LXR linux/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 */
  45int 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}
 103