1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * fs/f2fs/verity.c: fs-verity support for f2fs
4  *
5  * Copyright 2019 Google LLC
6  */
7 
8 /*
9  * Implementation of fsverity_operations for f2fs.
10  *
11  * Like ext4, f2fs stores the verity metadata (Merkle tree and
12  * fsverity_descriptor) past the end of the file, starting at the first 64K
13  * boundary beyond i_size.  This approach works because (a) verity files are
14  * readonly, and (b) pages fully beyond i_size aren't visible to userspace but
15  * can be read/written internally by f2fs with only some relatively small
16  * changes to f2fs.  Extended attributes cannot be used because (a) f2fs limits
17  * the total size of an inode's xattr entries to 4096 bytes, which wouldn't be
18  * enough for even a single Merkle tree block, and (b) f2fs encryption doesn't
19  * encrypt xattrs, yet the verity metadata *must* be encrypted when the file is
20  * because it contains hashes of the plaintext data.
21  *
22  * Using a 64K boundary rather than a 4K one keeps things ready for
23  * architectures with 64K pages, and it doesn't necessarily waste space on-disk
24  * since there can be a hole between i_size and the start of the Merkle tree.
25  */
26 
27 #include <linux/f2fs_fs.h>
28 
29 #include "f2fs.h"
30 #include "xattr.h"
31 
32 #define F2FS_VERIFY_VER	(1)
33 
f2fs_verity_metadata_pos(const struct inode * inode)34 static inline loff_t f2fs_verity_metadata_pos(const struct inode *inode)
35 {
36 	return round_up(inode->i_size, 65536);
37 }
38 
39 /*
40  * Read some verity metadata from the inode.  __vfs_read() can't be used because
41  * we need to read beyond i_size.
42  */
pagecache_read(struct inode * inode,void * buf,size_t count,loff_t pos)43 static int pagecache_read(struct inode *inode, void *buf, size_t count,
44 			  loff_t pos)
45 {
46 	while (count) {
47 		size_t n = min_t(size_t, count,
48 				 PAGE_SIZE - offset_in_page(pos));
49 		struct page *page;
50 
51 		page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
52 					 NULL);
53 		if (IS_ERR(page))
54 			return PTR_ERR(page);
55 
56 		memcpy_from_page(buf, page, offset_in_page(pos), n);
57 
58 		put_page(page);
59 
60 		buf += n;
61 		pos += n;
62 		count -= n;
63 	}
64 	return 0;
65 }
66 
67 /*
68  * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
69  * kernel_write() can't be used because the file descriptor is readonly.
70  */
pagecache_write(struct inode * inode,const void * buf,size_t count,loff_t pos)71 static int pagecache_write(struct inode *inode, const void *buf, size_t count,
72 			   loff_t pos)
73 {
74 	struct address_space *mapping = inode->i_mapping;
75 	const struct address_space_operations *aops = mapping->a_ops;
76 
77 	if (pos + count > inode->i_sb->s_maxbytes)
78 		return -EFBIG;
79 
80 	while (count) {
81 		size_t n = min_t(size_t, count,
82 				 PAGE_SIZE - offset_in_page(pos));
83 		struct page *page;
84 		void *fsdata = NULL;
85 		int res;
86 
87 		res = aops->write_begin(NULL, mapping, pos, n, &page, &fsdata);
88 		if (res)
89 			return res;
90 
91 		memcpy_to_page(page, offset_in_page(pos), buf, n);
92 
93 		res = aops->write_end(NULL, mapping, pos, n, n, page, fsdata);
94 		if (res < 0)
95 			return res;
96 		if (res != n)
97 			return -EIO;
98 
99 		buf += n;
100 		pos += n;
101 		count -= n;
102 	}
103 	return 0;
104 }
105 
106 /*
107  * Format of f2fs verity xattr.  This points to the location of the verity
108  * descriptor within the file data rather than containing it directly because
109  * the verity descriptor *must* be encrypted when f2fs encryption is used.  But,
110  * f2fs encryption does not encrypt xattrs.
111  */
112 struct fsverity_descriptor_location {
113 	__le32 version;
114 	__le32 size;
115 	__le64 pos;
116 };
117 
f2fs_begin_enable_verity(struct file * filp)118 static int f2fs_begin_enable_verity(struct file *filp)
119 {
120 	struct inode *inode = file_inode(filp);
121 	int err;
122 
123 	if (f2fs_verity_in_progress(inode))
124 		return -EBUSY;
125 
126 	if (f2fs_is_atomic_file(inode))
127 		return -EOPNOTSUPP;
128 
129 	/*
130 	 * Since the file was opened readonly, we have to initialize the quotas
131 	 * here and not rely on ->open() doing it.  This must be done before
132 	 * evicting the inline data.
133 	 */
134 	err = f2fs_dquot_initialize(inode);
135 	if (err)
136 		return err;
137 
138 	err = f2fs_convert_inline_inode(inode);
139 	if (err)
140 		return err;
141 
142 	set_inode_flag(inode, FI_VERITY_IN_PROGRESS);
143 	return 0;
144 }
145 
f2fs_end_enable_verity(struct file * filp,const void * desc,size_t desc_size,u64 merkle_tree_size)146 static int f2fs_end_enable_verity(struct file *filp, const void *desc,
147 				  size_t desc_size, u64 merkle_tree_size)
148 {
149 	struct inode *inode = file_inode(filp);
150 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
151 	u64 desc_pos = f2fs_verity_metadata_pos(inode) + merkle_tree_size;
152 	struct fsverity_descriptor_location dloc = {
153 		.version = cpu_to_le32(F2FS_VERIFY_VER),
154 		.size = cpu_to_le32(desc_size),
155 		.pos = cpu_to_le64(desc_pos),
156 	};
157 	int err = 0, err2 = 0;
158 
159 	/*
160 	 * If an error already occurred (which fs/verity/ signals by passing
161 	 * desc == NULL), then only clean-up is needed.
162 	 */
163 	if (desc == NULL)
164 		goto cleanup;
165 
166 	/* Append the verity descriptor. */
167 	err = pagecache_write(inode, desc, desc_size, desc_pos);
168 	if (err)
169 		goto cleanup;
170 
171 	/*
172 	 * Write all pages (both data and verity metadata).  Note that this must
173 	 * happen before clearing FI_VERITY_IN_PROGRESS; otherwise pages beyond
174 	 * i_size won't be written properly.  For crash consistency, this also
175 	 * must happen before the verity inode flag gets persisted.
176 	 */
177 	err = filemap_write_and_wait(inode->i_mapping);
178 	if (err)
179 		goto cleanup;
180 
181 	/* Set the verity xattr. */
182 	err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
183 			    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
184 			    NULL, XATTR_CREATE);
185 	if (err)
186 		goto cleanup;
187 
188 	/* Finally, set the verity inode flag. */
189 	file_set_verity(inode);
190 	f2fs_set_inode_flags(inode);
191 	f2fs_mark_inode_dirty_sync(inode, true);
192 
193 	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
194 	return 0;
195 
196 cleanup:
197 	/*
198 	 * Verity failed to be enabled, so clean up by truncating any verity
199 	 * metadata that was written beyond i_size (both from cache and from
200 	 * disk) and clearing FI_VERITY_IN_PROGRESS.
201 	 *
202 	 * Taking i_gc_rwsem[WRITE] is needed to stop f2fs garbage collection
203 	 * from re-instantiating cached pages we are truncating (since unlike
204 	 * normal file accesses, garbage collection isn't limited by i_size).
205 	 */
206 	f2fs_down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
207 	truncate_inode_pages(inode->i_mapping, inode->i_size);
208 	err2 = f2fs_truncate(inode);
209 	if (err2) {
210 		f2fs_err(sbi, "Truncating verity metadata failed (errno=%d)",
211 			 err2);
212 		set_sbi_flag(sbi, SBI_NEED_FSCK);
213 	}
214 	f2fs_up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
215 	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
216 	return err ?: err2;
217 }
218 
f2fs_get_verity_descriptor(struct inode * inode,void * buf,size_t buf_size)219 static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
220 				      size_t buf_size)
221 {
222 	struct fsverity_descriptor_location dloc;
223 	int res;
224 	u32 size;
225 	u64 pos;
226 
227 	/* Get the descriptor location */
228 	res = f2fs_getxattr(inode, F2FS_XATTR_INDEX_VERITY,
229 			    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc), NULL);
230 	if (res < 0 && res != -ERANGE)
231 		return res;
232 	if (res != sizeof(dloc) || dloc.version != cpu_to_le32(F2FS_VERIFY_VER)) {
233 		f2fs_warn(F2FS_I_SB(inode), "unknown verity xattr format");
234 		return -EINVAL;
235 	}
236 	size = le32_to_cpu(dloc.size);
237 	pos = le64_to_cpu(dloc.pos);
238 
239 	/* Get the descriptor */
240 	if (pos + size < pos || pos + size > inode->i_sb->s_maxbytes ||
241 	    pos < f2fs_verity_metadata_pos(inode) || size > INT_MAX) {
242 		f2fs_warn(F2FS_I_SB(inode), "invalid verity xattr");
243 		f2fs_handle_error(F2FS_I_SB(inode),
244 				ERROR_CORRUPTED_VERITY_XATTR);
245 		return -EFSCORRUPTED;
246 	}
247 	if (buf_size) {
248 		if (size > buf_size)
249 			return -ERANGE;
250 		res = pagecache_read(inode, buf, size, pos);
251 		if (res)
252 			return res;
253 	}
254 	return size;
255 }
256 
f2fs_read_merkle_tree_page(struct inode * inode,pgoff_t index,unsigned long num_ra_pages)257 static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
258 					       pgoff_t index,
259 					       unsigned long num_ra_pages)
260 {
261 	struct page *page;
262 
263 	index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
264 
265 	page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
266 	if (!page || !PageUptodate(page)) {
267 		DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
268 
269 		if (page)
270 			put_page(page);
271 		else if (num_ra_pages > 1)
272 			page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
273 		page = read_mapping_page(inode->i_mapping, index, NULL);
274 	}
275 	return page;
276 }
277 
f2fs_write_merkle_tree_block(struct inode * inode,const void * buf,u64 pos,unsigned int size)278 static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
279 					u64 pos, unsigned int size)
280 {
281 	pos += f2fs_verity_metadata_pos(inode);
282 
283 	return pagecache_write(inode, buf, size, pos);
284 }
285 
286 const struct fsverity_operations f2fs_verityops = {
287 	.begin_enable_verity	= f2fs_begin_enable_verity,
288 	.end_enable_verity	= f2fs_end_enable_verity,
289 	.get_verity_descriptor	= f2fs_get_verity_descriptor,
290 	.read_merkle_tree_page	= f2fs_read_merkle_tree_page,
291 	.write_merkle_tree_block = f2fs_write_merkle_tree_block,
292 };
293