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 };
233
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