mst.c 6.94 KB
Newer Older
Linus Torvalds's avatar
Linus Torvalds committed
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203
/*
 * mst.c - NTFS multi sector transfer protection handling code. Part of the
 *	   Linux-NTFS project.
 *
 * Copyright (c) 2001-2004 Anton Altaparmakov
 *
 * This program/include file is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as published
 * by the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program/include file is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
 * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program (in the main directory of the Linux-NTFS
 * distribution in the file COPYING); if not, write to the Free Software
 * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include "ntfs.h"

/**
 * post_read_mst_fixup - deprotect multi sector transfer protected data
 * @b:		pointer to the data to deprotect
 * @size:	size in bytes of @b
 *
 * Perform the necessary post read multi sector transfer fixup and detect the
 * presence of incomplete multi sector transfers. - In that case, overwrite the
 * magic of the ntfs record header being processed with "BAAD" (in memory only!)
 * and abort processing.
 *
 * Return 0 on success and -EINVAL on error ("BAAD" magic will be present).
 *
 * NOTE: We consider the absence / invalidity of an update sequence array to
 * mean that the structure is not protected at all and hence doesn't need to
 * be fixed up. Thus, we return success and not failure in this case. This is
 * in contrast to pre_write_mst_fixup(), see below.
 */
int post_read_mst_fixup(NTFS_RECORD *b, const u32 size)
{
	u16 usa_ofs, usa_count, usn;
	u16 *usa_pos, *data_pos;

	/* Setup the variables. */
	usa_ofs = le16_to_cpu(b->usa_ofs);
	/* Decrement usa_count to get number of fixups. */
	usa_count = le16_to_cpu(b->usa_count) - 1;
	/* Size and alignment checks. */
	if ( size & (NTFS_BLOCK_SIZE - 1)	||
	     usa_ofs & 1			||
	     usa_ofs + (usa_count * 2) > size	||
	     (size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
		return 0;
	/* Position of usn in update sequence array. */
	usa_pos = (u16*)b + usa_ofs/sizeof(u16);
	/*
	 * The update sequence number which has to be equal to each of the
	 * u16 values before they are fixed up. Note no need to care for
	 * endianness since we are comparing and moving data for on disk
	 * structures which means the data is consistent. - If it is
	 * consistenty the wrong endianness it doesn't make any difference.
	 */
	usn = *usa_pos;
	/*
	 * Position in protected data of first u16 that needs fixing up.
	 */
	data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
	/*
	 * Check for incomplete multi sector transfer(s).
	 */
	while (usa_count--) {
		if (*data_pos != usn) {
			/*
			 * Incomplete multi sector transfer detected! )-:
			 * Set the magic to "BAAD" and return failure.
			 * Note that magic_BAAD is already converted to le32.
			 */
			b->magic = magic_BAAD;
			return -EINVAL;
		}
		data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
	}
	/* Re-setup the variables. */
	usa_count = le16_to_cpu(b->usa_count) - 1;
	data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
	/* Fixup all sectors. */
	while (usa_count--) {
		/*
		 * Increment position in usa and restore original data from
		 * the usa into the data buffer.
		 */
		*data_pos = *(++usa_pos);
		/* Increment position in data as well. */
		data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
	}
	return 0;
}

/**
 * pre_write_mst_fixup - apply multi sector transfer protection
 * @b:		pointer to the data to protect
 * @size:	size in bytes of @b
 *
 * Perform the necessary pre write multi sector transfer fixup on the data
 * pointer to by @b of @size.
 *
 * Return 0 if fixup applied (success) or -EINVAL if no fixup was performed
 * (assumed not needed). This is in contrast to post_read_mst_fixup() above.
 *
 * NOTE: We consider the absence / invalidity of an update sequence array to
 * mean that the structure is not subject to protection and hence doesn't need
 * to be fixed up. This means that you have to create a valid update sequence
 * array header in the ntfs record before calling this function, otherwise it
 * will fail (the header needs to contain the position of the update sequence
 * array together with the number of elements in the array). You also need to
 * initialise the update sequence number before calling this function
 * otherwise a random word will be used (whatever was in the record at that
 * position at that time).
 */
int pre_write_mst_fixup(NTFS_RECORD *b, const u32 size)
{
	le16 *usa_pos, *data_pos;
	u16 usa_ofs, usa_count, usn;
	le16 le_usn;

	/* Sanity check + only fixup if it makes sense. */
	if (!b || ntfs_is_baad_record(b->magic) ||
			ntfs_is_hole_record(b->magic))
		return -EINVAL;
	/* Setup the variables. */
	usa_ofs = le16_to_cpu(b->usa_ofs);
	/* Decrement usa_count to get number of fixups. */
	usa_count = le16_to_cpu(b->usa_count) - 1;
	/* Size and alignment checks. */
	if ( size & (NTFS_BLOCK_SIZE - 1)	||
	     usa_ofs & 1			||
	     usa_ofs + (usa_count * 2) > size	||
	     (size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
		return -EINVAL;
	/* Position of usn in update sequence array. */
	usa_pos = (le16*)((u8*)b + usa_ofs);
	/*
	 * Cyclically increment the update sequence number
	 * (skipping 0 and -1, i.e. 0xffff).
	 */
	usn = le16_to_cpup(usa_pos) + 1;
	if (usn == 0xffff || !usn)
		usn = 1;
	le_usn = cpu_to_le16(usn);
	*usa_pos = le_usn;
	/* Position in data of first u16 that needs fixing up. */
	data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;
	/* Fixup all sectors. */
	while (usa_count--) {
		/*
		 * Increment the position in the usa and save the
		 * original data from the data buffer into the usa.
		 */
		*(++usa_pos) = *data_pos;
		/* Apply fixup to data. */
		*data_pos = le_usn;
		/* Increment position in data as well. */
		data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
	}
	return 0;
}

/**
 * post_write_mst_fixup - fast deprotect multi sector transfer protected data
 * @b:		pointer to the data to deprotect
 *
 * Perform the necessary post write multi sector transfer fixup, not checking
 * for any errors, because we assume we have just used pre_write_mst_fixup(),
 * thus the data will be fine or we would never have gotten here.
 */
void post_write_mst_fixup(NTFS_RECORD *b)
{
	le16 *usa_pos, *data_pos;

	u16 usa_ofs = le16_to_cpu(b->usa_ofs);
	u16 usa_count = le16_to_cpu(b->usa_count) - 1;

	/* Position of usn in update sequence array. */
	usa_pos = (le16*)b + usa_ofs/sizeof(le16);

	/* Position in protected data of first u16 that needs fixing up. */
	data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;

	/* Fixup all sectors. */
	while (usa_count--) {
		/*
		 * Increment position in usa and restore original data from
		 * the usa into the data buffer.
		 */
		*data_pos = *(++usa_pos);

		/* Increment position in data as well. */
		data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
	}
}