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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 | // SPDX-License-Identifier: GPL-2.0 /* * Ioctl to enable verity on a file * * Copyright 2019 Google LLC */ #include "fsverity_private.h" #include <crypto/hash.h> #include <linux/backing-dev.h> #include <linux/mount.h> #include <linux/pagemap.h> #include <linux/sched/signal.h> #include <linux/uaccess.h> /* * Read a file data page for Merkle tree construction. Do aggressive readahead, * since we're sequentially reading the entire file. */ static struct page *read_file_data_page(struct file *file, pgoff_t index, struct file_ra_state *ra, unsigned long remaining_pages) { DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, index); struct folio *folio; folio = __filemap_get_folio(ractl.mapping, index, FGP_ACCESSED, 0); if (!folio || !folio_test_uptodate(folio)) { if (folio) folio_put(folio); else page_cache_sync_ra(&ractl, remaining_pages); folio = read_cache_folio(ractl.mapping, index, NULL, file); if (IS_ERR(folio)) return &folio->page; } if (folio_test_readahead(folio)) page_cache_async_ra(&ractl, folio, remaining_pages); return folio_file_page(folio, index); } static int build_merkle_tree_level(struct file *filp, unsigned int level, u64 num_blocks_to_hash, const struct merkle_tree_params *params, u8 *pending_hashes, struct ahash_request *req) { struct inode *inode = file_inode(filp); const struct fsverity_operations *vops = inode->i_sb->s_vop; struct file_ra_state ra = { 0 }; unsigned int pending_size = 0; u64 dst_block_num; u64 i; int err; if (WARN_ON(params->block_size != PAGE_SIZE)) /* checked earlier too */ return -EINVAL; if (level < params->num_levels) { dst_block_num = params->level_start[level]; } else { if (WARN_ON(num_blocks_to_hash != 1)) return -EINVAL; dst_block_num = 0; /* unused */ } file_ra_state_init(&ra, filp->f_mapping); for (i = 0; i < num_blocks_to_hash; i++) { struct page *src_page; if ((pgoff_t)i % 10000 == 0 || i + 1 == num_blocks_to_hash) pr_debug("Hashing block %llu of %llu for level %u\n", i + 1, num_blocks_to_hash, level); if (level == 0) { /* Leaf: hashing a data block */ src_page = read_file_data_page(filp, i, &ra, num_blocks_to_hash - i); if (IS_ERR(src_page)) { err = PTR_ERR(src_page); fsverity_err(inode, "Error %d reading data page %llu", err, i); return err; } } else { unsigned long num_ra_pages = min_t(unsigned long, num_blocks_to_hash - i, inode->i_sb->s_bdi->io_pages); /* Non-leaf: hashing hash block from level below */ src_page = vops->read_merkle_tree_page(inode, params->level_start[level - 1] + i, num_ra_pages); if (IS_ERR(src_page)) { err = PTR_ERR(src_page); fsverity_err(inode, "Error %d reading Merkle tree page %llu", err, params->level_start[level - 1] + i); return err; } } err = fsverity_hash_page(params, inode, req, src_page, &pending_hashes[pending_size]); put_page(src_page); if (err) return err; pending_size += params->digest_size; if (level == params->num_levels) /* Root hash? */ return 0; if (pending_size + params->digest_size > params->block_size || i + 1 == num_blocks_to_hash) { /* Flush the pending hash block */ memset(&pending_hashes[pending_size], 0, params->block_size - pending_size); err = vops->write_merkle_tree_block(inode, pending_hashes, dst_block_num, params->log_blocksize); if (err) { fsverity_err(inode, "Error %d writing Merkle tree block %llu", err, dst_block_num); return err; } dst_block_num++; pending_size = 0; } if (fatal_signal_pending(current)) return -EINTR; cond_resched(); } return 0; } /* * Build the Merkle tree for the given file using the given parameters, and * return the root hash in @root_hash. * * The tree is written to a filesystem-specific location as determined by the * ->write_merkle_tree_block() method. However, the blocks that comprise the * tree are the same for all filesystems. */ static int build_merkle_tree(struct file *filp, const struct merkle_tree_params *params, u8 *root_hash) { struct inode *inode = file_inode(filp); u8 *pending_hashes; struct ahash_request *req; u64 blocks; unsigned int level; int err = -ENOMEM; if (inode->i_size == 0) { /* Empty file is a special case; root hash is all 0's */ memset(root_hash, 0, params->digest_size); return 0; } /* This allocation never fails, since it's mempool-backed. */ req = fsverity_alloc_hash_request(params->hash_alg, GFP_KERNEL); pending_hashes = kmalloc(params->block_size, GFP_KERNEL); if (!pending_hashes) goto out; /* * Build each level of the Merkle tree, starting at the leaf level * (level 0) and ascending to the root node (level 'num_levels - 1'). * Then at the end (level 'num_levels'), calculate the root hash. */ blocks = ((u64)inode->i_size + params->block_size - 1) >> params->log_blocksize; for (level = 0; level <= params->num_levels; level++) { err = build_merkle_tree_level(filp, level, blocks, params, pending_hashes, req); if (err) goto out; blocks = (blocks + params->hashes_per_block - 1) >> params->log_arity; } memcpy(root_hash, pending_hashes, params->digest_size); err = 0; out: kfree(pending_hashes); fsverity_free_hash_request(params->hash_alg, req); return err; } static int enable_verity(struct file *filp, const struct fsverity_enable_arg *arg) { struct inode *inode = file_inode(filp); const struct fsverity_operations *vops = inode->i_sb->s_vop; struct merkle_tree_params params = { }; struct fsverity_descriptor *desc; size_t desc_size = struct_size(desc, signature, arg->sig_size); struct fsverity_info *vi; int err; /* Start initializing the fsverity_descriptor */ desc = kzalloc(desc_size, GFP_KERNEL); if (!desc) return -ENOMEM; desc->version = 1; desc->hash_algorithm = arg->hash_algorithm; desc->log_blocksize = ilog2(arg->block_size); /* Get the salt if the user provided one */ if (arg->salt_size && copy_from_user(desc->salt, u64_to_user_ptr(arg->salt_ptr), arg->salt_size)) { err = -EFAULT; goto out; } desc->salt_size = arg->salt_size; /* Get the signature if the user provided one */ if (arg->sig_size && copy_from_user(desc->signature, u64_to_user_ptr(arg->sig_ptr), arg->sig_size)) { err = -EFAULT; goto out; } desc->sig_size = cpu_to_le32(arg->sig_size); desc->data_size = cpu_to_le64(inode->i_size); /* Prepare the Merkle tree parameters */ err = fsverity_init_merkle_tree_params(¶ms, inode, arg->hash_algorithm, desc->log_blocksize, desc->salt, desc->salt_size); if (err) goto out; /* * Start enabling verity on this file, serialized by the inode lock. * Fail if verity is already enabled or is already being enabled. */ inode_lock(inode); if (IS_VERITY(inode)) err = -EEXIST; else err = vops->begin_enable_verity(filp); inode_unlock(inode); if (err) goto out; /* * Build the Merkle tree. Don't hold the inode lock during this, since * on huge files this may take a very long time and we don't want to * force unrelated syscalls like chown() to block forever. We don't * need the inode lock here because deny_write_access() already prevents * the file from being written to or truncated, and we still serialize * ->begin_enable_verity() and ->end_enable_verity() using the inode * lock and only allow one process to be here at a time on a given file. */ pr_debug("Building Merkle tree...\n"); BUILD_BUG_ON(sizeof(desc->root_hash) < FS_VERITY_MAX_DIGEST_SIZE); err = build_merkle_tree(filp, ¶ms, desc->root_hash); if (err) { fsverity_err(inode, "Error %d building Merkle tree", err); goto rollback; } pr_debug("Done building Merkle tree. Root hash is %s:%*phN\n", params.hash_alg->name, params.digest_size, desc->root_hash); /* * Create the fsverity_info. Don't bother trying to save work by * reusing the merkle_tree_params from above. Instead, just create the * fsverity_info from the fsverity_descriptor as if it were just loaded * from disk. This is simpler, and it serves as an extra check that the * metadata we're writing is valid before actually enabling verity. */ vi = fsverity_create_info(inode, desc); if (IS_ERR(vi)) { err = PTR_ERR(vi); goto rollback; } if (arg->sig_size) pr_debug("Storing a %u-byte PKCS#7 signature alongside the file\n", arg->sig_size); /* * Tell the filesystem to finish enabling verity on the file. * Serialized with ->begin_enable_verity() by the inode lock. */ inode_lock(inode); err = vops->end_enable_verity(filp, desc, desc_size, params.tree_size); inode_unlock(inode); if (err) { fsverity_err(inode, "%ps() failed with err %d", vops->end_enable_verity, err); fsverity_free_info(vi); } else if (WARN_ON(!IS_VERITY(inode))) { err = -EINVAL; fsverity_free_info(vi); } else { /* Successfully enabled verity */ /* * Readers can start using ->i_verity_info immediately, so it * can't be rolled back once set. So don't set it until just * after the filesystem has successfully enabled verity. */ fsverity_set_info(inode, vi); } out: kfree(params.hashstate); kfree(desc); return err; rollback: inode_lock(inode); (void)vops->end_enable_verity(filp, NULL, 0, params.tree_size); inode_unlock(inode); goto out; } /** * fsverity_ioctl_enable() - enable verity on a file * @filp: file to enable verity on * @uarg: user pointer to fsverity_enable_arg * * Enable fs-verity on a file. See the "FS_IOC_ENABLE_VERITY" section of * Documentation/filesystems/fsverity.rst for the documentation. * * Return: 0 on success, -errno on failure */ int fsverity_ioctl_enable(struct file *filp, const void __user *uarg) { struct inode *inode = file_inode(filp); struct fsverity_enable_arg arg; int err; if (copy_from_user(&arg, uarg, sizeof(arg))) return -EFAULT; if (arg.version != 1) return -EINVAL; if (arg.__reserved1 || memchr_inv(arg.__reserved2, 0, sizeof(arg.__reserved2))) return -EINVAL; if (arg.block_size != PAGE_SIZE) return -EINVAL; if (arg.salt_size > sizeof_field(struct fsverity_descriptor, salt)) return -EMSGSIZE; if (arg.sig_size > FS_VERITY_MAX_SIGNATURE_SIZE) return -EMSGSIZE; /* * Require a regular file with write access. But the actual fd must * still be readonly so that we can lock out all writers. This is * needed to guarantee that no writable fds exist to the file once it * has verity enabled, and to stabilize the data being hashed. */ err = file_permission(filp, MAY_WRITE); if (err) return err; if (IS_APPEND(inode)) return -EPERM; if (S_ISDIR(inode->i_mode)) return -EISDIR; if (!S_ISREG(inode->i_mode)) return -EINVAL; err = mnt_want_write_file(filp); if (err) /* -EROFS */ return err; err = deny_write_access(filp); if (err) /* -ETXTBSY */ goto out_drop_write; err = enable_verity(filp, &arg); /* * We no longer drop the inode's pagecache after enabling verity. This * used to be done to try to avoid a race condition where pages could be * evicted after being used in the Merkle tree construction, then * re-instantiated by a concurrent read. Such pages are unverified, and * the backing storage could have filled them with different content, so * they shouldn't be used to fulfill reads once verity is enabled. * * But, dropping the pagecache has a big performance impact, and it * doesn't fully solve the race condition anyway. So for those reasons, * and also because this race condition isn't very important relatively * speaking (especially for small-ish files, where the chance of a page * being used, evicted, *and* re-instantiated all while enabling verity * is quite small), we no longer drop the inode's pagecache. */ /* * allow_write_access() is needed to pair with deny_write_access(). * Regardless, the filesystem won't allow writing to verity files. */ allow_write_access(filp); out_drop_write: mnt_drop_write_file(filp); return err; } EXPORT_SYMBOL_GPL(fsverity_ioctl_enable); |