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Linux/fs/ntfs/mst.c

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  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  */
 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  */
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  */
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 

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