fs/squashfs/namei.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  * Squashfs - a compressed read only filesystem for Linux
0004  *
0005  * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
0006  * Phillip Lougher <phillip@squashfs.org.uk>
0007  *
0008  * namei.c
0009  */
0010
0011 /*
0012  * This file implements code to do filename lookup in directories.
0013  *
0014  * Like inodes, directories are packed into compressed metadata blocks, stored
0015  * in a directory table.  Directories are accessed using the start address of
0016  * the metablock containing the directory and the offset into the
0017  * decompressed block (<block, offset>).
0018  *
0019  * Directories are organised in a slightly complex way, and are not simply
0020  * a list of file names.  The organisation takes advantage of the
0021  * fact that (in most cases) the inodes of the files will be in the same
0022  * compressed metadata block, and therefore, can share the start block.
0023  * Directories are therefore organised in a two level list, a directory
0024  * header containing the shared start block value, and a sequence of directory
0025  * entries, each of which share the shared start block.  A new directory header
0026  * is written once/if the inode start block changes.  The directory
0027  * header/directory entry list is repeated as many times as necessary.
0028  *
0029  * Directories are sorted, and can contain a directory index to speed up
0030  * file lookup.  Directory indexes store one entry per metablock, each entry
0031  * storing the index/filename mapping to the first directory header
0032  * in each metadata block.  Directories are sorted in alphabetical order,
0033  * and at lookup the index is scanned linearly looking for the first filename
0034  * alphabetically larger than the filename being looked up.  At this point the
0035  * location of the metadata block the filename is in has been found.
0036  * The general idea of the index is ensure only one metadata block needs to be
0037  * decompressed to do a lookup irrespective of the length of the directory.
0038  * This scheme has the advantage that it doesn't require extra memory overhead
0039  * and doesn't require much extra storage on disk.
0040  */
0041
0042 #include <linux/fs.h>
0043 #include <linux/vfs.h>
0044 #include <linux/slab.h>
0045 #include <linux/string.h>
0046 #include <linux/dcache.h>
0047 #include <linux/xattr.h>
0048
0049 #include "squashfs_fs.h"
0050 #include "squashfs_fs_sb.h"
0051 #include "squashfs_fs_i.h"
0052 #include "squashfs.h"
0053 #include "xattr.h"
0054
0055 /*
0056  * Lookup name in the directory index, returning the location of the metadata
0057  * block containing it, and the directory index this represents.
0058  *
0059  * If we get an error reading the index then return the part of the index
0060  * (if any) we have managed to read - the index isn't essential, just
0061  * quicker.
0062  */
0063 static int get_dir_index_using_name(struct super_block *sb,
0064             u64 *next_block, int *next_offset, u64 index_start,
0065             int index_offset, int i_count, const char *name,
0066             int len)
0067 {
0068     struct squashfs_sb_info *msblk = sb->s_fs_info;
0069     int i, length = 0, err;
0070     unsigned int size;
0071     struct squashfs_dir_index *index;
0072     char *str;
0073
0074     TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
0075
0076     index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
0077     if (index == NULL) {
0078         ERROR("Failed to allocate squashfs_dir_index\n");
0079         goto out;
0080     }
0081
0082     str = &index->name[SQUASHFS_NAME_LEN + 1];
0083     strncpy(str, name, len);
0084     str[len] = '\0';
0085
0086     for (i = 0; i < i_count; i++) {
0087         err = squashfs_read_metadata(sb, index, &index_start,
0088                     &index_offset, sizeof(*index));
0089         if (err < 0)
0090             break;
0091
0092
0093         size = le32_to_cpu(index->size) + 1;
0094         if (size > SQUASHFS_NAME_LEN)
0095             break;
0096
0097         err = squashfs_read_metadata(sb, index->name, &index_start,
0098                     &index_offset, size);
0099         if (err < 0)
0100             break;
0101
0102         index->name[size] = '\0';
0103
0104         if (strcmp(index->name, str) > 0)
0105             break;
0106
0107         length = le32_to_cpu(index->index);
0108         *next_block = le32_to_cpu(index->start_block) +
0109                     msblk->directory_table;
0110     }
0111
0112     *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
0113     kfree(index);
0114
0115 out:
0116     /*
0117      * Return index (f_pos) of the looked up metadata block.  Translate
0118      * from internal f_pos to external f_pos which is offset by 3 because
0119      * we invent "." and ".." entries which are not actually stored in the
0120      * directory.
0121      */
0122     return length + 3;
0123 }
0124
0125
0126 static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
0127                  unsigned int flags)
0128 {
0129     const unsigned char *name = dentry->d_name.name;
0130     int len = dentry->d_name.len;
0131     struct inode *inode = NULL;
0132     struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
0133     struct squashfs_dir_header dirh;
0134     struct squashfs_dir_entry *dire;
0135     u64 block = squashfs_i(dir)->start + msblk->directory_table;
0136     int offset = squashfs_i(dir)->offset;
0137     int err, length;
0138     unsigned int dir_count, size;
0139
0140     TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset);
0141
0142     dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
0143     if (dire == NULL) {
0144         ERROR("Failed to allocate squashfs_dir_entry\n");
0145         return ERR_PTR(-ENOMEM);
0146     }
0147
0148     if (len > SQUASHFS_NAME_LEN) {
0149         err = -ENAMETOOLONG;
0150         goto failed;
0151     }
0152
0153     length = get_dir_index_using_name(dir->i_sb, &block, &offset,
0154                 squashfs_i(dir)->dir_idx_start,
0155                 squashfs_i(dir)->dir_idx_offset,
0156                 squashfs_i(dir)->dir_idx_cnt, name, len);
0157
0158     while (length < i_size_read(dir)) {
0159         /*
0160          * Read directory header.
0161          */
0162         err = squashfs_read_metadata(dir->i_sb, &dirh, &block,
0163                 &offset, sizeof(dirh));
0164         if (err < 0)
0165             goto read_failure;
0166
0167         length += sizeof(dirh);
0168
0169         dir_count = le32_to_cpu(dirh.count) + 1;
0170
0171         if (dir_count > SQUASHFS_DIR_COUNT)
0172             goto data_error;
0173
0174         while (dir_count--) {
0175             /*
0176              * Read directory entry.
0177              */
0178             err = squashfs_read_metadata(dir->i_sb, dire, &block,
0179                     &offset, sizeof(*dire));
0180             if (err < 0)
0181                 goto read_failure;
0182
0183             size = le16_to_cpu(dire->size) + 1;
0184
0185             /* size should never be larger than SQUASHFS_NAME_LEN */
0186             if (size > SQUASHFS_NAME_LEN)
0187                 goto data_error;
0188
0189             err = squashfs_read_metadata(dir->i_sb, dire->name,
0190                     &block, &offset, size);
0191             if (err < 0)
0192                 goto read_failure;
0193
0194             length += sizeof(*dire) + size;
0195
0196             if (name[0] < dire->name[0])
0197                 goto exit_lookup;
0198
0199             if (len == size && !strncmp(name, dire->name, len)) {
0200                 unsigned int blk, off, ino_num;
0201                 long long ino;
0202                 blk = le32_to_cpu(dirh.start_block);
0203                 off = le16_to_cpu(dire->offset);
0204                 ino_num = le32_to_cpu(dirh.inode_number) +
0205                     (short) le16_to_cpu(dire->inode_number);
0206                 ino = SQUASHFS_MKINODE(blk, off);
0207
0208                 TRACE("calling squashfs_iget for directory "
0209                     "entry %s, inode  %x:%x, %d\n", name,
0210                     blk, off, ino_num);
0211
0212                 inode = squashfs_iget(dir->i_sb, ino, ino_num);
0213                 goto exit_lookup;
0214             }
0215         }
0216     }
0217
0218 exit_lookup:
0219     kfree(dire);
0220     return d_splice_alias(inode, dentry);
0221
0222 data_error:
0223     err = -EIO;
0224
0225 read_failure:
0226     ERROR("Unable to read directory block [%llx:%x]\n",
0227         squashfs_i(dir)->start + msblk->directory_table,
0228         squashfs_i(dir)->offset);
0229 failed:
0230     kfree(dire);
0231     return ERR_PTR(err);
0232 }
0233
0234
0235 const struct inode_operations squashfs_dir_inode_ops = {
0236     .lookup = squashfs_lookup,
0237     .listxattr = squashfs_listxattr
0238 };