aboutsummaryrefslogtreecommitdiff
path: root/fs/ntfs/mst.c
blob: 16b3c884abfc41aa97106abe1c3af075e2efa916 (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
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * mst.c - NTFS multi sector transfer protection handling code. Part of the
 *	   Linux-NTFS project.
 *
 * Copyright (c) 2001-2004 Anton Altaparmakov
 */

#include "ntfs.h"

/**
 * post_read_mst_fixup - deprotect multi sector transfer protected data
 * @b:		pointer to the data to deprotect
 * @size:	size in bytes of @b
 *
 * Perform the necessary post read multi sector transfer fixup and detect the
 * presence of incomplete multi sector transfers. - In that case, overwrite the
 * magic of the ntfs record header being processed with "BAAD" (in memory only!)
 * and abort processing.
 *
 * Return 0 on success and -EINVAL on error ("BAAD" magic will be present).
 *
 * NOTE: We consider the absence / invalidity of an update sequence array to
 * mean that the structure is not protected at all and hence doesn't need to
 * be fixed up. Thus, we return success and not failure in this case. This is
 * in contrast to pre_write_mst_fixup(), see below.
 */
int post_read_mst_fixup(NTFS_RECORD *b, const u32 size)
{
	u16 usa_ofs, usa_count, usn;
	u16 *usa_pos, *data_pos;

	/* Setup the variables. */
	usa_ofs = le16_to_cpu(b->usa_ofs);
	/* Decrement usa_count to get number of fixups. */
	usa_count = le16_to_cpu(b->usa_count) - 1;
	/* Size and alignment checks. */
	if ( size & (NTFS_BLOCK_SIZE - 1)	||
	     usa_ofs & 1			||
	     usa_ofs + (usa_count * 2) > size	||
	     (size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
		return 0;
	/* Position of usn in update sequence array. */
	usa_pos = (u16*)b + usa_ofs/sizeof(u16);
	/*
	 * The update sequence number which has to be equal to each of the
	 * u16 values before they are fixed up. Note no need to care for
	 * endianness since we are comparing and moving data for on disk
	 * structures which means the data is consistent. - If it is
	 * consistenty the wrong endianness it doesn't make any difference.
	 */
	usn = *usa_pos;
	/*
	 * Position in protected data of first u16 that needs fixing up.
	 */
	data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
	/*
	 * Check for incomplete multi sector transfer(s).
	 */
	while (usa_count--) {
		if (*data_pos != usn) {
			/*
			 * Incomplete multi sector transfer detected! )-:
			 * Set the magic to "BAAD" and return failure.
			 * Note that magic_BAAD is already converted to le32.
			 */
			b->magic = magic_BAAD;
			return -EINVAL;
		}
		data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
	}
	/* Re-setup the variables. */
	usa_count = le16_to_cpu(b->usa_count) - 1;
	data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
	/* Fixup all sectors. */
	while (usa_count--) {
		/*
		 * Increment position in usa and restore original data from
		 * the usa into the data buffer.
		 */
		*data_pos = *(++usa_pos);
		/* Increment position in data as well. */
		data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
	}
	return 0;
}

/**
 * pre_write_mst_fixup - apply multi sector transfer protection
 * @b:		pointer to the data to protect
 * @size:	size in bytes of @b
 *
 * Perform the necessary pre write multi sector transfer fixup on the data
 * pointer to by @b of @size.
 *
 * Return 0 if fixup applied (success) or -EINVAL if no fixup was performed
 * (assumed not needed). This is in contrast to post_read_mst_fixup() above.
 *
 * NOTE: We consider the absence / invalidity of an update sequence array to
 * mean that the structure is not subject to protection and hence doesn't need
 * to be fixed up. This means that you have to create a valid update sequence
 * array header in the ntfs record before calling this function, otherwise it
 * will fail (the header needs to contain the position of the update sequence
 * array together with the number of elements in the array). You also need to
 * initialise the update sequence number before calling this function
 * otherwise a random word will be used (whatever was in the record at that
 * position at that time).
 */
int pre_write_mst_fixup(NTFS_RECORD *b, const u32 size)
{
	le16 *usa_pos, *data_pos;
	u16 usa_ofs, usa_count, usn;
	le16 le_usn;

	/* Sanity check + only fixup if it makes sense. */
	if (!b || ntfs_is_baad_record(b->magic) ||
			ntfs_is_hole_record(b->magic))
		return -EINVAL;
	/* Setup the variables. */
	usa_ofs = le16_to_cpu(b->usa_ofs);
	/* Decrement usa_count to get number of fixups. */
	usa_count = le16_to_cpu(b->usa_count) - 1;
	/* Size and alignment checks. */
	if ( size & (NTFS_BLOCK_SIZE - 1)	||
	     usa_ofs & 1			||
	     usa_ofs + (usa_count * 2) > size	||
	     (size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
		return -EINVAL;
	/* Position of usn in update sequence array. */
	usa_pos = (le16*)((u8*)b + usa_ofs);
	/*
	 * Cyclically increment the update sequence number
	 * (skipping 0 and -1, i.e. 0xffff).
	 */
	usn = le16_to_cpup(usa_pos) + 1;
	if (usn == 0xffff || !usn)
		usn = 1;
	le_usn = cpu_to_le16(usn);
	*usa_pos = le_usn;
	/* Position in data of first u16 that needs fixing up. */
	data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;
	/* Fixup all sectors. */
	while (usa_count--) {
		/*
		 * Increment the position in the usa and save the
		 * original data from the data buffer into the usa.
		 */
		*(++usa_pos) = *data_pos;
		/* Apply fixup to data. */
		*data_pos = le_usn;
		/* Increment position in data as well. */
		data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
	}
	return 0;
}

/**
 * post_write_mst_fixup - fast deprotect multi sector transfer protected data
 * @b:		pointer to the data to deprotect
 *
 * Perform the necessary post write multi sector transfer fixup, not checking
 * for any errors, because we assume we have just used pre_write_mst_fixup(),
 * thus the data will be fine or we would never have gotten here.
 */
void post_write_mst_fixup(NTFS_RECORD *b)
{
	le16 *usa_pos, *data_pos;

	u16 usa_ofs = le16_to_cpu(b->usa_ofs);
	u16 usa_count = le16_to_cpu(b->usa_count) - 1;

	/* Position of usn in update sequence array. */
	usa_pos = (le16*)b + usa_ofs/sizeof(le16);

	/* Position in protected data of first u16 that needs fixing up. */
	data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;

	/* Fixup all sectors. */
	while (usa_count--) {
		/*
		 * Increment position in usa and restore original data from
		 * the usa into the data buffer.
		 */
		*data_pos = *(++usa_pos);

		/* Increment position in data as well. */
		data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
	}
}