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
