1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * fs/ext4/verity.c: fs-verity support for ext4
4 *
5 * Copyright 2019 Google LLC
6 */
7
8 /*
9 * Implementation of fsverity_operations for ext4.
10 *
11 * ext4 stores the verity metadata (Merkle tree and fsverity_descriptor) past
12 * the end of the file, starting at the first 64K boundary beyond i_size. This
13 * approach works because (a) verity files are readonly, and (b) pages fully
14 * beyond i_size aren't visible to userspace but can be read/written internally
15 * by ext4 with only some relatively small changes to ext4. This approach
16 * avoids having to depend on the EA_INODE feature and on rearchitecturing
17 * ext4's xattr support to support paging multi-gigabyte xattrs into memory, and
18 * to support encrypting xattrs. Note that the verity metadata *must* be
19 * encrypted when the file is, since it contains hashes of the plaintext data.
20 *
21 * Using a 64K boundary rather than a 4K one keeps things ready for
22 * architectures with 64K pages, and it doesn't necessarily waste space on-disk
23 * since there can be a hole between i_size and the start of the Merkle tree.
24 */
25
26 #include <linux/quotaops.h>
27
28 #include "ext4.h"
29 #include "ext4_extents.h"
30 #include "ext4_jbd2.h"
31
ext4_verity_metadata_pos(const struct inode * inode)32 static inline loff_t ext4_verity_metadata_pos(const struct inode *inode)
33 {
34 return round_up(inode->i_size, 65536);
35 }
36
37 /*
38 * Read some verity metadata from the inode. __vfs_read() can't be used because
39 * we need to read beyond i_size.
40 */
pagecache_read(struct inode * inode,void * buf,size_t count,loff_t pos)41 static int pagecache_read(struct inode *inode, void *buf, size_t count,
42 loff_t pos)
43 {
44 while (count) {
45 struct folio *folio;
46 size_t n;
47
48 folio = read_mapping_folio(inode->i_mapping, pos >> PAGE_SHIFT,
49 NULL);
50 if (IS_ERR(folio))
51 return PTR_ERR(folio);
52
53 n = memcpy_from_file_folio(buf, folio, pos, count);
54 folio_put(folio);
55
56 buf += n;
57 pos += n;
58 count -= n;
59 }
60 return 0;
61 }
62
63 /*
64 * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
65 * kernel_write() can't be used because the file descriptor is readonly.
66 */
pagecache_write(struct inode * inode,const void * buf,size_t count,loff_t pos)67 static int pagecache_write(struct inode *inode, const void *buf, size_t count,
68 loff_t pos)
69 {
70 struct address_space *mapping = inode->i_mapping;
71 const struct address_space_operations *aops = mapping->a_ops;
72
73 if (pos + count > inode->i_sb->s_maxbytes)
74 return -EFBIG;
75
76 while (count) {
77 size_t n = min_t(size_t, count,
78 PAGE_SIZE - offset_in_page(pos));
79 struct page *page;
80 void *fsdata = NULL;
81 int res;
82
83 res = aops->write_begin(NULL, mapping, pos, n, &page, &fsdata);
84 if (res)
85 return res;
86
87 memcpy_to_page(page, offset_in_page(pos), buf, n);
88
89 res = aops->write_end(NULL, mapping, pos, n, n, page, fsdata);
90 if (res < 0)
91 return res;
92 if (res != n)
93 return -EIO;
94
95 buf += n;
96 pos += n;
97 count -= n;
98 }
99 return 0;
100 }
101
ext4_begin_enable_verity(struct file * filp)102 static int ext4_begin_enable_verity(struct file *filp)
103 {
104 struct inode *inode = file_inode(filp);
105 const int credits = 2; /* superblock and inode for ext4_orphan_add() */
106 handle_t *handle;
107 int err;
108
109 if (IS_DAX(inode) || ext4_test_inode_flag(inode, EXT4_INODE_DAX))
110 return -EINVAL;
111
112 if (ext4_verity_in_progress(inode))
113 return -EBUSY;
114
115 /*
116 * Since the file was opened readonly, we have to initialize the jbd
117 * inode and quotas here and not rely on ->open() doing it. This must
118 * be done before evicting the inline data.
119 */
120
121 err = ext4_inode_attach_jinode(inode);
122 if (err)
123 return err;
124
125 err = dquot_initialize(inode);
126 if (err)
127 return err;
128
129 err = ext4_convert_inline_data(inode);
130 if (err)
131 return err;
132
133 if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
134 ext4_warning_inode(inode,
135 "verity is only allowed on extent-based files");
136 return -EOPNOTSUPP;
137 }
138
139 /*
140 * ext4 uses the last allocated block to find the verity descriptor, so
141 * we must remove any other blocks past EOF which might confuse things.
142 */
143 err = ext4_truncate(inode);
144 if (err)
145 return err;
146
147 handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
148 if (IS_ERR(handle))
149 return PTR_ERR(handle);
150
151 err = ext4_orphan_add(handle, inode);
152 if (err == 0)
153 ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
154
155 ext4_journal_stop(handle);
156 return err;
157 }
158
159 /*
160 * ext4 stores the verity descriptor beginning on the next filesystem block
161 * boundary after the Merkle tree. Then, the descriptor size is stored in the
162 * last 4 bytes of the last allocated filesystem block --- which is either the
163 * block in which the descriptor ends, or the next block after that if there
164 * weren't at least 4 bytes remaining.
165 *
166 * We can't simply store the descriptor in an xattr because it *must* be
167 * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt
168 * xattrs. Also, if the descriptor includes a large signature blob it may be
169 * too large to store in an xattr without the EA_INODE feature.
170 */
ext4_write_verity_descriptor(struct inode * inode,const void * desc,size_t desc_size,u64 merkle_tree_size)171 static int ext4_write_verity_descriptor(struct inode *inode, const void *desc,
172 size_t desc_size, u64 merkle_tree_size)
173 {
174 const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +
175 merkle_tree_size, i_blocksize(inode));
176 const u64 desc_end = desc_pos + desc_size;
177 const __le32 desc_size_disk = cpu_to_le32(desc_size);
178 const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),
179 i_blocksize(inode)) -
180 sizeof(desc_size_disk);
181 int err;
182
183 err = pagecache_write(inode, desc, desc_size, desc_pos);
184 if (err)
185 return err;
186
187 return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),
188 desc_size_pos);
189 }
190
ext4_end_enable_verity(struct file * filp,const void * desc,size_t desc_size,u64 merkle_tree_size)191 static int ext4_end_enable_verity(struct file *filp, const void *desc,
192 size_t desc_size, u64 merkle_tree_size)
193 {
194 struct inode *inode = file_inode(filp);
195 const int credits = 2; /* superblock and inode for ext4_orphan_del() */
196 handle_t *handle;
197 struct ext4_iloc iloc;
198 int err = 0;
199
200 /*
201 * If an error already occurred (which fs/verity/ signals by passing
202 * desc == NULL), then only clean-up is needed.
203 */
204 if (desc == NULL)
205 goto cleanup;
206
207 /* Append the verity descriptor. */
208 err = ext4_write_verity_descriptor(inode, desc, desc_size,
209 merkle_tree_size);
210 if (err)
211 goto cleanup;
212
213 /*
214 * Write all pages (both data and verity metadata). Note that this must
215 * happen before clearing EXT4_STATE_VERITY_IN_PROGRESS; otherwise pages
216 * beyond i_size won't be written properly. For crash consistency, this
217 * also must happen before the verity inode flag gets persisted.
218 */
219 err = filemap_write_and_wait(inode->i_mapping);
220 if (err)
221 goto cleanup;
222
223 /*
224 * Finally, set the verity inode flag and remove the inode from the
225 * orphan list (in a single transaction).
226 */
227
228 handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
229 if (IS_ERR(handle)) {
230 err = PTR_ERR(handle);
231 goto cleanup;
232 }
233
234 err = ext4_orphan_del(handle, inode);
235 if (err)
236 goto stop_and_cleanup;
237
238 err = ext4_reserve_inode_write(handle, inode, &iloc);
239 if (err)
240 goto stop_and_cleanup;
241
242 ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
243 ext4_set_inode_flags(inode, false);
244 err = ext4_mark_iloc_dirty(handle, inode, &iloc);
245 if (err)
246 goto stop_and_cleanup;
247
248 ext4_journal_stop(handle);
249
250 ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
251 return 0;
252
253 stop_and_cleanup:
254 ext4_journal_stop(handle);
255 cleanup:
256 /*
257 * Verity failed to be enabled, so clean up by truncating any verity
258 * metadata that was written beyond i_size (both from cache and from
259 * disk), removing the inode from the orphan list (if it wasn't done
260 * already), and clearing EXT4_STATE_VERITY_IN_PROGRESS.
261 */
262 truncate_inode_pages(inode->i_mapping, inode->i_size);
263 ext4_truncate(inode);
264 ext4_orphan_del(NULL, inode);
265 ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
266 return err;
267 }
268
ext4_get_verity_descriptor_location(struct inode * inode,size_t * desc_size_ret,u64 * desc_pos_ret)269 static int ext4_get_verity_descriptor_location(struct inode *inode,
270 size_t *desc_size_ret,
271 u64 *desc_pos_ret)
272 {
273 struct ext4_ext_path *path;
274 struct ext4_extent *last_extent;
275 u32 end_lblk;
276 u64 desc_size_pos;
277 __le32 desc_size_disk;
278 u32 desc_size;
279 u64 desc_pos;
280 int err;
281
282 /*
283 * Descriptor size is in last 4 bytes of last allocated block.
284 * See ext4_write_verity_descriptor().
285 */
286
287 if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
288 EXT4_ERROR_INODE(inode, "verity file doesn't use extents");
289 return -EFSCORRUPTED;
290 }
291
292 path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
293 if (IS_ERR(path))
294 return PTR_ERR(path);
295
296 last_extent = path[path->p_depth].p_ext;
297 if (!last_extent) {
298 EXT4_ERROR_INODE(inode, "verity file has no extents");
299 ext4_free_ext_path(path);
300 return -EFSCORRUPTED;
301 }
302
303 end_lblk = le32_to_cpu(last_extent->ee_block) +
304 ext4_ext_get_actual_len(last_extent);
305 desc_size_pos = (u64)end_lblk << inode->i_blkbits;
306 ext4_free_ext_path(path);
307
308 if (desc_size_pos < sizeof(desc_size_disk))
309 goto bad;
310 desc_size_pos -= sizeof(desc_size_disk);
311
312 err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),
313 desc_size_pos);
314 if (err)
315 return err;
316 desc_size = le32_to_cpu(desc_size_disk);
317
318 /*
319 * The descriptor is stored just before the desc_size_disk, but starting
320 * on a filesystem block boundary.
321 */
322
323 if (desc_size > INT_MAX || desc_size > desc_size_pos)
324 goto bad;
325
326 desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));
327 if (desc_pos < ext4_verity_metadata_pos(inode))
328 goto bad;
329
330 *desc_size_ret = desc_size;
331 *desc_pos_ret = desc_pos;
332 return 0;
333
334 bad:
335 EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");
336 return -EFSCORRUPTED;
337 }
338
ext4_get_verity_descriptor(struct inode * inode,void * buf,size_t buf_size)339 static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
340 size_t buf_size)
341 {
342 size_t desc_size = 0;
343 u64 desc_pos = 0;
344 int err;
345
346 err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);
347 if (err)
348 return err;
349
350 if (buf_size) {
351 if (desc_size > buf_size)
352 return -ERANGE;
353 err = pagecache_read(inode, buf, desc_size, desc_pos);
354 if (err)
355 return err;
356 }
357 return desc_size;
358 }
359
ext4_read_merkle_tree_page(struct inode * inode,pgoff_t index,unsigned long num_ra_pages)360 static struct page *ext4_read_merkle_tree_page(struct inode *inode,
361 pgoff_t index,
362 unsigned long num_ra_pages)
363 {
364 struct folio *folio;
365
366 index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
367
368 folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
369 if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
370 DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
371
372 if (!IS_ERR(folio))
373 folio_put(folio);
374 else if (num_ra_pages > 1)
375 page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
376 folio = read_mapping_folio(inode->i_mapping, index, NULL);
377 if (IS_ERR(folio))
378 return ERR_CAST(folio);
379 }
380 return folio_file_page(folio, index);
381 }
382
ext4_write_merkle_tree_block(struct inode * inode,const void * buf,u64 pos,unsigned int size)383 static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf,
384 u64 pos, unsigned int size)
385 {
386 pos += ext4_verity_metadata_pos(inode);
387
388 return pagecache_write(inode, buf, size, pos);
389 }
390
391 const struct fsverity_operations ext4_verityops = {
392 .begin_enable_verity = ext4_begin_enable_verity,
393 .end_enable_verity = ext4_end_enable_verity,
394 .get_verity_descriptor = ext4_get_verity_descriptor,
395 .read_merkle_tree_page = ext4_read_merkle_tree_page,
396 .write_merkle_tree_block = ext4_write_merkle_tree_block,
397 };
398