190 lines
6.2 KiB
C
190 lines
6.2 KiB
C
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// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* mst.c - NTFS multi sector transfer protection handling code. Part of the
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* Linux-NTFS project.
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*
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* Copyright (c) 2001-2004 Anton Altaparmakov
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*/
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#include "ntfs.h"
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/**
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* post_read_mst_fixup - deprotect multi sector transfer protected data
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* @b: pointer to the data to deprotect
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* @size: size in bytes of @b
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*
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* Perform the necessary post read multi sector transfer fixup and detect the
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* presence of incomplete multi sector transfers. - In that case, overwrite the
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* magic of the ntfs record header being processed with "BAAD" (in memory only!)
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* and abort processing.
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*
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* Return 0 on success and -EINVAL on error ("BAAD" magic will be present).
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*
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* NOTE: We consider the absence / invalidity of an update sequence array to
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* mean that the structure is not protected at all and hence doesn't need to
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* be fixed up. Thus, we return success and not failure in this case. This is
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* in contrast to pre_write_mst_fixup(), see below.
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*/
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int post_read_mst_fixup(NTFS_RECORD *b, const u32 size)
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{
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u16 usa_ofs, usa_count, usn;
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u16 *usa_pos, *data_pos;
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/* Setup the variables. */
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usa_ofs = le16_to_cpu(b->usa_ofs);
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/* Decrement usa_count to get number of fixups. */
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usa_count = le16_to_cpu(b->usa_count) - 1;
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/* Size and alignment checks. */
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if ( size & (NTFS_BLOCK_SIZE - 1) ||
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usa_ofs & 1 ||
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usa_ofs + (usa_count * 2) > size ||
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(size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
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return 0;
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/* Position of usn in update sequence array. */
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usa_pos = (u16*)b + usa_ofs/sizeof(u16);
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/*
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* The update sequence number which has to be equal to each of the
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* u16 values before they are fixed up. Note no need to care for
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* endianness since we are comparing and moving data for on disk
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* structures which means the data is consistent. - If it is
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* consistenty the wrong endianness it doesn't make any difference.
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*/
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usn = *usa_pos;
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/*
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* Position in protected data of first u16 that needs fixing up.
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*/
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data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
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/*
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* Check for incomplete multi sector transfer(s).
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*/
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while (usa_count--) {
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if (*data_pos != usn) {
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/*
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* Incomplete multi sector transfer detected! )-:
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* Set the magic to "BAAD" and return failure.
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* Note that magic_BAAD is already converted to le32.
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*/
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b->magic = magic_BAAD;
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return -EINVAL;
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}
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data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
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}
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/* Re-setup the variables. */
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usa_count = le16_to_cpu(b->usa_count) - 1;
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data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
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/* Fixup all sectors. */
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while (usa_count--) {
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/*
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* Increment position in usa and restore original data from
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* the usa into the data buffer.
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*/
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*data_pos = *(++usa_pos);
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/* Increment position in data as well. */
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data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
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}
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return 0;
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}
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/**
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* pre_write_mst_fixup - apply multi sector transfer protection
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* @b: pointer to the data to protect
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* @size: size in bytes of @b
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*
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* Perform the necessary pre write multi sector transfer fixup on the data
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* pointer to by @b of @size.
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*
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* Return 0 if fixup applied (success) or -EINVAL if no fixup was performed
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* (assumed not needed). This is in contrast to post_read_mst_fixup() above.
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*
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* NOTE: We consider the absence / invalidity of an update sequence array to
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* mean that the structure is not subject to protection and hence doesn't need
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* to be fixed up. This means that you have to create a valid update sequence
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* array header in the ntfs record before calling this function, otherwise it
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* will fail (the header needs to contain the position of the update sequence
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* array together with the number of elements in the array). You also need to
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* initialise the update sequence number before calling this function
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* otherwise a random word will be used (whatever was in the record at that
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* position at that time).
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*/
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int pre_write_mst_fixup(NTFS_RECORD *b, const u32 size)
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{
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le16 *usa_pos, *data_pos;
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u16 usa_ofs, usa_count, usn;
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le16 le_usn;
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/* Sanity check + only fixup if it makes sense. */
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if (!b || ntfs_is_baad_record(b->magic) ||
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ntfs_is_hole_record(b->magic))
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return -EINVAL;
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/* Setup the variables. */
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usa_ofs = le16_to_cpu(b->usa_ofs);
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/* Decrement usa_count to get number of fixups. */
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usa_count = le16_to_cpu(b->usa_count) - 1;
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/* Size and alignment checks. */
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if ( size & (NTFS_BLOCK_SIZE - 1) ||
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usa_ofs & 1 ||
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usa_ofs + (usa_count * 2) > size ||
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(size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
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return -EINVAL;
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/* Position of usn in update sequence array. */
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usa_pos = (le16*)((u8*)b + usa_ofs);
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/*
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* Cyclically increment the update sequence number
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* (skipping 0 and -1, i.e. 0xffff).
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*/
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usn = le16_to_cpup(usa_pos) + 1;
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if (usn == 0xffff || !usn)
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usn = 1;
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le_usn = cpu_to_le16(usn);
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*usa_pos = le_usn;
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/* Position in data of first u16 that needs fixing up. */
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data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;
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/* Fixup all sectors. */
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while (usa_count--) {
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/*
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* Increment the position in the usa and save the
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* original data from the data buffer into the usa.
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*/
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*(++usa_pos) = *data_pos;
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/* Apply fixup to data. */
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*data_pos = le_usn;
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/* Increment position in data as well. */
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data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
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}
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return 0;
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}
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/**
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* post_write_mst_fixup - fast deprotect multi sector transfer protected data
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* @b: pointer to the data to deprotect
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*
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* Perform the necessary post write multi sector transfer fixup, not checking
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* for any errors, because we assume we have just used pre_write_mst_fixup(),
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* thus the data will be fine or we would never have gotten here.
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*/
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void post_write_mst_fixup(NTFS_RECORD *b)
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{
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le16 *usa_pos, *data_pos;
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u16 usa_ofs = le16_to_cpu(b->usa_ofs);
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u16 usa_count = le16_to_cpu(b->usa_count) - 1;
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/* Position of usn in update sequence array. */
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usa_pos = (le16*)b + usa_ofs/sizeof(le16);
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/* Position in protected data of first u16 that needs fixing up. */
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data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;
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/* Fixup all sectors. */
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while (usa_count--) {
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/*
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* Increment position in usa and restore original data from
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* the usa into the data buffer.
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*/
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*data_pos = *(++usa_pos);
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/* Increment position in data as well. */
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data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
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}
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}
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