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1// SPDX-License-Identifier: GPL-2.0-only2/*3 * fs/crypto/hooks.c4 *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 file12 * @inode: the inode being opened13 * @filp: the struct file being set up14 *15 * Currently, an encrypted regular file can only be opened if its encryption key16 * 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 file21 * is being opened) is encrypted, then the inode being opened uses the same22 * encryption policy. This is needed as part of the enforcement that all files23 * in an encrypted directory tree use the same encryption policy, as a24 * protection against certain types of offline attacks. Note that this check is25 * needed even when opening an *unencrypted* file, since it's forbidden to have26 * an unencrypted file in an encrypted directory.27 *28 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code29 */30int fscrypt_file_open(struct inode *inode, struct file *filp)31{32 int err;33 struct dentry *dentry, *dentry_parent;34 struct inode *inode_parent;35 36 err = fscrypt_require_key(inode);37 if (err)38 return err;39 40 dentry = file_dentry(filp);41 42 /*43 * Getting a reference to the parent dentry is needed for the actual44 * encryption policy comparison, but it's expensive on multi-core45 * systems. Since this function runs on unencrypted files too, start46 * with a lightweight RCU-mode check for the parent directory being47 * unencrypted (in which case it's fine for the child to be either48 * unencrypted, or encrypted with any policy). Only continue on to the49 * full policy check if the parent directory is actually encrypted.50 */51 rcu_read_lock();52 dentry_parent = READ_ONCE(dentry->d_parent);53 inode_parent = d_inode_rcu(dentry_parent);54 if (inode_parent != NULL && !IS_ENCRYPTED(inode_parent)) {55 rcu_read_unlock();56 return 0;57 }58 rcu_read_unlock();59 60 dentry_parent = dget_parent(dentry);61 if (!fscrypt_has_permitted_context(d_inode(dentry_parent), inode)) {62 fscrypt_warn(inode,63 "Inconsistent encryption context (parent directory: %lu)",64 d_inode(dentry_parent)->i_ino);65 err = -EPERM;66 }67 dput(dentry_parent);68 return err;69}70EXPORT_SYMBOL_GPL(fscrypt_file_open);71 72int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,73 struct dentry *dentry)74{75 if (fscrypt_is_nokey_name(dentry))76 return -ENOKEY;77 /*78 * We don't need to separately check that the directory inode's key is79 * available, as it's implied by the dentry not being a no-key name.80 */81 82 if (!fscrypt_has_permitted_context(dir, inode))83 return -EXDEV;84 85 return 0;86}87EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);88 89int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,90 struct inode *new_dir, struct dentry *new_dentry,91 unsigned int flags)92{93 if (fscrypt_is_nokey_name(old_dentry) ||94 fscrypt_is_nokey_name(new_dentry))95 return -ENOKEY;96 /*97 * We don't need to separately check that the directory inodes' keys are98 * available, as it's implied by the dentries not being no-key names.99 */100 101 if (old_dir != new_dir) {102 if (IS_ENCRYPTED(new_dir) &&103 !fscrypt_has_permitted_context(new_dir,104 d_inode(old_dentry)))105 return -EXDEV;106 107 if ((flags & RENAME_EXCHANGE) &&108 IS_ENCRYPTED(old_dir) &&109 !fscrypt_has_permitted_context(old_dir,110 d_inode(new_dentry)))111 return -EXDEV;112 }113 return 0;114}115EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);116 117int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,118 struct fscrypt_name *fname)119{120 int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname);121 122 if (err && err != -ENOENT)123 return err;124 125 fscrypt_prepare_dentry(dentry, fname->is_nokey_name);126 127 return err;128}129EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);130 131/**132 * fscrypt_prepare_lookup_partial() - prepare lookup without filename setup133 * @dir: the encrypted directory being searched134 * @dentry: the dentry being looked up in @dir135 *136 * This function should be used by the ->lookup and ->atomic_open methods of137 * filesystems that handle filename encryption and no-key name encoding138 * themselves and thus can't use fscrypt_prepare_lookup(). Like139 * fscrypt_prepare_lookup(), this will try to set up the directory's encryption140 * key and will set DCACHE_NOKEY_NAME on the dentry if the key is unavailable.141 * However, this function doesn't set up a struct fscrypt_name for the filename.142 *143 * Return: 0 on success; -errno on error. Note that the encryption key being144 * unavailable is not considered an error. It is also not an error if145 * the encryption policy is unsupported by this kernel; that is treated146 * like the key being unavailable, so that files can still be deleted.147 */148int fscrypt_prepare_lookup_partial(struct inode *dir, struct dentry *dentry)149{150 int err = fscrypt_get_encryption_info(dir, true);151 bool is_nokey_name = (!err && !fscrypt_has_encryption_key(dir));152 153 fscrypt_prepare_dentry(dentry, is_nokey_name);154 155 return err;156}157EXPORT_SYMBOL_GPL(fscrypt_prepare_lookup_partial);158 159int __fscrypt_prepare_readdir(struct inode *dir)160{161 return fscrypt_get_encryption_info(dir, true);162}163EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir);164 165int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr)166{167 if (attr->ia_valid & ATTR_SIZE)168 return fscrypt_require_key(d_inode(dentry));169 return 0;170}171EXPORT_SYMBOL_GPL(__fscrypt_prepare_setattr);172 173/**174 * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS175 * @inode: the inode on which flags are being changed176 * @oldflags: the old flags177 * @flags: the new flags178 *179 * The caller should be holding i_rwsem for write.180 *181 * Return: 0 on success; -errno if the flags change isn't allowed or if182 * another error occurs.183 */184int fscrypt_prepare_setflags(struct inode *inode,185 unsigned int oldflags, unsigned int flags)186{187 struct fscrypt_inode_info *ci;188 struct fscrypt_master_key *mk;189 int err;190 191 /*192 * When the CASEFOLD flag is set on an encrypted directory, we must193 * derive the secret key needed for the dirhash. This is only possible194 * if the directory uses a v2 encryption policy.195 */196 if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) {197 err = fscrypt_require_key(inode);198 if (err)199 return err;200 ci = inode->i_crypt_info;201 if (ci->ci_policy.version != FSCRYPT_POLICY_V2)202 return -EINVAL;203 mk = ci->ci_master_key;204 down_read(&mk->mk_sem);205 if (mk->mk_present)206 err = fscrypt_derive_dirhash_key(ci, mk);207 else208 err = -ENOKEY;209 up_read(&mk->mk_sem);210 return err;211 }212 return 0;213}214 215/**216 * fscrypt_prepare_symlink() - prepare to create a possibly-encrypted symlink217 * @dir: directory in which the symlink is being created218 * @target: plaintext symlink target219 * @len: length of @target excluding null terminator220 * @max_len: space the filesystem has available to store the symlink target221 * @disk_link: (out) the on-disk symlink target being prepared222 *223 * This function computes the size the symlink target will require on-disk,224 * stores it in @disk_link->len, and validates it against @max_len. An225 * encrypted symlink may be longer than the original.226 *227 * Additionally, @disk_link->name is set to @target if the symlink will be228 * unencrypted, but left NULL if the symlink will be encrypted. For encrypted229 * symlinks, the filesystem must call fscrypt_encrypt_symlink() to create the230 * on-disk target later. (The reason for the two-step process is that some231 * filesystems need to know the size of the symlink target before creating the232 * inode, e.g. to determine whether it will be a "fast" or "slow" symlink.)233 *234 * Return: 0 on success, -ENAMETOOLONG if the symlink target is too long,235 * -ENOKEY if the encryption key is missing, or another -errno code if a problem236 * occurred while setting up the encryption key.237 */238int fscrypt_prepare_symlink(struct inode *dir, const char *target,239 unsigned int len, unsigned int max_len,240 struct fscrypt_str *disk_link)241{242 const union fscrypt_policy *policy;243 244 /*245 * To calculate the size of the encrypted symlink target we need to know246 * the amount of NUL padding, which is determined by the flags set in247 * the encryption policy which will be inherited from the directory.248 */249 policy = fscrypt_policy_to_inherit(dir);250 if (policy == NULL) {251 /* Not encrypted */252 disk_link->name = (unsigned char *)target;253 disk_link->len = len + 1;254 if (disk_link->len > max_len)255 return -ENAMETOOLONG;256 return 0;257 }258 if (IS_ERR(policy))259 return PTR_ERR(policy);260 261 /*262 * Calculate the size of the encrypted symlink and verify it won't263 * exceed max_len. Note that for historical reasons, encrypted symlink264 * targets are prefixed with the ciphertext length, despite this265 * actually being redundant with i_size. This decreases by 2 bytes the266 * longest symlink target we can accept.267 *268 * We could recover 1 byte by not counting a null terminator, but269 * counting it (even though it is meaningless for ciphertext) is simpler270 * for now since filesystems will assume it is there and subtract it.271 */272 if (!__fscrypt_fname_encrypted_size(policy, len,273 max_len - sizeof(struct fscrypt_symlink_data) - 1,274 &disk_link->len))275 return -ENAMETOOLONG;276 disk_link->len += sizeof(struct fscrypt_symlink_data) + 1;277 278 disk_link->name = NULL;279 return 0;280}281EXPORT_SYMBOL_GPL(fscrypt_prepare_symlink);282 283int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,284 unsigned int len, struct fscrypt_str *disk_link)285{286 int err;287 struct qstr iname = QSTR_INIT(target, len);288 struct fscrypt_symlink_data *sd;289 unsigned int ciphertext_len;290 291 /*292 * fscrypt_prepare_new_inode() should have already set up the new293 * symlink inode's encryption key. We don't wait until now to do it,294 * since we may be in a filesystem transaction now.295 */296 if (WARN_ON_ONCE(!fscrypt_has_encryption_key(inode)))297 return -ENOKEY;298 299 if (disk_link->name) {300 /* filesystem-provided buffer */301 sd = (struct fscrypt_symlink_data *)disk_link->name;302 } else {303 sd = kmalloc(disk_link->len, GFP_NOFS);304 if (!sd)305 return -ENOMEM;306 }307 ciphertext_len = disk_link->len - sizeof(*sd) - 1;308 sd->len = cpu_to_le16(ciphertext_len);309 310 err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path,311 ciphertext_len);312 if (err)313 goto err_free_sd;314 315 /*316 * Null-terminating the ciphertext doesn't make sense, but we still317 * count the null terminator in the length, so we might as well318 * initialize it just in case the filesystem writes it out.319 */320 sd->encrypted_path[ciphertext_len] = '\0';321 322 /* Cache the plaintext symlink target for later use by get_link() */323 err = -ENOMEM;324 inode->i_link = kmemdup(target, len + 1, GFP_NOFS);325 if (!inode->i_link)326 goto err_free_sd;327 328 if (!disk_link->name)329 disk_link->name = (unsigned char *)sd;330 return 0;331 332err_free_sd:333 if (!disk_link->name)334 kfree(sd);335 return err;336}337EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);338 339/**340 * fscrypt_get_symlink() - get the target of an encrypted symlink341 * @inode: the symlink inode342 * @caddr: the on-disk contents of the symlink343 * @max_size: size of @caddr buffer344 * @done: if successful, will be set up to free the returned target if needed345 *346 * If the symlink's encryption key is available, we decrypt its target.347 * Otherwise, we encode its target for presentation.348 *349 * This may sleep, so the filesystem must have dropped out of RCU mode already.350 *351 * Return: the presentable symlink target or an ERR_PTR()352 */353const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,354 unsigned int max_size,355 struct delayed_call *done)356{357 const struct fscrypt_symlink_data *sd;358 struct fscrypt_str cstr, pstr;359 bool has_key;360 int err;361 362 /* This is for encrypted symlinks only */363 if (WARN_ON_ONCE(!IS_ENCRYPTED(inode)))364 return ERR_PTR(-EINVAL);365 366 /* If the decrypted target is already cached, just return it. */367 pstr.name = READ_ONCE(inode->i_link);368 if (pstr.name)369 return pstr.name;370 371 /*372 * Try to set up the symlink's encryption key, but we can continue373 * regardless of whether the key is available or not.374 */375 err = fscrypt_get_encryption_info(inode, false);376 if (err)377 return ERR_PTR(err);378 has_key = fscrypt_has_encryption_key(inode);379 380 /*381 * For historical reasons, encrypted symlink targets are prefixed with382 * the ciphertext length, even though this is redundant with i_size.383 */384 385 if (max_size < sizeof(*sd) + 1)386 return ERR_PTR(-EUCLEAN);387 sd = caddr;388 cstr.name = (unsigned char *)sd->encrypted_path;389 cstr.len = le16_to_cpu(sd->len);390 391 if (cstr.len == 0)392 return ERR_PTR(-EUCLEAN);393 394 if (cstr.len + sizeof(*sd) > max_size)395 return ERR_PTR(-EUCLEAN);396 397 err = fscrypt_fname_alloc_buffer(cstr.len, &pstr);398 if (err)399 return ERR_PTR(err);400 401 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);402 if (err)403 goto err_kfree;404 405 err = -EUCLEAN;406 if (pstr.name[0] == '\0')407 goto err_kfree;408 409 pstr.name[pstr.len] = '\0';410 411 /*412 * Cache decrypted symlink targets in i_link for later use. Don't cache413 * symlink targets encoded without the key, since those become outdated414 * once the key is added. This pairs with the READ_ONCE() above and in415 * the VFS path lookup code.416 */417 if (!has_key ||418 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL)419 set_delayed_call(done, kfree_link, pstr.name);420 421 return pstr.name;422 423err_kfree:424 kfree(pstr.name);425 return ERR_PTR(err);426}427EXPORT_SYMBOL_GPL(fscrypt_get_symlink);428 429/**430 * fscrypt_symlink_getattr() - set the correct st_size for encrypted symlinks431 * @path: the path for the encrypted symlink being queried432 * @stat: the struct being filled with the symlink's attributes433 *434 * Override st_size of encrypted symlinks to be the length of the decrypted435 * symlink target (or the no-key encoded symlink target, if the key is436 * unavailable) rather than the length of the encrypted symlink target. This is437 * necessary for st_size to match the symlink target that userspace actually438 * sees. POSIX requires this, and some userspace programs depend on it.439 *440 * This requires reading the symlink target from disk if needed, setting up the441 * inode's encryption key if possible, and then decrypting or encoding the442 * symlink target. This makes lstat() more heavyweight than is normally the443 * case. However, decrypted symlink targets will be cached in ->i_link, so444 * usually the symlink won't have to be read and decrypted again later if/when445 * it is actually followed, readlink() is called, or lstat() is called again.446 *447 * Return: 0 on success, -errno on failure448 */449int fscrypt_symlink_getattr(const struct path *path, struct kstat *stat)450{451 struct dentry *dentry = path->dentry;452 struct inode *inode = d_inode(dentry);453 const char *link;454 DEFINE_DELAYED_CALL(done);455 456 /*457 * To get the symlink target that userspace will see (whether it's the458 * decrypted target or the no-key encoded target), we can just get it in459 * the same way the VFS does during path resolution and readlink().460 */461 link = READ_ONCE(inode->i_link);462 if (!link) {463 link = inode->i_op->get_link(dentry, inode, &done);464 if (IS_ERR(link))465 return PTR_ERR(link);466 }467 stat->size = strlen(link);468 do_delayed_call(&done);469 return 0;470}471EXPORT_SYMBOL_GPL(fscrypt_symlink_getattr);472