1 /*
2 * mst.c - NTFS multi sector transfer protection handling code. Part of the
3 * Linux-NTFS project.
4 *
5 * Copyright (c) 2001-2004 Anton Altaparmakov
6 *
7 * This program/include file is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License as published
9 * by the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
11 *
12 * This program/include file is distributed in the hope that it will be
13 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
14 * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program (in the main directory of the Linux-NTFS
19 * distribution in the file COPYING); if not, write to the Free Software
20 * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
21 */
22
23 #include "ntfs.h"
24
25 /**
26 * post_read_mst_fixup - deprotect multi sector transfer protected data
27 * @b: pointer to the data to deprotect
28 * @size: size in bytes of @b
29 *
30 * Perform the necessary post read multi sector transfer fixup and detect the
31 * presence of incomplete multi sector transfers. - In that case, overwrite the
32 * magic of the ntfs record header being processed with "BAAD" (in memory only!)
33 * and abort processing.
34 *
35 * Return 0 on success and -EINVAL on error ("BAAD" magic will be present).
36 *
37 * NOTE: We consider the absence / invalidity of an update sequence array to
38 * mean that the structure is not protected at all and hence doesn't need to
39 * be fixed up. Thus, we return success and not failure in this case. This is
40 * in contrast to pre_write_mst_fixup(), see below.
41 */
post_read_mst_fixup(NTFS_RECORD * b,const u32 size)42 int post_read_mst_fixup(NTFS_RECORD *b, const u32 size)
43 {
44 u16 usa_ofs, usa_count, usn;
45 u16 *usa_pos, *data_pos;
46
47 /* Setup the variables. */
48 usa_ofs = le16_to_cpu(b->usa_ofs);
49 /* Decrement usa_count to get number of fixups. */
50 usa_count = le16_to_cpu(b->usa_count) - 1;
51 /* Size and alignment checks. */
52 if ( size & (NTFS_BLOCK_SIZE - 1) ||
53 usa_ofs & 1 ||
54 usa_ofs + (usa_count * 2) > size ||
55 (size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
56 return 0;
57 /* Position of usn in update sequence array. */
58 usa_pos = (u16*)b + usa_ofs/sizeof(u16);
59 /*
60 * The update sequence number which has to be equal to each of the
61 * u16 values before they are fixed up. Note no need to care for
62 * endianness since we are comparing and moving data for on disk
63 * structures which means the data is consistent. - If it is
64 * consistenty the wrong endianness it doesn't make any difference.
65 */
66 usn = *usa_pos;
67 /*
68 * Position in protected data of first u16 that needs fixing up.
69 */
70 data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
71 /*
72 * Check for incomplete multi sector transfer(s).
73 */
74 while (usa_count--) {
75 if (*data_pos != usn) {
76 /*
77 * Incomplete multi sector transfer detected! )-:
78 * Set the magic to "BAAD" and return failure.
79 * Note that magic_BAAD is already converted to le32.
80 */
81 b->magic = magic_BAAD;
82 return -EINVAL;
83 }
84 data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
85 }
86 /* Re-setup the variables. */
87 usa_count = le16_to_cpu(b->usa_count) - 1;
88 data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
89 /* Fixup all sectors. */
90 while (usa_count--) {
91 /*
92 * Increment position in usa and restore original data from
93 * the usa into the data buffer.
94 */
95 *data_pos = *(++usa_pos);
96 /* Increment position in data as well. */
97 data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
98 }
99 return 0;
100 }
101
102 /**
103 * pre_write_mst_fixup - apply multi sector transfer protection
104 * @b: pointer to the data to protect
105 * @size: size in bytes of @b
106 *
107 * Perform the necessary pre write multi sector transfer fixup on the data
108 * pointer to by @b of @size.
109 *
110 * Return 0 if fixup applied (success) or -EINVAL if no fixup was performed
111 * (assumed not needed). This is in contrast to post_read_mst_fixup() above.
112 *
113 * NOTE: We consider the absence / invalidity of an update sequence array to
114 * mean that the structure is not subject to protection and hence doesn't need
115 * to be fixed up. This means that you have to create a valid update sequence
116 * array header in the ntfs record before calling this function, otherwise it
117 * will fail (the header needs to contain the position of the update sequence
118 * array together with the number of elements in the array). You also need to
119 * initialise the update sequence number before calling this function
120 * otherwise a random word will be used (whatever was in the record at that
121 * position at that time).
122 */
pre_write_mst_fixup(NTFS_RECORD * b,const u32 size)123 int pre_write_mst_fixup(NTFS_RECORD *b, const u32 size)
124 {
125 le16 *usa_pos, *data_pos;
126 u16 usa_ofs, usa_count, usn;
127 le16 le_usn;
128
129 /* Sanity check + only fixup if it makes sense. */
130 if (!b || ntfs_is_baad_record(b->magic) ||
131 ntfs_is_hole_record(b->magic))
132 return -EINVAL;
133 /* Setup the variables. */
134 usa_ofs = le16_to_cpu(b->usa_ofs);
135 /* Decrement usa_count to get number of fixups. */
136 usa_count = le16_to_cpu(b->usa_count) - 1;
137 /* Size and alignment checks. */
138 if ( size & (NTFS_BLOCK_SIZE - 1) ||
139 usa_ofs & 1 ||
140 usa_ofs + (usa_count * 2) > size ||
141 (size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
142 return -EINVAL;
143 /* Position of usn in update sequence array. */
144 usa_pos = (le16*)((u8*)b + usa_ofs);
145 /*
146 * Cyclically increment the update sequence number
147 * (skipping 0 and -1, i.e. 0xffff).
148 */
149 usn = le16_to_cpup(usa_pos) + 1;
150 if (usn == 0xffff || !usn)
151 usn = 1;
152 le_usn = cpu_to_le16(usn);
153 *usa_pos = le_usn;
154 /* Position in data of first u16 that needs fixing up. */
155 data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;
156 /* Fixup all sectors. */
157 while (usa_count--) {
158 /*
159 * Increment the position in the usa and save the
160 * original data from the data buffer into the usa.
161 */
162 *(++usa_pos) = *data_pos;
163 /* Apply fixup to data. */
164 *data_pos = le_usn;
165 /* Increment position in data as well. */
166 data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
167 }
168 return 0;
169 }
170
171 /**
172 * post_write_mst_fixup - fast deprotect multi sector transfer protected data
173 * @b: pointer to the data to deprotect
174 *
175 * Perform the necessary post write multi sector transfer fixup, not checking
176 * for any errors, because we assume we have just used pre_write_mst_fixup(),
177 * thus the data will be fine or we would never have gotten here.
178 */
post_write_mst_fixup(NTFS_RECORD * b)179 void post_write_mst_fixup(NTFS_RECORD *b)
180 {
181 le16 *usa_pos, *data_pos;
182
183 u16 usa_ofs = le16_to_cpu(b->usa_ofs);
184 u16 usa_count = le16_to_cpu(b->usa_count) - 1;
185
186 /* Position of usn in update sequence array. */
187 usa_pos = (le16*)b + usa_ofs/sizeof(le16);
188
189 /* Position in protected data of first u16 that needs fixing up. */
190 data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;
191
192 /* Fixup all sectors. */
193 while (usa_count--) {
194 /*
195 * Increment position in usa and restore original data from
196 * the usa into the data buffer.
197 */
198 *data_pos = *(++usa_pos);
199
200 /* Increment position in data as well. */
201 data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
202 }
203 }
204