xref: /openbmc/linux/fs/ntfs/mst.c (revision b5f184fbdb03b4fcc1141de34dd5ec964ca5d99e)
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