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Diffstat (limited to 'fs/ntfs/mst.c')
| -rw-r--r-- | fs/ntfs/mst.c | 203 |
1 files changed, 203 insertions, 0 deletions
diff --git a/fs/ntfs/mst.c b/fs/ntfs/mst.c new file mode 100644 index 0000000..5a858d8 --- /dev/null +++ b/fs/ntfs/mst.c @@ -0,0 +1,203 @@ +/* + * 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); + } +} |
