xref: /openbmc/linux/fs/squashfs/namei.c (revision 68252eb5)
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  */
get_dir_index_using_name(struct super_block * sb,u64 * next_block,int * next_offset,u64 index_start,int index_offset,int i_count,const char * name,int len)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 
squashfs_lookup(struct inode * dir,struct dentry * dentry,unsigned int flags)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 };
239