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 > F2FS_BLK_TO_BYTES(max_file_blocks(inode)))
 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 folio *folio;
 84		void *fsdata = NULL;
 85		int res;
 86
 87		res = aops->write_begin(NULL, mapping, pos, n, &folio, &fsdata);
 88		if (res)
 89			return res;
 90
 91		memcpy_to_folio(folio, offset_in_folio(folio, pos), buf, n);
 92
 93		res = aops->write_end(NULL, mapping, pos, n, n, folio, 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 ||
241	    pos + size > F2FS_BLK_TO_BYTES(max_file_blocks(inode)) ||
242	    pos < f2fs_verity_metadata_pos(inode) || size > INT_MAX) {
243		f2fs_warn(F2FS_I_SB(inode), "invalid verity xattr");
244		f2fs_handle_error(F2FS_I_SB(inode),
245				ERROR_CORRUPTED_VERITY_XATTR);
246		return -EFSCORRUPTED;
247	}
248	if (buf_size) {
249		if (size > buf_size)
250			return -ERANGE;
251		res = pagecache_read(inode, buf, size, pos);
252		if (res)
253			return res;
254	}
255	return size;
256}
257
258static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
259					       pgoff_t index,
260					       unsigned long num_ra_pages)
261{
262	struct folio *folio;
263
264	index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
265
266	folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
267	if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
268		DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
269
270		if (!IS_ERR(folio))
271			folio_put(folio);
272		else if (num_ra_pages > 1)
273			page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
274		folio = read_mapping_folio(inode->i_mapping, index, NULL);
275		if (IS_ERR(folio))
276			return ERR_CAST(folio);
277	}
278	return folio_file_page(folio, index);
279}
280
281static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
282					u64 pos, unsigned int size)
283{
284	pos += f2fs_verity_metadata_pos(inode);
285
286	return pagecache_write(inode, buf, size, pos);
287}
288
289const struct fsverity_operations f2fs_verityops = {
290	.begin_enable_verity	= f2fs_begin_enable_verity,
291	.end_enable_verity	= f2fs_end_enable_verity,
292	.get_verity_descriptor	= f2fs_get_verity_descriptor,
293	.read_merkle_tree_page	= f2fs_read_merkle_tree_page,
294	.write_merkle_tree_block = f2fs_write_merkle_tree_block,
295};