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 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         u16 usa_ofs, usa_count, usn;
 126         u16 *usa_pos, *data_pos;
 127
 128         /* Sanity check + only fixup if it makes sense. */
 129         if (!b || is_baad_record(b->magic) || is_hole_record(b->magic))
 130                 return -EINVAL;
 131         /* Setup the variables. */
 132         usa_ofs = le16_to_cpu(b->usa_ofs);
 133         /* Decrement usa_count to get number of fixups. */
 134         usa_count = le16_to_cpu(b->usa_count) - 1;
 135         /* Size and alignment checks. */
 136         if ( size & (NTFS_BLOCK_SIZE - 1)       ||
 137              usa_ofs & 1                        ||
 138              usa_ofs + (usa_count * 2) > size   ||
 139              (size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
 140                 return -EINVAL;
 141         /* Position of usn in update sequence array. */
 142         usa_pos = (u16*)((u8*)b + usa_ofs);
 143         /*
 144          * Cyclically increment the update sequence number
 145          * (skipping 0 and -1, i.e. 0xffff).
 146          */
 147         usn = le16_to_cpup(usa_pos) + 1;
 148         if (usn == 0xffff || !usn)
 149                 usn = 1;
 150         usn = cpu_to_le16(usn);
 151         *usa_pos = usn;
 152         /* Position in data of first u16 that needs fixing up. */
 153         data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
 154         /* Fixup all sectors. */
 155         while (usa_count--) {
 156                 /*
 157                  * Increment the position in the usa and save the
 158                  * original data from the data buffer into the usa.
 159                  */
 160                 *(++usa_pos) = *data_pos;
 161                 /* Apply fixup to data. */
 162                 *data_pos = usn;
 163                 /* Increment position in data as well. */
 164                 data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
 165         }
 166         return 0;
 167 }
 168
 169 /**
 170  * post_write_mst_fixup - fast deprotect multi sector transfer protected data
 171  * @b:          pointer to the data to deprotect
 172  *
 173  * Perform the necessary post write multi sector transfer fixup, not checking
 174  * for any errors, because we assume we have just used pre_write_mst_fixup(),
 175  * thus the data will be fine or we would never have gotten here.
 176  */
 177 void post_write_mst_fixup(NTFS_RECORD *b)
 178 {
 179         u16 *usa_pos, *data_pos;
 180
 181         u16 usa_ofs = le16_to_cpu(b->usa_ofs);
 182         u16 usa_count = le16_to_cpu(b->usa_count) - 1;
 183
 184         /* Position of usn in update sequence array. */
 185         usa_pos = (u16*)b + usa_ofs/sizeof(u16);
 186
 187         /* Position in protected data of first u16 that needs fixing up. */
 188         data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
 189
 190         /* Fixup all sectors. */
 191         while (usa_count--) {
 192                 /*
 193                  * Increment position in usa and restore original data from
 194                  * the usa into the data buffer.
 195                  */
 196                 *data_pos = *(++usa_pos);
 197
 198                 /* Increment position in data as well. */
 199                 data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
 200         }
 201 }
 202