fs/squashfs/id.c

   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  * id.c
  22  */
  23
  24 /*
  25  * This file implements code to handle uids and gids.
  26  *
  27  * For space efficiency regular files store uid and gid indexes, which are
  28  * converted to 32-bit uids/gids using an id look up table.  This table is
  29  * stored compressed into metadata blocks.  A second index table is used to
  30  * locate these.  This second index table for speed of access (and because it
  31  * is small) is read at mount time and cached in memory.
  32  */
  33
  34 #include <linux/fs.h>
  35 #include <linux/vfs.h>
  36 #include <linux/slab.h>
  37
  38 #include "squashfs_fs.h"
  39 #include "squashfs_fs_sb.h"
  40 #include "squashfs.h"
  41
  42 /*
  43  * Map uid/gid index into real 32-bit uid/gid using the id look up table
  44  */
  45 int squashfs_get_id(struct super_block *sb, unsigned int index,
  46                                         unsigned int *id)
  47 {
  48         struct squashfs_sb_info *msblk = sb->s_fs_info;
  49         int block = SQUASHFS_ID_BLOCK(index);
  50         int offset = SQUASHFS_ID_BLOCK_OFFSET(index);
  51         u64 start_block = le64_to_cpu(msblk->id_table[block]);
  52         __le32 disk_id;
  53         int err;
  54
  55         err = squashfs_read_metadata(sb, &disk_id, &start_block, &offset,
  56                                                         sizeof(disk_id));
  57         if (err < 0)
  58                 return err;
  59
  60         *id = le32_to_cpu(disk_id);
  61         return 0;
  62 }
  63
  64
  65 /*
  66  * Read uncompressed id lookup table indexes from disk into memory
  67  */
  68 __le64 *squashfs_read_id_index_table(struct super_block *sb,
  69                 u64 id_table_start, u64 next_table, unsigned short no_ids)
  70 {
  71         unsigned int length = SQUASHFS_ID_BLOCK_BYTES(no_ids);
  72         __le64 *table;
  73
  74         TRACE("In read_id_index_table, length %d\n", length);
  75
  76         /* Sanity check values */
  77
  78         /* there should always be at least one id */
  79         if (no_ids == 0)
  80                 return ERR_PTR(-EINVAL);
  81
  82         /*
  83          * length bytes should not extend into the next table - this check
  84          * also traps instances where id_table_start is incorrectly larger
  85          * than the next table start
  86          */
  87         if (id_table_start + length > next_table)
  88                 return ERR_PTR(-EINVAL);
  89
  90         table = squashfs_read_table(sb, id_table_start, length);
  91
  92         /*
  93          * table[0] points to the first id lookup table metadata block, this
  94          * should be less than id_table_start
  95          */
  96         if (!IS_ERR(table) && le64_to_cpu(table[0]) >= id_table_start) {
  97                 kfree(table);
  98                 return ERR_PTR(-EINVAL);
  99         }
 100
 101         return table;
 102 }