fs/squashfs/dir.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  * dir.c
   9  */
  10
  11 /*
  12  * This file implements code to read directories from disk.
  13  *
  14  * See namei.c for a description of directory organisation on disk.
  15  */
  16
  17 #include <linux/fs.h>
  18 #include <linux/vfs.h>
  19 #include <linux/slab.h>
  20
  21 #include "squashfs_fs.h"
  22 #include "squashfs_fs_sb.h"
  23 #include "squashfs_fs_i.h"
  24 #include "squashfs.h"
  25
  26 static const unsigned char squashfs_filetype_table[] = {
  27         DT_UNKNOWN, DT_DIR, DT_REG, DT_LNK, DT_BLK, DT_CHR, DT_FIFO, DT_SOCK
  28 };
  29
  30 /*
  31  * Lookup offset (f_pos) in the directory index, returning the
  32  * metadata block containing it.
  33  *
  34  * If we get an error reading the index then return the part of the index
  35  * (if any) we have managed to read - the index isn't essential, just
  36  * quicker.
  37  */
  38 static int get_dir_index_using_offset(struct super_block *sb,
  39         u64 *next_block, int *next_offset, u64 index_start, int index_offset,
  40         int i_count, u64 f_pos)
  41 {
  42         struct squashfs_sb_info *msblk = sb->s_fs_info;
  43         int err, i, index, length = 0;
  44         unsigned int size;
  45         struct squashfs_dir_index dir_index;
  46
  47         TRACE("Entered get_dir_index_using_offset, i_count %d, f_pos %lld\n",
  48                                         i_count, f_pos);
  49
  50         /*
  51          * Translate from external f_pos to the internal f_pos.  This
  52          * is offset by 3 because we invent "." and ".." entries which are
  53          * not actually stored in the directory.
  54          */
  55         if (f_pos <= 3)
  56                 return f_pos;
  57         f_pos -= 3;
  58
  59         for (i = 0; i < i_count; i++) {
  60                 err = squashfs_read_metadata(sb, &dir_index, &index_start,
  61                                 &index_offset, sizeof(dir_index));
  62                 if (err < 0)
  63                         break;
  64
  65                 index = le32_to_cpu(dir_index.index);
  66                 if (index > f_pos)
  67                         /*
  68                          * Found the index we're looking for.
  69                          */
  70                         break;
  71
  72                 size = le32_to_cpu(dir_index.size) + 1;
  73
  74                 /* size should never be larger than SQUASHFS_NAME_LEN */
  75                 if (size > SQUASHFS_NAME_LEN)
  76                         break;
  77
  78                 err = squashfs_read_metadata(sb, NULL, &index_start,
  79                                 &index_offset, size);
  80                 if (err < 0)
  81                         break;
  82
  83                 length = index;
  84                 *next_block = le32_to_cpu(dir_index.start_block) +
  85                                         msblk->directory_table;
  86         }
  87
  88         *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
  89
  90         /*
  91          * Translate back from internal f_pos to external f_pos.
  92          */
  93         return length + 3;
  94 }
  95
  96
  97 static int squashfs_readdir(struct file *file, struct dir_context *ctx)
  98 {
  99         struct inode *inode = file_inode(file);
 100         struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
 101         u64 block = squashfs_i(inode)->start + msblk->directory_table;
 102         int offset = squashfs_i(inode)->offset, length, err;
 103         unsigned int inode_number, dir_count, size, type;
 104         struct squashfs_dir_header dirh;
 105         struct squashfs_dir_entry *dire;
 106
 107         TRACE("Entered squashfs_readdir [%llx:%x]\n", block, offset);
 108
 109         dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
 110         if (dire == NULL) {
 111                 ERROR("Failed to allocate squashfs_dir_entry\n");
 112                 goto finish;
 113         }
 114
 115         /*
 116          * Return "." and  ".." entries as the first two filenames in the
 117          * directory.  To maximise compression these two entries are not
 118          * stored in the directory, and so we invent them here.
 119          *
 120          * It also means that the external f_pos is offset by 3 from the
 121          * on-disk directory f_pos.
 122          */
 123         while (ctx->pos < 3) {
 124                 char *name;
 125                 int i_ino;
 126
 127                 if (ctx->pos == 0) {
 128                         name = ".";
 129                         size = 1;
 130                         i_ino = inode->i_ino;
 131                 } else {
 132                         name = "..";
 133                         size = 2;
 134                         i_ino = squashfs_i(inode)->parent;
 135                 }
 136
 137                 if (!dir_emit(ctx, name, size, i_ino,
 138                                 squashfs_filetype_table[1]))
 139                         goto finish;
 140
 141                 ctx->pos += size;
 142         }
 143
 144         length = get_dir_index_using_offset(inode->i_sb, &block, &offset,
 145                                 squashfs_i(inode)->dir_idx_start,
 146                                 squashfs_i(inode)->dir_idx_offset,
 147                                 squashfs_i(inode)->dir_idx_cnt,
 148                                 ctx->pos);
 149
 150         while (length < i_size_read(inode)) {
 151                 /*
 152                  * Read directory header
 153                  */
 154                 err = squashfs_read_metadata(inode->i_sb, &dirh, &block,
 155                                         &offset, sizeof(dirh));
 156                 if (err < 0)
 157                         goto failed_read;
 158
 159                 length += sizeof(dirh);
 160
 161                 dir_count = le32_to_cpu(dirh.count) + 1;
 162
 163                 if (dir_count > SQUASHFS_DIR_COUNT)
 164                         goto failed_read;
 165
 166                 while (dir_count--) {
 167                         /*
 168                          * Read directory entry.
 169                          */
 170                         err = squashfs_read_metadata(inode->i_sb, dire, &block,
 171                                         &offset, sizeof(*dire));
 172                         if (err < 0)
 173                                 goto failed_read;
 174
 175                         size = le16_to_cpu(dire->size) + 1;
 176
 177                         /* size should never be larger than SQUASHFS_NAME_LEN */
 178                         if (size > SQUASHFS_NAME_LEN)
 179                                 goto failed_read;
 180
 181                         err = squashfs_read_metadata(inode->i_sb, dire->name,
 182                                         &block, &offset, size);
 183                         if (err < 0)
 184                                 goto failed_read;
 185
 186                         length += sizeof(*dire) + size;
 187
 188                         if (ctx->pos >= length)
 189                                 continue;
 190
 191                         dire->name[size] = '\0';
 192                         inode_number = le32_to_cpu(dirh.inode_number) +
 193                                 ((short) le16_to_cpu(dire->inode_number));
 194                         type = le16_to_cpu(dire->type);
 195
 196                         if (type > SQUASHFS_MAX_DIR_TYPE)
 197                                 goto failed_read;
 198
 199                         if (!dir_emit(ctx, dire->name, size,
 200                                         inode_number,
 201                                         squashfs_filetype_table[type]))
 202                                 goto finish;
 203
 204                         ctx->pos = length;
 205                 }
 206         }
 207
 208 finish:
 209         kfree(dire);
 210         return 0;
 211
 212 failed_read:
 213         ERROR("Unable to read directory block [%llx:%x]\n", block, offset);
 214         kfree(dire);
 215         return 0;
 216 }
 217
 218
 219 const struct file_operations squashfs_dir_ops = {
 220         .read = generic_read_dir,
 221         .iterate_shared = squashfs_readdir,
 222         .llseek = generic_file_llseek,
 223 };