1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * 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 */ 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 digest by hashing the fsverity_descriptor excluding the 128 * signature and with the sig_size field set to 0. 129 */ 130 static int compute_file_digest(struct fsverity_hash_alg *hash_alg, 131 struct fsverity_descriptor *desc, 132 u8 *file_digest) 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), file_digest); 139 desc->sig_size = sig_size; 140 141 return err; 142 } 143 144 /* 145 * Create a new fsverity_info from the given fsverity_descriptor (with optional 146 * appended signature), and check the signature if present. The 147 * fsverity_descriptor must have already undergone basic validation. 148 */ 149 struct fsverity_info *fsverity_create_info(const struct inode *inode, 150 struct fsverity_descriptor *desc, 151 size_t desc_size) 152 { 153 struct fsverity_info *vi; 154 int err; 155 156 vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL); 157 if (!vi) 158 return ERR_PTR(-ENOMEM); 159 vi->inode = inode; 160 161 err = fsverity_init_merkle_tree_params(&vi->tree_params, inode, 162 desc->hash_algorithm, 163 desc->log_blocksize, 164 desc->salt, desc->salt_size); 165 if (err) { 166 fsverity_err(inode, 167 "Error %d initializing Merkle tree parameters", 168 err); 169 goto out; 170 } 171 172 memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size); 173 174 err = compute_file_digest(vi->tree_params.hash_alg, desc, 175 vi->file_digest); 176 if (err) { 177 fsverity_err(inode, "Error %d computing file digest", err); 178 goto out; 179 } 180 pr_debug("Computed file digest: %s:%*phN\n", 181 vi->tree_params.hash_alg->name, 182 vi->tree_params.digest_size, vi->file_digest); 183 184 err = fsverity_verify_signature(vi, desc->signature, 185 le32_to_cpu(desc->sig_size)); 186 out: 187 if (err) { 188 fsverity_free_info(vi); 189 vi = ERR_PTR(err); 190 } 191 return vi; 192 } 193 194 void fsverity_set_info(struct inode *inode, struct fsverity_info *vi) 195 { 196 /* 197 * Multiple tasks may race to set ->i_verity_info, so use 198 * cmpxchg_release(). This pairs with the smp_load_acquire() in 199 * fsverity_get_info(). I.e., here we publish ->i_verity_info with a 200 * RELEASE barrier so that other tasks can ACQUIRE it. 201 */ 202 if (cmpxchg_release(&inode->i_verity_info, NULL, vi) != NULL) { 203 /* Lost the race, so free the fsverity_info we allocated. */ 204 fsverity_free_info(vi); 205 /* 206 * Afterwards, the caller may access ->i_verity_info directly, 207 * so make sure to ACQUIRE the winning fsverity_info. 208 */ 209 (void)fsverity_get_info(inode); 210 } 211 } 212 213 void fsverity_free_info(struct fsverity_info *vi) 214 { 215 if (!vi) 216 return; 217 kfree(vi->tree_params.hashstate); 218 kmem_cache_free(fsverity_info_cachep, vi); 219 } 220 221 static bool validate_fsverity_descriptor(struct inode *inode, 222 const struct fsverity_descriptor *desc, 223 size_t desc_size) 224 { 225 if (desc_size < sizeof(*desc)) { 226 fsverity_err(inode, "Unrecognized descriptor size: %zu bytes", 227 desc_size); 228 return false; 229 } 230 231 if (desc->version != 1) { 232 fsverity_err(inode, "Unrecognized descriptor version: %u", 233 desc->version); 234 return false; 235 } 236 237 if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) { 238 fsverity_err(inode, "Reserved bits set in descriptor"); 239 return false; 240 } 241 242 if (desc->salt_size > sizeof(desc->salt)) { 243 fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size); 244 return false; 245 } 246 247 if (le64_to_cpu(desc->data_size) != inode->i_size) { 248 fsverity_err(inode, 249 "Wrong data_size: %llu (desc) != %lld (inode)", 250 le64_to_cpu(desc->data_size), inode->i_size); 251 return false; 252 } 253 254 if (le32_to_cpu(desc->sig_size) > desc_size - sizeof(*desc)) { 255 fsverity_err(inode, "Signature overflows verity descriptor"); 256 return false; 257 } 258 259 return true; 260 } 261 262 /* 263 * Read the inode's fsverity_descriptor (with optional appended signature) from 264 * the filesystem, and do basic validation of it. 265 */ 266 int fsverity_get_descriptor(struct inode *inode, 267 struct fsverity_descriptor **desc_ret, 268 size_t *desc_size_ret) 269 { 270 int res; 271 struct fsverity_descriptor *desc; 272 273 res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0); 274 if (res < 0) { 275 fsverity_err(inode, 276 "Error %d getting verity descriptor size", res); 277 return res; 278 } 279 if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) { 280 fsverity_err(inode, "Verity descriptor is too large (%d bytes)", 281 res); 282 return -EMSGSIZE; 283 } 284 desc = kmalloc(res, GFP_KERNEL); 285 if (!desc) 286 return -ENOMEM; 287 res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res); 288 if (res < 0) { 289 fsverity_err(inode, "Error %d reading verity descriptor", res); 290 kfree(desc); 291 return res; 292 } 293 294 if (!validate_fsverity_descriptor(inode, desc, res)) { 295 kfree(desc); 296 return -EINVAL; 297 } 298 299 *desc_ret = desc; 300 *desc_size_ret = res; 301 return 0; 302 } 303 304 /* Ensure the inode has an ->i_verity_info */ 305 static int ensure_verity_info(struct inode *inode) 306 { 307 struct fsverity_info *vi = fsverity_get_info(inode); 308 struct fsverity_descriptor *desc; 309 size_t desc_size; 310 int err; 311 312 if (vi) 313 return 0; 314 315 err = fsverity_get_descriptor(inode, &desc, &desc_size); 316 if (err) 317 return err; 318 319 vi = fsverity_create_info(inode, desc, desc_size); 320 if (IS_ERR(vi)) { 321 err = PTR_ERR(vi); 322 goto out_free_desc; 323 } 324 325 fsverity_set_info(inode, vi); 326 err = 0; 327 out_free_desc: 328 kfree(desc); 329 return err; 330 } 331 332 /** 333 * fsverity_file_open() - prepare to open a verity file 334 * @inode: the inode being opened 335 * @filp: the struct file being set up 336 * 337 * When opening a verity file, deny the open if it is for writing. Otherwise, 338 * set up the inode's ->i_verity_info if not already done. 339 * 340 * When combined with fscrypt, this must be called after fscrypt_file_open(). 341 * Otherwise, we won't have the key set up to decrypt the verity metadata. 342 * 343 * Return: 0 on success, -errno on failure 344 */ 345 int fsverity_file_open(struct inode *inode, struct file *filp) 346 { 347 if (!IS_VERITY(inode)) 348 return 0; 349 350 if (filp->f_mode & FMODE_WRITE) { 351 pr_debug("Denying opening verity file (ino %lu) for write\n", 352 inode->i_ino); 353 return -EPERM; 354 } 355 356 return ensure_verity_info(inode); 357 } 358 EXPORT_SYMBOL_GPL(fsverity_file_open); 359 360 /** 361 * fsverity_prepare_setattr() - prepare to change a verity inode's attributes 362 * @dentry: dentry through which the inode is being changed 363 * @attr: attributes to change 364 * 365 * Verity files are immutable, so deny truncates. This isn't covered by the 366 * open-time check because sys_truncate() takes a path, not a file descriptor. 367 * 368 * Return: 0 on success, -errno on failure 369 */ 370 int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr) 371 { 372 if (IS_VERITY(d_inode(dentry)) && (attr->ia_valid & ATTR_SIZE)) { 373 pr_debug("Denying truncate of verity file (ino %lu)\n", 374 d_inode(dentry)->i_ino); 375 return -EPERM; 376 } 377 return 0; 378 } 379 EXPORT_SYMBOL_GPL(fsverity_prepare_setattr); 380 381 /** 382 * fsverity_cleanup_inode() - free the inode's verity info, if present 383 * @inode: an inode being evicted 384 * 385 * Filesystems must call this on inode eviction to free ->i_verity_info. 386 */ 387 void fsverity_cleanup_inode(struct inode *inode) 388 { 389 fsverity_free_info(inode->i_verity_info); 390 inode->i_verity_info = NULL; 391 } 392 EXPORT_SYMBOL_GPL(fsverity_cleanup_inode); 393 394 int __init fsverity_init_info_cache(void) 395 { 396 fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info, 397 SLAB_RECLAIM_ACCOUNT, 398 file_digest); 399 if (!fsverity_info_cachep) 400 return -ENOMEM; 401 return 0; 402 } 403 404 void __init fsverity_exit_info_cache(void) 405 { 406 kmem_cache_destroy(fsverity_info_cachep); 407 fsverity_info_cachep = NULL; 408 } 409