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 #if 0
  20 #include "pt-mbr.h"
  21 #endif
  22
  23 #include "superblocks.h"
  24
  25 /* Yucky misaligned values */
  26 struct vfat_super_block {
  27 /* 00*/ unsigned char   vs_ignored[3];
  28 /* 03*/ unsigned char   vs_sysid[8];
  29 /* 0b*/ unsigned char   vs_sector_size[2];
  30 /* 0d*/ uint8_t         vs_cluster_size;
  31 /* 0e*/ uint16_t        vs_reserved;
  32 /* 10*/ uint8_t         vs_fats;
  33 /* 11*/ unsigned char   vs_dir_entries[2];
  34 /* 13*/ unsigned char   vs_sectors[2];
  35 /* 15*/ unsigned char   vs_media;
  36 /* 16*/ uint16_t        vs_fat_length;
  37 /* 18*/ uint16_t        vs_secs_track;
  38 /* 1a*/ uint16_t        vs_heads;
  39 /* 1c*/ uint32_t        vs_hidden;
  40 /* 20*/ uint32_t        vs_total_sect;
  41 /* 24*/ uint32_t        vs_fat32_length;
  42 /* 28*/ uint16_t        vs_flags;
  43 /* 2a*/ uint8_t         vs_version[2];
  44 /* 2c*/ uint32_t        vs_root_cluster;
  45 /* 30*/ uint16_t        vs_fsinfo_sector;
  46 /* 32*/ uint16_t        vs_backup_boot;
  47 /* 34*/ uint16_t        vs_reserved2[6];
  48 /* 40*/ unsigned char   vs_unknown[3];
  49 /* 43*/ unsigned char   vs_serno[4];
  50 /* 47*/ unsigned char   vs_label[11];
  51 /* 52*/ unsigned char   vs_magic[8];
  52 /* 5a*/ unsigned char   vs_dummy2[0x1fe - 0x5a];
  53 /*1fe*/ unsigned char   vs_pmagic[2];
  54 } __attribute__((packed));
  55
  56 /* Yucky misaligned values */
  57 struct msdos_super_block {
  58 /* 00*/ unsigned char   ms_ignored[3];
  59 /* 03*/ unsigned char   ms_sysid[8];
  60 /* 0b*/ unsigned char   ms_sector_size[2];
  61 /* 0d*/ uint8_t         ms_cluster_size;
  62 /* 0e*/ uint16_t        ms_reserved;
  63 /* 10*/ uint8_t         ms_fats;
  64 /* 11*/ unsigned char   ms_dir_entries[2];
  65 /* 13*/ unsigned char   ms_sectors[2]; /* =0 iff V3 or later */
  66 /* 15*/ unsigned char   ms_media;
  67 /* 16*/ uint16_t        ms_fat_length; /* Sectors per FAT */
  68 /* 18*/ uint16_t        ms_secs_track;
  69 /* 1a*/ uint16_t        ms_heads;
  70 /* 1c*/ uint32_t        ms_hidden;
  71 /* V3 BPB */
  72 /* 20*/ uint32_t        ms_total_sect; /* iff ms_sectors == 0 */
  73 /* V4 BPB */
  74 /* 24*/ unsigned char   ms_unknown[3]; /* Phys drive no., resvd, V4 sig (0x29) */
  75 /* 27*/ unsigned char   ms_serno[4];
  76 /* 2b*/ unsigned char   ms_label[11];
  77 /* 36*/ unsigned char   ms_magic[8];
  78 /* 3e*/ unsigned char   ms_dummy2[0x1fe - 0x3e];
  79 /*1fe*/ unsigned char   ms_pmagic[2];
  80 } __attribute__((packed));
  81
  82 struct vfat_dir_entry {
  83         uint8_t         name[11];
  84         uint8_t         attr;
  85         uint16_t        time_creat;
  86         uint16_t        date_creat;
  87         uint16_t        time_acc;
  88         uint16_t        date_acc;
  89         uint16_t        cluster_high;
  90         uint16_t        time_write;
  91         uint16_t        date_write;
  92         uint16_t        cluster_low;
  93         uint32_t        size;
  94 } __attribute__((packed));
  95
  96 struct fat32_fsinfo {
  97         uint8_t signature1[4];
  98         uint32_t reserved1[120];
  99         uint8_t signature2[4];
 100         uint32_t free_clusters;
 101         uint32_t next_cluster;
 102         uint32_t reserved2[4];
 103 } __attribute__((packed));
 104
 105 /* maximum number of clusters */
 106 #define FAT12_MAX 0xFF4
 107 #define FAT16_MAX 0xFFF4
 108 #define FAT32_MAX 0x0FFFFFF6
 109
 110 #define FAT_ATTR_VOLUME_ID              0x08
 111 #define FAT_ATTR_DIR                    0x10
 112 #define FAT_ATTR_LONG_NAME              0x0f
 113 #define FAT_ATTR_MASK                   0x3f
 114 #define FAT_ENTRY_FREE                  0xe5
 115
 116 static const char *no_name = "NO NAME    ";
 117
 118 #define unaligned_le16(x) \
 119                 (((unsigned char *) x)[0] + (((unsigned char *) x)[1] << 8))
 120
 121 /*
 122  * Look for LABEL (name) in the FAT root directory.
 123  */
 124 static unsigned char *search_fat_label(blkid_probe pr,
 125                                 uint64_t offset, uint32_t entries)
 126 {
 127         struct vfat_dir_entry *ent, *dir = NULL;
 128         uint32_t i;
 129
 130         DBG(LOWPROBE, ul_debug("\tlook for label in root-dir "
 131                         "(entries: %d, offset: %jd)", entries, offset));
 132
 133         if (!blkid_probe_is_tiny(pr)) {
 134                 /* large disk, read whole root directory */
 135                 dir = (struct vfat_dir_entry *)
 136                         blkid_probe_get_buffer(pr,
 137                                         offset,
 138                                         (blkid_loff_t) entries *
 139                                                 sizeof(struct vfat_dir_entry));
 140                 if (!dir)
 141                         return NULL;
 142         }
 143
 144         for (i = 0; i < entries; i++) {
 145                 /*
 146                  * The root directory could be relatively large (4-16kB).
 147                  * Fortunately, the LABEL is usually the first entry in the
 148                  * directory. On tiny disks we call read() per entry.
 149                  */
 150                 if (!dir)
 151                         ent = (struct vfat_dir_entry *)
 152                                 blkid_probe_get_buffer(pr,
 153                                         (blkid_loff_t) offset + (i *
 154                                                 sizeof(struct vfat_dir_entry)),
 155                                         sizeof(struct vfat_dir_entry));
 156                 else
 157                         ent = &dir[i];
 158
 159                 if (!ent || ent->name[0] == 0x00)
 160                         break;
 161
 162                 if ((ent->name[0] == FAT_ENTRY_FREE) ||
 163                     (ent->cluster_high != 0 || ent->cluster_low != 0) ||
 164                     ((ent->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME))
 165                         continue;
 166
 167                 if ((ent->attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) ==
 168                     FAT_ATTR_VOLUME_ID) {
 169                         DBG(LOWPROBE, ul_debug("\tfound fs LABEL at entry %d", i));
 170                         return ent->name;
 171                 }
 172         }
 173         return NULL;
 174 }
 175
 176 static int fat_valid_superblock(blkid_probe pr,
 177                         const struct blkid_idmag *mag,
 178                         struct msdos_super_block *ms,
 179                         struct vfat_super_block *vs,
 180                         uint32_t *cluster_count, uint32_t *fat_size)
 181 {
 182         uint16_t sector_size, dir_entries, reserved;
 183         uint32_t sect_count, __fat_size, dir_size, __cluster_count, fat_length;
 184         uint32_t max_count;
 185
 186         /* extra check for FATs without magic strings */
 187         if (mag->len <= 2) {
 188                 /* Old floppies have a valid MBR signature */
 189                 if (ms->ms_pmagic[0] != 0x55 || ms->ms_pmagic[1] != 0xAA)
 190                         return 0;
 191
 192                 /*
 193                  * OS/2 and apparently DFSee will place a FAT12/16-like
 194                  * pseudo-superblock in the first 512 bytes of non-FAT
 195                  * filesystems --- at least JFS and HPFS, and possibly others.
 196                  * So we explicitly check for those filesystems at the
 197                  * FAT12/16 filesystem magic field identifier, and if they are
 198                  * present, we rule this out as a FAT filesystem, despite the
 199                  * FAT-like pseudo-header.
 200                  */
 201                 if ((memcmp(ms->ms_magic, "JFS     ", 8) == 0) ||
 202                     (memcmp(ms->ms_magic, "HPFS    ", 8) == 0))
 203                         return 0;
 204         }
 205
 206         /* fat counts(Linux kernel expects at least 1 FAT table) */
 207         if (!ms->ms_fats)
 208                 return 0;
 209         if (!ms->ms_reserved)
 210                 return 0;
 211         if (!(0xf8 <= ms->ms_media || ms->ms_media == 0xf0))
 212                 return 0;
 213         if (!is_power_of_2(ms->ms_cluster_size))
 214                 return 0;
 215
 216         sector_size = unaligned_le16(&ms->ms_sector_size);
 217         if (!is_power_of_2(sector_size) ||
 218             sector_size < 512 || sector_size > 4096)
 219                 return 0;
 220
 221         dir_entries = unaligned_le16(&ms->ms_dir_entries);
 222         reserved =  le16_to_cpu(ms->ms_reserved);
 223         sect_count = unaligned_le16(&ms->ms_sectors);
 224
 225         if (sect_count == 0)
 226                 sect_count = le32_to_cpu(ms->ms_total_sect);
 227
 228         fat_length = le16_to_cpu(ms->ms_fat_length);
 229         if (fat_length == 0)
 230                 fat_length = le32_to_cpu(vs->vs_fat32_length);
 231
 232         __fat_size = fat_length * ms->ms_fats;
 233         dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
 234                                         (sector_size-1)) / sector_size;
 235
 236         __cluster_count = (sect_count - (reserved + __fat_size + dir_size)) /
 237                                                         ms->ms_cluster_size;
 238         if (!ms->ms_fat_length && vs->vs_fat32_length)
 239                 max_count = FAT32_MAX;
 240         else
 241                 max_count = __cluster_count > FAT12_MAX ? FAT16_MAX : FAT12_MAX;
 242
 243         if (__cluster_count > max_count)
 244                 return 0;
 245
 246         if (fat_size)
 247                 *fat_size = __fat_size;
 248         if (cluster_count)
 249                 *cluster_count = __cluster_count;
 250
 251 #if 0
 252         if (blkid_probe_is_wholedisk(pr)) {
 253                 /* OK, seems like FAT, but it's possible that we found boot
 254                  * sector with crazy FAT-like stuff (magic strings, media,
 255                  * etc..) before MBR. Let's make sure that there is no MBR with
 256                  * usable partition. */
 257                 unsigned char *buf = (unsigned char *) ms;
 258                 if (mbr_is_valid_magic(buf)) {
 259                         struct dos_partition *p0 = mbr_get_partition(buf, 0);
 260                         if (dos_partition_get_size(p0) != 0 &&
 261                             (p0->boot_ind == 0 || p0->boot_ind == 0x80))
 262                                 return 0;
 263                 }
 264         }
 265 #endif
 266
 267         return 1;       /* valid */
 268 }
 269
 270 #if 0
 271 /*
 272  * This function is used by MBR partition table parser to avoid
 273  * misinterpretation of FAT filesystem.
 274  */
 275 int blkid_probe_is_vfat(blkid_probe pr)
 276 {
 277         struct vfat_super_block *vs;
 278         struct msdos_super_block *ms;
 279         const struct blkid_idmag *mag = NULL;
 280         int rc;
 281
 282         rc = blkid_probe_get_idmag(pr, &vfat_idinfo, NULL, &mag);
 283         if (rc < 0)
 284                 return rc;      /* error */
 285         if (rc != BLKID_PROBE_OK || !mag)
 286                 return 0;
 287
 288         ms = blkid_probe_get_sb(pr, mag, struct msdos_super_block);
 289         if (!ms)
 290                 return errno ? -errno : 0;
 291         vs = blkid_probe_get_sb(pr, mag, struct vfat_super_block);
 292         if (!vs)
 293                 return errno ? -errno : 0;
 294
 295         return fat_valid_superblock(pr, mag, ms, vs, NULL, NULL);
 296 }
 297 #endif
 298
 299 /* FAT label extraction from the root directory taken from Kay
 300  * Sievers's volume_id library */
 301 static int probe_vfat(blkid_probe pr, const struct blkid_idmag *mag)
 302 {
 303         struct vfat_super_block *vs;
 304         struct msdos_super_block *ms;
 305         const unsigned char *vol_label = 0;
 306         unsigned char *vol_serno = NULL, vol_label_buf[11];
 307         uint16_t sector_size = 0, reserved;
 308         uint32_t cluster_count, fat_size;
 309         const char *version = NULL;
 310
 311         ms = blkid_probe_get_sb(pr, mag, struct msdos_super_block);
 312         if (!ms)
 313                 return errno ? -errno : 1;
 314
 315         vs = blkid_probe_get_sb(pr, mag, struct vfat_super_block);
 316         if (!vs)
 317                 return errno ? -errno : 1;
 318
 319         if (!fat_valid_superblock(pr, mag, ms, vs, &cluster_count, &fat_size))
 320                 return 1;
 321
 322         sector_size = unaligned_le16(&ms->ms_sector_size);
 323         reserved =  le16_to_cpu(ms->ms_reserved);
 324
 325         if (ms->ms_fat_length) {
 326                 /* the label may be an attribute in the root directory */
 327                 uint32_t root_start = (reserved + fat_size) * sector_size;
 328                 uint32_t root_dir_entries = unaligned_le16(&vs->vs_dir_entries);
 329
 330                 vol_label = search_fat_label(pr, root_start, root_dir_entries);
 331                 if (vol_label) {
 332                         memcpy(vol_label_buf, vol_label, 11);
 333                         vol_label = vol_label_buf;
 334                 }
 335
 336                 if (!vol_label || !memcmp(vol_label, no_name, 11))
 337                         vol_label = ms->ms_label;
 338                 vol_serno = ms->ms_serno;
 339
 340                 blkid_probe_set_value(pr, "SEC_TYPE", (unsigned char *) "msdos",
 341                               sizeof("msdos"));
 342
 343                 if (cluster_count < FAT12_MAX)
 344                         version = "FAT12";
 345                 else if (cluster_count < FAT16_MAX)
 346                         version = "FAT16";
 347
 348         } else if (vs->vs_fat32_length) {
 349                 unsigned char *buf;
 350                 uint16_t fsinfo_sect;
 351                 int maxloop = 100;
 352
 353                 /* Search the FAT32 root dir for the label attribute */
 354                 uint32_t buf_size = vs->vs_cluster_size * sector_size;
 355                 uint32_t start_data_sect = reserved + fat_size;
 356                 uint32_t entries = le32_to_cpu(vs->vs_fat32_length) *
 357                                         sector_size / sizeof(uint32_t);
 358                 uint32_t next = le32_to_cpu(vs->vs_root_cluster);
 359
 360                 while (next && next < entries && --maxloop) {
 361                         uint32_t next_sect_off;
 362                         uint64_t next_off, fat_entry_off;
 363                         int count;
 364
 365                         next_sect_off = (next - 2) * vs->vs_cluster_size;
 366                         next_off = (uint64_t)(start_data_sect + next_sect_off) *
 367                                 sector_size;
 368
 369                         count = buf_size / sizeof(struct vfat_dir_entry);
 370
 371                         vol_label = search_fat_label(pr, next_off, count);
 372                         if (vol_label) {
 373                                 memcpy(vol_label_buf, vol_label, 11);
 374                                 vol_label = vol_label_buf;
 375                                 break;
 376                         }
 377
 378                         /* get FAT entry */
 379                         fat_entry_off = ((uint64_t) reserved * sector_size) +
 380                                 (next * sizeof(uint32_t));
 381                         buf = blkid_probe_get_buffer(pr, fat_entry_off, buf_size);
 382                         if (buf == NULL)
 383                                 break;
 384
 385                         /* set next cluster */
 386                         next = le32_to_cpu(*((uint32_t *) buf)) & 0x0fffffff;
 387                 }
 388
 389                 version = "FAT32";
 390
 391                 if (!vol_label || !memcmp(vol_label, no_name, 11))
 392                         vol_label = vs->vs_label;
 393                 vol_serno = vs->vs_serno;
 394
 395                 /*
 396                  * FAT32 should have a valid signature in the fsinfo block,
 397                  * but also allow all bytes set to '\0', because some volumes
 398                  * do not set the signature at all.
 399                  */
 400                 fsinfo_sect = le16_to_cpu(vs->vs_fsinfo_sector);
 401                 if (fsinfo_sect) {
 402                         struct fat32_fsinfo *fsinfo;
 403
 404                         buf = blkid_probe_get_buffer(pr,
 405                                         (blkid_loff_t) fsinfo_sect * sector_size,
 406                                         sizeof(struct fat32_fsinfo));
 407                         if (buf == NULL)
 408                                 return errno ? -errno : 1;
 409
 410                         fsinfo = (struct fat32_fsinfo *) buf;
 411                         if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0 &&
 412                             memcmp(fsinfo->signature1, "\x52\x52\x64\x41", 4) != 0 &&
 413                             memcmp(fsinfo->signature1, "\x00\x00\x00\x00", 4) != 0)
 414                                 return 1;
 415                         if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0 &&
 416                             memcmp(fsinfo->signature2, "\x00\x00\x00\x00", 4) != 0)
 417                                 return 1;
 418                 }
 419         }
 420
 421         if (vol_label && memcmp(vol_label, no_name, 11))
 422                 blkid_probe_set_label(pr, (unsigned char *) vol_label, 11);
 423
 424         /* We can't just print them as %04X, because they are unaligned */
 425         if (vol_serno)
 426                 blkid_probe_sprintf_uuid(pr, vol_serno, 4, "%02X%02X-%02X%02X",
 427                         vol_serno[3], vol_serno[2], vol_serno[1], vol_serno[0]);
 428         if (version)
 429                 blkid_probe_set_version(pr, version);
 430
 431         return 0;
 432 }
 433
 434
 435 const struct blkid_idinfo vfat_idinfo =
 436 {
 437         .name           = "vfat",
 438         .usage          = BLKID_USAGE_FILESYSTEM,
 439         .probefunc      = probe_vfat,
 440         .magics         =
 441         {
 442                 { .magic = "MSWIN",    .len = 5, .sboff = 0x52 },
 443                 { .magic = "FAT32   ", .len = 8, .sboff = 0x52 },
 444                 { .magic = "MSDOS",    .len = 5, .sboff = 0x36 },
 445                 { .magic = "FAT16   ", .len = 8, .sboff = 0x36 },
 446                 { .magic = "FAT12   ", .len = 8, .sboff = 0x36 },
 447                 { .magic = "FAT     ", .len = 8, .sboff = 0x36 },
 448                 { .magic = "\353",     .len = 1, },
 449                 { .magic = "\351",     .len = 1, },
 450                 { .magic = "\125\252", .len = 2, .sboff = 0x1fe },
 451                 { NULL }
 452         }
 453 };
 454