1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * fs/crypto/hooks.c 4 * 5 * Encryption hooks for higher-level filesystem operations. 6 */ 7 8 #include <linux/export.h> 9 10 #include "fscrypt_private.h" 11 12 /** 13 * fscrypt_file_open() - prepare to open a possibly-encrypted regular file 14 * @inode: the inode being opened 15 * @filp: the struct file being set up 16 * 17 * Currently, an encrypted regular file can only be opened if its encryption key 18 * is available; access to the raw encrypted contents is not supported. 19 * Therefore, we first set up the inode's encryption key (if not already done) 20 * and return an error if it's unavailable. 21 * 22 * We also verify that if the parent directory (from the path via which the file 23 * is being opened) is encrypted, then the inode being opened uses the same 24 * encryption policy. This is needed as part of the enforcement that all files 25 * in an encrypted directory tree use the same encryption policy, as a 26 * protection against certain types of offline attacks. Note that this check is 27 * needed even when opening an *unencrypted* file, since it's forbidden to have 28 * an unencrypted file in an encrypted directory. 29 * 30 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code 31 */ 32 int fscrypt_file_open(struct inode *inode, struct file *filp) 33 { 34 int err; 35 struct dentry *dentry, *dentry_parent; 36 struct inode *inode_parent; 37 38 err = fscrypt_require_key(inode); 39 if (err) 40 return err; 41 42 dentry = file_dentry(filp); 43 44 /* 45 * Getting a reference to the parent dentry is needed for the actual 46 * encryption policy comparison, but it's expensive on multi-core 47 * systems. Since this function runs on unencrypted files too, start 48 * with a lightweight RCU-mode check for the parent directory being 49 * unencrypted (in which case it's fine for the child to be either 50 * unencrypted, or encrypted with any policy). Only continue on to the 51 * full policy check if the parent directory is actually encrypted. 52 */ 53 rcu_read_lock(); 54 dentry_parent = READ_ONCE(dentry->d_parent); 55 inode_parent = d_inode_rcu(dentry_parent); 56 if (inode_parent != NULL && !IS_ENCRYPTED(inode_parent)) { 57 rcu_read_unlock(); 58 return 0; 59 } 60 rcu_read_unlock(); 61 62 dentry_parent = dget_parent(dentry); 63 if (!fscrypt_has_permitted_context(d_inode(dentry_parent), inode)) { 64 fscrypt_warn(inode, 65 "Inconsistent encryption context (parent directory: %lu)", 66 d_inode(dentry_parent)->i_ino); 67 err = -EPERM; 68 } 69 dput(dentry_parent); 70 return err; 71 } 72 EXPORT_SYMBOL_GPL(fscrypt_file_open); 73 74 int __fscrypt_prepare_link(struct inode *inode, struct inode *dir, 75 struct dentry *dentry) 76 { 77 if (fscrypt_is_nokey_name(dentry)) 78 return -ENOKEY; 79 /* 80 * We don't need to separately check that the directory inode's key is 81 * available, as it's implied by the dentry not being a no-key name. 82 */ 83 84 if (!fscrypt_has_permitted_context(dir, inode)) 85 return -EXDEV; 86 87 return 0; 88 } 89 EXPORT_SYMBOL_GPL(__fscrypt_prepare_link); 90 91 int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry, 92 struct inode *new_dir, struct dentry *new_dentry, 93 unsigned int flags) 94 { 95 if (fscrypt_is_nokey_name(old_dentry) || 96 fscrypt_is_nokey_name(new_dentry)) 97 return -ENOKEY; 98 /* 99 * We don't need to separately check that the directory inodes' keys are 100 * available, as it's implied by the dentries not being no-key names. 101 */ 102 103 if (old_dir != new_dir) { 104 if (IS_ENCRYPTED(new_dir) && 105 !fscrypt_has_permitted_context(new_dir, 106 d_inode(old_dentry))) 107 return -EXDEV; 108 109 if ((flags & RENAME_EXCHANGE) && 110 IS_ENCRYPTED(old_dir) && 111 !fscrypt_has_permitted_context(old_dir, 112 d_inode(new_dentry))) 113 return -EXDEV; 114 } 115 return 0; 116 } 117 EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename); 118 119 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry, 120 struct fscrypt_name *fname) 121 { 122 int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname); 123 124 if (err && err != -ENOENT) 125 return err; 126 127 fscrypt_prepare_dentry(dentry, fname->is_nokey_name); 128 129 return err; 130 } 131 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup); 132 133 /** 134 * fscrypt_prepare_lookup_partial() - prepare lookup without filename setup 135 * @dir: the encrypted directory being searched 136 * @dentry: the dentry being looked up in @dir 137 * 138 * This function should be used by the ->lookup and ->atomic_open methods of 139 * filesystems that handle filename encryption and no-key name encoding 140 * themselves and thus can't use fscrypt_prepare_lookup(). Like 141 * fscrypt_prepare_lookup(), this will try to set up the directory's encryption 142 * key and will set DCACHE_NOKEY_NAME on the dentry if the key is unavailable. 143 * However, this function doesn't set up a struct fscrypt_name for the filename. 144 * 145 * Return: 0 on success; -errno on error. Note that the encryption key being 146 * unavailable is not considered an error. It is also not an error if 147 * the encryption policy is unsupported by this kernel; that is treated 148 * like the key being unavailable, so that files can still be deleted. 149 */ 150 int fscrypt_prepare_lookup_partial(struct inode *dir, struct dentry *dentry) 151 { 152 int err = fscrypt_get_encryption_info(dir, true); 153 bool is_nokey_name = (!err && !fscrypt_has_encryption_key(dir)); 154 155 fscrypt_prepare_dentry(dentry, is_nokey_name); 156 157 return err; 158 } 159 EXPORT_SYMBOL_GPL(fscrypt_prepare_lookup_partial); 160 161 int __fscrypt_prepare_readdir(struct inode *dir) 162 { 163 return fscrypt_get_encryption_info(dir, true); 164 } 165 EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir); 166 167 int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr) 168 { 169 if (attr->ia_valid & ATTR_SIZE) 170 return fscrypt_require_key(d_inode(dentry)); 171 return 0; 172 } 173 EXPORT_SYMBOL_GPL(__fscrypt_prepare_setattr); 174 175 /** 176 * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS 177 * @inode: the inode on which flags are being changed 178 * @oldflags: the old flags 179 * @flags: the new flags 180 * 181 * The caller should be holding i_rwsem for write. 182 * 183 * Return: 0 on success; -errno if the flags change isn't allowed or if 184 * another error occurs. 185 */ 186 int fscrypt_prepare_setflags(struct inode *inode, 187 unsigned int oldflags, unsigned int flags) 188 { 189 struct fscrypt_inode_info *ci; 190 struct fscrypt_master_key *mk; 191 int err; 192 193 /* 194 * When the CASEFOLD flag is set on an encrypted directory, we must 195 * derive the secret key needed for the dirhash. This is only possible 196 * if the directory uses a v2 encryption policy. 197 */ 198 if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) { 199 err = fscrypt_require_key(inode); 200 if (err) 201 return err; 202 ci = inode->i_crypt_info; 203 if (ci->ci_policy.version != FSCRYPT_POLICY_V2) 204 return -EINVAL; 205 mk = ci->ci_master_key; 206 down_read(&mk->mk_sem); 207 if (mk->mk_present) 208 err = fscrypt_derive_dirhash_key(ci, mk); 209 else 210 err = -ENOKEY; 211 up_read(&mk->mk_sem); 212 return err; 213 } 214 return 0; 215 } 216 217 /** 218 * fscrypt_prepare_symlink() - prepare to create a possibly-encrypted symlink 219 * @dir: directory in which the symlink is being created 220 * @target: plaintext symlink target 221 * @len: length of @target excluding null terminator 222 * @max_len: space the filesystem has available to store the symlink target 223 * @disk_link: (out) the on-disk symlink target being prepared 224 * 225 * This function computes the size the symlink target will require on-disk, 226 * stores it in @disk_link->len, and validates it against @max_len. An 227 * encrypted symlink may be longer than the original. 228 * 229 * Additionally, @disk_link->name is set to @target if the symlink will be 230 * unencrypted, but left NULL if the symlink will be encrypted. For encrypted 231 * symlinks, the filesystem must call fscrypt_encrypt_symlink() to create the 232 * on-disk target later. (The reason for the two-step process is that some 233 * filesystems need to know the size of the symlink target before creating the 234 * inode, e.g. to determine whether it will be a "fast" or "slow" symlink.) 235 * 236 * Return: 0 on success, -ENAMETOOLONG if the symlink target is too long, 237 * -ENOKEY if the encryption key is missing, or another -errno code if a problem 238 * occurred while setting up the encryption key. 239 */ 240 int fscrypt_prepare_symlink(struct inode *dir, const char *target, 241 unsigned int len, unsigned int max_len, 242 struct fscrypt_str *disk_link) 243 { 244 const union fscrypt_policy *policy; 245 246 /* 247 * To calculate the size of the encrypted symlink target we need to know 248 * the amount of NUL padding, which is determined by the flags set in 249 * the encryption policy which will be inherited from the directory. 250 */ 251 policy = fscrypt_policy_to_inherit(dir); 252 if (policy == NULL) { 253 /* Not encrypted */ 254 disk_link->name = (unsigned char *)target; 255 disk_link->len = len + 1; 256 if (disk_link->len > max_len) 257 return -ENAMETOOLONG; 258 return 0; 259 } 260 if (IS_ERR(policy)) 261 return PTR_ERR(policy); 262 263 /* 264 * Calculate the size of the encrypted symlink and verify it won't 265 * exceed max_len. Note that for historical reasons, encrypted symlink 266 * targets are prefixed with the ciphertext length, despite this 267 * actually being redundant with i_size. This decreases by 2 bytes the 268 * longest symlink target we can accept. 269 * 270 * We could recover 1 byte by not counting a null terminator, but 271 * counting it (even though it is meaningless for ciphertext) is simpler 272 * for now since filesystems will assume it is there and subtract it. 273 */ 274 if (!__fscrypt_fname_encrypted_size(policy, len, 275 max_len - sizeof(struct fscrypt_symlink_data) - 1, 276 &disk_link->len)) 277 return -ENAMETOOLONG; 278 disk_link->len += sizeof(struct fscrypt_symlink_data) + 1; 279 280 disk_link->name = NULL; 281 return 0; 282 } 283 EXPORT_SYMBOL_GPL(fscrypt_prepare_symlink); 284 285 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 286 unsigned int len, struct fscrypt_str *disk_link) 287 { 288 int err; 289 struct qstr iname = QSTR_INIT(target, len); 290 struct fscrypt_symlink_data *sd; 291 unsigned int ciphertext_len; 292 293 /* 294 * fscrypt_prepare_new_inode() should have already set up the new 295 * symlink inode's encryption key. We don't wait until now to do it, 296 * since we may be in a filesystem transaction now. 297 */ 298 if (WARN_ON_ONCE(!fscrypt_has_encryption_key(inode))) 299 return -ENOKEY; 300 301 if (disk_link->name) { 302 /* filesystem-provided buffer */ 303 sd = (struct fscrypt_symlink_data *)disk_link->name; 304 } else { 305 sd = kmalloc(disk_link->len, GFP_NOFS); 306 if (!sd) 307 return -ENOMEM; 308 } 309 ciphertext_len = disk_link->len - sizeof(*sd) - 1; 310 sd->len = cpu_to_le16(ciphertext_len); 311 312 err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path, 313 ciphertext_len); 314 if (err) 315 goto err_free_sd; 316 317 /* 318 * Null-terminating the ciphertext doesn't make sense, but we still 319 * count the null terminator in the length, so we might as well 320 * initialize it just in case the filesystem writes it out. 321 */ 322 sd->encrypted_path[ciphertext_len] = '\0'; 323 324 /* Cache the plaintext symlink target for later use by get_link() */ 325 err = -ENOMEM; 326 inode->i_link = kmemdup(target, len + 1, GFP_NOFS); 327 if (!inode->i_link) 328 goto err_free_sd; 329 330 if (!disk_link->name) 331 disk_link->name = (unsigned char *)sd; 332 return 0; 333 334 err_free_sd: 335 if (!disk_link->name) 336 kfree(sd); 337 return err; 338 } 339 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); 340 341 /** 342 * fscrypt_get_symlink() - get the target of an encrypted symlink 343 * @inode: the symlink inode 344 * @caddr: the on-disk contents of the symlink 345 * @max_size: size of @caddr buffer 346 * @done: if successful, will be set up to free the returned target if needed 347 * 348 * If the symlink's encryption key is available, we decrypt its target. 349 * Otherwise, we encode its target for presentation. 350 * 351 * This may sleep, so the filesystem must have dropped out of RCU mode already. 352 * 353 * Return: the presentable symlink target or an ERR_PTR() 354 */ 355 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, 356 unsigned int max_size, 357 struct delayed_call *done) 358 { 359 const struct fscrypt_symlink_data *sd; 360 struct fscrypt_str cstr, pstr; 361 bool has_key; 362 int err; 363 364 /* This is for encrypted symlinks only */ 365 if (WARN_ON_ONCE(!IS_ENCRYPTED(inode))) 366 return ERR_PTR(-EINVAL); 367 368 /* If the decrypted target is already cached, just return it. */ 369 pstr.name = READ_ONCE(inode->i_link); 370 if (pstr.name) 371 return pstr.name; 372 373 /* 374 * Try to set up the symlink's encryption key, but we can continue 375 * regardless of whether the key is available or not. 376 */ 377 err = fscrypt_get_encryption_info(inode, false); 378 if (err) 379 return ERR_PTR(err); 380 has_key = fscrypt_has_encryption_key(inode); 381 382 /* 383 * For historical reasons, encrypted symlink targets are prefixed with 384 * the ciphertext length, even though this is redundant with i_size. 385 */ 386 387 if (max_size < sizeof(*sd) + 1) 388 return ERR_PTR(-EUCLEAN); 389 sd = caddr; 390 cstr.name = (unsigned char *)sd->encrypted_path; 391 cstr.len = le16_to_cpu(sd->len); 392 393 if (cstr.len == 0) 394 return ERR_PTR(-EUCLEAN); 395 396 if (cstr.len + sizeof(*sd) > max_size) 397 return ERR_PTR(-EUCLEAN); 398 399 err = fscrypt_fname_alloc_buffer(cstr.len, &pstr); 400 if (err) 401 return ERR_PTR(err); 402 403 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr); 404 if (err) 405 goto err_kfree; 406 407 err = -EUCLEAN; 408 if (pstr.name[0] == '\0') 409 goto err_kfree; 410 411 pstr.name[pstr.len] = '\0'; 412 413 /* 414 * Cache decrypted symlink targets in i_link for later use. Don't cache 415 * symlink targets encoded without the key, since those become outdated 416 * once the key is added. This pairs with the READ_ONCE() above and in 417 * the VFS path lookup code. 418 */ 419 if (!has_key || 420 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL) 421 set_delayed_call(done, kfree_link, pstr.name); 422 423 return pstr.name; 424 425 err_kfree: 426 kfree(pstr.name); 427 return ERR_PTR(err); 428 } 429 EXPORT_SYMBOL_GPL(fscrypt_get_symlink); 430 431 /** 432 * fscrypt_symlink_getattr() - set the correct st_size for encrypted symlinks 433 * @path: the path for the encrypted symlink being queried 434 * @stat: the struct being filled with the symlink's attributes 435 * 436 * Override st_size of encrypted symlinks to be the length of the decrypted 437 * symlink target (or the no-key encoded symlink target, if the key is 438 * unavailable) rather than the length of the encrypted symlink target. This is 439 * necessary for st_size to match the symlink target that userspace actually 440 * sees. POSIX requires this, and some userspace programs depend on it. 441 * 442 * This requires reading the symlink target from disk if needed, setting up the 443 * inode's encryption key if possible, and then decrypting or encoding the 444 * symlink target. This makes lstat() more heavyweight than is normally the 445 * case. However, decrypted symlink targets will be cached in ->i_link, so 446 * usually the symlink won't have to be read and decrypted again later if/when 447 * it is actually followed, readlink() is called, or lstat() is called again. 448 * 449 * Return: 0 on success, -errno on failure 450 */ 451 int fscrypt_symlink_getattr(const struct path *path, struct kstat *stat) 452 { 453 struct dentry *dentry = path->dentry; 454 struct inode *inode = d_inode(dentry); 455 const char *link; 456 DEFINE_DELAYED_CALL(done); 457 458 /* 459 * To get the symlink target that userspace will see (whether it's the 460 * decrypted target or the no-key encoded target), we can just get it in 461 * the same way the VFS does during path resolution and readlink(). 462 */ 463 link = READ_ONCE(inode->i_link); 464 if (!link) { 465 link = inode->i_op->get_link(dentry, inode, &done); 466 if (IS_ERR(link)) 467 return PTR_ERR(link); 468 } 469 stat->size = strlen(link); 470 do_delayed_call(&done); 471 return 0; 472 } 473 EXPORT_SYMBOL_GPL(fscrypt_symlink_getattr); 474