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
34static 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 */
43static 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 */
71static 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 */
112struct fsverity_descriptor_location {
113	__le32 version;
114	__le32 size;
115	__le64 pos;
116};
117
118static 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
146static 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
196cleanup:
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
219static 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
257static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
258					       pgoff_t index,
259					       unsigned long num_ra_pages)
260{
261	struct folio *folio;
262
263	index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
264
265	folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
266	if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
267		DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
268
269		if (!IS_ERR(folio))
270			folio_put(folio);
271		else if (num_ra_pages > 1)
272			page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
273		folio = read_mapping_folio(inode->i_mapping, index, NULL);
274		if (IS_ERR(folio))
275			return ERR_CAST(folio);
276	}
277	return folio_file_page(folio, index);
278}
279
280static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
281					u64 pos, unsigned int size)
282{
283	pos += f2fs_verity_metadata_pos(inode);
284
285	return pagecache_write(inode, buf, size, pos);
286}
287
288const struct fsverity_operations f2fs_verityops = {
289	.begin_enable_verity	= f2fs_begin_enable_verity,
290	.end_enable_verity	= f2fs_end_enable_verity,
291	.get_verity_descriptor	= f2fs_get_verity_descriptor,
292	.read_merkle_tree_page	= f2fs_read_merkle_tree_page,
293	.write_merkle_tree_block = f2fs_write_merkle_tree_block,
294};
295