fs/squashfs/fragment.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  * Squashfs - a compressed read only filesystem for Linux
0004  *
0005  * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
0006  * Phillip Lougher <phillip@squashfs.org.uk>
0007  *
0008  * fragment.c
0009  */
0010
0011 /*
0012  * This file implements code to handle compressed fragments (tail-end packed
0013  * datablocks).
0014  *
0015  * Regular files contain a fragment index which is mapped to a fragment
0016  * location on disk and compressed size using a fragment lookup table.
0017  * Like everything in Squashfs this fragment lookup table is itself stored
0018  * compressed into metadata blocks.  A second index table is used to locate
0019  * these.  This second index table for speed of access (and because it
0020  * is small) is read at mount time and cached in memory.
0021  */
0022
0023 #include <linux/fs.h>
0024 #include <linux/vfs.h>
0025 #include <linux/slab.h>
0026
0027 #include "squashfs_fs.h"
0028 #include "squashfs_fs_sb.h"
0029 #include "squashfs.h"
0030
0031 /*
0032  * Look-up fragment using the fragment index table.  Return the on disk
0033  * location of the fragment and its compressed size
0034  */
0035 int squashfs_frag_lookup(struct super_block *sb, unsigned int fragment,
0036                 u64 *fragment_block)
0037 {
0038     struct squashfs_sb_info *msblk = sb->s_fs_info;
0039     int block, offset, size;
0040     struct squashfs_fragment_entry fragment_entry;
0041     u64 start_block;
0042
0043     if (fragment >= msblk->fragments)
0044         return -EIO;
0045     block = SQUASHFS_FRAGMENT_INDEX(fragment);
0046     offset = SQUASHFS_FRAGMENT_INDEX_OFFSET(fragment);
0047
0048     start_block = le64_to_cpu(msblk->fragment_index[block]);
0049
0050     size = squashfs_read_metadata(sb, &fragment_entry, &start_block,
0051                     &offset, sizeof(fragment_entry));
0052     if (size < 0)
0053         return size;
0054
0055     *fragment_block = le64_to_cpu(fragment_entry.start_block);
0056     return squashfs_block_size(fragment_entry.size);
0057 }
0058
0059
0060 /*
0061  * Read the uncompressed fragment lookup table indexes off disk into memory
0062  */
0063 __le64 *squashfs_read_fragment_index_table(struct super_block *sb,
0064     u64 fragment_table_start, u64 next_table, unsigned int fragments)
0065 {
0066     unsigned int length = SQUASHFS_FRAGMENT_INDEX_BYTES(fragments);
0067     __le64 *table;
0068
0069     /*
0070      * Sanity check, length bytes should not extend into the next table -
0071      * this check also traps instances where fragment_table_start is
0072      * incorrectly larger than the next table start
0073      */
0074     if (fragment_table_start + length > next_table)
0075         return ERR_PTR(-EINVAL);
0076
0077     table = squashfs_read_table(sb, fragment_table_start, length);
0078
0079     /*
0080      * table[0] points to the first fragment table metadata block, this
0081      * should be less than fragment_table_start
0082      */
0083     if (!IS_ERR(table) && le64_to_cpu(table[0]) >= fragment_table_start) {
0084         kfree(table);
0085         return ERR_PTR(-EINVAL);
0086     }
0087
0088     return table;
0089 }