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