summaryrefslogtreecommitdiff
path: root/fs/verity/enable.c
blob: 5ab3bbec810873d260923b159cce06823a2dfd48 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
// SPDX-License-Identifier: GPL-2.0
/*
 * fs/verity/enable.c: ioctl to enable verity on a file
 *
 * Copyright 2019 Google LLC
 */

#include "fsverity_private.h"

#include <crypto/hash.h>
#include <linux/backing-dev.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/sched/signal.h>
#include <linux/uaccess.h>

/*
 * Read a file data page for Merkle tree construction.  Do aggressive readahead,
 * since we're sequentially reading the entire file.
 */
static struct page *read_file_data_page(struct file *filp, pgoff_t index,
					struct file_ra_state *ra,
					unsigned long remaining_pages)
{
	struct page *page;

	page = find_get_page_flags(filp->f_mapping, index, FGP_ACCESSED);
	if (!page || !PageUptodate(page)) {
		if (page)
			put_page(page);
		else
			page_cache_sync_readahead(filp->f_mapping, ra, filp,
						  index, remaining_pages);
		page = read_mapping_page(filp->f_mapping, index, NULL);
		if (IS_ERR(page))
			return page;
	}
	if (PageReadahead(page))
		page_cache_async_readahead(filp->f_mapping, ra, filp, page,
					   index, remaining_pages);
	return page;
}

static int build_merkle_tree_level(struct file *filp, unsigned int level,
				   u64 num_blocks_to_hash,
				   const struct merkle_tree_params *params,
				   u8 *pending_hashes,
				   struct ahash_request *req)
{
	struct inode *inode = file_inode(filp);
	const struct fsverity_operations *vops = inode->i_sb->s_vop;
	struct file_ra_state ra = { 0 };
	unsigned int pending_size = 0;
	u64 dst_block_num;
	u64 i;
	int err;

	if (WARN_ON(params->block_size != PAGE_SIZE)) /* checked earlier too */
		return -EINVAL;

	if (level < params->num_levels) {
		dst_block_num = params->level_start[level];
	} else {
		if (WARN_ON(num_blocks_to_hash != 1))
			return -EINVAL;
		dst_block_num = 0; /* unused */
	}

	file_ra_state_init(&ra, filp->f_mapping);

	for (i = 0; i < num_blocks_to_hash; i++) {
		struct page *src_page;

		if ((pgoff_t)i % 10000 == 0 || i + 1 == num_blocks_to_hash)
			pr_debug("Hashing block %llu of %llu for level %u\n",
				 i + 1, num_blocks_to_hash, level);

		if (level == 0) {
			/* Leaf: hashing a data block */
			src_page = read_file_data_page(filp, i, &ra,
						       num_blocks_to_hash - i);
			if (IS_ERR(src_page)) {
				err = PTR_ERR(src_page);
				fsverity_err(inode,
					     "Error %d reading data page %llu",
					     err, i);
				return err;
			}
		} else {
			unsigned long num_ra_pages =
				min_t(unsigned long, num_blocks_to_hash - i,
				      inode->i_sb->s_bdi->io_pages);

			/* Non-leaf: hashing hash block from level below */
			src_page = vops->read_merkle_tree_page(inode,
					params->level_start[level - 1] + i,
					num_ra_pages);
			if (IS_ERR(src_page)) {
				err = PTR_ERR(src_page);
				fsverity_err(inode,
					     "Error %d reading Merkle tree page %llu",
					     err, params->level_start[level - 1] + i);
				return err;
			}
		}

		err = fsverity_hash_page(params, inode, req, src_page,
					 &pending_hashes[pending_size]);
		put_page(src_page);
		if (err)
			return err;
		pending_size += params->digest_size;

		if (level == params->num_levels) /* Root hash? */
			return 0;

		if (pending_size + params->digest_size > params->block_size ||
		    i + 1 == num_blocks_to_hash) {
			/* Flush the pending hash block */
			memset(&pending_hashes[pending_size], 0,
			       params->block_size - pending_size);
			err = vops->write_merkle_tree_block(inode,
					pending_hashes,
					dst_block_num,
					params->log_blocksize);
			if (err) {
				fsverity_err(inode,
					     "Error %d writing Merkle tree block %llu",
					     err, dst_block_num);
				return err;
			}
			dst_block_num++;
			pending_size = 0;
		}

		if (fatal_signal_pending(current))
			return -EINTR;
		cond_resched();
	}
	return 0;
}

/*
 * Build the Merkle tree for the given file using the given parameters, and
 * return the root hash in @root_hash.
 *
 * The tree is written to a filesystem-specific location as determined by the
 * ->write_merkle_tree_block() method.  However, the blocks that comprise the
 * tree are the same for all filesystems.
 */
static int build_merkle_tree(struct file *filp,
			     const struct merkle_tree_params *params,
			     u8 *root_hash)
{
	struct inode *inode = file_inode(filp);
	u8 *pending_hashes;
	struct ahash_request *req;
	u64 blocks;
	unsigned int level;
	int err = -ENOMEM;

	if (inode->i_size == 0) {
		/* Empty file is a special case; root hash is all 0's */
		memset(root_hash, 0, params->digest_size);
		return 0;
	}

	/* This allocation never fails, since it's mempool-backed. */
	req = fsverity_alloc_hash_request(params->hash_alg, GFP_KERNEL);

	pending_hashes = kmalloc(params->block_size, GFP_KERNEL);
	if (!pending_hashes)
		goto out;

	/*
	 * Build each level of the Merkle tree, starting at the leaf level
	 * (level 0) and ascending to the root node (level 'num_levels - 1').
	 * Then at the end (level 'num_levels'), calculate the root hash.
	 */
	blocks = (inode->i_size + params->block_size - 1) >>
		 params->log_blocksize;
	for (level = 0; level <= params->num_levels; level++) {
		err = build_merkle_tree_level(filp, level, blocks, params,
					      pending_hashes, req);
		if (err)
			goto out;
		blocks = (blocks + params->hashes_per_block - 1) >>
			 params->log_arity;
	}
	memcpy(root_hash, pending_hashes, params->digest_size);
	err = 0;
out:
	kfree(pending_hashes);
	fsverity_free_hash_request(params->hash_alg, req);
	return err;
}

static int enable_verity(struct file *filp,
			 const struct fsverity_enable_arg *arg)
{
	struct inode *inode = file_inode(filp);
	const struct fsverity_operations *vops = inode->i_sb->s_vop;
	struct merkle_tree_params params = { };
	struct fsverity_descriptor *desc;
	size_t desc_size = sizeof(*desc) + arg->sig_size;
	struct fsverity_info *vi;
	int err;

	/* Start initializing the fsverity_descriptor */
	desc = kzalloc(desc_size, GFP_KERNEL);
	if (!desc)
		return -ENOMEM;
	desc->version = 1;
	desc->hash_algorithm = arg->hash_algorithm;
	desc->log_blocksize = ilog2(arg->block_size);

	/* Get the salt if the user provided one */
	if (arg->salt_size &&
	    copy_from_user(desc->salt, u64_to_user_ptr(arg->salt_ptr),
			   arg->salt_size)) {
		err = -EFAULT;
		goto out;
	}
	desc->salt_size = arg->salt_size;

	/* Get the signature if the user provided one */
	if (arg->sig_size &&
	    copy_from_user(desc->signature, u64_to_user_ptr(arg->sig_ptr),
			   arg->sig_size)) {
		err = -EFAULT;
		goto out;
	}
	desc->sig_size = cpu_to_le32(arg->sig_size);

	desc->data_size = cpu_to_le64(inode->i_size);

	/* Prepare the Merkle tree parameters */
	err = fsverity_init_merkle_tree_params(&params, inode,
					       arg->hash_algorithm,
					       desc->log_blocksize,
					       desc->salt, desc->salt_size);
	if (err)
		goto out;

	/*
	 * Start enabling verity on this file, serialized by the inode lock.
	 * Fail if verity is already enabled or is already being enabled.
	 */
	inode_lock(inode);
	if (IS_VERITY(inode))
		err = -EEXIST;
	else
		err = vops->begin_enable_verity(filp);
	inode_unlock(inode);
	if (err)
		goto out;

	/*
	 * Build the Merkle tree.  Don't hold the inode lock during this, since
	 * on huge files this may take a very long time and we don't want to
	 * force unrelated syscalls like chown() to block forever.  We don't
	 * need the inode lock here because deny_write_access() already prevents
	 * the file from being written to or truncated, and we still serialize
	 * ->begin_enable_verity() and ->end_enable_verity() using the inode
	 * lock and only allow one process to be here at a time on a given file.
	 */
	pr_debug("Building Merkle tree...\n");
	BUILD_BUG_ON(sizeof(desc->root_hash) < FS_VERITY_MAX_DIGEST_SIZE);
	err = build_merkle_tree(filp, &params, desc->root_hash);
	if (err) {
		fsverity_err(inode, "Error %d building Merkle tree", err);
		goto rollback;
	}
	pr_debug("Done building Merkle tree.  Root hash is %s:%*phN\n",
		 params.hash_alg->name, params.digest_size, desc->root_hash);

	/*
	 * Create the fsverity_info.  Don't bother trying to save work by
	 * reusing the merkle_tree_params from above.  Instead, just create the
	 * fsverity_info from the fsverity_descriptor as if it were just loaded
	 * from disk.  This is simpler, and it serves as an extra check that the
	 * metadata we're writing is valid before actually enabling verity.
	 */
	vi = fsverity_create_info(inode, desc, desc_size);
	if (IS_ERR(vi)) {
		err = PTR_ERR(vi);
		goto rollback;
	}

	if (arg->sig_size)
		pr_debug("Storing a %u-byte PKCS#7 signature alongside the file\n",
			 arg->sig_size);

	/*
	 * Tell the filesystem to finish enabling verity on the file.
	 * Serialized with ->begin_enable_verity() by the inode lock.
	 */
	inode_lock(inode);
	err = vops->end_enable_verity(filp, desc, desc_size, params.tree_size);
	inode_unlock(inode);
	if (err) {
		fsverity_err(inode, "%ps() failed with err %d",
			     vops->end_enable_verity, err);
		fsverity_free_info(vi);
	} else if (WARN_ON(!IS_VERITY(inode))) {
		err = -EINVAL;
		fsverity_free_info(vi);
	} else {
		/* Successfully enabled verity */

		/*
		 * Readers can start using ->i_verity_info immediately, so it
		 * can't be rolled back once set.  So don't set it until just
		 * after the filesystem has successfully enabled verity.
		 */
		fsverity_set_info(inode, vi);
	}
out:
	kfree(params.hashstate);
	kfree(desc);
	return err;

rollback:
	inode_lock(inode);
	(void)vops->end_enable_verity(filp, NULL, 0, params.tree_size);
	inode_unlock(inode);
	goto out;
}

/**
 * fsverity_ioctl_enable() - enable verity on a file
 * @filp: file to enable verity on
 * @uarg: user pointer to fsverity_enable_arg
 *
 * Enable fs-verity on a file.  See the "FS_IOC_ENABLE_VERITY" section of
 * Documentation/filesystems/fsverity.rst for the documentation.
 *
 * Return: 0 on success, -errno on failure
 */
int fsverity_ioctl_enable(struct file *filp, const void __user *uarg)
{
	struct inode *inode = file_inode(filp);
	struct fsverity_enable_arg arg;
	int err;

	if (copy_from_user(&arg, uarg, sizeof(arg)))
		return -EFAULT;

	if (arg.version != 1)
		return -EINVAL;

	if (arg.__reserved1 ||
	    memchr_inv(arg.__reserved2, 0, sizeof(arg.__reserved2)))
		return -EINVAL;

	if (arg.block_size != PAGE_SIZE)
		return -EINVAL;

	if (arg.salt_size > sizeof_field(struct fsverity_descriptor, salt))
		return -EMSGSIZE;

	if (arg.sig_size > FS_VERITY_MAX_SIGNATURE_SIZE)
		return -EMSGSIZE;

	/*
	 * Require a regular file with write access.  But the actual fd must
	 * still be readonly so that we can lock out all writers.  This is
	 * needed to guarantee that no writable fds exist to the file once it
	 * has verity enabled, and to stabilize the data being hashed.
	 */

	err = inode_permission(inode, MAY_WRITE);
	if (err)
		return err;

	if (IS_APPEND(inode))
		return -EPERM;

	if (S_ISDIR(inode->i_mode))
		return -EISDIR;

	if (!S_ISREG(inode->i_mode))
		return -EINVAL;

	err = mnt_want_write_file(filp);
	if (err) /* -EROFS */
		return err;

	err = deny_write_access(filp);
	if (err) /* -ETXTBSY */
		goto out_drop_write;

	err = enable_verity(filp, &arg);
	if (err)
		goto out_allow_write_access;

	/*
	 * Some pages of the file may have been evicted from pagecache after
	 * being used in the Merkle tree construction, then read into pagecache
	 * again by another process reading from the file concurrently.  Since
	 * these pages didn't undergo verification against the file measurement
	 * which fs-verity now claims to be enforcing, we have to wipe the
	 * pagecache to ensure that all future reads are verified.
	 */
	filemap_write_and_wait(inode->i_mapping);
	invalidate_inode_pages2(inode->i_mapping);

	/*
	 * allow_write_access() is needed to pair with deny_write_access().
	 * Regardless, the filesystem won't allow writing to verity files.
	 */
out_allow_write_access:
	allow_write_access(filp);
out_drop_write:
	mnt_drop_write_file(filp);
	return err;
}
EXPORT_SYMBOL_GPL(fsverity_ioctl_enable);