1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * fs/verity/open.c: opening fs-verity files
4 *
5 * Copyright 2019 Google LLC
6 */
7
8 #include "fsverity_private.h"
9
10 #include <linux/slab.h>
11
12 static struct kmem_cache *fsverity_info_cachep;
13
14 /**
15 * fsverity_init_merkle_tree_params() - initialize Merkle tree parameters
16 * @params: the parameters struct to initialize
17 * @inode: the inode for which the Merkle tree is being built
18 * @hash_algorithm: number of hash algorithm to use
19 * @log_blocksize: log base 2 of block size to use
20 * @salt: pointer to salt (optional)
21 * @salt_size: size of salt, possibly 0
22 *
23 * Validate the hash algorithm and block size, then compute the tree topology
24 * (num levels, num blocks in each level, etc.) and initialize @params.
25 *
26 * Return: 0 on success, -errno on failure
27 */
fsverity_init_merkle_tree_params(struct merkle_tree_params * params,const struct inode * inode,unsigned int hash_algorithm,unsigned int log_blocksize,const u8 * salt,size_t salt_size)28 int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
29 const struct inode *inode,
30 unsigned int hash_algorithm,
31 unsigned int log_blocksize,
32 const u8 *salt, size_t salt_size)
33 {
34 struct fsverity_hash_alg *hash_alg;
35 int err;
36 u64 blocks;
37 u64 offset;
38 int level;
39
40 memset(params, 0, sizeof(*params));
41
42 hash_alg = fsverity_get_hash_alg(inode, hash_algorithm);
43 if (IS_ERR(hash_alg))
44 return PTR_ERR(hash_alg);
45 params->hash_alg = hash_alg;
46 params->digest_size = hash_alg->digest_size;
47
48 params->hashstate = fsverity_prepare_hash_state(hash_alg, salt,
49 salt_size);
50 if (IS_ERR(params->hashstate)) {
51 err = PTR_ERR(params->hashstate);
52 params->hashstate = NULL;
53 fsverity_err(inode, "Error %d preparing hash state", err);
54 goto out_err;
55 }
56
57 if (log_blocksize != PAGE_SHIFT) {
58 fsverity_warn(inode, "Unsupported log_blocksize: %u",
59 log_blocksize);
60 err = -EINVAL;
61 goto out_err;
62 }
63 params->log_blocksize = log_blocksize;
64 params->block_size = 1 << log_blocksize;
65
66 if (WARN_ON(!is_power_of_2(params->digest_size))) {
67 err = -EINVAL;
68 goto out_err;
69 }
70 if (params->block_size < 2 * params->digest_size) {
71 fsverity_warn(inode,
72 "Merkle tree block size (%u) too small for hash algorithm \"%s\"",
73 params->block_size, hash_alg->name);
74 err = -EINVAL;
75 goto out_err;
76 }
77 params->log_arity = params->log_blocksize - ilog2(params->digest_size);
78 params->hashes_per_block = 1 << params->log_arity;
79
80 pr_debug("Merkle tree uses %s with %u-byte blocks (%u hashes/block), salt=%*phN\n",
81 hash_alg->name, params->block_size, params->hashes_per_block,
82 (int)salt_size, salt);
83
84 /*
85 * Compute the number of levels in the Merkle tree and create a map from
86 * level to the starting block of that level. Level 'num_levels - 1' is
87 * the root and is stored first. Level 0 is the level directly "above"
88 * the data blocks and is stored last.
89 */
90
91 /* Compute number of levels and the number of blocks in each level */
92 blocks = ((u64)inode->i_size + params->block_size - 1) >> log_blocksize;
93 pr_debug("Data is %lld bytes (%llu blocks)\n", inode->i_size, blocks);
94 while (blocks > 1) {
95 if (params->num_levels >= FS_VERITY_MAX_LEVELS) {
96 fsverity_err(inode, "Too many levels in Merkle tree");
97 err = -EINVAL;
98 goto out_err;
99 }
100 blocks = (blocks + params->hashes_per_block - 1) >>
101 params->log_arity;
102 /* temporarily using level_start[] to store blocks in level */
103 params->level_start[params->num_levels++] = blocks;
104 }
105 params->level0_blocks = params->level_start[0];
106
107 /* Compute the starting block of each level */
108 offset = 0;
109 for (level = (int)params->num_levels - 1; level >= 0; level--) {
110 blocks = params->level_start[level];
111 params->level_start[level] = offset;
112 pr_debug("Level %d is %llu blocks starting at index %llu\n",
113 level, blocks, offset);
114 offset += blocks;
115 }
116
117 params->tree_size = offset << log_blocksize;
118 return 0;
119
120 out_err:
121 kfree(params->hashstate);
122 memset(params, 0, sizeof(*params));
123 return err;
124 }
125
126 /*
127 * Compute the file measurement by hashing the fsverity_descriptor excluding the
128 * signature and with the sig_size field set to 0.
129 */
compute_file_measurement(struct fsverity_hash_alg * hash_alg,struct fsverity_descriptor * desc,u8 * measurement)130 static int compute_file_measurement(struct fsverity_hash_alg *hash_alg,
131 struct fsverity_descriptor *desc,
132 u8 *measurement)
133 {
134 __le32 sig_size = desc->sig_size;
135 int err;
136
137 desc->sig_size = 0;
138 err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), measurement);
139 desc->sig_size = sig_size;
140
141 return err;
142 }
143
144 /*
145 * Validate the given fsverity_descriptor and create a new fsverity_info from
146 * it. The signature (if present) is also checked.
147 */
fsverity_create_info(const struct inode * inode,void * _desc,size_t desc_size)148 struct fsverity_info *fsverity_create_info(const struct inode *inode,
149 void *_desc, size_t desc_size)
150 {
151 struct fsverity_descriptor *desc = _desc;
152 struct fsverity_info *vi;
153 int err;
154
155 if (desc_size < sizeof(*desc)) {
156 fsverity_err(inode, "Unrecognized descriptor size: %zu bytes",
157 desc_size);
158 return ERR_PTR(-EINVAL);
159 }
160
161 if (desc->version != 1) {
162 fsverity_err(inode, "Unrecognized descriptor version: %u",
163 desc->version);
164 return ERR_PTR(-EINVAL);
165 }
166
167 if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
168 fsverity_err(inode, "Reserved bits set in descriptor");
169 return ERR_PTR(-EINVAL);
170 }
171
172 if (desc->salt_size > sizeof(desc->salt)) {
173 fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
174 return ERR_PTR(-EINVAL);
175 }
176
177 if (le64_to_cpu(desc->data_size) != inode->i_size) {
178 fsverity_err(inode,
179 "Wrong data_size: %llu (desc) != %lld (inode)",
180 le64_to_cpu(desc->data_size), inode->i_size);
181 return ERR_PTR(-EINVAL);
182 }
183
184 vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL);
185 if (!vi)
186 return ERR_PTR(-ENOMEM);
187 vi->inode = inode;
188
189 err = fsverity_init_merkle_tree_params(&vi->tree_params, inode,
190 desc->hash_algorithm,
191 desc->log_blocksize,
192 desc->salt, desc->salt_size);
193 if (err) {
194 fsverity_err(inode,
195 "Error %d initializing Merkle tree parameters",
196 err);
197 goto out;
198 }
199
200 memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
201
202 err = compute_file_measurement(vi->tree_params.hash_alg, desc,
203 vi->measurement);
204 if (err) {
205 fsverity_err(inode, "Error %d computing file measurement", err);
206 goto out;
207 }
208 pr_debug("Computed file measurement: %s:%*phN\n",
209 vi->tree_params.hash_alg->name,
210 vi->tree_params.digest_size, vi->measurement);
211
212 err = fsverity_verify_signature(vi, desc, desc_size);
213 out:
214 if (err) {
215 fsverity_free_info(vi);
216 vi = ERR_PTR(err);
217 }
218 return vi;
219 }
220
fsverity_set_info(struct inode * inode,struct fsverity_info * vi)221 void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
222 {
223 /*
224 * Multiple processes may race to set ->i_verity_info, so use cmpxchg.
225 * This pairs with the READ_ONCE() in fsverity_get_info().
226 */
227 if (cmpxchg(&inode->i_verity_info, NULL, vi) != NULL)
228 fsverity_free_info(vi);
229 }
230
fsverity_free_info(struct fsverity_info * vi)231 void fsverity_free_info(struct fsverity_info *vi)
232 {
233 if (!vi)
234 return;
235 kfree(vi->tree_params.hashstate);
236 kmem_cache_free(fsverity_info_cachep, vi);
237 }
238
239 /* Ensure the inode has an ->i_verity_info */
ensure_verity_info(struct inode * inode)240 static int ensure_verity_info(struct inode *inode)
241 {
242 struct fsverity_info *vi = fsverity_get_info(inode);
243 struct fsverity_descriptor *desc;
244 int res;
245
246 if (vi)
247 return 0;
248
249 res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0);
250 if (res < 0) {
251 fsverity_err(inode,
252 "Error %d getting verity descriptor size", res);
253 return res;
254 }
255 if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
256 fsverity_err(inode, "Verity descriptor is too large (%d bytes)",
257 res);
258 return -EMSGSIZE;
259 }
260 desc = kmalloc(res, GFP_KERNEL);
261 if (!desc)
262 return -ENOMEM;
263 res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res);
264 if (res < 0) {
265 fsverity_err(inode, "Error %d reading verity descriptor", res);
266 goto out_free_desc;
267 }
268
269 vi = fsverity_create_info(inode, desc, res);
270 if (IS_ERR(vi)) {
271 res = PTR_ERR(vi);
272 goto out_free_desc;
273 }
274
275 fsverity_set_info(inode, vi);
276 res = 0;
277 out_free_desc:
278 kfree(desc);
279 return res;
280 }
281
282 /**
283 * fsverity_file_open() - prepare to open a verity file
284 * @inode: the inode being opened
285 * @filp: the struct file being set up
286 *
287 * When opening a verity file, deny the open if it is for writing. Otherwise,
288 * set up the inode's ->i_verity_info if not already done.
289 *
290 * When combined with fscrypt, this must be called after fscrypt_file_open().
291 * Otherwise, we won't have the key set up to decrypt the verity metadata.
292 *
293 * Return: 0 on success, -errno on failure
294 */
fsverity_file_open(struct inode * inode,struct file * filp)295 int fsverity_file_open(struct inode *inode, struct file *filp)
296 {
297 if (!IS_VERITY(inode))
298 return 0;
299
300 if (filp->f_mode & FMODE_WRITE) {
301 pr_debug("Denying opening verity file (ino %lu) for write\n",
302 inode->i_ino);
303 return -EPERM;
304 }
305
306 return ensure_verity_info(inode);
307 }
308 EXPORT_SYMBOL_GPL(fsverity_file_open);
309
310 /**
311 * fsverity_prepare_setattr() - prepare to change a verity inode's attributes
312 * @dentry: dentry through which the inode is being changed
313 * @attr: attributes to change
314 *
315 * Verity files are immutable, so deny truncates. This isn't covered by the
316 * open-time check because sys_truncate() takes a path, not a file descriptor.
317 *
318 * Return: 0 on success, -errno on failure
319 */
fsverity_prepare_setattr(struct dentry * dentry,struct iattr * attr)320 int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
321 {
322 if (IS_VERITY(d_inode(dentry)) && (attr->ia_valid & ATTR_SIZE)) {
323 pr_debug("Denying truncate of verity file (ino %lu)\n",
324 d_inode(dentry)->i_ino);
325 return -EPERM;
326 }
327 return 0;
328 }
329 EXPORT_SYMBOL_GPL(fsverity_prepare_setattr);
330
331 /**
332 * fsverity_cleanup_inode() - free the inode's verity info, if present
333 * @inode: an inode being evicted
334 *
335 * Filesystems must call this on inode eviction to free ->i_verity_info.
336 */
fsverity_cleanup_inode(struct inode * inode)337 void fsverity_cleanup_inode(struct inode *inode)
338 {
339 fsverity_free_info(inode->i_verity_info);
340 inode->i_verity_info = NULL;
341 }
342 EXPORT_SYMBOL_GPL(fsverity_cleanup_inode);
343
fsverity_init_info_cache(void)344 int __init fsverity_init_info_cache(void)
345 {
346 fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info,
347 SLAB_RECLAIM_ACCOUNT,
348 measurement);
349 if (!fsverity_info_cachep)
350 return -ENOMEM;
351 return 0;
352 }
353
fsverity_exit_info_cache(void)354 void __init fsverity_exit_info_cache(void)
355 {
356 kmem_cache_destroy(fsverity_info_cachep);
357 fsverity_info_cachep = NULL;
358 }
359