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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 */
30int 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}
50EXPORT_SYMBOL_GPL(fscrypt_file_open);
51
52int __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}
70EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
71
72int __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}
105EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);
106
107int __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}
123EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
124
125int __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}
166EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink);
167
168int __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
212err_free_sd:
213 if (!disk_link->name)
214 kfree(sd);
215 return err;
216}
217EXPORT_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 */
233const 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
303err_kfree:
304 kfree(pstr.name);
305 return ERR_PTR(err);
306}
307EXPORT_SYMBOL_GPL(fscrypt_get_symlink);
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 <linux/key.h>
9
10#include "fscrypt_private.h"
11
12/**
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
16 *
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.
21 *
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.
29 *
30 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
31 */
32int fscrypt_file_open(struct inode *inode, struct file *filp)
33{
34 int err;
35 struct dentry *dir;
36
37 err = fscrypt_require_key(inode);
38 if (err)
39 return err;
40
41 dir = dget_parent(file_dentry(filp));
42 if (IS_ENCRYPTED(d_inode(dir)) &&
43 !fscrypt_has_permitted_context(d_inode(dir), inode)) {
44 fscrypt_warn(inode,
45 "Inconsistent encryption context (parent directory: %lu)",
46 d_inode(dir)->i_ino);
47 err = -EPERM;
48 }
49 dput(dir);
50 return err;
51}
52EXPORT_SYMBOL_GPL(fscrypt_file_open);
53
54int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
55 struct dentry *dentry)
56{
57 if (fscrypt_is_nokey_name(dentry))
58 return -ENOKEY;
59 /*
60 * We don't need to separately check that the directory inode's key is
61 * available, as it's implied by the dentry not being a no-key name.
62 */
63
64 if (!fscrypt_has_permitted_context(dir, inode))
65 return -EXDEV;
66
67 return 0;
68}
69EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
70
71int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
72 struct inode *new_dir, struct dentry *new_dentry,
73 unsigned int flags)
74{
75 if (fscrypt_is_nokey_name(old_dentry) ||
76 fscrypt_is_nokey_name(new_dentry))
77 return -ENOKEY;
78 /*
79 * We don't need to separately check that the directory inodes' keys are
80 * available, as it's implied by the dentries not being no-key names.
81 */
82
83 if (old_dir != new_dir) {
84 if (IS_ENCRYPTED(new_dir) &&
85 !fscrypt_has_permitted_context(new_dir,
86 d_inode(old_dentry)))
87 return -EXDEV;
88
89 if ((flags & RENAME_EXCHANGE) &&
90 IS_ENCRYPTED(old_dir) &&
91 !fscrypt_has_permitted_context(old_dir,
92 d_inode(new_dentry)))
93 return -EXDEV;
94 }
95 return 0;
96}
97EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);
98
99int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
100 struct fscrypt_name *fname)
101{
102 int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname);
103
104 if (err && err != -ENOENT)
105 return err;
106
107 if (fname->is_nokey_name) {
108 spin_lock(&dentry->d_lock);
109 dentry->d_flags |= DCACHE_NOKEY_NAME;
110 spin_unlock(&dentry->d_lock);
111 }
112 return err;
113}
114EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
115
116int __fscrypt_prepare_readdir(struct inode *dir)
117{
118 return fscrypt_get_encryption_info(dir, true);
119}
120EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir);
121
122int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr)
123{
124 if (attr->ia_valid & ATTR_SIZE)
125 return fscrypt_require_key(d_inode(dentry));
126 return 0;
127}
128EXPORT_SYMBOL_GPL(__fscrypt_prepare_setattr);
129
130/**
131 * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS
132 * @inode: the inode on which flags are being changed
133 * @oldflags: the old flags
134 * @flags: the new flags
135 *
136 * The caller should be holding i_rwsem for write.
137 *
138 * Return: 0 on success; -errno if the flags change isn't allowed or if
139 * another error occurs.
140 */
141int fscrypt_prepare_setflags(struct inode *inode,
142 unsigned int oldflags, unsigned int flags)
143{
144 struct fscrypt_info *ci;
145 struct key *key;
146 struct fscrypt_master_key *mk;
147 int err;
148
149 /*
150 * When the CASEFOLD flag is set on an encrypted directory, we must
151 * derive the secret key needed for the dirhash. This is only possible
152 * if the directory uses a v2 encryption policy.
153 */
154 if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) {
155 err = fscrypt_require_key(inode);
156 if (err)
157 return err;
158 ci = inode->i_crypt_info;
159 if (ci->ci_policy.version != FSCRYPT_POLICY_V2)
160 return -EINVAL;
161 key = ci->ci_master_key;
162 mk = key->payload.data[0];
163 down_read(&key->sem);
164 if (is_master_key_secret_present(&mk->mk_secret))
165 err = fscrypt_derive_dirhash_key(ci, mk);
166 else
167 err = -ENOKEY;
168 up_read(&key->sem);
169 return err;
170 }
171 return 0;
172}
173
174/**
175 * fscrypt_prepare_symlink() - prepare to create a possibly-encrypted symlink
176 * @dir: directory in which the symlink is being created
177 * @target: plaintext symlink target
178 * @len: length of @target excluding null terminator
179 * @max_len: space the filesystem has available to store the symlink target
180 * @disk_link: (out) the on-disk symlink target being prepared
181 *
182 * This function computes the size the symlink target will require on-disk,
183 * stores it in @disk_link->len, and validates it against @max_len. An
184 * encrypted symlink may be longer than the original.
185 *
186 * Additionally, @disk_link->name is set to @target if the symlink will be
187 * unencrypted, but left NULL if the symlink will be encrypted. For encrypted
188 * symlinks, the filesystem must call fscrypt_encrypt_symlink() to create the
189 * on-disk target later. (The reason for the two-step process is that some
190 * filesystems need to know the size of the symlink target before creating the
191 * inode, e.g. to determine whether it will be a "fast" or "slow" symlink.)
192 *
193 * Return: 0 on success, -ENAMETOOLONG if the symlink target is too long,
194 * -ENOKEY if the encryption key is missing, or another -errno code if a problem
195 * occurred while setting up the encryption key.
196 */
197int fscrypt_prepare_symlink(struct inode *dir, const char *target,
198 unsigned int len, unsigned int max_len,
199 struct fscrypt_str *disk_link)
200{
201 const union fscrypt_policy *policy;
202
203 /*
204 * To calculate the size of the encrypted symlink target we need to know
205 * the amount of NUL padding, which is determined by the flags set in
206 * the encryption policy which will be inherited from the directory.
207 */
208 policy = fscrypt_policy_to_inherit(dir);
209 if (policy == NULL) {
210 /* Not encrypted */
211 disk_link->name = (unsigned char *)target;
212 disk_link->len = len + 1;
213 if (disk_link->len > max_len)
214 return -ENAMETOOLONG;
215 return 0;
216 }
217 if (IS_ERR(policy))
218 return PTR_ERR(policy);
219
220 /*
221 * Calculate the size of the encrypted symlink and verify it won't
222 * exceed max_len. Note that for historical reasons, encrypted symlink
223 * targets are prefixed with the ciphertext length, despite this
224 * actually being redundant with i_size. This decreases by 2 bytes the
225 * longest symlink target we can accept.
226 *
227 * We could recover 1 byte by not counting a null terminator, but
228 * counting it (even though it is meaningless for ciphertext) is simpler
229 * for now since filesystems will assume it is there and subtract it.
230 */
231 if (!fscrypt_fname_encrypted_size(policy, len,
232 max_len - sizeof(struct fscrypt_symlink_data),
233 &disk_link->len))
234 return -ENAMETOOLONG;
235 disk_link->len += sizeof(struct fscrypt_symlink_data);
236
237 disk_link->name = NULL;
238 return 0;
239}
240EXPORT_SYMBOL_GPL(fscrypt_prepare_symlink);
241
242int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
243 unsigned int len, struct fscrypt_str *disk_link)
244{
245 int err;
246 struct qstr iname = QSTR_INIT(target, len);
247 struct fscrypt_symlink_data *sd;
248 unsigned int ciphertext_len;
249
250 /*
251 * fscrypt_prepare_new_inode() should have already set up the new
252 * symlink inode's encryption key. We don't wait until now to do it,
253 * since we may be in a filesystem transaction now.
254 */
255 if (WARN_ON_ONCE(!fscrypt_has_encryption_key(inode)))
256 return -ENOKEY;
257
258 if (disk_link->name) {
259 /* filesystem-provided buffer */
260 sd = (struct fscrypt_symlink_data *)disk_link->name;
261 } else {
262 sd = kmalloc(disk_link->len, GFP_NOFS);
263 if (!sd)
264 return -ENOMEM;
265 }
266 ciphertext_len = disk_link->len - sizeof(*sd);
267 sd->len = cpu_to_le16(ciphertext_len);
268
269 err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path,
270 ciphertext_len);
271 if (err)
272 goto err_free_sd;
273
274 /*
275 * Null-terminating the ciphertext doesn't make sense, but we still
276 * count the null terminator in the length, so we might as well
277 * initialize it just in case the filesystem writes it out.
278 */
279 sd->encrypted_path[ciphertext_len] = '\0';
280
281 /* Cache the plaintext symlink target for later use by get_link() */
282 err = -ENOMEM;
283 inode->i_link = kmemdup(target, len + 1, GFP_NOFS);
284 if (!inode->i_link)
285 goto err_free_sd;
286
287 if (!disk_link->name)
288 disk_link->name = (unsigned char *)sd;
289 return 0;
290
291err_free_sd:
292 if (!disk_link->name)
293 kfree(sd);
294 return err;
295}
296EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
297
298/**
299 * fscrypt_get_symlink() - get the target of an encrypted symlink
300 * @inode: the symlink inode
301 * @caddr: the on-disk contents of the symlink
302 * @max_size: size of @caddr buffer
303 * @done: if successful, will be set up to free the returned target if needed
304 *
305 * If the symlink's encryption key is available, we decrypt its target.
306 * Otherwise, we encode its target for presentation.
307 *
308 * This may sleep, so the filesystem must have dropped out of RCU mode already.
309 *
310 * Return: the presentable symlink target or an ERR_PTR()
311 */
312const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
313 unsigned int max_size,
314 struct delayed_call *done)
315{
316 const struct fscrypt_symlink_data *sd;
317 struct fscrypt_str cstr, pstr;
318 bool has_key;
319 int err;
320
321 /* This is for encrypted symlinks only */
322 if (WARN_ON(!IS_ENCRYPTED(inode)))
323 return ERR_PTR(-EINVAL);
324
325 /* If the decrypted target is already cached, just return it. */
326 pstr.name = READ_ONCE(inode->i_link);
327 if (pstr.name)
328 return pstr.name;
329
330 /*
331 * Try to set up the symlink's encryption key, but we can continue
332 * regardless of whether the key is available or not.
333 */
334 err = fscrypt_get_encryption_info(inode, false);
335 if (err)
336 return ERR_PTR(err);
337 has_key = fscrypt_has_encryption_key(inode);
338
339 /*
340 * For historical reasons, encrypted symlink targets are prefixed with
341 * the ciphertext length, even though this is redundant with i_size.
342 */
343
344 if (max_size < sizeof(*sd))
345 return ERR_PTR(-EUCLEAN);
346 sd = caddr;
347 cstr.name = (unsigned char *)sd->encrypted_path;
348 cstr.len = le16_to_cpu(sd->len);
349
350 if (cstr.len == 0)
351 return ERR_PTR(-EUCLEAN);
352
353 if (cstr.len + sizeof(*sd) - 1 > max_size)
354 return ERR_PTR(-EUCLEAN);
355
356 err = fscrypt_fname_alloc_buffer(cstr.len, &pstr);
357 if (err)
358 return ERR_PTR(err);
359
360 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
361 if (err)
362 goto err_kfree;
363
364 err = -EUCLEAN;
365 if (pstr.name[0] == '\0')
366 goto err_kfree;
367
368 pstr.name[pstr.len] = '\0';
369
370 /*
371 * Cache decrypted symlink targets in i_link for later use. Don't cache
372 * symlink targets encoded without the key, since those become outdated
373 * once the key is added. This pairs with the READ_ONCE() above and in
374 * the VFS path lookup code.
375 */
376 if (!has_key ||
377 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL)
378 set_delayed_call(done, kfree_link, pstr.name);
379
380 return pstr.name;
381
382err_kfree:
383 kfree(pstr.name);
384 return ERR_PTR(err);
385}
386EXPORT_SYMBOL_GPL(fscrypt_get_symlink);
387
388/**
389 * fscrypt_symlink_getattr() - set the correct st_size for encrypted symlinks
390 * @path: the path for the encrypted symlink being queried
391 * @stat: the struct being filled with the symlink's attributes
392 *
393 * Override st_size of encrypted symlinks to be the length of the decrypted
394 * symlink target (or the no-key encoded symlink target, if the key is
395 * unavailable) rather than the length of the encrypted symlink target. This is
396 * necessary for st_size to match the symlink target that userspace actually
397 * sees. POSIX requires this, and some userspace programs depend on it.
398 *
399 * This requires reading the symlink target from disk if needed, setting up the
400 * inode's encryption key if possible, and then decrypting or encoding the
401 * symlink target. This makes lstat() more heavyweight than is normally the
402 * case. However, decrypted symlink targets will be cached in ->i_link, so
403 * usually the symlink won't have to be read and decrypted again later if/when
404 * it is actually followed, readlink() is called, or lstat() is called again.
405 *
406 * Return: 0 on success, -errno on failure
407 */
408int fscrypt_symlink_getattr(const struct path *path, struct kstat *stat)
409{
410 struct dentry *dentry = path->dentry;
411 struct inode *inode = d_inode(dentry);
412 const char *link;
413 DEFINE_DELAYED_CALL(done);
414
415 /*
416 * To get the symlink target that userspace will see (whether it's the
417 * decrypted target or the no-key encoded target), we can just get it in
418 * the same way the VFS does during path resolution and readlink().
419 */
420 link = READ_ONCE(inode->i_link);
421 if (!link) {
422 link = inode->i_op->get_link(dentry, inode, &done);
423 if (IS_ERR(link))
424 return PTR_ERR(link);
425 }
426 stat->size = strlen(link);
427 do_delayed_call(&done);
428 return 0;
429}
430EXPORT_SYMBOL_GPL(fscrypt_symlink_getattr);