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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
32static inline loff_t ext4_verity_metadata_pos(const struct inode *inode)
33{
34 return round_up(inode->i_size, 65536);
35}
36
37/*
38 * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
39 * kernel_write() can't be used because the file descriptor is readonly.
40 */
41static int pagecache_write(struct inode *inode, const void *buf, size_t count,
42 loff_t pos)
43{
44 struct address_space *mapping = inode->i_mapping;
45 const struct address_space_operations *aops = mapping->a_ops;
46
47 if (pos + count > inode->i_sb->s_maxbytes)
48 return -EFBIG;
49
50 while (count) {
51 size_t n = min_t(size_t, count,
52 PAGE_SIZE - offset_in_page(pos));
53 struct folio *folio;
54 void *fsdata = NULL;
55 int res;
56
57 res = aops->write_begin(NULL, mapping, pos, n, &folio, &fsdata);
58 if (res)
59 return res;
60
61 memcpy_to_folio(folio, offset_in_folio(folio, pos), buf, n);
62
63 res = aops->write_end(NULL, mapping, pos, n, n, folio, fsdata);
64 if (res < 0)
65 return res;
66 if (res != n)
67 return -EIO;
68
69 buf += n;
70 pos += n;
71 count -= n;
72 }
73 return 0;
74}
75
76static int ext4_begin_enable_verity(struct file *filp)
77{
78 struct inode *inode = file_inode(filp);
79 const int credits = 2; /* superblock and inode for ext4_orphan_add() */
80 handle_t *handle;
81 int err;
82
83 if (IS_DAX(inode) || ext4_test_inode_flag(inode, EXT4_INODE_DAX))
84 return -EINVAL;
85
86 if (ext4_verity_in_progress(inode))
87 return -EBUSY;
88
89 /*
90 * Since the file was opened readonly, we have to initialize the jbd
91 * inode and quotas here and not rely on ->open() doing it. This must
92 * be done before evicting the inline data.
93 */
94
95 err = ext4_inode_attach_jinode(inode);
96 if (err)
97 return err;
98
99 err = dquot_initialize(inode);
100 if (err)
101 return err;
102
103 err = ext4_convert_inline_data(inode);
104 if (err)
105 return err;
106
107 if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
108 ext4_warning_inode(inode,
109 "verity is only allowed on extent-based files");
110 return -EOPNOTSUPP;
111 }
112
113 /*
114 * ext4 uses the last allocated block to find the verity descriptor, so
115 * we must remove any other blocks past EOF which might confuse things.
116 */
117 err = ext4_truncate(inode);
118 if (err)
119 return err;
120
121 handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
122 if (IS_ERR(handle))
123 return PTR_ERR(handle);
124
125 err = ext4_orphan_add(handle, inode);
126 if (err == 0)
127 ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
128
129 ext4_journal_stop(handle);
130 return err;
131}
132
133/*
134 * ext4 stores the verity descriptor beginning on the next filesystem block
135 * boundary after the Merkle tree. Then, the descriptor size is stored in the
136 * last 4 bytes of the last allocated filesystem block --- which is either the
137 * block in which the descriptor ends, or the next block after that if there
138 * weren't at least 4 bytes remaining.
139 *
140 * We can't simply store the descriptor in an xattr because it *must* be
141 * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt
142 * xattrs. Also, if the descriptor includes a large signature blob it may be
143 * too large to store in an xattr without the EA_INODE feature.
144 */
145static int ext4_write_verity_descriptor(struct inode *inode, const void *desc,
146 size_t desc_size, u64 merkle_tree_size)
147{
148 const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +
149 merkle_tree_size, i_blocksize(inode));
150 const u64 desc_end = desc_pos + desc_size;
151 const __le32 desc_size_disk = cpu_to_le32(desc_size);
152 const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),
153 i_blocksize(inode)) -
154 sizeof(desc_size_disk);
155 int err;
156
157 err = pagecache_write(inode, desc, desc_size, desc_pos);
158 if (err)
159 return err;
160
161 return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),
162 desc_size_pos);
163}
164
165static int ext4_end_enable_verity(struct file *filp, const void *desc,
166 size_t desc_size, u64 merkle_tree_size)
167{
168 struct inode *inode = file_inode(filp);
169 const int credits = 2; /* superblock and inode for ext4_orphan_del() */
170 handle_t *handle;
171 struct ext4_iloc iloc;
172 int err = 0;
173
174 /*
175 * If an error already occurred (which fs/verity/ signals by passing
176 * desc == NULL), then only clean-up is needed.
177 */
178 if (desc == NULL)
179 goto cleanup;
180
181 /* Append the verity descriptor. */
182 err = ext4_write_verity_descriptor(inode, desc, desc_size,
183 merkle_tree_size);
184 if (err)
185 goto cleanup;
186
187 /*
188 * Write all pages (both data and verity metadata). Note that this must
189 * happen before clearing EXT4_STATE_VERITY_IN_PROGRESS; otherwise pages
190 * beyond i_size won't be written properly. For crash consistency, this
191 * also must happen before the verity inode flag gets persisted.
192 */
193 err = filemap_write_and_wait(inode->i_mapping);
194 if (err)
195 goto cleanup;
196
197 /*
198 * Finally, set the verity inode flag and remove the inode from the
199 * orphan list (in a single transaction).
200 */
201
202 handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
203 if (IS_ERR(handle)) {
204 err = PTR_ERR(handle);
205 goto cleanup;
206 }
207
208 ext4_fc_mark_ineligible(inode->i_sb, EXT4_FC_REASON_VERITY, handle);
209
210 err = ext4_orphan_del(handle, inode);
211 if (err)
212 goto stop_and_cleanup;
213
214 err = ext4_reserve_inode_write(handle, inode, &iloc);
215 if (err)
216 goto stop_and_cleanup;
217
218 ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
219 ext4_set_inode_flags(inode, false);
220 err = ext4_mark_iloc_dirty(handle, inode, &iloc);
221 if (err)
222 goto stop_and_cleanup;
223
224 ext4_journal_stop(handle);
225
226 ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
227 return 0;
228
229stop_and_cleanup:
230 ext4_journal_stop(handle);
231cleanup:
232 /*
233 * Verity failed to be enabled, so clean up by truncating any verity
234 * metadata that was written beyond i_size (both from cache and from
235 * disk), removing the inode from the orphan list (if it wasn't done
236 * already), and clearing EXT4_STATE_VERITY_IN_PROGRESS.
237 */
238 truncate_inode_pages(inode->i_mapping, inode->i_size);
239 ext4_truncate(inode);
240 ext4_orphan_del(NULL, inode);
241 ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
242 return err;
243}
244
245static int ext4_get_verity_descriptor_location(struct inode *inode,
246 size_t *desc_size_ret,
247 u64 *desc_pos_ret)
248{
249 struct ext4_ext_path *path;
250 struct ext4_extent *last_extent;
251 u32 end_lblk;
252 u64 desc_size_pos;
253 __le32 desc_size_disk;
254 u32 desc_size;
255 u64 desc_pos;
256 int err;
257
258 /*
259 * Descriptor size is in last 4 bytes of last allocated block.
260 * See ext4_write_verity_descriptor().
261 */
262
263 if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
264 EXT4_ERROR_INODE(inode, "verity file doesn't use extents");
265 return -EFSCORRUPTED;
266 }
267
268 path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
269 if (IS_ERR(path))
270 return PTR_ERR(path);
271
272 last_extent = path[path->p_depth].p_ext;
273 if (!last_extent) {
274 EXT4_ERROR_INODE(inode, "verity file has no extents");
275 ext4_free_ext_path(path);
276 return -EFSCORRUPTED;
277 }
278
279 end_lblk = le32_to_cpu(last_extent->ee_block) +
280 ext4_ext_get_actual_len(last_extent);
281 desc_size_pos = EXT4_LBLK_TO_B(inode, end_lblk);
282 ext4_free_ext_path(path);
283
284 if (desc_size_pos < sizeof(desc_size_disk))
285 goto bad;
286 desc_size_pos -= sizeof(desc_size_disk);
287
288 err = fsverity_pagecache_read(inode, &desc_size_disk,
289 sizeof(desc_size_disk), desc_size_pos);
290 if (err)
291 return err;
292 desc_size = le32_to_cpu(desc_size_disk);
293
294 /*
295 * The descriptor is stored just before the desc_size_disk, but starting
296 * on a filesystem block boundary.
297 */
298
299 if (desc_size > INT_MAX || desc_size > desc_size_pos)
300 goto bad;
301
302 desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));
303 if (desc_pos < ext4_verity_metadata_pos(inode))
304 goto bad;
305
306 *desc_size_ret = desc_size;
307 *desc_pos_ret = desc_pos;
308 return 0;
309
310bad:
311 EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");
312 return -EFSCORRUPTED;
313}
314
315static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
316 size_t buf_size)
317{
318 size_t desc_size = 0;
319 u64 desc_pos = 0;
320 int err;
321
322 err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);
323 if (err)
324 return err;
325
326 if (buf_size) {
327 if (desc_size > buf_size)
328 return -ERANGE;
329 err = fsverity_pagecache_read(inode, buf, desc_size, desc_pos);
330 if (err)
331 return err;
332 }
333 return desc_size;
334}
335
336static struct page *ext4_read_merkle_tree_page(struct inode *inode,
337 pgoff_t index)
338{
339 index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
340 return generic_read_merkle_tree_page(inode, index);
341}
342
343static void ext4_readahead_merkle_tree(struct inode *inode, pgoff_t index,
344 unsigned long nr_pages)
345{
346 index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
347 generic_readahead_merkle_tree(inode, index, nr_pages);
348}
349
350static int ext4_write_merkle_tree_block(struct file *file, const void *buf,
351 u64 pos, unsigned int size,
352 const u8 *zero_digest,
353 unsigned int digest_size)
354{
355 pos += ext4_verity_metadata_pos(file_inode(file));
356
357 return pagecache_write(file_inode(file), buf, size, pos);
358}
359
360const struct fsverity_operations ext4_verityops = {
361 .begin_enable_verity = ext4_begin_enable_verity,
362 .end_enable_verity = ext4_end_enable_verity,
363 .get_verity_descriptor = ext4_get_verity_descriptor,
364 .read_merkle_tree_page = ext4_read_merkle_tree_page,
365 .readahead_merkle_tree = ext4_readahead_merkle_tree,
366 .write_merkle_tree_block = ext4_write_merkle_tree_block,
367};