Branch data Line data Source code
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 : 6087198 : int fscrypt_file_open(struct inode *inode, struct file *filp)
31 : : {
32 : : int err;
33 : : struct dentry *dir;
34 : :
35 : 6087198 : err = fscrypt_require_key(inode);
36 [ + + ]: 6086694 : if (err)
37 : : return err;
38 : :
39 : 6086694 : dir = dget_parent(file_dentry(filp));
40 [ - + # # ]: 6087184 : if (IS_ENCRYPTED(d_inode(dir)) &&
41 : 0 : !fscrypt_has_permitted_context(d_inode(dir), inode)) {
42 : 0 : fscrypt_warn(inode,
43 : : "Inconsistent encryption context (parent directory: %lu)",
44 : : d_inode(dir)->i_ino);
45 : : err = -EPERM;
46 : : }
47 : 6087184 : dput(dir);
48 : 6087314 : return err;
49 : : }
50 : : EXPORT_SYMBOL_GPL(fscrypt_file_open);
51 : :
52 : 0 : int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
53 : : struct dentry *dentry)
54 : : {
55 : : int err;
56 : :
57 : 0 : err = fscrypt_require_key(dir);
58 [ # # ]: 0 : if (err)
59 : : return err;
60 : :
61 : : /* ... in case we looked up ciphertext name before key was added */
62 [ # # ]: 0 : if (dentry->d_flags & DCACHE_ENCRYPTED_NAME)
63 : : return -ENOKEY;
64 : :
65 [ # # ]: 0 : if (!fscrypt_has_permitted_context(dir, inode))
66 : : return -EXDEV;
67 : :
68 : 0 : return 0;
69 : : }
70 : : EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
71 : :
72 : 0 : 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 : 0 : err = fscrypt_require_key(old_dir);
79 [ # # ]: 0 : if (err)
80 : : return err;
81 : :
82 : 0 : err = fscrypt_require_key(new_dir);
83 [ # # ]: 0 : if (err)
84 : : return err;
85 : :
86 : : /* ... in case we looked up ciphertext name(s) before key was added */
87 [ # # ]: 0 : if ((old_dentry->d_flags | new_dentry->d_flags) &
88 : : DCACHE_ENCRYPTED_NAME)
89 : : return -ENOKEY;
90 : :
91 [ # # ]: 0 : if (old_dir != new_dir) {
92 [ # # # # ]: 0 : if (IS_ENCRYPTED(new_dir) &&
93 : 0 : !fscrypt_has_permitted_context(new_dir,
94 : : d_inode(old_dentry)))
95 : : return -EXDEV;
96 : :
97 [ # # # # ]: 0 : if ((flags & RENAME_EXCHANGE) &&
98 [ # # ]: 0 : IS_ENCRYPTED(old_dir) &&
99 : 0 : !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 : 0 : int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
108 : : struct fscrypt_name *fname)
109 : : {
110 : 0 : int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname);
111 : :
112 [ # # ]: 0 : if (err && err != -ENOENT)
113 : : return err;
114 : :
115 [ # # ]: 0 : if (fname->is_ciphertext_name) {
116 : : spin_lock(&dentry->d_lock);
117 : 0 : dentry->d_flags |= DCACHE_ENCRYPTED_NAME;
118 : : spin_unlock(&dentry->d_lock);
119 : 0 : d_set_d_op(dentry, &fscrypt_d_ops);
120 : : }
121 : : return err;
122 : : }
123 : : EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
124 : :
125 : 0 : 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 : 0 : err = fscrypt_get_encryption_info(dir);
141 [ # # ]: 0 : if (err)
142 : : return err;
143 [ # # ]: 0 : 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 [ # # ]: 0 : if (!fscrypt_fname_encrypted_size(dir, len,
158 : : max_len - sizeof(struct fscrypt_symlink_data),
159 : : &disk_link->len))
160 : : return -ENAMETOOLONG;
161 : 0 : disk_link->len += sizeof(struct fscrypt_symlink_data);
162 : :
163 : 0 : disk_link->name = NULL;
164 : 0 : return 0;
165 : : }
166 : : EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink);
167 : :
168 : 0 : int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
169 : : unsigned int len, struct fscrypt_str *disk_link)
170 : : {
171 : : int err;
172 : 0 : struct qstr iname = QSTR_INIT(target, len);
173 : : struct fscrypt_symlink_data *sd;
174 : : unsigned int ciphertext_len;
175 : :
176 : 0 : err = fscrypt_require_key(inode);
177 [ # # ]: 0 : if (err)
178 : : return err;
179 : :
180 [ # # ]: 0 : if (disk_link->name) {
181 : : /* filesystem-provided buffer */
182 : : sd = (struct fscrypt_symlink_data *)disk_link->name;
183 : : } else {
184 : 0 : sd = kmalloc(disk_link->len, GFP_NOFS);
185 [ # # ]: 0 : if (!sd)
186 : : return -ENOMEM;
187 : : }
188 : 0 : ciphertext_len = disk_link->len - sizeof(*sd);
189 : 0 : sd->len = cpu_to_le16(ciphertext_len);
190 : :
191 : 0 : err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len);
192 [ # # ]: 0 : 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 : 0 : sd->encrypted_path[ciphertext_len] = '\0';
201 : :
202 : : /* Cache the plaintext symlink target for later use by get_link() */
203 : : err = -ENOMEM;
204 : 0 : inode->i_link = kmemdup(target, len + 1, GFP_NOFS);
205 [ # # ]: 0 : if (!inode->i_link)
206 : : goto err_free_sd;
207 : :
208 [ # # ]: 0 : if (!disk_link->name)
209 : 0 : disk_link->name = (unsigned char *)sd;
210 : : return 0;
211 : :
212 : : err_free_sd:
213 [ # # ]: 0 : if (!disk_link->name)
214 : 0 : kfree(sd);
215 : 0 : 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 : 0 : 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 [ # # # # ]: 0 : if (WARN_ON(!IS_ENCRYPTED(inode)))
244 : : return ERR_PTR(-EINVAL);
245 : :
246 : : /* If the decrypted target is already cached, just return it. */
247 : 0 : pstr.name = READ_ONCE(inode->i_link);
248 [ # # ]: 0 : 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 : 0 : err = fscrypt_get_encryption_info(inode);
256 [ # # ]: 0 : if (err)
257 : 0 : 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 [ # # ]: 0 : if (max_size < sizeof(*sd))
266 : : return ERR_PTR(-EUCLEAN);
267 : : sd = caddr;
268 : 0 : cstr.name = (unsigned char *)sd->encrypted_path;
269 : 0 : cstr.len = le16_to_cpu(sd->len);
270 : :
271 [ # # ]: 0 : if (cstr.len == 0)
272 : : return ERR_PTR(-EUCLEAN);
273 : :
274 [ # # ]: 0 : if (cstr.len + sizeof(*sd) - 1 > max_size)
275 : : return ERR_PTR(-EUCLEAN);
276 : :
277 : 0 : err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);
278 [ # # ]: 0 : if (err)
279 : 0 : return ERR_PTR(err);
280 : :
281 : 0 : err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
282 [ # # ]: 0 : if (err)
283 : : goto err_kfree;
284 : :
285 : : err = -EUCLEAN;
286 [ # # ]: 0 : if (pstr.name[0] == '\0')
287 : : goto err_kfree;
288 : :
289 : 0 : 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 [ # # # # ]: 0 : if (!has_key ||
298 : 0 : cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL)
299 : 0 : set_delayed_call(done, kfree_link, pstr.name);
300 : :
301 : 0 : return pstr.name;
302 : :
303 : : err_kfree:
304 : 0 : kfree(pstr.name);
305 : 0 : return ERR_PTR(err);
306 : : }
307 : : EXPORT_SYMBOL_GPL(fscrypt_get_symlink);
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