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  * symlink.c
9  */
10 
11 /*
12  * This file implements code to handle symbolic links.
13  *
14  * The data contents of symbolic links are stored inside the symbolic
15  * link inode within the inode table.  This allows the normally small symbolic
16  * link to be compressed as part of the inode table, achieving much greater
17  * compression than if the symbolic link was compressed individually.
18  */
19 
20 #include <linux/fs.h>
21 #include <linux/vfs.h>
22 #include <linux/kernel.h>
23 #include <linux/string.h>
24 #include <linux/pagemap.h>
25 #include <linux/xattr.h>
26 
27 #include "squashfs_fs.h"
28 #include "squashfs_fs_sb.h"
29 #include "squashfs_fs_i.h"
30 #include "squashfs.h"
31 #include "xattr.h"
32 
squashfs_symlink_read_folio(struct file * file,struct folio * folio)33 static int squashfs_symlink_read_folio(struct file *file, struct folio *folio)
34 {
35 	struct inode *inode = folio->mapping->host;
36 	struct super_block *sb = inode->i_sb;
37 	struct squashfs_sb_info *msblk = sb->s_fs_info;
38 	int index = folio_pos(folio);
39 	u64 block = squashfs_i(inode)->start;
40 	int offset = squashfs_i(inode)->offset;
41 	int length = min_t(int, i_size_read(inode) - index, PAGE_SIZE);
42 	int bytes, copied, error;
43 	void *pageaddr;
44 	struct squashfs_cache_entry *entry;
45 
46 	TRACE("Entered squashfs_symlink_readpage, page index %ld, start block "
47 			"%llx, offset %x\n", folio->index, block, offset);
48 
49 	/*
50 	 * Skip index bytes into symlink metadata.
51 	 */
52 	if (index) {
53 		bytes = squashfs_read_metadata(sb, NULL, &block, &offset,
54 								index);
55 		if (bytes < 0) {
56 			ERROR("Unable to read symlink [%llx:%x]\n",
57 				squashfs_i(inode)->start,
58 				squashfs_i(inode)->offset);
59 			error = bytes;
60 			goto out;
61 		}
62 	}
63 
64 	/*
65 	 * Read length bytes from symlink metadata.  Squashfs_read_metadata
66 	 * is not used here because it can sleep and we want to use
67 	 * kmap_local to map the folio.  Instead call the underlying
68 	 * squashfs_cache_get routine.  As length bytes may overlap metadata
69 	 * blocks, we may need to call squashfs_cache_get multiple times.
70 	 */
71 	for (bytes = 0; bytes < length; offset = 0, bytes += copied) {
72 		entry = squashfs_cache_get(sb, msblk->block_cache, block, 0);
73 		if (entry->error) {
74 			ERROR("Unable to read symlink [%llx:%x]\n",
75 				squashfs_i(inode)->start,
76 				squashfs_i(inode)->offset);
77 			squashfs_cache_put(entry);
78 			error = entry->error;
79 			goto out;
80 		}
81 
82 		pageaddr = kmap_local_folio(folio, 0);
83 		copied = squashfs_copy_data(pageaddr + bytes, entry, offset,
84 								length - bytes);
85 		if (copied == length - bytes)
86 			memset(pageaddr + length, 0, PAGE_SIZE - length);
87 		else
88 			block = entry->next_index;
89 		kunmap_local(pageaddr);
90 		squashfs_cache_put(entry);
91 	}
92 
93 	flush_dcache_folio(folio);
94 	error = 0;
95 out:
96 	folio_end_read(folio, error == 0);
97 	return error;
98 }
99 
100 
101 const struct address_space_operations squashfs_symlink_aops = {
102 	.read_folio = squashfs_symlink_read_folio
103 };
104 
105 const struct inode_operations squashfs_symlink_inode_ops = {
106 	.get_link = page_get_link,
107 	.listxattr = squashfs_listxattr
108 };
109 
110