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