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_readpage(struct file * file,struct page * page)33 static int squashfs_symlink_readpage(struct file *file, struct page *page)
34 {
35 	struct inode *inode = page->mapping->host;
36 	struct super_block *sb = inode->i_sb;
37 	struct squashfs_sb_info *msblk = sb->s_fs_info;
38 	int index = page->index << PAGE_SHIFT;
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;
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", page->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 			goto error_out;
60 		}
61 	}
62 
63 	/*
64 	 * Read length bytes from symlink metadata.  Squashfs_read_metadata
65 	 * is not used here because it can sleep and we want to use
66 	 * kmap_atomic to map the page.  Instead call the underlying
67 	 * squashfs_cache_get routine.  As length bytes may overlap metadata
68 	 * blocks, we may need to call squashfs_cache_get multiple times.
69 	 */
70 	for (bytes = 0; bytes < length; offset = 0, bytes += copied) {
71 		entry = squashfs_cache_get(sb, msblk->block_cache, block, 0);
72 		if (entry->error) {
73 			ERROR("Unable to read symlink [%llx:%x]\n",
74 				squashfs_i(inode)->start,
75 				squashfs_i(inode)->offset);
76 			squashfs_cache_put(entry);
77 			goto error_out;
78 		}
79 
80 		pageaddr = kmap_atomic(page);
81 		copied = squashfs_copy_data(pageaddr + bytes, entry, offset,
82 								length - bytes);
83 		if (copied == length - bytes)
84 			memset(pageaddr + length, 0, PAGE_SIZE - length);
85 		else
86 			block = entry->next_index;
87 		kunmap_atomic(pageaddr);
88 		squashfs_cache_put(entry);
89 	}
90 
91 	flush_dcache_page(page);
92 	SetPageUptodate(page);
93 	unlock_page(page);
94 	return 0;
95 
96 error_out:
97 	SetPageError(page);
98 	unlock_page(page);
99 	return 0;
100 }
101 
102 
103 const struct address_space_operations squashfs_symlink_aops = {
104 	.readpage = squashfs_symlink_readpage
105 };
106 
107 const struct inode_operations squashfs_symlink_inode_ops = {
108 	.get_link = page_get_link,
109 	.listxattr = squashfs_listxattr
110 };
111 
112