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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 const 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
106 /* Compute the starting block of each level */
107 offset = 0;
108 for (level = (int)params->num_levels - 1; level >= 0; level--) {
109 blocks = params->level_start[level];
110 params->level_start[level] = offset;
111 pr_debug("Level %d is %llu blocks starting at index %llu\n",
112 level, blocks, offset);
113 offset += blocks;
114 }
115
116 params->tree_size = offset << log_blocksize;
117 return 0;
118
119out_err:
120 kfree(params->hashstate);
121 memset(params, 0, sizeof(*params));
122 return err;
123}
124
125/*
126 * Compute the file measurement by hashing the fsverity_descriptor excluding the
127 * signature and with the sig_size field set to 0.
128 */
129static int compute_file_measurement(const struct fsverity_hash_alg *hash_alg,
130 struct fsverity_descriptor *desc,
131 u8 *measurement)
132{
133 __le32 sig_size = desc->sig_size;
134 int err;
135
136 desc->sig_size = 0;
137 err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), measurement);
138 desc->sig_size = sig_size;
139
140 return err;
141}
142
143/*
144 * Validate the given fsverity_descriptor and create a new fsverity_info from
145 * it. The signature (if present) is also checked.
146 */
147struct fsverity_info *fsverity_create_info(const struct inode *inode,
148 void *_desc, size_t desc_size)
149{
150 struct fsverity_descriptor *desc = _desc;
151 struct fsverity_info *vi;
152 int err;
153
154 if (desc_size < sizeof(*desc)) {
155 fsverity_err(inode, "Unrecognized descriptor size: %zu bytes",
156 desc_size);
157 return ERR_PTR(-EINVAL);
158 }
159
160 if (desc->version != 1) {
161 fsverity_err(inode, "Unrecognized descriptor version: %u",
162 desc->version);
163 return ERR_PTR(-EINVAL);
164 }
165
166 if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
167 fsverity_err(inode, "Reserved bits set in descriptor");
168 return ERR_PTR(-EINVAL);
169 }
170
171 if (desc->salt_size > sizeof(desc->salt)) {
172 fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
173 return ERR_PTR(-EINVAL);
174 }
175
176 if (le64_to_cpu(desc->data_size) != inode->i_size) {
177 fsverity_err(inode,
178 "Wrong data_size: %llu (desc) != %lld (inode)",
179 le64_to_cpu(desc->data_size), inode->i_size);
180 return ERR_PTR(-EINVAL);
181 }
182
183 vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL);
184 if (!vi)
185 return ERR_PTR(-ENOMEM);
186 vi->inode = inode;
187
188 err = fsverity_init_merkle_tree_params(&vi->tree_params, inode,
189 desc->hash_algorithm,
190 desc->log_blocksize,
191 desc->salt, desc->salt_size);
192 if (err) {
193 fsverity_err(inode,
194 "Error %d initializing Merkle tree parameters",
195 err);
196 goto out;
197 }
198
199 memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
200
201 err = compute_file_measurement(vi->tree_params.hash_alg, desc,
202 vi->measurement);
203 if (err) {
204 fsverity_err(inode, "Error %d computing file measurement", err);
205 goto out;
206 }
207 pr_debug("Computed file measurement: %s:%*phN\n",
208 vi->tree_params.hash_alg->name,
209 vi->tree_params.digest_size, vi->measurement);
210
211 err = fsverity_verify_signature(vi, desc, desc_size);
212out:
213 if (err) {
214 fsverity_free_info(vi);
215 vi = ERR_PTR(err);
216 }
217 return vi;
218}
219
220void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
221{
222 /*
223 * Multiple processes may race to set ->i_verity_info, so use cmpxchg.
224 * This pairs with the READ_ONCE() in fsverity_get_info().
225 */
226 if (cmpxchg(&inode->i_verity_info, NULL, vi) != NULL)
227 fsverity_free_info(vi);
228}
229
230void fsverity_free_info(struct fsverity_info *vi)
231{
232 if (!vi)
233 return;
234 kfree(vi->tree_params.hashstate);
235 kmem_cache_free(fsverity_info_cachep, vi);
236}
237
238/* Ensure the inode has an ->i_verity_info */
239static int ensure_verity_info(struct inode *inode)
240{
241 struct fsverity_info *vi = fsverity_get_info(inode);
242 struct fsverity_descriptor *desc;
243 int res;
244
245 if (vi)
246 return 0;
247
248 res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0);
249 if (res < 0) {
250 fsverity_err(inode,
251 "Error %d getting verity descriptor size", res);
252 return res;
253 }
254 if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
255 fsverity_err(inode, "Verity descriptor is too large (%d bytes)",
256 res);
257 return -EMSGSIZE;
258 }
259 desc = kmalloc(res, GFP_KERNEL);
260 if (!desc)
261 return -ENOMEM;
262 res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res);
263 if (res < 0) {
264 fsverity_err(inode, "Error %d reading verity descriptor", res);
265 goto out_free_desc;
266 }
267
268 vi = fsverity_create_info(inode, desc, res);
269 if (IS_ERR(vi)) {
270 res = PTR_ERR(vi);
271 goto out_free_desc;
272 }
273
274 fsverity_set_info(inode, vi);
275 res = 0;
276out_free_desc:
277 kfree(desc);
278 return res;
279}
280
281/**
282 * fsverity_file_open() - prepare to open a verity file
283 * @inode: the inode being opened
284 * @filp: the struct file being set up
285 *
286 * When opening a verity file, deny the open if it is for writing. Otherwise,
287 * set up the inode's ->i_verity_info if not already done.
288 *
289 * When combined with fscrypt, this must be called after fscrypt_file_open().
290 * Otherwise, we won't have the key set up to decrypt the verity metadata.
291 *
292 * Return: 0 on success, -errno on failure
293 */
294int fsverity_file_open(struct inode *inode, struct file *filp)
295{
296 if (!IS_VERITY(inode))
297 return 0;
298
299 if (filp->f_mode & FMODE_WRITE) {
300 pr_debug("Denying opening verity file (ino %lu) for write\n",
301 inode->i_ino);
302 return -EPERM;
303 }
304
305 return ensure_verity_info(inode);
306}
307EXPORT_SYMBOL_GPL(fsverity_file_open);
308
309/**
310 * fsverity_prepare_setattr() - prepare to change a verity inode's attributes
311 * @dentry: dentry through which the inode is being changed
312 * @attr: attributes to change
313 *
314 * Verity files are immutable, so deny truncates. This isn't covered by the
315 * open-time check because sys_truncate() takes a path, not a file descriptor.
316 *
317 * Return: 0 on success, -errno on failure
318 */
319int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
320{
321 if (IS_VERITY(d_inode(dentry)) && (attr->ia_valid & ATTR_SIZE)) {
322 pr_debug("Denying truncate of verity file (ino %lu)\n",
323 d_inode(dentry)->i_ino);
324 return -EPERM;
325 }
326 return 0;
327}
328EXPORT_SYMBOL_GPL(fsverity_prepare_setattr);
329
330/**
331 * fsverity_cleanup_inode() - free the inode's verity info, if present
332 *
333 * Filesystems must call this on inode eviction to free ->i_verity_info.
334 */
335void fsverity_cleanup_inode(struct inode *inode)
336{
337 fsverity_free_info(inode->i_verity_info);
338 inode->i_verity_info = NULL;
339}
340EXPORT_SYMBOL_GPL(fsverity_cleanup_inode);
341
342int __init fsverity_init_info_cache(void)
343{
344 fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info,
345 SLAB_RECLAIM_ACCOUNT,
346 measurement);
347 if (!fsverity_info_cachep)
348 return -ENOMEM;
349 return 0;
350}
351
352void __init fsverity_exit_info_cache(void)
353{
354 kmem_cache_destroy(fsverity_info_cachep);
355 fsverity_info_cachep = NULL;
356}