fs/squashfs/fragment.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Squashfs - a compressed read only filesystem for Linux
   4  *
   5  * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
   6  * Phillip Lougher <phillip@squashfs.org.uk>
   7  *
   8  * fragment.c
   9  */
  10
  11 /*
  12  * This file implements code to handle compressed fragments (tail-end packed
  13  * datablocks).
  14  *
  15  * Regular files contain a fragment index which is mapped to a fragment
  16  * location on disk and compressed size using a fragment lookup table.
  17  * Like everything in Squashfs this fragment lookup table is itself stored
  18  * compressed into metadata blocks.  A second index table is used to locate
  19  * these.  This second index table for speed of access (and because it
  20  * is small) is read at mount time and cached in memory.
  21  */
  22
  23 #include <linux/fs.h>
  24 #include <linux/vfs.h>
  25 #include <linux/slab.h>
  26
  27 #include "squashfs_fs.h"
  28 #include "squashfs_fs_sb.h"
  29 #include "squashfs.h"
  30
  31 /*
  32  * Look-up fragment using the fragment index table.  Return the on disk
  33  * location of the fragment and its compressed size
  34  */
  35 int squashfs_frag_lookup(struct super_block *sb, unsigned int fragment,
  36                                 u64 *fragment_block)
  37 {
  38         struct squashfs_sb_info *msblk = sb->s_fs_info;
  39         int block, offset, size;
  40         struct squashfs_fragment_entry fragment_entry;
  41         u64 start_block;
  42
  43         if (fragment >= msblk->fragments)
  44                 return -EIO;
  45         block = SQUASHFS_FRAGMENT_INDEX(fragment);
  46         offset = SQUASHFS_FRAGMENT_INDEX_OFFSET(fragment);
  47
  48         start_block = le64_to_cpu(msblk->fragment_index[block]);
  49
  50         size = squashfs_read_metadata(sb, &fragment_entry, &start_block,
  51                                         &offset, sizeof(fragment_entry));
  52         if (size < 0)
  53                 return size;
  54
  55         *fragment_block = le64_to_cpu(fragment_entry.start_block);
  56         return squashfs_block_size(fragment_entry.size);
  57 }
  58
  59
  60 /*
  61  * Read the uncompressed fragment lookup table indexes off disk into memory
  62  */
  63 __le64 *squashfs_read_fragment_index_table(struct super_block *sb,
  64         u64 fragment_table_start, u64 next_table, unsigned int fragments)
  65 {
  66         unsigned int length = SQUASHFS_FRAGMENT_INDEX_BYTES(fragments);
  67         __le64 *table;
  68
  69         /*
  70          * Sanity check, length bytes should not extend into the next table -
  71          * this check also traps instances where fragment_table_start is
  72          * incorrectly larger than the next table start
  73          */
  74         if (fragment_table_start + length > next_table)
  75                 return ERR_PTR(-EINVAL);
  76
  77         table = squashfs_read_table(sb, fragment_table_start, length);
  78
  79         /*
  80          * table[0] points to the first fragment table metadata block, this
  81          * should be less than fragment_table_start
  82          */
  83         if (!IS_ERR(table) && le64_to_cpu(table[0]) >= fragment_table_start) {
  84                 kfree(table);
  85                 return ERR_PTR(-EINVAL);
  86         }
  87
  88         return table;
  89 }