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                         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
 115 out:
 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
 126 static 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
 218 exit_lookup:
 219         kfree(dire);
 220         return d_splice_alias(inode, dentry);
 221
 222 data_error:
 223         err = -EIO;
 224
 225 read_failure:
 226         ERROR("Unable to read directory block [%llx:%x]\n",
 227                 squashfs_i(dir)->start + msblk->directory_table,
 228                 squashfs_i(dir)->offset);
 229 failed:
 230         kfree(dire);
 231         return ERR_PTR(err);
 232 }
 233
 234
 235 const struct inode_operations squashfs_dir_inode_ops = {
 236         .lookup = squashfs_lookup,
 237         .listxattr = squashfs_listxattr
 238 };