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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* mst.c - NTFS multi sector transfer protection handling code. Part of the
* Linux-NTFS project.
*
* Copyright (c) 2001-2004 Anton Altaparmakov
*/
#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);
}
}
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