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  * export.c
9  */
10 
11 /*
12  * This file implements code to make Squashfs filesystems exportable (NFS etc.)
13  *
14  * The export code uses an inode lookup table to map inode numbers passed in
15  * filehandles to an inode location on disk.  This table is stored compressed
16  * into metadata blocks.  A second index table is used to locate these.  This
17  * second index table for speed of access (and because it is small) is read at
18  * mount time and cached in memory.
19  *
20  * The inode lookup table is used only by the export code, inode disk
21  * locations are directly encoded in directories, enabling direct access
22  * without an intermediate lookup for all operations except the export ops.
23  */
24 
25 #include <linux/fs.h>
26 #include <linux/vfs.h>
27 #include <linux/dcache.h>
28 #include <linux/exportfs.h>
29 #include <linux/slab.h>
30 
31 #include "squashfs_fs.h"
32 #include "squashfs_fs_sb.h"
33 #include "squashfs_fs_i.h"
34 #include "squashfs.h"
35 
36 /*
37  * Look-up inode number (ino) in table, returning the inode location.
38  */
squashfs_inode_lookup(struct super_block * sb,int ino_num)39 static long long squashfs_inode_lookup(struct super_block *sb, int ino_num)
40 {
41 	struct squashfs_sb_info *msblk = sb->s_fs_info;
42 	int blk = SQUASHFS_LOOKUP_BLOCK(ino_num - 1);
43 	int offset = SQUASHFS_LOOKUP_BLOCK_OFFSET(ino_num - 1);
44 	u64 start;
45 	__le64 ino;
46 	int err;
47 
48 	TRACE("Entered squashfs_inode_lookup, inode_number = %d\n", ino_num);
49 
50 	if (ino_num == 0 || (ino_num - 1) >= msblk->inodes)
51 		return -EINVAL;
52 
53 	start = le64_to_cpu(msblk->inode_lookup_table[blk]);
54 
55 	err = squashfs_read_metadata(sb, &ino, &start, &offset, sizeof(ino));
56 	if (err < 0)
57 		return err;
58 
59 	TRACE("squashfs_inode_lookup, inode = 0x%llx\n",
60 		(u64) le64_to_cpu(ino));
61 
62 	return le64_to_cpu(ino);
63 }
64 
65 
squashfs_export_iget(struct super_block * sb,unsigned int ino_num)66 static struct dentry *squashfs_export_iget(struct super_block *sb,
67 	unsigned int ino_num)
68 {
69 	long long ino;
70 	struct dentry *dentry = ERR_PTR(-ENOENT);
71 
72 	TRACE("Entered squashfs_export_iget\n");
73 
74 	ino = squashfs_inode_lookup(sb, ino_num);
75 	if (ino >= 0)
76 		dentry = d_obtain_alias(squashfs_iget(sb, ino, ino_num));
77 
78 	return dentry;
79 }
80 
81 
squashfs_fh_to_dentry(struct super_block * sb,struct fid * fid,int fh_len,int fh_type)82 static struct dentry *squashfs_fh_to_dentry(struct super_block *sb,
83 		struct fid *fid, int fh_len, int fh_type)
84 {
85 	if ((fh_type != FILEID_INO32_GEN && fh_type != FILEID_INO32_GEN_PARENT)
86 			|| fh_len < 2)
87 		return NULL;
88 
89 	return squashfs_export_iget(sb, fid->i32.ino);
90 }
91 
92 
squashfs_fh_to_parent(struct super_block * sb,struct fid * fid,int fh_len,int fh_type)93 static struct dentry *squashfs_fh_to_parent(struct super_block *sb,
94 		struct fid *fid, int fh_len, int fh_type)
95 {
96 	if (fh_type != FILEID_INO32_GEN_PARENT || fh_len < 4)
97 		return NULL;
98 
99 	return squashfs_export_iget(sb, fid->i32.parent_ino);
100 }
101 
102 
squashfs_get_parent(struct dentry * child)103 static struct dentry *squashfs_get_parent(struct dentry *child)
104 {
105 	struct inode *inode = d_inode(child);
106 	unsigned int parent_ino = squashfs_i(inode)->parent;
107 
108 	return squashfs_export_iget(inode->i_sb, parent_ino);
109 }
110 
111 
112 /*
113  * Read uncompressed inode lookup table indexes off disk into memory
114  */
squashfs_read_inode_lookup_table(struct super_block * sb,u64 lookup_table_start,u64 next_table,unsigned int inodes)115 __le64 *squashfs_read_inode_lookup_table(struct super_block *sb,
116 		u64 lookup_table_start, u64 next_table, unsigned int inodes)
117 {
118 	unsigned int length = SQUASHFS_LOOKUP_BLOCK_BYTES(inodes);
119 	unsigned int indexes = SQUASHFS_LOOKUP_BLOCKS(inodes);
120 	int n;
121 	__le64 *table;
122 	u64 start, end;
123 
124 	TRACE("In read_inode_lookup_table, length %d\n", length);
125 
126 	/* Sanity check values */
127 
128 	/* there should always be at least one inode */
129 	if (inodes == 0)
130 		return ERR_PTR(-EINVAL);
131 
132 	/*
133 	 * The computed size of the lookup table (length bytes) should exactly
134 	 * match the table start and end points
135 	 */
136 	if (length != (next_table - lookup_table_start))
137 		return ERR_PTR(-EINVAL);
138 
139 	table = squashfs_read_table(sb, lookup_table_start, length);
140 	if (IS_ERR(table))
141 		return table;
142 
143 	/*
144 	 * table0], table[1], ... table[indexes - 1] store the locations
145 	 * of the compressed inode lookup blocks.  Each entry should be
146 	 * less than the next (i.e. table[0] < table[1]), and the difference
147 	 * between them should be SQUASHFS_METADATA_SIZE or less.
148 	 * table[indexes - 1] should  be less than lookup_table_start, and
149 	 * again the difference should be SQUASHFS_METADATA_SIZE or less
150 	 */
151 	for (n = 0; n < (indexes - 1); n++) {
152 		start = le64_to_cpu(table[n]);
153 		end = le64_to_cpu(table[n + 1]);
154 
155 		if (start >= end
156 		    || (end - start) >
157 		    (SQUASHFS_METADATA_SIZE + SQUASHFS_BLOCK_OFFSET)) {
158 			kfree(table);
159 			return ERR_PTR(-EINVAL);
160 		}
161 	}
162 
163 	start = le64_to_cpu(table[indexes - 1]);
164 	if (start >= lookup_table_start ||
165 	    (lookup_table_start - start) >
166 	    (SQUASHFS_METADATA_SIZE + SQUASHFS_BLOCK_OFFSET)) {
167 		kfree(table);
168 		return ERR_PTR(-EINVAL);
169 	}
170 
171 	return table;
172 }
173 
174 
175 const struct export_operations squashfs_export_ops = {
176 	.fh_to_dentry = squashfs_fh_to_dentry,
177 	.fh_to_parent = squashfs_fh_to_parent,
178 	.get_parent = squashfs_get_parent
179 };
180