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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
12static 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 */
28int 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 = (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
120out_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 */
130static 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 */
148struct 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);
213out:
214 if (err) {
215 fsverity_free_info(vi);
216 vi = ERR_PTR(err);
217 }
218 return vi;
219}
220
221void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
222{
223 /*
224 * Multiple tasks may race to set ->i_verity_info, so use
225 * cmpxchg_release(). This pairs with the smp_load_acquire() in
226 * fsverity_get_info(). I.e., here we publish ->i_verity_info with a
227 * RELEASE barrier so that other tasks can ACQUIRE it.
228 */
229 if (cmpxchg_release(&inode->i_verity_info, NULL, vi) != NULL) {
230 /* Lost the race, so free the fsverity_info we allocated. */
231 fsverity_free_info(vi);
232 /*
233 * Afterwards, the caller may access ->i_verity_info directly,
234 * so make sure to ACQUIRE the winning fsverity_info.
235 */
236 (void)fsverity_get_info(inode);
237 }
238}
239
240void fsverity_free_info(struct fsverity_info *vi)
241{
242 if (!vi)
243 return;
244 kfree(vi->tree_params.hashstate);
245 kmem_cache_free(fsverity_info_cachep, vi);
246}
247
248/* Ensure the inode has an ->i_verity_info */
249static int ensure_verity_info(struct inode *inode)
250{
251 struct fsverity_info *vi = fsverity_get_info(inode);
252 struct fsverity_descriptor *desc;
253 int res;
254
255 if (vi)
256 return 0;
257
258 res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0);
259 if (res < 0) {
260 fsverity_err(inode,
261 "Error %d getting verity descriptor size", res);
262 return res;
263 }
264 if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
265 fsverity_err(inode, "Verity descriptor is too large (%d bytes)",
266 res);
267 return -EMSGSIZE;
268 }
269 desc = kmalloc(res, GFP_KERNEL);
270 if (!desc)
271 return -ENOMEM;
272 res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res);
273 if (res < 0) {
274 fsverity_err(inode, "Error %d reading verity descriptor", res);
275 goto out_free_desc;
276 }
277
278 vi = fsverity_create_info(inode, desc, res);
279 if (IS_ERR(vi)) {
280 res = PTR_ERR(vi);
281 goto out_free_desc;
282 }
283
284 fsverity_set_info(inode, vi);
285 res = 0;
286out_free_desc:
287 kfree(desc);
288 return res;
289}
290
291/**
292 * fsverity_file_open() - prepare to open a verity file
293 * @inode: the inode being opened
294 * @filp: the struct file being set up
295 *
296 * When opening a verity file, deny the open if it is for writing. Otherwise,
297 * set up the inode's ->i_verity_info if not already done.
298 *
299 * When combined with fscrypt, this must be called after fscrypt_file_open().
300 * Otherwise, we won't have the key set up to decrypt the verity metadata.
301 *
302 * Return: 0 on success, -errno on failure
303 */
304int fsverity_file_open(struct inode *inode, struct file *filp)
305{
306 if (!IS_VERITY(inode))
307 return 0;
308
309 if (filp->f_mode & FMODE_WRITE) {
310 pr_debug("Denying opening verity file (ino %lu) for write\n",
311 inode->i_ino);
312 return -EPERM;
313 }
314
315 return ensure_verity_info(inode);
316}
317EXPORT_SYMBOL_GPL(fsverity_file_open);
318
319/**
320 * fsverity_prepare_setattr() - prepare to change a verity inode's attributes
321 * @dentry: dentry through which the inode is being changed
322 * @attr: attributes to change
323 *
324 * Verity files are immutable, so deny truncates. This isn't covered by the
325 * open-time check because sys_truncate() takes a path, not a file descriptor.
326 *
327 * Return: 0 on success, -errno on failure
328 */
329int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
330{
331 if (IS_VERITY(d_inode(dentry)) && (attr->ia_valid & ATTR_SIZE)) {
332 pr_debug("Denying truncate of verity file (ino %lu)\n",
333 d_inode(dentry)->i_ino);
334 return -EPERM;
335 }
336 return 0;
337}
338EXPORT_SYMBOL_GPL(fsverity_prepare_setattr);
339
340/**
341 * fsverity_cleanup_inode() - free the inode's verity info, if present
342 * @inode: an inode being evicted
343 *
344 * Filesystems must call this on inode eviction to free ->i_verity_info.
345 */
346void fsverity_cleanup_inode(struct inode *inode)
347{
348 fsverity_free_info(inode->i_verity_info);
349 inode->i_verity_info = NULL;
350}
351EXPORT_SYMBOL_GPL(fsverity_cleanup_inode);
352
353int __init fsverity_init_info_cache(void)
354{
355 fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info,
356 SLAB_RECLAIM_ACCOUNT,
357 measurement);
358 if (!fsverity_info_cachep)
359 return -ENOMEM;
360 return 0;
361}
362
363void __init fsverity_exit_info_cache(void)
364{
365 kmem_cache_destroy(fsverity_info_cachep);
366 fsverity_info_cachep = NULL;
367}