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Linux/fs/squashfs/fragment.c

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  1 /*
  2  * Squashfs - a compressed read only filesystem for Linux
  3  *
  4  * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
  5  * Phillip Lougher <phillip@squashfs.org.uk>
  6  *
  7  * This program is free software; you can redistribute it and/or
  8  * modify it under the terms of the GNU General Public License
  9  * as published by the Free Software Foundation; either version 2,
 10  * or (at your option) any later version.
 11  *
 12  * This program is distributed in the hope that it will be useful,
 13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 15  * GNU General Public License for more details.
 16  *
 17  * You should have received a copy of the GNU General Public License
 18  * along with this program; if not, write to the Free Software
 19  * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 20  *
 21  * fragment.c
 22  */
 23 
 24 /*
 25  * This file implements code to handle compressed fragments (tail-end packed
 26  * datablocks).
 27  *
 28  * Regular files contain a fragment index which is mapped to a fragment
 29  * location on disk and compressed size using a fragment lookup table.
 30  * Like everything in Squashfs this fragment lookup table is itself stored
 31  * compressed into metadata blocks.  A second index table is used to locate
 32  * these.  This second index table for speed of access (and because it
 33  * is small) is read at mount time and cached in memory.
 34  */
 35 
 36 #include <linux/fs.h>
 37 #include <linux/vfs.h>
 38 #include <linux/slab.h>
 39 
 40 #include "squashfs_fs.h"
 41 #include "squashfs_fs_sb.h"
 42 #include "squashfs.h"
 43 
 44 /*
 45  * Look-up fragment using the fragment index table.  Return the on disk
 46  * location of the fragment and its compressed size
 47  */
 48 int squashfs_frag_lookup(struct super_block *sb, unsigned int fragment,
 49                                 u64 *fragment_block)
 50 {
 51         struct squashfs_sb_info *msblk = sb->s_fs_info;
 52         int block, offset, size;
 53         struct squashfs_fragment_entry fragment_entry;
 54         u64 start_block;
 55 
 56         if (fragment >= msblk->fragments)
 57                 return -EIO;
 58         block = SQUASHFS_FRAGMENT_INDEX(fragment);
 59         offset = SQUASHFS_FRAGMENT_INDEX_OFFSET(fragment);
 60 
 61         start_block = le64_to_cpu(msblk->fragment_index[block]);
 62 
 63         size = squashfs_read_metadata(sb, &fragment_entry, &start_block,
 64                                         &offset, sizeof(fragment_entry));
 65         if (size < 0)
 66                 return size;
 67 
 68         *fragment_block = le64_to_cpu(fragment_entry.start_block);
 69         return squashfs_block_size(fragment_entry.size);
 70 }
 71 
 72 
 73 /*
 74  * Read the uncompressed fragment lookup table indexes off disk into memory
 75  */
 76 __le64 *squashfs_read_fragment_index_table(struct super_block *sb,
 77         u64 fragment_table_start, u64 next_table, unsigned int fragments)
 78 {
 79         unsigned int length = SQUASHFS_FRAGMENT_INDEX_BYTES(fragments);
 80         __le64 *table;
 81 
 82         /*
 83          * Sanity check, length bytes should not extend into the next table -
 84          * this check also traps instances where fragment_table_start is
 85          * incorrectly larger than the next table start
 86          */
 87         if (fragment_table_start + length > next_table)
 88                 return ERR_PTR(-EINVAL);
 89 
 90         table = squashfs_read_table(sb, fragment_table_start, length);
 91 
 92         /*
 93          * table[0] points to the first fragment table metadata block, this
 94          * should be less than fragment_table_start
 95          */
 96         if (!IS_ERR(table) && le64_to_cpu(table[0]) >= fragment_table_start) {
 97                 kfree(table);
 98                 return ERR_PTR(-EINVAL);
 99         }
100 
101         return table;
102 }
103 

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