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 * dir.c
9 */
10
11/*
12 * This file implements code to read directories from disk.
13 *
14 * See namei.c for a description of directory organisation on disk.
15 */
16
17#include <linux/fs.h>
18#include <linux/vfs.h>
19#include <linux/slab.h>
20
21#include "squashfs_fs.h"
22#include "squashfs_fs_sb.h"
23#include "squashfs_fs_i.h"
24#include "squashfs.h"
25
26static const unsigned char squashfs_filetype_table[] = {
27	DT_UNKNOWN, DT_DIR, DT_REG, DT_LNK, DT_BLK, DT_CHR, DT_FIFO, DT_SOCK
28};
29
30/*
31 * Lookup offset (f_pos) in the directory index, returning the
32 * metadata block containing it.
33 *
34 * If we get an error reading the index then return the part of the index
35 * (if any) we have managed to read - the index isn't essential, just
36 * quicker.
37 */
38static int get_dir_index_using_offset(struct super_block *sb,
39	u64 *next_block, int *next_offset, u64 index_start, int index_offset,
40	int i_count, u64 f_pos)
41{
42	struct squashfs_sb_info *msblk = sb->s_fs_info;
43	int err, i, index, length = 0;
44	unsigned int size;
45	struct squashfs_dir_index dir_index;
46
47	TRACE("Entered get_dir_index_using_offset, i_count %d, f_pos %lld\n",
48					i_count, f_pos);
49
50	/*
51	 * Translate from external f_pos to the internal f_pos.  This
52	 * is offset by 3 because we invent "." and ".." entries which are
53	 * not actually stored in the directory.
54	 */
55	if (f_pos <= 3)
56		return f_pos;
57	f_pos -= 3;
58
59	for (i = 0; i < i_count; i++) {
60		err = squashfs_read_metadata(sb, &dir_index, &index_start,
61				&index_offset, sizeof(dir_index));
62		if (err < 0)
63			break;
64
65		index = le32_to_cpu(dir_index.index);
66		if (index > f_pos)
67			/*
68			 * Found the index we're looking for.
69			 */
70			break;
71
72		size = le32_to_cpu(dir_index.size) + 1;
73
74		/* size should never be larger than SQUASHFS_NAME_LEN */
75		if (size > SQUASHFS_NAME_LEN)
76			break;
77
78		err = squashfs_read_metadata(sb, NULL, &index_start,
79				&index_offset, size);
80		if (err < 0)
81			break;
82
83		length = index;
84		*next_block = le32_to_cpu(dir_index.start_block) +
85					msblk->directory_table;
86	}
87
88	*next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
89
90	/*
91	 * Translate back from internal f_pos to external f_pos.
92	 */
93	return length + 3;
94}
95
96
97static int squashfs_readdir(struct file *file, struct dir_context *ctx)
98{
99	struct inode *inode = file_inode(file);
100	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
101	u64 block = squashfs_i(inode)->start + msblk->directory_table;
102	int offset = squashfs_i(inode)->offset, length, err;
103	unsigned int inode_number, dir_count, size, type;
104	struct squashfs_dir_header dirh;
105	struct squashfs_dir_entry *dire;
106
107	TRACE("Entered squashfs_readdir [%llx:%x]\n", block, offset);
108
109	dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
110	if (dire == NULL) {
111		ERROR("Failed to allocate squashfs_dir_entry\n");
112		goto finish;
113	}
114
115	/*
116	 * Return "." and  ".." entries as the first two filenames in the
117	 * directory.  To maximise compression these two entries are not
118	 * stored in the directory, and so we invent them here.
119	 *
120	 * It also means that the external f_pos is offset by 3 from the
121	 * on-disk directory f_pos.
122	 */
123	while (ctx->pos < 3) {
124		char *name;
125		int i_ino;
126
127		if (ctx->pos == 0) {
128			name = ".";
129			size = 1;
130			i_ino = inode->i_ino;
131		} else {
132			name = "..";
133			size = 2;
134			i_ino = squashfs_i(inode)->parent;
135		}
136
137		if (!dir_emit(ctx, name, size, i_ino,
138				squashfs_filetype_table[1]))
139			goto finish;
140
141		ctx->pos += size;
142	}
143
144	length = get_dir_index_using_offset(inode->i_sb, &block, &offset,
145				squashfs_i(inode)->dir_idx_start,
146				squashfs_i(inode)->dir_idx_offset,
147				squashfs_i(inode)->dir_idx_cnt,
148				ctx->pos);
149
150	while (length < i_size_read(inode)) {
151		/*
152		 * Read directory header
153		 */
154		err = squashfs_read_metadata(inode->i_sb, &dirh, &block,
155					&offset, sizeof(dirh));
156		if (err < 0)
157			goto failed_read;
158
159		length += sizeof(dirh);
160
161		dir_count = le32_to_cpu(dirh.count) + 1;
162
163		if (dir_count > SQUASHFS_DIR_COUNT)
164			goto failed_read;
165
166		while (dir_count--) {
167			/*
168			 * Read directory entry.
169			 */
170			err = squashfs_read_metadata(inode->i_sb, dire, &block,
171					&offset, sizeof(*dire));
172			if (err < 0)
173				goto failed_read;
174
175			size = le16_to_cpu(dire->size) + 1;
176
177			/* size should never be larger than SQUASHFS_NAME_LEN */
178			if (size > SQUASHFS_NAME_LEN)
179				goto failed_read;
180
181			err = squashfs_read_metadata(inode->i_sb, dire->name,
182					&block, &offset, size);
183			if (err < 0)
184				goto failed_read;
185
186			length += sizeof(*dire) + size;
187
188			if (ctx->pos >= length)
189				continue;
190
191			dire->name[size] = '\0';
192			inode_number = le32_to_cpu(dirh.inode_number) +
193				((short) le16_to_cpu(dire->inode_number));
194			type = le16_to_cpu(dire->type);
195
196			if (type > SQUASHFS_MAX_DIR_TYPE)
197				goto failed_read;
198
199			if (!dir_emit(ctx, dire->name, size,
200					inode_number,
201					squashfs_filetype_table[type]))
202				goto finish;
203
204			ctx->pos = length;
205		}
206	}
207
208finish:
209	kfree(dire);
210	return 0;
211
212failed_read:
213	ERROR("Unable to read directory block [%llx:%x]\n", block, offset);
214	kfree(dire);
215	return 0;
216}
217
218
219const struct file_operations squashfs_dir_ops = {
220	.read = generic_read_dir,
221	.iterate_shared = squashfs_readdir,
222	.llseek = generic_file_llseek,
223};
224