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 */ 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 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; 118 119 out_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 */ 129 static 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 */ 147 struct 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); 212 out: 213 if (err) { 214 fsverity_free_info(vi); 215 vi = ERR_PTR(err); 216 } 217 return vi; 218 } 219 220 void 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 } 229 230 void 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 */ 239 static 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; 276 out_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 */ 294 int 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 } 307 EXPORT_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 */ 319 int 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 } 328 EXPORT_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 */ 335 void fsverity_cleanup_inode(struct inode *inode) 336 { 337 fsverity_free_info(inode->i_verity_info); 338 inode->i_verity_info = NULL; 339 } 340 EXPORT_SYMBOL_GPL(fsverity_cleanup_inode); 341 342 int __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 } 351 352 void __init fsverity_exit_info_cache(void) 353 { 354 kmem_cache_destroy(fsverity_info_cachep); 355 fsverity_info_cachep = NULL; 356 } 357