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(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 }
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 int err;
56
57 err = fscrypt_require_key(dir);
58 if (err)
59 return err;
60
61 /* ... in case we looked up ciphertext name before key was added */
62 if (dentry->d_flags & DCACHE_ENCRYPTED_NAME)
63 return -ENOKEY;
64
65 if (!fscrypt_has_permitted_context(dir, inode))
66 return -EXDEV;
67
68 return 0;
69 }
70 EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
71
72 int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
73 struct inode *new_dir, struct dentry *new_dentry,
74 unsigned int flags)
75 {
76 int err;
77
78 err = fscrypt_require_key(old_dir);
79 if (err)
80 return err;
81
82 err = fscrypt_require_key(new_dir);
83 if (err)
84 return err;
85
86 /* ... in case we looked up ciphertext name(s) before key was added */
87 if ((old_dentry->d_flags | new_dentry->d_flags) &
88 DCACHE_ENCRYPTED_NAME)
89 return -ENOKEY;
90
91 if (old_dir != new_dir) {
92 if (IS_ENCRYPTED(new_dir) &&
93 !fscrypt_has_permitted_context(new_dir,
94 d_inode(old_dentry)))
95 return -EXDEV;
96
97 if ((flags & RENAME_EXCHANGE) &&
98 IS_ENCRYPTED(old_dir) &&
99 !fscrypt_has_permitted_context(old_dir,
100 d_inode(new_dentry)))
101 return -EXDEV;
102 }
103 return 0;
104 }
105 EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);
106
107 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
108 struct fscrypt_name *fname)
109 {
110 int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname);
111
112 if (err && err != -ENOENT)
113 return err;
114
115 if (fname->is_ciphertext_name) {
116 spin_lock(&dentry->d_lock);
117 dentry->d_flags |= DCACHE_ENCRYPTED_NAME;
118 spin_unlock(&dentry->d_lock);
119 d_set_d_op(dentry, &fscrypt_d_ops);
120 }
121 return err;
122 }
123 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
124
125 int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
126 unsigned int max_len,
127 struct fscrypt_str *disk_link)
128 {
129 int err;
130
131 /*
132 * To calculate the size of the encrypted symlink target we need to know
133 * the amount of NUL padding, which is determined by the flags set in
134 * the encryption policy which will be inherited from the directory.
135 * The easiest way to get access to this is to just load the directory's
136 * fscrypt_info, since we'll need it to create the dir_entry anyway.
137 *
138 * Note: in test_dummy_encryption mode, @dir may be unencrypted.
139 */
140 err = fscrypt_get_encryption_info(dir);
141 if (err)
142 return err;
143 if (!fscrypt_has_encryption_key(dir))
144 return -ENOKEY;
145
146 /*
147 * Calculate the size of the encrypted symlink and verify it won't
148 * exceed max_len. Note that for historical reasons, encrypted symlink
149 * targets are prefixed with the ciphertext length, despite this
150 * actually being redundant with i_size. This decreases by 2 bytes the
151 * longest symlink target we can accept.
152 *
153 * We could recover 1 byte by not counting a null terminator, but
154 * counting it (even though it is meaningless for ciphertext) is simpler
155 * for now since filesystems will assume it is there and subtract it.
156 */
157 if (!fscrypt_fname_encrypted_size(dir, len,
158 max_len - sizeof(struct fscrypt_symlink_data),
159 &disk_link->len))
160 return -ENAMETOOLONG;
161 disk_link->len += sizeof(struct fscrypt_symlink_data);
162
163 disk_link->name = NULL;
164 return 0;
165 }
166 EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink);
167
168 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
169 unsigned int len, struct fscrypt_str *disk_link)
170 {
171 int err;
172 struct qstr iname = QSTR_INIT(target, len);
173 struct fscrypt_symlink_data *sd;
174 unsigned int ciphertext_len;
175
176 err = fscrypt_require_key(inode);
177 if (err)
178 return err;
179
180 if (disk_link->name) {
181 /* filesystem-provided buffer */
182 sd = (struct fscrypt_symlink_data *)disk_link->name;
183 } else {
184 sd = kmalloc(disk_link->len, GFP_NOFS);
185 if (!sd)
186 return -ENOMEM;
187 }
188 ciphertext_len = disk_link->len - sizeof(*sd);
189 sd->len = cpu_to_le16(ciphertext_len);
190
191 err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len);
192 if (err)
193 goto err_free_sd;
194
195 /*
196 * Null-terminating the ciphertext doesn't make sense, but we still
197 * count the null terminator in the length, so we might as well
198 * initialize it just in case the filesystem writes it out.
199 */
200 sd->encrypted_path[ciphertext_len] = '\0';
201
202 /* Cache the plaintext symlink target for later use by get_link() */
203 err = -ENOMEM;
204 inode->i_link = kmemdup(target, len + 1, GFP_NOFS);
205 if (!inode->i_link)
206 goto err_free_sd;
207
208 if (!disk_link->name)
209 disk_link->name = (unsigned char *)sd;
210 return 0;
211
212 err_free_sd:
213 if (!disk_link->name)
214 kfree(sd);
215 return err;
216 }
217 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
218
219 /**
220 * fscrypt_get_symlink - get the target of an encrypted symlink
221 * @inode: the symlink inode
222 * @caddr: the on-disk contents of the symlink
223 * @max_size: size of @caddr buffer
224 * @done: if successful, will be set up to free the returned target if needed
225 *
226 * If the symlink's encryption key is available, we decrypt its target.
227 * Otherwise, we encode its target for presentation.
228 *
229 * This may sleep, so the filesystem must have dropped out of RCU mode already.
230 *
231 * Return: the presentable symlink target or an ERR_PTR()
232 */
233 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
234 unsigned int max_size,
235 struct delayed_call *done)
236 {
237 const struct fscrypt_symlink_data *sd;
238 struct fscrypt_str cstr, pstr;
239 bool has_key;
240 int err;
241
242 /* This is for encrypted symlinks only */
243 if (WARN_ON(!IS_ENCRYPTED(inode)))
244 return ERR_PTR(-EINVAL);
245
246 /* If the decrypted target is already cached, just return it. */
247 pstr.name = READ_ONCE(inode->i_link);
248 if (pstr.name)
249 return pstr.name;
250
251 /*
252 * Try to set up the symlink's encryption key, but we can continue
253 * regardless of whether the key is available or not.
254 */
255 err = fscrypt_get_encryption_info(inode);
256 if (err)
257 return ERR_PTR(err);
258 has_key = fscrypt_has_encryption_key(inode);
259
260 /*
261 * For historical reasons, encrypted symlink targets are prefixed with
262 * the ciphertext length, even though this is redundant with i_size.
263 */
264
265 if (max_size < sizeof(*sd))
266 return ERR_PTR(-EUCLEAN);
267 sd = caddr;
268 cstr.name = (unsigned char *)sd->encrypted_path;
269 cstr.len = le16_to_cpu(sd->len);
270
271 if (cstr.len == 0)
272 return ERR_PTR(-EUCLEAN);
273
274 if (cstr.len + sizeof(*sd) - 1 > max_size)
275 return ERR_PTR(-EUCLEAN);
276
277 err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);
278 if (err)
279 return ERR_PTR(err);
280
281 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
282 if (err)
283 goto err_kfree;
284
285 err = -EUCLEAN;
286 if (pstr.name[0] == '\0')
287 goto err_kfree;
288
289 pstr.name[pstr.len] = '\0';
290
291 /*
292 * Cache decrypted symlink targets in i_link for later use. Don't cache
293 * symlink targets encoded without the key, since those become outdated
294 * once the key is added. This pairs with the READ_ONCE() above and in
295 * the VFS path lookup code.
296 */
297 if (!has_key ||
298 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL)
299 set_delayed_call(done, kfree_link, pstr.name);
300
301 return pstr.name;
302
303 err_kfree:
304 kfree(pstr.name);
305 return ERR_PTR(err);
306 }
307 EXPORT_SYMBOL_GPL(fscrypt_get_symlink);