1/*
2 * volume_id - reads filesystem label and uuid
3 *
4 * Copyright (C) 2004-2007 Kay Sievers <kay.sievers@vrfy.org>
5 * Copyright (C) 2007 Ryan Lortie <desrt@desrt.ca>
6 *
7 *	This program is free software; you can redistribute it and/or modify it
8 *	under the terms of the GNU General Public License as published by the
9 *	Free Software Foundation version 2 of the License.
10 */
11
12#ifndef _GNU_SOURCE
13#define _GNU_SOURCE 1
14#endif
15
16#ifdef HAVE_CONFIG_H
17#  include <config.h>
18#endif
19
20#include <stdio.h>
21#include <stdlib.h>
22#include <unistd.h>
23#include <string.h>
24#include <errno.h>
25#include <ctype.h>
26
27#include "libvolume_id.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#define VFAT_LFN_SEQ_MASK		0x3f
39#define VFAT_LFN_SEQ_LAST		0x40
40#define VFAT_LFN_SEQ_MAX		20
41#define VFAT_LFN_CHARS_PER_ENTRY	(5 + 6 + 2)
42#define VFAT_LOWERCASE_NAME		0x10
43#define VFAT_LOWERCASE_EXT		0x08
44
45struct vfat_super_block {
46	uint8_t		boot_jump[3];
47	uint8_t		sysid[8];
48	uint16_t	sector_size;
49	uint8_t		sectors_per_cluster;
50	uint16_t	reserved;
51	uint8_t		fats;
52	uint16_t	dir_entries;
53	uint16_t	sectors;
54	uint8_t		media;
55	uint16_t	fat_length;
56	uint16_t	secs_track;
57	uint16_t	heads;
58	uint32_t	hidden;
59	uint32_t	total_sect;
60	union {
61		struct fat_super_block {
62			uint8_t		unknown[3];
63			uint8_t		serno[4];
64			uint8_t		label[11];
65			uint8_t		magic[8];
66			uint8_t		dummy2[192];
67			uint8_t		pmagic[2];
68		} PACKED fat;
69		struct fat32_super_block {
70			uint32_t	fat32_length;
71			uint16_t	flags;
72			uint8_t		version[2];
73			uint32_t	root_cluster;
74			uint16_t	fsinfo_sector;
75			uint16_t	backup_boot;
76			uint16_t	reserved2[6];
77			uint8_t		unknown[3];
78			uint8_t		serno[4];
79			uint8_t		label[11];
80			uint8_t		magic[8];
81			uint8_t		dummy2[164];
82			uint8_t		pmagic[2];
83		} PACKED fat32;
84	} PACKED type;
85} PACKED;
86
87struct fat32_fsinfo {
88	uint8_t signature1[4];
89	uint32_t reserved1[120];
90	uint8_t signature2[4];
91	uint32_t free_clusters;
92	uint32_t next_cluster;
93	uint32_t reserved2[4];
94} PACKED;
95
96struct vfat_dir_entry {
97	uint8_t		name[11];
98	uint8_t		attr;
99	uint8_t		lowercase;
100	uint8_t		fine_time_creat;
101	uint16_t	time_creat;
102	uint16_t	date_creat;
103	uint16_t	date_acc;
104	uint16_t	cluster_high;
105	uint16_t	time_write;
106	uint16_t	date_write;
107	uint16_t	cluster_low;
108	uint32_t	size;
109} PACKED;
110
111
112struct vfat_lfn_entry {
113	uint8_t		seq;
114	uint16_t	name0[5];
115	uint8_t		attr;
116	uint8_t		reserved;
117	uint8_t		cksum;
118	uint16_t	name1[6];
119	uint16_t	cluster;
120	uint16_t	name2[2];
121} PACKED;
122
123static uint8_t fat_lfn_checksum(const uint8_t name[11])
124{
125	uint8_t cksum = 0;
126	int i;
127
128	/* http://en.wikipedia.org/wiki/File_Allocation_Table */
129	for (i = 0; i < 11; i++)
130		cksum = ((cksum & 1) ? 0x80 : 0) + (cksum >> 1) + name[i];
131
132	return cksum;
133}
134
135static size_t fat_read_lfn(uint8_t *filename, size_t fnsize,
136			   struct vfat_dir_entry *dir,
137			   struct vfat_dir_entry *entry)
138{
139	uint8_t buffer[VFAT_LFN_SEQ_MAX * VFAT_LFN_CHARS_PER_ENTRY * 2];
140	uint8_t expected_seq = 1;
141	uint8_t cksum;
142	size_t len = 0;
143	size_t fnlen = 0;
144
145	cksum = fat_lfn_checksum(entry->name);
146
147	while (--entry >= dir) {
148		struct vfat_lfn_entry *lfn = (struct vfat_lfn_entry *) entry;
149
150		if (expected_seq > VFAT_LFN_SEQ_MAX)
151			break;
152
153		if ((lfn->attr & FAT_ATTR_MASK) != FAT_ATTR_LONG_NAME)
154			break;
155
156		if (lfn->cksum != cksum)
157			break;
158
159		if ((lfn->seq & VFAT_LFN_SEQ_MASK) != expected_seq++)
160			break;
161
162		if (lfn->cluster != 0)
163			break;
164
165		/* extra paranoia -- should never happen */
166		if (len + sizeof(lfn->name0) + sizeof(lfn->name1) +
167		    sizeof(lfn->name2) > sizeof(buffer))
168			break;
169
170		memcpy (&buffer[len], lfn->name0, sizeof(lfn->name0));
171		len += sizeof(lfn->name0);
172		memcpy (&buffer[len], lfn->name1, sizeof(lfn->name1));
173		len += sizeof(lfn->name1);
174		memcpy (&buffer[len], lfn->name2, sizeof(lfn->name2));
175		len += sizeof(lfn->name2);
176
177		if (lfn->seq & VFAT_LFN_SEQ_LAST) {
178			fnlen = volume_id_set_unicode16(filename, fnsize, buffer, LE, len);
179			break;
180		}
181	}
182
183	return fnlen;
184}
185
186static size_t fat_read_filename(uint8_t *filename, size_t fnsize,
187				struct vfat_dir_entry *dir, struct vfat_dir_entry *entry)
188{
189	size_t len;
190	int i;
191
192	/* check if maybe we have LFN entries */
193	len = fat_read_lfn(filename, fnsize, dir, entry);
194	if (len > 0)
195		goto out;
196
197	/* else, read the normal 8.3 name */
198	for (i = 0; i < 11; i++) {
199		if (entry->lowercase & ((i < 8) ? VFAT_LOWERCASE_NAME : VFAT_LOWERCASE_EXT))
200			filename[i] = tolower(entry->name[i]);
201		else
202			filename[i] = entry->name[i];
203	}
204	len = 11;
205
206out:
207	filename[len] = '\0';
208	return len;
209}
210
211/* fills filename, returns string length */
212static size_t get_fat_attr_volume_id(uint8_t *filename, size_t fnsize,
213				     struct vfat_dir_entry *dir, unsigned int count)
214{
215	unsigned int i;
216
217	for (i = 0; i < count; i++) {
218		/* end marker */
219		if (dir[i].name[0] == 0x00) {
220			dbg("end of dir");
221			break;
222		}
223
224		/* empty entry */
225		if (dir[i].name[0] == FAT_ENTRY_FREE)
226			continue;
227
228		/* long name */
229		if ((dir[i].attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
230			continue;
231
232		if ((dir[i].attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
233			/* labels do not have file data */
234			if (dir[i].cluster_high != 0 || dir[i].cluster_low != 0)
235				continue;
236
237			dbg("found ATTR_VOLUME_ID id in root dir");
238			return fat_read_filename(filename, fnsize, dir, &dir[i]);
239		}
240
241		dbg("skip dir entry");
242	}
243
244	return 0;
245}
246
247int volume_id_probe_vfat(struct volume_id *id, uint64_t off, uint64_t size)
248{
249	uint8_t filename[255 * 3];
250	struct vfat_super_block *vs;
251	struct vfat_dir_entry *dir;
252	struct fat32_fsinfo *fsinfo;
253	uint16_t sector_size;
254	uint16_t dir_entries;
255	uint32_t sect_count;
256	uint16_t reserved;
257	uint32_t fat_size;
258	uint32_t root_cluster;
259	uint32_t dir_size;
260	uint32_t cluster_count;
261	uint16_t fat_length;
262	uint32_t fat32_length;
263	uint64_t root_start;
264	uint32_t start_data_sect;
265	uint16_t root_dir_entries;
266	uint16_t fsinfo_sect;
267	uint8_t *buf;
268	uint32_t buf_size;
269	uint32_t next;
270	int maxloop;
271	size_t fnlen;
272
273	info("probing at offset 0x%llx", (unsigned long long) off);
274
275	buf = volume_id_get_buffer(id, off, 0x400);
276	if (buf == NULL)
277		return -1;
278
279	/* check signature */
280	if (buf[510] != 0x55 || buf[511] != 0xaa)
281		return -1;
282
283	vs = (struct vfat_super_block *) buf;
284	if (memcmp(vs->sysid, "NTFS", 4) == 0)
285		return -1;
286
287	/* believe only that's fat, don't trust the version */
288	if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
289		goto magic;
290
291	if (memcmp(vs->type.fat32.magic, "FAT32   ", 8) == 0)
292		goto magic;
293
294	if (memcmp(vs->type.fat.magic, "FAT16   ", 8) == 0)
295		goto magic;
296
297	if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
298		goto magic;
299
300	if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
301		goto magic;
302
303	/* some old floppies don't have a magic, expect the boot jump address to match */
304	if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
305	     vs->boot_jump[0] != 0xe9)
306		return -1;
307
308magic:
309	/* reserverd sector count */
310	if (!vs->reserved)
311		return -1;
312
313	/* fat count*/
314	if (!vs->fats)
315		return -1;
316
317	/* media check */
318	if (vs->media < 0xf8 && vs->media != 0xf0)
319		return -1;
320
321	/* cluster size check*/
322	if (vs->sectors_per_cluster == 0 ||
323	    (vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
324		return -1;
325
326	/* sector size check */
327	sector_size = le16_to_cpu(vs->sector_size);
328	if (sector_size != 0x200 && sector_size != 0x400 &&
329	    sector_size != 0x800 && sector_size != 0x1000)
330		return -1;
331
332	dbg("sector_size 0x%x", sector_size);
333	dbg("sectors_per_cluster 0x%x", vs->sectors_per_cluster);
334
335	dir_entries = le16_to_cpu(vs->dir_entries);
336	reserved = le16_to_cpu(vs->reserved);
337	dbg("reserved 0x%x", reserved);
338
339	sect_count = le16_to_cpu(vs->sectors);
340	if (sect_count == 0)
341		sect_count = le32_to_cpu(vs->total_sect);
342	dbg("sect_count 0x%x", sect_count);
343
344	fat_length = le16_to_cpu(vs->fat_length);
345	dbg("fat_length 0x%x", fat_length);
346	fat32_length = le32_to_cpu(vs->type.fat32.fat32_length);
347	dbg("fat32_length 0x%x", fat32_length);
348
349	if (fat_length)
350		fat_size = fat_length * vs->fats;
351	else if (fat32_length)
352		fat_size = fat32_length * vs->fats;
353	else
354		return -1;
355	dbg("fat_size 0x%x", fat_size);
356
357	dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
358			(sector_size-1)) / sector_size;
359	dbg("dir_size 0x%x", dir_size);
360
361	cluster_count = sect_count - (reserved + fat_size + dir_size);
362	cluster_count /= vs->sectors_per_cluster;
363	dbg("cluster_count 0x%x", cluster_count);
364
365	/* must be FAT32 */
366	if (!fat_length && fat32_length)
367		goto fat32;
368
369	/* cluster_count tells us the format */
370	if (cluster_count < FAT12_MAX)
371		strcpy(id->type_version, "FAT12");
372	else if (cluster_count < FAT16_MAX)
373		strcpy(id->type_version, "FAT16");
374	else
375		goto fat32;
376
377	/* the label may be an attribute in the root directory */
378	root_start = (reserved + fat_size) * sector_size;
379	dbg("root dir start 0x%llx", (unsigned long long) root_start);
380	root_dir_entries = le16_to_cpu(vs->dir_entries);
381	dbg("expected entries 0x%x", root_dir_entries);
382
383	buf_size = root_dir_entries * sizeof(struct vfat_dir_entry);
384	buf = volume_id_get_buffer(id, off + root_start, buf_size);
385	if (buf == NULL)
386		goto found;
387
388	dir = (struct vfat_dir_entry*) buf;
389
390	fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, root_dir_entries);
391
392	vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
393	if (vs == NULL)
394		return -1;
395
396	if (fnlen > 0 && memcmp(filename, "NO NAME    ", 11) != 0) {
397		volume_id_set_label_raw(id, filename, fnlen);
398		volume_id_set_label_string(id, filename, fnlen);
399	} else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
400		volume_id_set_label_raw(id, vs->type.fat.label, 11);
401		volume_id_set_label_string(id, vs->type.fat.label, 11);
402	}
403	volume_id_set_uuid(id, vs->type.fat.serno, 0, UUID_DOS);
404	goto found;
405
406fat32:
407	/* FAT32 should have a valid signature in the fsinfo block */
408	fsinfo_sect = le16_to_cpu(vs->type.fat32.fsinfo_sector);
409	buf = volume_id_get_buffer(id, off + (fsinfo_sect * sector_size), 0x200);
410	if (buf == NULL)
411		return -1;
412	fsinfo = (struct fat32_fsinfo *) buf;
413	if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0)
414		return -1;
415	if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0)
416		return -1 ;
417
418	vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
419	if (vs == NULL)
420		return -1;
421
422	strcpy(id->type_version, "FAT32");
423
424	/* FAT32 root dir is a cluster chain like any other directory */
425	buf_size = vs->sectors_per_cluster * sector_size;
426	root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
427	dbg("root dir cluster %u", root_cluster);
428	start_data_sect = reserved + fat_size;
429
430	next = root_cluster;
431	maxloop = 100;
432	while (--maxloop) {
433		uint32_t next_sect_off;
434		uint64_t next_off;
435		uint64_t fat_entry_off;
436		int count;
437
438		dbg("next cluster %u", next);
439		next_sect_off = (next - 2) * vs->sectors_per_cluster;
440		next_off = (start_data_sect + next_sect_off) * sector_size;
441		dbg("cluster offset 0x%llx", (unsigned long long) next_off);
442
443		/* get cluster */
444		buf = volume_id_get_buffer(id, off + next_off, buf_size);
445		if (buf == NULL)
446			goto found;
447
448		dir = (struct vfat_dir_entry*) buf;
449		count = buf_size / sizeof(struct vfat_dir_entry);
450		dbg("expected entries 0x%x", count);
451
452		fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, count);
453		if (fnlen > 0)
454			break;
455
456		/* get FAT entry */
457		fat_entry_off = (reserved * sector_size) + (next * sizeof(uint32_t));
458		buf = volume_id_get_buffer(id, off + fat_entry_off, buf_size);
459		if (buf == NULL)
460			goto found;
461
462		/* set next cluster */
463		next = le32_to_cpu(*((uint32_t *) buf)) & 0x0fffffff;
464		if (next < 2 || next >= 0x0ffffff0)
465			break;
466	}
467	if (maxloop == 0)
468		dbg("reached maximum follow count of root cluster chain, give up");
469
470	vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
471	if (vs == NULL)
472		return -1;
473
474	if (fnlen > 0 && memcmp(filename, "NO NAME    ", 11) != 0) {
475		volume_id_set_label_raw(id, filename, fnlen);
476		volume_id_set_label_string(id, filename, fnlen);
477	} else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
478		volume_id_set_label_raw(id, vs->type.fat32.label, 11);
479		volume_id_set_label_string(id, vs->type.fat32.label, 11);
480	}
481	volume_id_set_uuid(id, vs->type.fat32.serno, 0, UUID_DOS);
482
483found:
484	volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
485	id->type = "vfat";
486
487	return 0;
488}
489