Root/fs/ntfs/mst.c

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 */
42int 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 */
123int 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 */
179void 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

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