LXR linux/fs/squashfs/namei.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 * namei.c
   9 */
  10
  11/*
  12 * This file implements code to do filename lookup in directories.
  13 *
  14 * Like inodes, directories are packed into compressed metadata blocks, stored
  15 * in a directory table.  Directories are accessed using the start address of
  16 * the metablock containing the directory and the offset into the
  17 * decompressed block (<block, offset>).
  18 *
  19 * Directories are organised in a slightly complex way, and are not simply
  20 * a list of file names.  The organisation takes advantage of the
  21 * fact that (in most cases) the inodes of the files will be in the same
  22 * compressed metadata block, and therefore, can share the start block.
  23 * Directories are therefore organised in a two level list, a directory
  24 * header containing the shared start block value, and a sequence of directory
  25 * entries, each of which share the shared start block.  A new directory header
  26 * is written once/if the inode start block changes.  The directory
  27 * header/directory entry list is repeated as many times as necessary.
  28 *
  29 * Directories are sorted, and can contain a directory index to speed up
  30 * file lookup.  Directory indexes store one entry per metablock, each entry
  31 * storing the index/filename mapping to the first directory header
  32 * in each metadata block.  Directories are sorted in alphabetical order,
  33 * and at lookup the index is scanned linearly looking for the first filename
  34 * alphabetically larger than the filename being looked up.  At this point the
  35 * location of the metadata block the filename is in has been found.
  36 * The general idea of the index is ensure only one metadata block needs to be
  37 * decompressed to do a lookup irrespective of the length of the directory.
  38 * This scheme has the advantage that it doesn't require extra memory overhead
  39 * and doesn't require much extra storage on disk.
  40 */
  41
  42#include <linux/fs.h>
  43#include <linux/vfs.h>
  44#include <linux/slab.h>
  45#include <linux/string.h>
  46#include <linux/dcache.h>
  47#include <linux/xattr.h>
  48
  49#include "squashfs_fs.h"
  50#include "squashfs_fs_sb.h"
  51#include "squashfs_fs_i.h"
  52#include "squashfs.h"
  53#include "xattr.h"
  54
  55/*
  56 * Lookup name in the directory index, returning the location of the metadata
  57 * block containing it, and the directory index this represents.
  58 *
  59 * If we get an error reading the index then return the part of the index
  60 * (if any) we have managed to read - the index isn't essential, just
  61 * quicker.
  62 */
  63static int get_dir_index_using_name(struct super_block *sb,
  64                        u64 *next_block, int *next_offset, u64 index_start,
  65                        int index_offset, int i_count, const char *name,
  66                        int len)
  67{
  68        struct squashfs_sb_info *msblk = sb->s_fs_info;
  69        int i, length = 0, err;
  70        unsigned int size;
  71        struct squashfs_dir_index *index;
  72        char *str;
  73
  74        TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
  75
  76        index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
  77        if (index == NULL) {
  78                ERROR("Failed to allocate squashfs_dir_index\n");
  79                goto out;
  80        }
  81
  82        str = &index->name[SQUASHFS_NAME_LEN + 1];
  83        strncpy(str, name, len);
  84        str[len] = '\0';
  85
  86        for (i = 0; i < i_count; i++) {
  87                err = squashfs_read_metadata(sb, index, &index_start,
  88                                        &index_offset, sizeof(*index));
  89                if (err < 0)
  90                        break;
  91
  92
  93                size = le32_to_cpu(index->size) + 1;
  94                if (size > SQUASHFS_NAME_LEN)
  95                        break;
  96
  97                err = squashfs_read_metadata(sb, index->name, &index_start,
  98                                        &index_offset, size);
  99                if (err < 0)
 100                        break;
 101
 102                index->name[size] = '\0';
 103
 104                if (strcmp(index->name, str) > 0)
 105                        break;
 106
 107                length = le32_to_cpu(index->index);
 108                *next_block = le32_to_cpu(index->start_block) +
 109                                        msblk->directory_table;
 110        }
 111
 112        *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
 113        kfree(index);
 114
 115out:
 116        /*
 117         * Return index (f_pos) of the looked up metadata block.  Translate
 118         * from internal f_pos to external f_pos which is offset by 3 because
 119         * we invent "." and ".." entries which are not actually stored in the
 120         * directory.
 121         */
 122        return length + 3;
 123}
 124
 125
 126static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
 127                                 unsigned int flags)
 128{
 129        const unsigned char *name = dentry->d_name.name;
 130        int len = dentry->d_name.len;
 131        struct inode *inode = NULL;
 132        struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
 133        struct squashfs_dir_header dirh;
 134        struct squashfs_dir_entry *dire;
 135        u64 block = squashfs_i(dir)->start + msblk->directory_table;
 136        int offset = squashfs_i(dir)->offset;
 137        int err, length;
 138        unsigned int dir_count, size;
 139
 140        TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset);
 141
 142        dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
 143        if (dire == NULL) {
 144                ERROR("Failed to allocate squashfs_dir_entry\n");
 145                return ERR_PTR(-ENOMEM);
 146        }
 147
 148        if (len > SQUASHFS_NAME_LEN) {
 149                err = -ENAMETOOLONG;
 150                goto failed;
 151        }
 152
 153        length = get_dir_index_using_name(dir->i_sb, &block, &offset,
 154                                squashfs_i(dir)->dir_idx_start,
 155                                squashfs_i(dir)->dir_idx_offset,
 156                                squashfs_i(dir)->dir_idx_cnt, name, len);
 157
 158        while (length < i_size_read(dir)) {
 159                /*
 160                 * Read directory header.
 161                 */
 162                err = squashfs_read_metadata(dir->i_sb, &dirh, &block,
 163                                &offset, sizeof(dirh));
 164                if (err < 0)
 165                        goto read_failure;
 166
 167                length += sizeof(dirh);
 168
 169                dir_count = le32_to_cpu(dirh.count) + 1;
 170
 171                if (dir_count > SQUASHFS_DIR_COUNT)
 172                        goto data_error;
 173
 174                while (dir_count--) {
 175                        /*
 176                         * Read directory entry.
 177                         */
 178                        err = squashfs_read_metadata(dir->i_sb, dire, &block,
 179                                        &offset, sizeof(*dire));
 180                        if (err < 0)
 181                                goto read_failure;
 182
 183                        size = le16_to_cpu(dire->size) + 1;
 184
 185                        /* size should never be larger than SQUASHFS_NAME_LEN */
 186                        if (size > SQUASHFS_NAME_LEN)
 187                                goto data_error;
 188
 189                        err = squashfs_read_metadata(dir->i_sb, dire->name,
 190                                        &block, &offset, size);
 191                        if (err < 0)
 192                                goto read_failure;
 193
 194                        length += sizeof(*dire) + size;
 195
 196                        if (name[0] < dire->name[0])
 197                                goto exit_lookup;
 198
 199                        if (len == size && !strncmp(name, dire->name, len)) {
 200                                unsigned int blk, off, ino_num;
 201                                long long ino;
 202                                blk = le32_to_cpu(dirh.start_block);
 203                                off = le16_to_cpu(dire->offset);
 204                                ino_num = le32_to_cpu(dirh.inode_number) +
 205                                        (short) le16_to_cpu(dire->inode_number);
 206                                ino = SQUASHFS_MKINODE(blk, off);
 207
 208                                TRACE("calling squashfs_iget for directory "
 209                                        "entry %s, inode  %x:%x, %d\n", name,
 210                                        blk, off, ino_num);
 211
 212                                inode = squashfs_iget(dir->i_sb, ino, ino_num);
 213                                goto exit_lookup;
 214                        }
 215                }
 216        }
 217
 218exit_lookup:
 219        kfree(dire);
 220        return d_splice_alias(inode, dentry);
 221
 222data_error:
 223        err = -EIO;
 224
 225read_failure:
 226        ERROR("Unable to read directory block [%llx:%x]\n",
 227                squashfs_i(dir)->start + msblk->directory_table,
 228                squashfs_i(dir)->offset);
 229failed:
 230        kfree(dire);
 231        return ERR_PTR(err);
 232}
 233
 234
 235const struct inode_operations squashfs_dir_inode_ops = {
 236        .lookup = squashfs_lookup,
 237        .listxattr = squashfs_listxattr
 238};
 239