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  */
  63 static 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 {
  67         struct squashfs_sb_info *msblk = sb->s_fs_info;
  68         int i, length = 0, err;
  69         unsigned int size;
  70         struct squashfs_dir_index *index;
  71
  72         TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
  73
  74         index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
  75         if (index == NULL) {
  76                 ERROR("Failed to allocate squashfs_dir_index\n");
  77                 goto out;
  78         }
  79
  80         for (i = 0; i < i_count; i++) {
  81                 err = squashfs_read_metadata(sb, index, &index_start,
  82                                         &index_offset, sizeof(*index));
  83                 if (err < 0)
  84                         break;
  85
  86
  87                 size = le32_to_cpu(index->size) + 1;
  88                 if (size > SQUASHFS_NAME_LEN)
  89                         break;
  90
  91                 err = squashfs_read_metadata(sb, index->name, &index_start,
  92                                         &index_offset, size);
  93                 if (err < 0)
  94                         break;
  95
  96                 index->name[size] = '\0';
  97
  98                 if (strcmp(index->name, name) > 0)
  99                         break;
 100
 101                 length = le32_to_cpu(index->index);
 102                 *next_block = le32_to_cpu(index->start_block) +
 103                                         msblk->directory_table;
 104         }
 105
 106         *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
 107         kfree(index);
 108
 109 out:
 110         /*
 111          * Return index (f_pos) of the looked up metadata block.  Translate
 112          * from internal f_pos to external f_pos which is offset by 3 because
 113          * we invent "." and ".." entries which are not actually stored in the
 114          * directory.
 115          */
 116         return length + 3;
 117 }
 118
 119
 120 static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
 121                                  unsigned int flags)
 122 {
 123         const unsigned char *name = dentry->d_name.name;
 124         int len = dentry->d_name.len;
 125         struct inode *inode = NULL;
 126         struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
 127         struct squashfs_dir_header dirh;
 128         struct squashfs_dir_entry *dire;
 129         u64 block = squashfs_i(dir)->start + msblk->directory_table;
 130         int offset = squashfs_i(dir)->offset;
 131         int err, length;
 132         unsigned int dir_count, size;
 133
 134         TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset);
 135
 136         dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
 137         if (dire == NULL) {
 138                 ERROR("Failed to allocate squashfs_dir_entry\n");
 139                 return ERR_PTR(-ENOMEM);
 140         }
 141
 142         if (len > SQUASHFS_NAME_LEN) {
 143                 err = -ENAMETOOLONG;
 144                 goto failed;
 145         }
 146
 147         length = get_dir_index_using_name(dir->i_sb, &block, &offset,
 148                                 squashfs_i(dir)->dir_idx_start,
 149                                 squashfs_i(dir)->dir_idx_offset,
 150                                 squashfs_i(dir)->dir_idx_cnt, name);
 151
 152         while (length < i_size_read(dir)) {
 153                 /*
 154                  * Read directory header.
 155                  */
 156                 err = squashfs_read_metadata(dir->i_sb, &dirh, &block,
 157                                 &offset, sizeof(dirh));
 158                 if (err < 0)
 159                         goto read_failure;
 160
 161                 length += sizeof(dirh);
 162
 163                 dir_count = le32_to_cpu(dirh.count) + 1;
 164
 165                 if (dir_count > SQUASHFS_DIR_COUNT)
 166                         goto data_error;
 167
 168                 while (dir_count--) {
 169                         /*
 170                          * Read directory entry.
 171                          */
 172                         err = squashfs_read_metadata(dir->i_sb, dire, &block,
 173                                         &offset, sizeof(*dire));
 174                         if (err < 0)
 175                                 goto read_failure;
 176
 177                         size = le16_to_cpu(dire->size) + 1;
 178
 179                         /* size should never be larger than SQUASHFS_NAME_LEN */
 180                         if (size > SQUASHFS_NAME_LEN)
 181                                 goto data_error;
 182
 183                         err = squashfs_read_metadata(dir->i_sb, dire->name,
 184                                         &block, &offset, size);
 185                         if (err < 0)
 186                                 goto read_failure;
 187
 188                         length += sizeof(*dire) + size;
 189
 190                         if (name[0] < dire->name[0])
 191                                 goto exit_lookup;
 192
 193                         if (len == size && !strncmp(name, dire->name, len)) {
 194                                 unsigned int blk, off, ino_num;
 195                                 long long ino;
 196                                 blk = le32_to_cpu(dirh.start_block);
 197                                 off = le16_to_cpu(dire->offset);
 198                                 ino_num = le32_to_cpu(dirh.inode_number) +
 199                                         (short) le16_to_cpu(dire->inode_number);
 200                                 ino = SQUASHFS_MKINODE(blk, off);
 201
 202                                 TRACE("calling squashfs_iget for directory "
 203                                         "entry %s, inode  %x:%x, %d\n", name,
 204                                         blk, off, ino_num);
 205
 206                                 inode = squashfs_iget(dir->i_sb, ino, ino_num);
 207                                 goto exit_lookup;
 208                         }
 209                 }
 210         }
 211
 212 exit_lookup:
 213         kfree(dire);
 214         return d_splice_alias(inode, dentry);
 215
 216 data_error:
 217         err = -EIO;
 218
 219 read_failure:
 220         ERROR("Unable to read directory block [%llx:%x]\n",
 221                 squashfs_i(dir)->start + msblk->directory_table,
 222                 squashfs_i(dir)->offset);
 223 failed:
 224         kfree(dire);
 225         return ERR_PTR(err);
 226 }
 227
 228
 229 const struct inode_operations squashfs_dir_inode_ops = {
 230         .lookup = squashfs_lookup,
 231         .listxattr = squashfs_listxattr
 232 };