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 */
 63static 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
109out:
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
120static 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
212exit_lookup:
213	kfree(dire);
214	return d_splice_alias(inode, dentry);
215
216data_error:
217	err = -EIO;
218
219read_failure:
220	ERROR("Unable to read directory block [%llx:%x]\n",
221		squashfs_i(dir)->start + msblk->directory_table,
222		squashfs_i(dir)->offset);
223failed:
224	kfree(dire);
225	return ERR_PTR(err);
226}
227
228
229const struct inode_operations squashfs_dir_inode_ops = {
230	.lookup = squashfs_lookup,
231	.listxattr = squashfs_listxattr
232};