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Linux/fs/squashfs/id.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  * 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 }
103 

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