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
33static int squashfs_symlink_read_folio(struct file *file, struct folio *folio)
34{
35	struct page *page = &folio->page;
36	struct inode *inode = page->mapping->host;
37	struct super_block *sb = inode->i_sb;
38	struct squashfs_sb_info *msblk = sb->s_fs_info;
39	int index = page->index << PAGE_SHIFT;
40	u64 block = squashfs_i(inode)->start;
41	int offset = squashfs_i(inode)->offset;
42	int length = min_t(int, i_size_read(inode) - index, PAGE_SIZE);
43	int bytes, copied;
44	void *pageaddr;
45	struct squashfs_cache_entry *entry;
46
47	TRACE("Entered squashfs_symlink_readpage, page index %ld, start block "
48			"%llx, offset %x\n", page->index, block, offset);
49
50	/*
51	 * Skip index bytes into symlink metadata.
52	 */
53	if (index) {
54		bytes = squashfs_read_metadata(sb, NULL, &block, &offset,
55								index);
56		if (bytes < 0) {
57			ERROR("Unable to read symlink [%llx:%x]\n",
58				squashfs_i(inode)->start,
59				squashfs_i(inode)->offset);
60			goto error_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_atomic to map the page.  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			goto error_out;
79		}
80
81		pageaddr = kmap_atomic(page);
82		copied = squashfs_copy_data(pageaddr + bytes, entry, offset,
83								length - bytes);
84		if (copied == length - bytes)
85			memset(pageaddr + length, 0, PAGE_SIZE - length);
86		else
87			block = entry->next_index;
88		kunmap_atomic(pageaddr);
89		squashfs_cache_put(entry);
90	}
91
92	flush_dcache_page(page);
93	SetPageUptodate(page);
94	unlock_page(page);
95	return 0;
96
97error_out:
98	SetPageError(page);
99	unlock_page(page);
100	return 0;
101}
102
103
104const struct address_space_operations squashfs_symlink_aops = {
105	.read_folio = squashfs_symlink_read_folio
106};
107
108const struct inode_operations squashfs_symlink_inode_ops = {
109	.get_link = page_get_link,
110	.listxattr = squashfs_listxattr
111};
112
113