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