1 files changed, 189 insertions, 0 deletions
diff --git a/fs/ntfs/mst.c b/fs/ntfs/mst.c
new file mode 100644
index 000000000..16b3c884a
--- /dev/null
+++ b/fs/ntfs/mst.c
@@ -0,0 +1,189 @@
+// 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);
+	}
+}