linux/fs/ntfs/mst.c
<<
>>
Prefs
   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
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.