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Linux/fs/squashfs/namei.c

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  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                         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 
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 

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