1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Copyright (c) 2013
4  * Phillip Lougher <phillip@squashfs.org.uk>
5  */
6 
7 #include <linux/fs.h>
8 #include <linux/vfs.h>
9 #include <linux/kernel.h>
10 #include <linux/slab.h>
11 #include <linux/string.h>
12 #include <linux/pagemap.h>
13 #include <linux/mutex.h>
14 
15 #include "squashfs_fs.h"
16 #include "squashfs_fs_sb.h"
17 #include "squashfs_fs_i.h"
18 #include "squashfs.h"
19 #include "page_actor.h"
20 
21 static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
22 	int pages, struct page **page, int bytes);
23 
24 /* Read separately compressed datablock directly into page cache */
squashfs_readpage_block(struct page * target_page,u64 block,int bsize,int expected)25 int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
26 	int expected)
27 
28 {
29 	struct inode *inode = target_page->mapping->host;
30 	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
31 
32 	int file_end = (i_size_read(inode) - 1) >> PAGE_SHIFT;
33 	int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
34 	int start_index = target_page->index & ~mask;
35 	int end_index = start_index | mask;
36 	int i, n, pages, missing_pages, bytes, res = -ENOMEM;
37 	struct page **page;
38 	struct squashfs_page_actor *actor;
39 	void *pageaddr;
40 
41 	if (end_index > file_end)
42 		end_index = file_end;
43 
44 	pages = end_index - start_index + 1;
45 
46 	page = kmalloc_array(pages, sizeof(void *), GFP_KERNEL);
47 	if (page == NULL)
48 		return res;
49 
50 	/*
51 	 * Create a "page actor" which will kmap and kunmap the
52 	 * page cache pages appropriately within the decompressor
53 	 */
54 	actor = squashfs_page_actor_init_special(page, pages, 0);
55 	if (actor == NULL)
56 		goto out;
57 
58 	/* Try to grab all the pages covered by the Squashfs block */
59 	for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) {
60 		page[i] = (n == target_page->index) ? target_page :
61 			grab_cache_page_nowait(target_page->mapping, n);
62 
63 		if (page[i] == NULL) {
64 			missing_pages++;
65 			continue;
66 		}
67 
68 		if (PageUptodate(page[i])) {
69 			unlock_page(page[i]);
70 			put_page(page[i]);
71 			page[i] = NULL;
72 			missing_pages++;
73 		}
74 	}
75 
76 	if (missing_pages) {
77 		/*
78 		 * Couldn't get one or more pages, this page has either
79 		 * been VM reclaimed, but others are still in the page cache
80 		 * and uptodate, or we're racing with another thread in
81 		 * squashfs_readpage also trying to grab them.  Fall back to
82 		 * using an intermediate buffer.
83 		 */
84 		res = squashfs_read_cache(target_page, block, bsize, pages,
85 							page, expected);
86 		if (res < 0)
87 			goto mark_errored;
88 
89 		goto out;
90 	}
91 
92 	/* Decompress directly into the page cache buffers */
93 	res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
94 	if (res < 0)
95 		goto mark_errored;
96 
97 	if (res != expected) {
98 		res = -EIO;
99 		goto mark_errored;
100 	}
101 
102 	/* Last page may have trailing bytes not filled */
103 	bytes = res % PAGE_SIZE;
104 	if (bytes) {
105 		pageaddr = kmap_atomic(page[pages - 1]);
106 		memset(pageaddr + bytes, 0, PAGE_SIZE - bytes);
107 		kunmap_atomic(pageaddr);
108 	}
109 
110 	/* Mark pages as uptodate, unlock and release */
111 	for (i = 0; i < pages; i++) {
112 		flush_dcache_page(page[i]);
113 		SetPageUptodate(page[i]);
114 		unlock_page(page[i]);
115 		if (page[i] != target_page)
116 			put_page(page[i]);
117 	}
118 
119 	kfree(actor);
120 	kfree(page);
121 
122 	return 0;
123 
124 mark_errored:
125 	/* Decompression failed, mark pages as errored.  Target_page is
126 	 * dealt with by the caller
127 	 */
128 	for (i = 0; i < pages; i++) {
129 		if (page[i] == NULL || page[i] == target_page)
130 			continue;
131 		flush_dcache_page(page[i]);
132 		SetPageError(page[i]);
133 		unlock_page(page[i]);
134 		put_page(page[i]);
135 	}
136 
137 out:
138 	kfree(actor);
139 	kfree(page);
140 	return res;
141 }
142 
143 
squashfs_read_cache(struct page * target_page,u64 block,int bsize,int pages,struct page ** page,int bytes)144 static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
145 	int pages, struct page **page, int bytes)
146 {
147 	struct inode *i = target_page->mapping->host;
148 	struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
149 						 block, bsize);
150 	int res = buffer->error, n, offset = 0;
151 
152 	if (res) {
153 		ERROR("Unable to read page, block %llx, size %x\n", block,
154 			bsize);
155 		goto out;
156 	}
157 
158 	for (n = 0; n < pages && bytes > 0; n++,
159 			bytes -= PAGE_SIZE, offset += PAGE_SIZE) {
160 		int avail = min_t(int, bytes, PAGE_SIZE);
161 
162 		if (page[n] == NULL)
163 			continue;
164 
165 		squashfs_fill_page(page[n], buffer, offset, avail);
166 		unlock_page(page[n]);
167 		if (page[n] != target_page)
168 			put_page(page[n]);
169 	}
170 
171 out:
172 	squashfs_cache_put(buffer);
173 	return res;
174 }
175