1 // SPDX-License-Identifier: GPL-2.0-only
5 * Encryption hooks for higher-level filesystem operations.
10 #include "fscrypt_private.h"
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
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.
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.
30 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
32 int fscrypt_file_open(struct inode *inode, struct file *filp)
37 err = fscrypt_require_key(inode);
41 dir = dget_parent(file_dentry(filp));
42 if (IS_ENCRYPTED(d_inode(dir)) &&
43 !fscrypt_has_permitted_context(d_inode(dir), inode)) {
45 "Inconsistent encryption context (parent directory: %lu)",
52 EXPORT_SYMBOL_GPL(fscrypt_file_open);
54 int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
55 struct dentry *dentry)
59 err = fscrypt_require_key(dir);
63 /* ... in case we looked up ciphertext name before key was added */
64 if (dentry->d_flags & DCACHE_ENCRYPTED_NAME)
67 if (!fscrypt_has_permitted_context(dir, inode))
72 EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
74 int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
75 struct inode *new_dir, struct dentry *new_dentry,
80 err = fscrypt_require_key(old_dir);
84 err = fscrypt_require_key(new_dir);
88 /* ... in case we looked up ciphertext name(s) before key was added */
89 if ((old_dentry->d_flags | new_dentry->d_flags) &
90 DCACHE_ENCRYPTED_NAME)
93 if (old_dir != new_dir) {
94 if (IS_ENCRYPTED(new_dir) &&
95 !fscrypt_has_permitted_context(new_dir,
99 if ((flags & RENAME_EXCHANGE) &&
100 IS_ENCRYPTED(old_dir) &&
101 !fscrypt_has_permitted_context(old_dir,
102 d_inode(new_dentry)))
107 EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);
109 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
110 struct fscrypt_name *fname)
112 int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname);
114 if (err && err != -ENOENT)
117 if (fname->is_ciphertext_name) {
118 spin_lock(&dentry->d_lock);
119 dentry->d_flags |= DCACHE_ENCRYPTED_NAME;
120 spin_unlock(&dentry->d_lock);
121 d_set_d_op(dentry, &fscrypt_d_ops);
125 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
128 * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS
129 * @inode: the inode on which flags are being changed
130 * @oldflags: the old flags
131 * @flags: the new flags
133 * The caller should be holding i_rwsem for write.
135 * Return: 0 on success; -errno if the flags change isn't allowed or if
136 * another error occurs.
138 int fscrypt_prepare_setflags(struct inode *inode,
139 unsigned int oldflags, unsigned int flags)
141 struct fscrypt_info *ci;
142 struct fscrypt_master_key *mk;
146 * When the CASEFOLD flag is set on an encrypted directory, we must
147 * derive the secret key needed for the dirhash. This is only possible
148 * if the directory uses a v2 encryption policy.
150 if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) {
151 err = fscrypt_require_key(inode);
154 ci = inode->i_crypt_info;
155 if (ci->ci_policy.version != FSCRYPT_POLICY_V2)
157 mk = ci->ci_master_key->payload.data[0];
158 down_read(&mk->mk_secret_sem);
159 if (is_master_key_secret_present(&mk->mk_secret))
160 err = fscrypt_derive_dirhash_key(ci, mk);
163 up_read(&mk->mk_secret_sem);
169 int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
170 unsigned int max_len,
171 struct fscrypt_str *disk_link)
176 * To calculate the size of the encrypted symlink target we need to know
177 * the amount of NUL padding, which is determined by the flags set in
178 * the encryption policy which will be inherited from the directory.
179 * The easiest way to get access to this is to just load the directory's
180 * fscrypt_info, since we'll need it to create the dir_entry anyway.
182 * Note: in test_dummy_encryption mode, @dir may be unencrypted.
184 err = fscrypt_get_encryption_info(dir);
187 if (!fscrypt_has_encryption_key(dir))
191 * Calculate the size of the encrypted symlink and verify it won't
192 * exceed max_len. Note that for historical reasons, encrypted symlink
193 * targets are prefixed with the ciphertext length, despite this
194 * actually being redundant with i_size. This decreases by 2 bytes the
195 * longest symlink target we can accept.
197 * We could recover 1 byte by not counting a null terminator, but
198 * counting it (even though it is meaningless for ciphertext) is simpler
199 * for now since filesystems will assume it is there and subtract it.
201 if (!fscrypt_fname_encrypted_size(dir, len,
202 max_len - sizeof(struct fscrypt_symlink_data),
204 return -ENAMETOOLONG;
205 disk_link->len += sizeof(struct fscrypt_symlink_data);
207 disk_link->name = NULL;
210 EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink);
212 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
213 unsigned int len, struct fscrypt_str *disk_link)
216 struct qstr iname = QSTR_INIT(target, len);
217 struct fscrypt_symlink_data *sd;
218 unsigned int ciphertext_len;
220 err = fscrypt_require_key(inode);
224 if (disk_link->name) {
225 /* filesystem-provided buffer */
226 sd = (struct fscrypt_symlink_data *)disk_link->name;
228 sd = kmalloc(disk_link->len, GFP_NOFS);
232 ciphertext_len = disk_link->len - sizeof(*sd);
233 sd->len = cpu_to_le16(ciphertext_len);
235 err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path,
241 * Null-terminating the ciphertext doesn't make sense, but we still
242 * count the null terminator in the length, so we might as well
243 * initialize it just in case the filesystem writes it out.
245 sd->encrypted_path[ciphertext_len] = '\0';
247 /* Cache the plaintext symlink target for later use by get_link() */
249 inode->i_link = kmemdup(target, len + 1, GFP_NOFS);
253 if (!disk_link->name)
254 disk_link->name = (unsigned char *)sd;
258 if (!disk_link->name)
262 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
265 * fscrypt_get_symlink - get the target of an encrypted symlink
266 * @inode: the symlink inode
267 * @caddr: the on-disk contents of the symlink
268 * @max_size: size of @caddr buffer
269 * @done: if successful, will be set up to free the returned target if needed
271 * If the symlink's encryption key is available, we decrypt its target.
272 * Otherwise, we encode its target for presentation.
274 * This may sleep, so the filesystem must have dropped out of RCU mode already.
276 * Return: the presentable symlink target or an ERR_PTR()
278 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
279 unsigned int max_size,
280 struct delayed_call *done)
282 const struct fscrypt_symlink_data *sd;
283 struct fscrypt_str cstr, pstr;
287 /* This is for encrypted symlinks only */
288 if (WARN_ON(!IS_ENCRYPTED(inode)))
289 return ERR_PTR(-EINVAL);
291 /* If the decrypted target is already cached, just return it. */
292 pstr.name = READ_ONCE(inode->i_link);
297 * Try to set up the symlink's encryption key, but we can continue
298 * regardless of whether the key is available or not.
300 err = fscrypt_get_encryption_info(inode);
303 has_key = fscrypt_has_encryption_key(inode);
306 * For historical reasons, encrypted symlink targets are prefixed with
307 * the ciphertext length, even though this is redundant with i_size.
310 if (max_size < sizeof(*sd))
311 return ERR_PTR(-EUCLEAN);
313 cstr.name = (unsigned char *)sd->encrypted_path;
314 cstr.len = le16_to_cpu(sd->len);
317 return ERR_PTR(-EUCLEAN);
319 if (cstr.len + sizeof(*sd) - 1 > max_size)
320 return ERR_PTR(-EUCLEAN);
322 err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);
326 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
331 if (pstr.name[0] == '\0')
334 pstr.name[pstr.len] = '\0';
337 * Cache decrypted symlink targets in i_link for later use. Don't cache
338 * symlink targets encoded without the key, since those become outdated
339 * once the key is added. This pairs with the READ_ONCE() above and in
340 * the VFS path lookup code.
343 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL)
344 set_delayed_call(done, kfree_link, pstr.name);
352 EXPORT_SYMBOL_GPL(fscrypt_get_symlink);