if ((ent->name[0] == FAT_ENTRY_FREE) ||
 160                     (ent->cluster_high != 0 || ent->cluster_low != 0) ||
 161                     ((ent->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME))
 162                         continue;
 163
 164                 if ((ent->attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) ==
 165                     FAT_ATTR_VOLUME_ID) {
 166                         DBG(DEBUG_LOWPROBE,
 167                                 printf("\tfound fs LABEL at entry %d\n", i));
 168                         return ent->name;
 169                 }
 170         }
 171         return NULL;
 172 }
 173
 174 static int fat_valid_superblock(const struct blkid_idmag *mag,
 175                         struct msdos_super_block *ms,
 176                         struct vfat_super_block *vs,
 177                         uint32_t *cluster_count, uint32_t *fat_size)
 178 {
 179         uint16_t sector_size, dir_entries, reserved;
 180         uint32_t sect_count, __fat_size, dir_size, __cluster_count, fat_length;
 181         uint32_t max_count;
 182
 183         /* extra check for FATs without magic strings */
 184         if (mag->len <= 2) {
 185                 /* Old floppies have a valid MBR signature */
 186                 if (ms->ms_pmagic[0] != 0x55 || ms->ms_pmagic[1] != 0xAA)
 187                         return 0;
 188
 189                 /*
 190                  * OS/2 and apparently DFSee will place a FAT12/16-like
 191                  * pseudo-superblock in the first 512 bytes of non-FAT
 192                  * filesystems --- at least JFS and HPFS, and possibly others.
 193                  * So we explicitly check for those filesystems at the
 194                  * FAT12/16 filesystem magic field identifier, and if they are
 195                  * present, we rule this out as a FAT filesystem, despite the
 196                  * FAT-like pseudo-header.
 197                  */
 198                 if ((memcmp(ms->ms_magic, "JFS     ", 8) == 0) ||
 199                     (memcmp(ms->ms_magic, "HPFS    ", 8) == 0))
 200                         return 0;
 201         }
 202
 203         /* fat counts(Linux kernel expects at least 1 FAT table) */
 204         if (!ms->ms_fats)
 205                 return 0;
 206         if (!ms->ms_reserved)
 207                 return 0;
 208         if (!(0xf8 <= ms->ms_media || ms->ms_media == 0xf0))
 209                 return 0;
 210         if (!is_power_of_2(ms->ms_cluster_size))
 211                 return 0;
 212
 213         sector_size = unaligned_le16(&ms->ms_sector_size);
 214         if (!is_power_of_2(sector_size) ||
 215             sector_size < 512 || sector_size > 4096)
 216                 return 0;
 217
 218         dir_entries = unaligned_le16(&ms->ms_dir_entries);
 219         reserved =  le16_to_cpu(ms->ms_reserved);
 220         sect_count = unaligned_le16(&ms->ms_sectors);
 221
 222         if (sect_count == 0)
 223                 sect_count = le32_to_cpu(ms->ms_total_sect);
 224
 225         fat_length = le16_to_cpu(ms->ms_fat_length);
 226         if (fat_length == 0)
 227                 fat_length = le32_to_cpu(vs->vs_fat32_length);
 228
 229         __fat_size = fat_length * ms->ms_fats;
 230         dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
 231                                         (sector_size-1)) / sector_size;
 232
 233         __cluster_count = (sect_count - (reserved + __fat_size + dir_size)) /
 234                                                         ms->ms_cluster_size;
 235         if (!ms->ms_fat_length && vs->vs_fat32_length)
 236                 max_count = FAT32_MAX;
 237         else
 238                 max_count = __cluster_count > FAT12_MAX ? FAT16_MAX : FAT12_MAX;
 239
 240         if (__cluster_count > max_count)
 241                 return 0;
 242
 243         if (fat_size)
 244                 *fat_size = __fat_size;
 245         if (cluster_count)
 246                 *cluster_count = __cluster_count;
 247
 248         return 1;       /* valid */
 249 }
 250
 251 /*
 252  * This function is used by MBR partition table parser to avoid
 253  * misinterpretation of FAT filesystem.
 254  */
 255 /*static int blkid_probe_is_vfat(blkid_probe pr)
 256 {
 257         struct vfat_super_block *vs;
 258         struct msdos_super_block *ms;
 259         const struct blkid_idmag *mag = NULL;
 260
 261         if (blkid_probe_get_idmag(pr, &vfat_idinfo, NULL, &mag) || !mag)
 262                 return 0;
 263
 264         ms = blkid_probe_get_sb(pr, mag, struct msdos_super_block);
 265         if (!ms)
 266                 return 0;
 267         vs = blkid_probe_get_sb(pr, mag, struct vfat_super_block);
 268         if (!vs)
 269                 return 0;
 270
 271         return fat_valid_superblock(mag, ms, vs, NULL, NULL);
 272 }*/
 273 static struct vfat_super_block vs;
 274 static struct msdos_super_block ms;
 275
 276 /* FAT label extraction from the root directory taken from Kay
 277  * Sievers's volume_id library */
 278 static int probe_vfat(blkid_probe pr, const struct blkid_idmag *mag)
 279 {
 280         struct vfat_super_block *_vs;
 281         struct msdos_super_block *_ms;
 282         const unsigned char *vol_label = 0;
 283         unsigned char *vol_serno = NULL, vol_label_buf[11];
 284         uint16_t sector_size = 0, reserved;
 285         uint32_t cluster_count, fat_size;
 286         const char *version = NULL;
 287
 288         _ms = blkid_probe_get_sb(pr, mag, struct msdos_super_block);
 289         if (!_ms)
 290                 return 0;
 291         _vs = blkid_probe_get_sb(pr, mag, struct vfat_super_block);
 292         if (!_vs)
 293                 return 0;
 294         memcpy(&ms, _ms, sizeof(struct vfat_super_block));
 295         memcpy(&vs, _vs, sizeof(struct msdos_super_block));
 296         if (!fat_valid_superblock(mag, &ms, &vs, &cluster_count, &fat_size))
 297                 return 1;
 298
 299         sector_size = unaligned_le16(&ms.ms_sector_size);
 300         reserved =  le16_to_cpu(ms.ms_reserved);
 301
 302         if (ms.ms_fat_length) {
 303                 /* the label may be an attribute in the root directory */
 304                 uint32_t root_start = (reserved + fat_size) * sector_size;
 305                 uint32_t root_dir_entries = unaligned_le16(&vs.vs_dir_entries);
 306
 307                 vol_label = search_fat_label(pr, root_start, root_dir_entries);
 308                 if (vol_label) {
 309                         memcpy(vol_label_buf, vol_label, 11);
 310                         vol_label = vol_label_buf;
 311                 }
 312
 313                 if (!vol_label || !memcmp(vol_label, no_name, 11))
 314                         vol_label = ms.ms_label;
 315                 vol_serno = ms.ms_serno;
 316
 317                 blkid_probe_set_value(pr, "SEC_TYPE", (unsigned char *) "msdos",
 318                               sizeof("msdos"));
 319
 320                 if (cluster_count < FAT12_MAX)
 321                         version = "FAT12";
 322                 else if (cluster_count < FAT16_MAX)
 323                         version = "FAT16";
 324
 325         } else if (vs.vs_fat32_length) {
 326                 unsigned char *buf;
 327                 uint16_t fsinfo_sect;
 328                 int maxloop = 100;
 329
 330                 /* Search the FAT32 root dir for the label attribute */
 331                 uint32_t buf_size = vs.vs_cluster_size * sector_size;
 332                 uint32_t start_data_sect = reserved + fat_size;
 333                 uint32_t entries = le32_to_cpu(vs.vs_fat32_length) *
 334                                         sector_size / sizeof(uint32_t);
 335                 uint32_t next = le32_to_cpu(vs.vs_root_cluster);
 336
 337                 while (next && next < entries && --maxloop) {
 338                         uint32_t next_sect_off;
 339                         uint64_t next_off, fat_entry_off;
 340                         int count;
 341
 342                         next_sect_off = (next - 2) * le32_to_cpu(vs.vs_cluster_size);
 343                         next_off = (uint64_t)(start_data_sect + next_sect_off) *
 344                                 sector_size;
 345
 346                         count = buf_size / sizeof(struct vfat_dir_entry);
 347
 348                         vol_label = search_fat_label(pr, next_off, count);
 349                         if (vol_label) {
 350                                 memcpy(vol_label_buf, vol_label, 11);
 351                                 vol_label = vol_label_buf;
 352                                 break;
 353                         }
 354
 355                         /* get FAT entry */
 356                         fat_entry_off = ((uint64_t) reserved * sector_size) +
 357                                 (next * sizeof(uint32_t));
 358                         buf = blkid_probe_get_buffer(pr, fat_entry_off, buf_size);
 359                         if (buf == NULL)
 360                                 break;
 361
 362                         /* set next cluster */
 363                         next = le32_to_cpu(*((uint32_t *) buf)) & 0x0fffffff;
 364                 }
 365
 366                 version = "FAT32";
 367
 368                 if (!vol_label || !memcmp(vol_label, no_name, 11))
 369                         vol_label = NULL;
 370                 vol_serno = vs.vs_serno;
 371
 372                 /*
 373                  * FAT32 should have a valid signature in the fsinfo block,
 374                  * but also allow all bytes set to '\0', because some volumes
 375                  * do not set the signature at all.
 376                  */
 377                 fsinfo_sect = le16_to_cpu(vs.vs_fsinfo_sector);
 378                 if (fsinfo_sect) {
 379                         struct fat32_fsinfo *fsinfo;
 380
 381                         buf = blkid_probe_get_buffer(pr,
 382                                         (blkid_loff_t) fsinfo_sect * sector_size,
 383                                         sizeof(struct fat32_fsinfo));
 384                         if (buf == NULL)
 385                                 return -1;
 386
 387                         fsinfo = (struct fat32_fsinfo *) buf;
 388                         if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0 &&
 389                             memcmp(fsinfo->signature1, "\x52\x52\x64\x41", 4) != 0 &&
 390                             memcmp(fsinfo->signature1, "\x00\x00\x00\x00", 4) != 0)
 391                                 return -1;
 392                         if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0 &&
 393                             memcmp(fsinfo->signature2, "\x00\x00\x00\x00", 4) != 0)
 394                                 return -1;
 395                 }
 396         }
 397
 398         if (vol_label && memcmp(vol_label, no_name, 11))
 399                 blkid_probe_set_label(pr, (unsigned char *) vol_label, 11);
 400
 401         /* We can't just print them as %04X, because they are unaligned */
 402         if (vol_serno)
 403                 blkid_probe_sprintf_uuid(pr, vol_serno, 4, "%02x%02x-%02x%02x",
 404                         vol_serno[3], vol_serno[2], vol_serno[1], vol_serno[0]);
 405         if (version)
 406                 blkid_probe_set_version(pr, version);
 407
 408         return 0;
 409 }
 410
 411
 412 const struct blkid_idinfo vfat_idinfo =
 413 {
 414         .name           = "vfat",
 415         .usage          = BLKID_USAGE_FILESYSTEM,
 416         .probefunc      = probe_vfat,
 417         .magics         =
 418         {
 419                 { .magic = "MSWIN",    .len = 5, .sboff = 0x52 },
 420                 { .magic = "FAT32   ", .len = 8, .sboff = 0x52 },
 421                 { .magic = "MSDOS",    .len = 5, .sboff = 0x36 },
 422                 { .magic = "FAT16   ", .len = 8, .sboff = 0x36 },
 423                 { .magic = "FAT12   ", .len = 8, .sboff = 0x36 },
 424                 { .magic = "FAT     ", .len = 8, .sboff = 0x36 },
 425                 { .magic = "\353",     .len = 1, },
 426                 { .magic = "\351",     .len = 1, },
 427                 { .magic = "\125\252", .len = 2, .sboff = 0x1fe },
 428                 { NULL }
 429         }
 430 };
 431