Eric Biggers | fd2d1ac | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 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 | } |
Eric Biggers | fd39073 | 2020-01-06 12:55:33 -0800 | [diff] [blame^] | 105 | params->level0_blocks = params->level_start[0]; |
Eric Biggers | fd2d1ac | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 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 | |
Eric Biggers | 432434c | 2019-07-22 09:26:23 -0700 | [diff] [blame] | 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 | */ |
Eric Biggers | fd2d1ac | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 130 | static int compute_file_measurement(const struct fsverity_hash_alg *hash_alg, |
Eric Biggers | 432434c | 2019-07-22 09:26:23 -0700 | [diff] [blame] | 131 | struct fsverity_descriptor *desc, |
Eric Biggers | fd2d1ac | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 132 | u8 *measurement) |
| 133 | { |
Eric Biggers | 432434c | 2019-07-22 09:26:23 -0700 | [diff] [blame] | 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; |
Eric Biggers | fd2d1ac | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 142 | } |
| 143 | |
| 144 | /* |
| 145 | * Validate the given fsverity_descriptor and create a new fsverity_info from |
Eric Biggers | 432434c | 2019-07-22 09:26:23 -0700 | [diff] [blame] | 146 | * it. The signature (if present) is also checked. |
Eric Biggers | fd2d1ac | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 147 | */ |
| 148 | struct fsverity_info *fsverity_create_info(const struct inode *inode, |
Eric Biggers | 432434c | 2019-07-22 09:26:23 -0700 | [diff] [blame] | 149 | void *_desc, size_t desc_size) |
Eric Biggers | fd2d1ac | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 150 | { |
Eric Biggers | 432434c | 2019-07-22 09:26:23 -0700 | [diff] [blame] | 151 | struct fsverity_descriptor *desc = _desc; |
Eric Biggers | fd2d1ac | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 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 | |
Eric Biggers | 432434c | 2019-07-22 09:26:23 -0700 | [diff] [blame] | 167 | if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) { |
Eric Biggers | fd2d1ac | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 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); |
Eric Biggers | 432434c | 2019-07-22 09:26:23 -0700 | [diff] [blame] | 211 | |
| 212 | err = fsverity_verify_signature(vi, desc, desc_size); |
Eric Biggers | fd2d1ac | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 213 | out: |
| 214 | if (err) { |
| 215 | fsverity_free_info(vi); |
| 216 | vi = ERR_PTR(err); |
| 217 | } |
| 218 | return vi; |
| 219 | } |
| 220 | |
| 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 | |
| 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 */ |
| 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 | */ |
| 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 | /** |
Eric Biggers | c1d9b58 | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 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 | */ |
| 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 | /** |
Eric Biggers | fd2d1ac | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 332 | * fsverity_cleanup_inode() - free the inode's verity info, if present |
| 333 | * |
| 334 | * Filesystems must call this on inode eviction to free ->i_verity_info. |
| 335 | */ |
| 336 | void fsverity_cleanup_inode(struct inode *inode) |
| 337 | { |
| 338 | fsverity_free_info(inode->i_verity_info); |
| 339 | inode->i_verity_info = NULL; |
| 340 | } |
| 341 | EXPORT_SYMBOL_GPL(fsverity_cleanup_inode); |
| 342 | |
| 343 | int __init fsverity_init_info_cache(void) |
| 344 | { |
| 345 | fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info, |
| 346 | SLAB_RECLAIM_ACCOUNT, |
| 347 | measurement); |
| 348 | if (!fsverity_info_cachep) |
| 349 | return -ENOMEM; |
| 350 | return 0; |
| 351 | } |
Eric Biggers | 8a1d0f9 | 2019-07-22 09:26:22 -0700 | [diff] [blame] | 352 | |
| 353 | void __init fsverity_exit_info_cache(void) |
| 354 | { |
| 355 | kmem_cache_destroy(fsverity_info_cachep); |
| 356 | fsverity_info_cachep = NULL; |
| 357 | } |