1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * mst.c - NTFS multi sector transfer protection handling code. Part of the 4 * Linux-NTFS project. 5 * 6 * Copyright (c) 2001-2004 Anton Altaparmakov 7 */ 8 9 #include "ntfs.h" 10 11 /** 12 * post_read_mst_fixup - deprotect multi sector transfer protected data 13 * @b: pointer to the data to deprotect 14 * @size: size in bytes of @b 15 * 16 * Perform the necessary post read multi sector transfer fixup and detect the 17 * presence of incomplete multi sector transfers. - In that case, overwrite the 18 * magic of the ntfs record header being processed with "BAAD" (in memory only!) 19 * and abort processing. 20 * 21 * Return 0 on success and -EINVAL on error ("BAAD" magic will be present). 22 * 23 * NOTE: We consider the absence / invalidity of an update sequence array to 24 * mean that the structure is not protected at all and hence doesn't need to 25 * be fixed up. Thus, we return success and not failure in this case. This is 26 * in contrast to pre_write_mst_fixup(), see below. 27 */ 28 int post_read_mst_fixup(NTFS_RECORD *b, const u32 size) 29 { 30 u16 usa_ofs, usa_count, usn; 31 u16 *usa_pos, *data_pos; 32 33 /* Setup the variables. */ 34 usa_ofs = le16_to_cpu(b->usa_ofs); 35 /* Decrement usa_count to get number of fixups. */ 36 usa_count = le16_to_cpu(b->usa_count) - 1; 37 /* Size and alignment checks. */ 38 if ( size & (NTFS_BLOCK_SIZE - 1) || 39 usa_ofs & 1 || 40 usa_ofs + (usa_count * 2) > size || 41 (size >> NTFS_BLOCK_SIZE_BITS) != usa_count) 42 return 0; 43 /* Position of usn in update sequence array. */ 44 usa_pos = (u16*)b + usa_ofs/sizeof(u16); 45 /* 46 * The update sequence number which has to be equal to each of the 47 * u16 values before they are fixed up. Note no need to care for 48 * endianness since we are comparing and moving data for on disk 49 * structures which means the data is consistent. - If it is 50 * consistenty the wrong endianness it doesn't make any difference. 51 */ 52 usn = *usa_pos; 53 /* 54 * Position in protected data of first u16 that needs fixing up. 55 */ 56 data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1; 57 /* 58 * Check for incomplete multi sector transfer(s). 59 */ 60 while (usa_count--) { 61 if (*data_pos != usn) { 62 /* 63 * Incomplete multi sector transfer detected! )-: 64 * Set the magic to "BAAD" and return failure. 65 * Note that magic_BAAD is already converted to le32. 66 */ 67 b->magic = magic_BAAD; 68 return -EINVAL; 69 } 70 data_pos += NTFS_BLOCK_SIZE/sizeof(u16); 71 } 72 /* Re-setup the variables. */ 73 usa_count = le16_to_cpu(b->usa_count) - 1; 74 data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1; 75 /* Fixup all sectors. */ 76 while (usa_count--) { 77 /* 78 * Increment position in usa and restore original data from 79 * the usa into the data buffer. 80 */ 81 *data_pos = *(++usa_pos); 82 /* Increment position in data as well. */ 83 data_pos += NTFS_BLOCK_SIZE/sizeof(u16); 84 } 85 return 0; 86 } 87 88 /** 89 * pre_write_mst_fixup - apply multi sector transfer protection 90 * @b: pointer to the data to protect 91 * @size: size in bytes of @b 92 * 93 * Perform the necessary pre write multi sector transfer fixup on the data 94 * pointer to by @b of @size. 95 * 96 * Return 0 if fixup applied (success) or -EINVAL if no fixup was performed 97 * (assumed not needed). This is in contrast to post_read_mst_fixup() above. 98 * 99 * NOTE: We consider the absence / invalidity of an update sequence array to 100 * mean that the structure is not subject to protection and hence doesn't need 101 * to be fixed up. This means that you have to create a valid update sequence 102 * array header in the ntfs record before calling this function, otherwise it 103 * will fail (the header needs to contain the position of the update sequence 104 * array together with the number of elements in the array). You also need to 105 * initialise the update sequence number before calling this function 106 * otherwise a random word will be used (whatever was in the record at that 107 * position at that time). 108 */ 109 int pre_write_mst_fixup(NTFS_RECORD *b, const u32 size) 110 { 111 le16 *usa_pos, *data_pos; 112 u16 usa_ofs, usa_count, usn; 113 le16 le_usn; 114 115 /* Sanity check + only fixup if it makes sense. */ 116 if (!b || ntfs_is_baad_record(b->magic) || 117 ntfs_is_hole_record(b->magic)) 118 return -EINVAL; 119 /* Setup the variables. */ 120 usa_ofs = le16_to_cpu(b->usa_ofs); 121 /* Decrement usa_count to get number of fixups. */ 122 usa_count = le16_to_cpu(b->usa_count) - 1; 123 /* Size and alignment checks. */ 124 if ( size & (NTFS_BLOCK_SIZE - 1) || 125 usa_ofs & 1 || 126 usa_ofs + (usa_count * 2) > size || 127 (size >> NTFS_BLOCK_SIZE_BITS) != usa_count) 128 return -EINVAL; 129 /* Position of usn in update sequence array. */ 130 usa_pos = (le16*)((u8*)b + usa_ofs); 131 /* 132 * Cyclically increment the update sequence number 133 * (skipping 0 and -1, i.e. 0xffff). 134 */ 135 usn = le16_to_cpup(usa_pos) + 1; 136 if (usn == 0xffff || !usn) 137 usn = 1; 138 le_usn = cpu_to_le16(usn); 139 *usa_pos = le_usn; 140 /* Position in data of first u16 that needs fixing up. */ 141 data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1; 142 /* Fixup all sectors. */ 143 while (usa_count--) { 144 /* 145 * Increment the position in the usa and save the 146 * original data from the data buffer into the usa. 147 */ 148 *(++usa_pos) = *data_pos; 149 /* Apply fixup to data. */ 150 *data_pos = le_usn; 151 /* Increment position in data as well. */ 152 data_pos += NTFS_BLOCK_SIZE/sizeof(le16); 153 } 154 return 0; 155 } 156 157 /** 158 * post_write_mst_fixup - fast deprotect multi sector transfer protected data 159 * @b: pointer to the data to deprotect 160 * 161 * Perform the necessary post write multi sector transfer fixup, not checking 162 * for any errors, because we assume we have just used pre_write_mst_fixup(), 163 * thus the data will be fine or we would never have gotten here. 164 */ 165 void post_write_mst_fixup(NTFS_RECORD *b) 166 { 167 le16 *usa_pos, *data_pos; 168 169 u16 usa_ofs = le16_to_cpu(b->usa_ofs); 170 u16 usa_count = le16_to_cpu(b->usa_count) - 1; 171 172 /* Position of usn in update sequence array. */ 173 usa_pos = (le16*)b + usa_ofs/sizeof(le16); 174 175 /* Position in protected data of first u16 that needs fixing up. */ 176 data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1; 177 178 /* Fixup all sectors. */ 179 while (usa_count--) { 180 /* 181 * Increment position in usa and restore original data from 182 * the usa into the data buffer. 183 */ 184 *data_pos = *(++usa_pos); 185 186 /* Increment position in data as well. */ 187 data_pos += NTFS_BLOCK_SIZE/sizeof(le16); 188 } 189 } 190