summaryrefslogtreecommitdiff
path: root/extras/volume_id/lib/fat.c
blob: 9d26a987e0a818fd570ce5c96487120452a2f9fa (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
/*
 * volume_id - reads filesystem label and uuid
 *
 * Copyright (C) 2004-2007 Kay Sievers <kay.sievers@vrfy.org>
 * Copyright (C) 2007 Ryan Lortie <desrt@desrt.ca>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>

#include "libvolume_id.h"
#include "libvolume_id-private.h"

#define FAT12_MAX			0xff5
#define FAT16_MAX			0xfff5
#define FAT_ATTR_VOLUME_ID		0x08
#define FAT_ATTR_DIR			0x10
#define FAT_ATTR_LONG_NAME		0x0f
#define FAT_ATTR_MASK			0x3f
#define FAT_ENTRY_FREE			0xe5

#define VFAT_LFN_SEQ_MASK		0x3f
#define VFAT_LFN_SEQ_LAST		0x40
#define VFAT_LFN_SEQ_MAX		20
#define VFAT_LFN_CHARS_PER_ENTRY	(5 + 6 + 2)
#define VFAT_LOWERCASE_NAME		0x10
#define VFAT_LOWERCASE_EXT		0x08

struct vfat_super_block {
	uint8_t		boot_jump[3];
	uint8_t		sysid[8];
	uint16_t	sector_size;
	uint8_t		sectors_per_cluster;
	uint16_t	reserved;
	uint8_t		fats;
	uint16_t	dir_entries;
	uint16_t	sectors;
	uint8_t		media;
	uint16_t	fat_length;
	uint16_t	secs_track;
	uint16_t	heads;
	uint32_t	hidden;
	uint32_t	total_sect;
	union {
		struct fat_super_block {
			uint8_t		unknown[3];
			uint8_t		serno[4];
			uint8_t		label[11];
			uint8_t		magic[8];
			uint8_t		dummy2[192];
			uint8_t		pmagic[2];
		} PACKED fat;
		struct fat32_super_block {
			uint32_t	fat32_length;
			uint16_t	flags;
			uint8_t		version[2];
			uint32_t	root_cluster;
			uint16_t	fsinfo_sector;
			uint16_t	backup_boot;
			uint16_t	reserved2[6];
			uint8_t		unknown[3];
			uint8_t		serno[4];
			uint8_t		label[11];
			uint8_t		magic[8];
			uint8_t		dummy2[164];
			uint8_t		pmagic[2];
		} PACKED fat32;
	} PACKED type;
} PACKED;

struct fat32_fsinfo {
	uint8_t signature1[4];
	uint32_t reserved1[120];
	uint8_t signature2[4];
	uint32_t free_clusters;
	uint32_t next_cluster;
	uint32_t reserved2[4];
} PACKED;

struct vfat_dir_entry {
	uint8_t		name[11];
	uint8_t		attr;
	uint8_t		lowercase;
	uint8_t		fine_time_creat;
	uint16_t	time_creat;
	uint16_t	date_creat;
	uint16_t	date_acc;
	uint16_t	cluster_high;
	uint16_t	time_write;
	uint16_t	date_write;
	uint16_t	cluster_low;
	uint32_t	size;
} PACKED;


struct vfat_lfn_entry {
	uint8_t		seq;
	uint16_t	name0[5];
	uint8_t		attr;
	uint8_t		reserved;
	uint8_t		cksum;
	uint16_t	name1[6];
	uint16_t	cluster;
	uint16_t	name2[2];
} PACKED;

static uint8_t fat_lfn_checksum(const uint8_t name[11])
{
	uint8_t cksum = 0;
	int i;

	/* http://en.wikipedia.org/wiki/File_Allocation_Table */
	for (i = 0; i < 11; i++)
		cksum = ((cksum & 1) ? 0x80 : 0) + (cksum >> 1) + name[i];

	return cksum;
}

static size_t fat_read_lfn(uint8_t *filename, size_t fnsize,
			   struct vfat_dir_entry *dir,
			   struct vfat_dir_entry *entry)
{
	uint8_t buffer[VFAT_LFN_SEQ_MAX * VFAT_LFN_CHARS_PER_ENTRY * 2];
	uint8_t expected_seq = 1;
	uint8_t cksum;
	size_t len = 0;
	size_t fnlen = 0;

	cksum = fat_lfn_checksum(entry->name);

	while (--entry >= dir) {
		struct vfat_lfn_entry *lfn = (struct vfat_lfn_entry *) entry;

		if (expected_seq > VFAT_LFN_SEQ_MAX)
			break;

		if ((lfn->attr & FAT_ATTR_MASK) != FAT_ATTR_LONG_NAME)
			break;

		if (lfn->cksum != cksum)
			break;

		if ((lfn->seq & VFAT_LFN_SEQ_MASK) != expected_seq++)
			break;

		if (lfn->cluster != 0)
			break;

		/* extra paranoia -- should never happen */
		if (len + sizeof(lfn->name0) + sizeof(lfn->name1) +
		    sizeof(lfn->name2) > sizeof(buffer))
			break;

		memcpy (&buffer[len], lfn->name0, sizeof(lfn->name0));
		len += sizeof(lfn->name0);
		memcpy (&buffer[len], lfn->name1, sizeof(lfn->name1));
		len += sizeof(lfn->name1);
		memcpy (&buffer[len], lfn->name2, sizeof(lfn->name2));
		len += sizeof(lfn->name2);

		if (lfn->seq & VFAT_LFN_SEQ_LAST) {
			fnlen = volume_id_set_unicode16(filename, fnsize, buffer, LE, len);
			break;
		}
	}

	return fnlen;
}

static size_t fat_read_filename(uint8_t *filename, size_t fnsize,
				struct vfat_dir_entry *dir, struct vfat_dir_entry *entry)
{
	size_t len;
	int i;

	/* check if maybe we have LFN entries */
	len = fat_read_lfn(filename, fnsize, dir, entry);
	if (len > 0)
		goto out;

	/* else, read the normal 8.3 name */
	for (i = 0; i < 11; i++) {
		if (entry->lowercase & ((i < 8) ? VFAT_LOWERCASE_NAME : VFAT_LOWERCASE_EXT))
			filename[i] = tolower(entry->name[i]);
		else
			filename[i] = entry->name[i];
	}
	len = 11;

out:
	filename[len] = '\0';
	return len;
}

/* fills filename, returns string length */
static size_t get_fat_attr_volume_id(uint8_t *filename, size_t fnsize,
				     struct vfat_dir_entry *dir, unsigned int count)
{
	unsigned int i;

	for (i = 0; i < count; i++) {
		/* end marker */
		if (dir[i].name[0] == 0x00) {
			dbg("end of dir\n");
			break;
		}

		/* empty entry */
		if (dir[i].name[0] == FAT_ENTRY_FREE)
			continue;

		/* long name */
		if ((dir[i].attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
			continue;

		if ((dir[i].attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
			/* labels do not have file data */
			if (dir[i].cluster_high != 0 || dir[i].cluster_low != 0)
				continue;

			dbg("found ATTR_VOLUME_ID id in root dir\n");
			return fat_read_filename(filename, fnsize, dir, &dir[i]);
		}

		dbg("skip dir entry\n");
	}

	return 0;
}

int volume_id_probe_vfat(struct volume_id *id, uint64_t off, uint64_t size)
{
	uint8_t filename[255 * 3];
	struct vfat_super_block *vs;
	struct vfat_dir_entry *dir;
	struct fat32_fsinfo *fsinfo;
	uint16_t sector_size;
	uint16_t dir_entries;
	uint32_t sect_count;
	uint16_t reserved;
	uint32_t fat_size;
	uint32_t root_cluster;
	uint32_t dir_size;
	uint32_t cluster_count;
	uint16_t fat_length;
	uint32_t fat32_length;
	uint64_t root_start;
	uint32_t start_data_sect;
	uint16_t root_dir_entries;
	uint16_t fsinfo_sect;
	uint8_t *buf;
	uint32_t buf_size;
	uint32_t next;
	int maxloop;
	size_t fnlen;

	info("probing at offset 0x%" PRIx64 "\n", off);

	buf = volume_id_get_buffer(id, off, 0x400);
	if (buf == NULL)
		return -1;

	/* check signature */
	if (buf[510] != 0x55 || buf[511] != 0xaa)
		return -1;

	vs = (struct vfat_super_block *) buf;
	if (memcmp(vs->sysid, "NTFS", 4) == 0)
		return -1;

	/* believe only that's fat, don't trust the version */
	if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
		goto magic;

	if (memcmp(vs->type.fat32.magic, "FAT32   ", 8) == 0)
		goto magic;

	if (memcmp(vs->type.fat.magic, "FAT16   ", 8) == 0)
		goto magic;

	if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
		goto magic;

	if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
		goto magic;

	/* some old floppies don't have a magic, expect the boot jump address to match */
	if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
	     vs->boot_jump[0] != 0xe9)
		return -1;

magic:
	info("magic found\n");
	/* reserverd sector count */
	if (!vs->reserved)
		return -1;

	/* fat count */
	if (!vs->fats)
		return -1;

	/* media check */
	if (vs->media < 0xf8 && vs->media != 0xf0)
		return -1;

	/* cluster size check */
	if (vs->sectors_per_cluster == 0 ||
	    (vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
		return -1;

	/* sector size check */
	sector_size = le16_to_cpu(vs->sector_size);
	if (sector_size == 0 || ((sector_size & (sector_size-1)) != 0))
		return -1;

	info("checks passed\n");
	dbg("sector_size 0x%x\n", sector_size);
	dbg("sectors_per_cluster 0x%x\n", vs->sectors_per_cluster);

	dir_entries = le16_to_cpu(vs->dir_entries);
	reserved = le16_to_cpu(vs->reserved);
	dbg("reserved 0x%x\n", reserved);

	sect_count = le16_to_cpu(vs->sectors);
	if (sect_count == 0)
		sect_count = le32_to_cpu(vs->total_sect);
	dbg("sect_count 0x%x\n", sect_count);

	fat_length = le16_to_cpu(vs->fat_length);
	dbg("fat_length 0x%x\n", fat_length);
	fat32_length = le32_to_cpu(vs->type.fat32.fat32_length);
	dbg("fat32_length 0x%x\n", fat32_length);

	if (fat_length)
		fat_size = fat_length * vs->fats;
	else if (fat32_length)
		fat_size = fat32_length * vs->fats;
	else
		return -1;
	info("fat_size 0x%x\n", fat_size);

	dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
			(sector_size-1)) / sector_size;
	dbg("dir_size 0x%x\n", dir_size);

	cluster_count = sect_count - (reserved + fat_size + dir_size);
	cluster_count /= vs->sectors_per_cluster;
	info("cluster_count 0x%x\n", cluster_count);

	/* must be FAT32 */
	if (!fat_length && fat32_length)
		goto fat32;

	/* cluster_count tells us the format */
	if (cluster_count < FAT12_MAX)
		strcpy(id->type_version, "FAT12");
	else if (cluster_count < FAT16_MAX)
		strcpy(id->type_version, "FAT16");
	else
		goto fat32;

	/* the label may be an attribute in the root directory */
	root_start = (reserved + fat_size) * sector_size;
	dbg("root dir start 0x%" PRIx64 "\n", root_start);
	root_dir_entries = le16_to_cpu(vs->dir_entries);
	dbg("expected entries 0x%x\n", root_dir_entries);

	buf_size = root_dir_entries * sizeof(struct vfat_dir_entry);
	buf = volume_id_get_buffer(id, off + root_start, buf_size);
	if (buf == NULL)
		goto found;

	dir = (struct vfat_dir_entry*) buf;

	fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, root_dir_entries);

	vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
	if (vs == NULL)
		return -1;

	if (fnlen > 0 && memcmp(filename, "NO NAME    ", 11) != 0) {
		volume_id_set_label_raw(id, filename, fnlen);
		volume_id_set_label_string(id, filename, fnlen);
	} else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
		volume_id_set_label_raw(id, vs->type.fat.label, 11);
		volume_id_set_label_string(id, vs->type.fat.label, 11);
	}
	volume_id_set_uuid(id, vs->type.fat.serno, 0, UUID_DOS);
	goto found;

fat32:
	info("looking for FAT32\n");
	/* FAT32 should have a valid signature in the fsinfo block */
	fsinfo_sect = le16_to_cpu(vs->type.fat32.fsinfo_sector);
	buf = volume_id_get_buffer(id, off + (fsinfo_sect * sector_size), 0x200);
	if (buf == NULL)
		return -1;
	fsinfo = (struct fat32_fsinfo *) buf;
	info("signature1: 0x%02x%02x%02x%02x\n",
	     fsinfo->signature1[0], fsinfo->signature1[1],
	     fsinfo->signature1[2], fsinfo->signature1[3]);
	info("signature2: 0x%02x%02x%02x%02x\n",
	     fsinfo->signature2[0], fsinfo->signature2[1],
	     fsinfo->signature2[2], fsinfo->signature2[3]);
	if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0)
		return -1;
	if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0)
		return -1 ;
	info("FAT32 signatures match\n");

	vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
	if (vs == NULL)
		return -1;

	strcpy(id->type_version, "FAT32");

	/* FAT32 root dir is a cluster chain like any other directory */
	buf_size = vs->sectors_per_cluster * sector_size;
	root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
	dbg("root dir cluster %u\n", root_cluster);
	start_data_sect = reserved + fat_size;

	next = root_cluster;
	maxloop = 100;
	while (--maxloop) {
		uint32_t next_sect_off;
		uint64_t next_off;
		uint64_t fat_entry_off;
		int count;

		dbg("next cluster %u\n", next);
		next_sect_off = (next - 2) * vs->sectors_per_cluster;
		next_off = (start_data_sect + next_sect_off) * sector_size;
		dbg("cluster offset 0x%" PRIx64 "\n", next_off);

		/* get cluster */
		buf = volume_id_get_buffer(id, off + next_off, buf_size);
		if (buf == NULL)
			goto found;

		dir = (struct vfat_dir_entry*) buf;
		count = buf_size / sizeof(struct vfat_dir_entry);
		dbg("expected entries 0x%x\n", count);

		fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, count);
		if (fnlen > 0)
			break;

		/* get FAT entry */
		fat_entry_off = (reserved * sector_size) + (next * sizeof(uint32_t));
		buf = volume_id_get_buffer(id, off + fat_entry_off, buf_size);
		if (buf == NULL)
			goto found;

		/* set next cluster */
		next = le32_to_cpu(*((uint32_t *) buf)) & 0x0fffffff;
		if (next < 2 || next >= 0x0ffffff0)
			break;
	}
	if (maxloop == 0)
		dbg("reached maximum follow count of root cluster chain, give up\n");

	vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
	if (vs == NULL)
		return -1;

	if (fnlen > 0 && memcmp(filename, "NO NAME    ", 11) != 0) {
		volume_id_set_label_raw(id, filename, fnlen);
		volume_id_set_label_string(id, filename, fnlen);
	} else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
		volume_id_set_label_raw(id, vs->type.fat32.label, 11);
		volume_id_set_label_string(id, vs->type.fat32.label, 11);
	}
	volume_id_set_uuid(id, vs->type.fat32.serno, 0, UUID_DOS);

found:
	volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
	id->type = "vfat";

	return 0;
}