1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Ioctl to enable verity on a file
4 *
5 * Copyright 2019 Google LLC
6 */
7
8 #include "fsverity_private.h"
9
10 #include <crypto/hash.h>
11 #include <linux/mount.h>
12 #include <linux/sched/signal.h>
13 #include <linux/uaccess.h>
14
15 struct block_buffer {
16 u32 filled;
17 bool is_root_hash;
18 u8 *data;
19 };
20
21 /* Hash a block, writing the result to the next level's pending block buffer. */
22 static int hash_one_block(struct inode *inode,
23 const struct merkle_tree_params *params,
24 struct block_buffer *cur)
25 {
26 struct block_buffer *next = cur + 1;
27 int err;
28
29 /*
30 * Safety check to prevent a buffer overflow in case of a filesystem bug
31 * that allows the file size to change despite deny_write_access(), or a
32 * bug in the Merkle tree logic itself
33 */
34 if (WARN_ON_ONCE(next->is_root_hash && next->filled != 0))
35 return -EINVAL;
36
37 /* Zero-pad the block if it's shorter than the block size. */
38 memset(&cur->data[cur->filled], 0, params->block_size - cur->filled);
39
40 err = fsverity_hash_block(params, inode, cur->data,
41 &next->data[next->filled]);
42 if (err)
43 return err;
44 next->filled += params->digest_size;
45 cur->filled = 0;
46 return 0;
47 }
48
49 static int write_merkle_tree_block(struct inode *inode, const u8 *buf,
50 unsigned long index,
51 const struct merkle_tree_params *params)
52 {
53 u64 pos = (u64)index << params->log_blocksize;
54 int err;
55
56 err = inode->i_sb->s_vop->write_merkle_tree_block(inode, buf, pos,
57 params->block_size);
58 if (err)
59 fsverity_err(inode, "Error %d writing Merkle tree block %lu",
60 err, index);
61 return err;
62 }
63
64 /*
65 * Build the Merkle tree for the given file using the given parameters, and
66 * return the root hash in @root_hash.
67 *
68 * The tree is written to a filesystem-specific location as determined by the
69 * ->write_merkle_tree_block() method. However, the blocks that comprise the
70 * tree are the same for all filesystems.
71 */
72 static int build_merkle_tree(struct file *filp,
73 const struct merkle_tree_params *params,
74 u8 *root_hash)
75 {
76 struct inode *inode = file_inode(filp);
77 const u64 data_size = inode->i_size;
78 const int num_levels = params->num_levels;
79 struct block_buffer _buffers[1 + FS_VERITY_MAX_LEVELS + 1] = {};
80 struct block_buffer *buffers = &_buffers[1];
81 unsigned long level_offset[FS_VERITY_MAX_LEVELS];
82 int level;
83 u64 offset;
84 int err;
85
86 if (data_size == 0) {
87 /* Empty file is a special case; root hash is all 0's */
88 memset(root_hash, 0, params->digest_size);
89 return 0;
90 }
91
92 /*
93 * Allocate the block buffers. Buffer "-1" is for data blocks.
94 * Buffers 0 <= level < num_levels are for the actual tree levels.
95 * Buffer 'num_levels' is for the root hash.
96 */
97 for (level = -1; level < num_levels; level++) {
98 buffers[level].data = kzalloc(params->block_size, GFP_KERNEL);
99 if (!buffers[level].data) {
100 err = -ENOMEM;
101 goto out;
102 }
103 }
104 buffers[num_levels].data = root_hash;
105 buffers[num_levels].is_root_hash = true;
106
107 BUILD_BUG_ON(sizeof(level_offset) != sizeof(params->level_start));
108 memcpy(level_offset, params->level_start, sizeof(level_offset));
109
110 /* Hash each data block, also hashing the tree blocks as they fill up */
111 for (offset = 0; offset < data_size; offset += params->block_size) {
112 ssize_t bytes_read;
113 loff_t pos = offset;
114
115 buffers[-1].filled = min_t(u64, params->block_size,
116 data_size - offset);
117 bytes_read = __kernel_read(filp, buffers[-1].data,
118 buffers[-1].filled, &pos);
119 if (bytes_read < 0) {
120 err = bytes_read;
121 fsverity_err(inode, "Error %d reading file data", err);
122 goto out;
123 }
124 if (bytes_read != buffers[-1].filled) {
125 err = -EINVAL;
126 fsverity_err(inode, "Short read of file data");
127 goto out;
128 }
129 err = hash_one_block(inode, params, &buffers[-1]);
130 if (err)
131 goto out;
132 for (level = 0; level < num_levels; level++) {
133 if (buffers[level].filled + params->digest_size <=
134 params->block_size) {
135 /* Next block at @level isn't full yet */
136 break;
137 }
138 /* Next block at @level is full */
139
140 err = hash_one_block(inode, params, &buffers[level]);
141 if (err)
142 goto out;
143 err = write_merkle_tree_block(inode,
144 buffers[level].data,
145 level_offset[level],
146 params);
147 if (err)
148 goto out;
149 level_offset[level]++;
150 }
151 if (fatal_signal_pending(current)) {
152 err = -EINTR;
153 goto out;
154 }
155 cond_resched();
156 }
157 /* Finish all nonempty pending tree blocks. */
158 for (level = 0; level < num_levels; level++) {
159 if (buffers[level].filled != 0) {
160 err = hash_one_block(inode, params, &buffers[level]);
161 if (err)
162 goto out;
163 err = write_merkle_tree_block(inode,
164 buffers[level].data,
165 level_offset[level],
166 params);
167 if (err)
168 goto out;
169 }
170 }
171 /* The root hash was filled by the last call to hash_one_block(). */
172 if (WARN_ON_ONCE(buffers[num_levels].filled != params->digest_size)) {
173 err = -EINVAL;
174 goto out;
175 }
176 err = 0;
177 out:
178 for (level = -1; level < num_levels; level++)
179 kfree(buffers[level].data);
180 return err;
181 }
182
183 static int enable_verity(struct file *filp,
184 const struct fsverity_enable_arg *arg)
185 {
186 struct inode *inode = file_inode(filp);
187 const struct fsverity_operations *vops = inode->i_sb->s_vop;
188 struct merkle_tree_params params = { };
189 struct fsverity_descriptor *desc;
190 size_t desc_size = struct_size(desc, signature, arg->sig_size);
191 struct fsverity_info *vi;
192 int err;
193
194 /* Start initializing the fsverity_descriptor */
195 desc = kzalloc(desc_size, GFP_KERNEL);
196 if (!desc)
197 return -ENOMEM;
198 desc->version = 1;
199 desc->hash_algorithm = arg->hash_algorithm;
200 desc->log_blocksize = ilog2(arg->block_size);
201
202 /* Get the salt if the user provided one */
203 if (arg->salt_size &&
204 copy_from_user(desc->salt, u64_to_user_ptr(arg->salt_ptr),
205 arg->salt_size)) {
206 err = -EFAULT;
207 goto out;
208 }
209 desc->salt_size = arg->salt_size;
210
211 /* Get the builtin signature if the user provided one */
212 if (arg->sig_size &&
213 copy_from_user(desc->signature, u64_to_user_ptr(arg->sig_ptr),
214 arg->sig_size)) {
215 err = -EFAULT;
216 goto out;
217 }
218 desc->sig_size = cpu_to_le32(arg->sig_size);
219
220 desc->data_size = cpu_to_le64(inode->i_size);
221
222 /* Prepare the Merkle tree parameters */
223 err = fsverity_init_merkle_tree_params(¶ms, inode,
224 arg->hash_algorithm,
225 desc->log_blocksize,
226 desc->salt, desc->salt_size);
227 if (err)
228 goto out;
229
230 /*
231 * Start enabling verity on this file, serialized by the inode lock.
232 * Fail if verity is already enabled or is already being enabled.
233 */
234 inode_lock(inode);
235 if (IS_VERITY(inode))
236 err = -EEXIST;
237 else
238 err = vops->begin_enable_verity(filp);
239 inode_unlock(inode);
240 if (err)
241 goto out;
242
243 /*
244 * Build the Merkle tree. Don't hold the inode lock during this, since
245 * on huge files this may take a very long time and we don't want to
246 * force unrelated syscalls like chown() to block forever. We don't
247 * need the inode lock here because deny_write_access() already prevents
248 * the file from being written to or truncated, and we still serialize
249 * ->begin_enable_verity() and ->end_enable_verity() using the inode
250 * lock and only allow one process to be here at a time on a given file.
251 */
252 BUILD_BUG_ON(sizeof(desc->root_hash) < FS_VERITY_MAX_DIGEST_SIZE);
253 err = build_merkle_tree(filp, ¶ms, desc->root_hash);
254 if (err) {
255 fsverity_err(inode, "Error %d building Merkle tree", err);
256 goto rollback;
257 }
258
259 /*
260 * Create the fsverity_info. Don't bother trying to save work by
261 * reusing the merkle_tree_params from above. Instead, just create the
262 * fsverity_info from the fsverity_descriptor as if it were just loaded
263 * from disk. This is simpler, and it serves as an extra check that the
264 * metadata we're writing is valid before actually enabling verity.
265 */
266 vi = fsverity_create_info(inode, desc);
267 if (IS_ERR(vi)) {
268 err = PTR_ERR(vi);
269 goto rollback;
270 }
271
272 /*
273 * Tell the filesystem to finish enabling verity on the file.
274 * Serialized with ->begin_enable_verity() by the inode lock.
275 */
276 inode_lock(inode);
277 err = vops->end_enable_verity(filp, desc, desc_size, params.tree_size);
278 inode_unlock(inode);
279 if (err) {
280 fsverity_err(inode, "%ps() failed with err %d",
281 vops->end_enable_verity, err);
282 fsverity_free_info(vi);
283 } else if (WARN_ON_ONCE(!IS_VERITY(inode))) {
284 err = -EINVAL;
285 fsverity_free_info(vi);
286 } else {
287 /* Successfully enabled verity */
288
289 /*
290 * Readers can start using ->i_verity_info immediately, so it
291 * can't be rolled back once set. So don't set it until just
292 * after the filesystem has successfully enabled verity.
293 */
294 fsverity_set_info(inode, vi);
295 }
296 out:
297 kfree(params.hashstate);
298 kfree(desc);
299 return err;
300
301 rollback:
302 inode_lock(inode);
303 (void)vops->end_enable_verity(filp, NULL, 0, params.tree_size);
304 inode_unlock(inode);
305 goto out;
306 }
307
308 /**
309 * fsverity_ioctl_enable() - enable verity on a file
310 * @filp: file to enable verity on
311 * @uarg: user pointer to fsverity_enable_arg
312 *
313 * Enable fs-verity on a file. See the "FS_IOC_ENABLE_VERITY" section of
314 * Documentation/filesystems/fsverity.rst for the documentation.
315 *
316 * Return: 0 on success, -errno on failure
317 */
318 int fsverity_ioctl_enable(struct file *filp, const void __user *uarg)
319 {
320 struct inode *inode = file_inode(filp);
321 struct fsverity_enable_arg arg;
322 int err;
323
324 if (copy_from_user(&arg, uarg, sizeof(arg)))
325 return -EFAULT;
326
327 if (arg.version != 1)
328 return -EINVAL;
329
330 if (arg.__reserved1 ||
331 memchr_inv(arg.__reserved2, 0, sizeof(arg.__reserved2)))
332 return -EINVAL;
333
334 if (!is_power_of_2(arg.block_size))
335 return -EINVAL;
336
337 if (arg.salt_size > sizeof_field(struct fsverity_descriptor, salt))
338 return -EMSGSIZE;
339
340 if (arg.sig_size > FS_VERITY_MAX_SIGNATURE_SIZE)
341 return -EMSGSIZE;
342
343 /*
344 * Require a regular file with write access. But the actual fd must
345 * still be readonly so that we can lock out all writers. This is
346 * needed to guarantee that no writable fds exist to the file once it
347 * has verity enabled, and to stabilize the data being hashed.
348 */
349
350 err = file_permission(filp, MAY_WRITE);
351 if (err)
352 return err;
353 /*
354 * __kernel_read() is used while building the Merkle tree. So, we can't
355 * allow file descriptors that were opened for ioctl access only, using
356 * the special nonstandard access mode 3. O_RDONLY only, please!
357 */
358 if (!(filp->f_mode & FMODE_READ))
359 return -EBADF;
360
361 if (IS_APPEND(inode))
362 return -EPERM;
363
364 if (S_ISDIR(inode->i_mode))
365 return -EISDIR;
366
367 if (!S_ISREG(inode->i_mode))
368 return -EINVAL;
369
370 err = mnt_want_write_file(filp);
371 if (err) /* -EROFS */
372 return err;
373
374 err = deny_write_access(filp);
375 if (err) /* -ETXTBSY */
376 goto out_drop_write;
377
378 err = enable_verity(filp, &arg);
379
380 /*
381 * We no longer drop the inode's pagecache after enabling verity. This
382 * used to be done to try to avoid a race condition where pages could be
383 * evicted after being used in the Merkle tree construction, then
384 * re-instantiated by a concurrent read. Such pages are unverified, and
385 * the backing storage could have filled them with different content, so
386 * they shouldn't be used to fulfill reads once verity is enabled.
387 *
388 * But, dropping the pagecache has a big performance impact, and it
389 * doesn't fully solve the race condition anyway. So for those reasons,
390 * and also because this race condition isn't very important relatively
391 * speaking (especially for small-ish files, where the chance of a page
392 * being used, evicted, *and* re-instantiated all while enabling verity
393 * is quite small), we no longer drop the inode's pagecache.
394 */
395
396 /*
397 * allow_write_access() is needed to pair with deny_write_access().
398 * Regardless, the filesystem won't allow writing to verity files.
399 */
400 allow_write_access(filp);
401 out_drop_write:
402 mnt_drop_write_file(filp);
403 return err;
404 }
405 EXPORT_SYMBOL_GPL(fsverity_ioctl_enable);
406
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