1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * mst.c - NTFS multi sector transfer protection handling code. Part of the
4 * Linux-NTFS project.
5 *
6 * Copyright (c) 2001-2004 Anton Altaparmakov
7 */
8
9 #include "ntfs.h"
10
11 /**
12 * post_read_mst_fixup - deprotect multi sector transfer protected data
13 * @b: pointer to the data to deprotect
14 * @size: size in bytes of @b
15 *
16 * Perform the necessary post read multi sector transfer fixup and detect the
17 * presence of incomplete multi sector transfers. - In that case, overwrite the
18 * magic of the ntfs record header being processed with "BAAD" (in memory only!)
19 * and abort processing.
20 *
21 * Return 0 on success and -EINVAL on error ("BAAD" magic will be present).
22 *
23 * NOTE: We consider the absence / invalidity of an update sequence array to
24 * mean that the structure is not protected at all and hence doesn't need to
25 * be fixed up. Thus, we return success and not failure in this case. This is
26 * in contrast to pre_write_mst_fixup(), see below.
27 */
28 int post_read_mst_fixup(NTFS_RECORD *b, const u32 size)
29 {
30 u16 usa_ofs, usa_count, usn;
31 u16 *usa_pos, *data_pos;
32
33 /* Setup the variables. */
34 usa_ofs = le16_to_cpu(b->usa_ofs);
35 /* Decrement usa_count to get number of fixups. */
36 usa_count = le16_to_cpu(b->usa_count) - 1;
37 /* Size and alignment checks. */
38 if ( size & (NTFS_BLOCK_SIZE - 1) ||
39 usa_ofs & 1 ||
40 usa_ofs + (usa_count * 2) > size ||
41 (size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
42 return 0;
43 /* Position of usn in update sequence array. */
44 usa_pos = (u16*)b + usa_ofs/sizeof(u16);
45 /*
46 * The update sequence number which has to be equal to each of the
47 * u16 values before they are fixed up. Note no need to care for
48 * endianness since we are comparing and moving data for on disk
49 * structures which means the data is consistent. - If it is
50 * consistenty the wrong endianness it doesn't make any difference.
51 */
52 usn = *usa_pos;
53 /*
54 * Position in protected data of first u16 that needs fixing up.
55 */
56 data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
57 /*
58 * Check for incomplete multi sector transfer(s).
59 */
60 while (usa_count--) {
61 if (*data_pos != usn) {
62 /*
63 * Incomplete multi sector transfer detected! )-:
64 * Set the magic to "BAAD" and return failure.
65 * Note that magic_BAAD is already converted to le32.
66 */
67 b->magic = magic_BAAD;
68 return -EINVAL;
69 }
70 data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
71 }
72 /* Re-setup the variables. */
73 usa_count = le16_to_cpu(b->usa_count) - 1;
74 data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
75 /* Fixup all sectors. */
76 while (usa_count--) {
77 /*
78 * Increment position in usa and restore original data from
79 * the usa into the data buffer.
80 */
81 *data_pos = *(++usa_pos);
82 /* Increment position in data as well. */
83 data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
84 }
85 return 0;
86 }
87
88 /**
89 * pre_write_mst_fixup - apply multi sector transfer protection
90 * @b: pointer to the data to protect
91 * @size: size in bytes of @b
92 *
93 * Perform the necessary pre write multi sector transfer fixup on the data
94 * pointer to by @b of @size.
95 *
96 * Return 0 if fixup applied (success) or -EINVAL if no fixup was performed
97 * (assumed not needed). This is in contrast to post_read_mst_fixup() above.
98 *
99 * NOTE: We consider the absence / invalidity of an update sequence array to
100 * mean that the structure is not subject to protection and hence doesn't need
101 * to be fixed up. This means that you have to create a valid update sequence
102 * array header in the ntfs record before calling this function, otherwise it
103 * will fail (the header needs to contain the position of the update sequence
104 * array together with the number of elements in the array). You also need to
105 * initialise the update sequence number before calling this function
106 * otherwise a random word will be used (whatever was in the record at that
107 * position at that time).
108 */
109 int pre_write_mst_fixup(NTFS_RECORD *b, const u32 size)
110 {
111 le16 *usa_pos, *data_pos;
112 u16 usa_ofs, usa_count, usn;
113 le16 le_usn;
114
115 /* Sanity check + only fixup if it makes sense. */
116 if (!b || ntfs_is_baad_record(b->magic) ||
117 ntfs_is_hole_record(b->magic))
118 return -EINVAL;
119 /* Setup the variables. */
120 usa_ofs = le16_to_cpu(b->usa_ofs);
121 /* Decrement usa_count to get number of fixups. */
122 usa_count = le16_to_cpu(b->usa_count) - 1;
123 /* Size and alignment checks. */
124 if ( size & (NTFS_BLOCK_SIZE - 1) ||
125 usa_ofs & 1 ||
126 usa_ofs + (usa_count * 2) > size ||
127 (size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
128 return -EINVAL;
129 /* Position of usn in update sequence array. */
130 usa_pos = (le16*)((u8*)b + usa_ofs);
131 /*
132 * Cyclically increment the update sequence number
133 * (skipping 0 and -1, i.e. 0xffff).
134 */
135 usn = le16_to_cpup(usa_pos) + 1;
136 if (usn == 0xffff || !usn)
137 usn = 1;
138 le_usn = cpu_to_le16(usn);
139 *usa_pos = le_usn;
140 /* Position in data of first u16 that needs fixing up. */
141 data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;
142 /* Fixup all sectors. */
143 while (usa_count--) {
144 /*
145 * Increment the position in the usa and save the
146 * original data from the data buffer into the usa.
147 */
148 *(++usa_pos) = *data_pos;
149 /* Apply fixup to data. */
150 *data_pos = le_usn;
151 /* Increment position in data as well. */
152 data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
153 }
154 return 0;
155 }
156
157 /**
158 * post_write_mst_fixup - fast deprotect multi sector transfer protected data
159 * @b: pointer to the data to deprotect
160 *
161 * Perform the necessary post write multi sector transfer fixup, not checking
162 * for any errors, because we assume we have just used pre_write_mst_fixup(),
163 * thus the data will be fine or we would never have gotten here.
164 */
165 void post_write_mst_fixup(NTFS_RECORD *b)
166 {
167 le16 *usa_pos, *data_pos;
168
169 u16 usa_ofs = le16_to_cpu(b->usa_ofs);
170 u16 usa_count = le16_to_cpu(b->usa_count) - 1;
171
172 /* Position of usn in update sequence array. */
173 usa_pos = (le16*)b + usa_ofs/sizeof(le16);
174
175 /* Position in protected data of first u16 that needs fixing up. */
176 data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;
177
178 /* Fixup all sectors. */
179 while (usa_count--) {
180 /*
181 * Increment position in usa and restore original data from
182 * the usa into the data buffer.
183 */
184 *data_pos = *(++usa_pos);
185
186 /* Increment position in data as well. */
187 data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
188 }
189 }