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1/*
2 * fs/crypto/hooks.c
3 *
4 * Encryption hooks for higher-level filesystem operations.
5 */
6
7#include <linux/ratelimit.h>
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 pr_warn_ratelimited("fscrypt: inconsistent encryption contexts: %lu/%lu",
43 d_inode(dir)->i_ino, inode->i_ino);
44 err = -EPERM;
45 }
46 dput(dir);
47 return err;
48}
49EXPORT_SYMBOL_GPL(fscrypt_file_open);
50
51int __fscrypt_prepare_link(struct inode *inode, struct inode *dir)
52{
53 int err;
54
55 err = fscrypt_require_key(dir);
56 if (err)
57 return err;
58
59 if (!fscrypt_has_permitted_context(dir, inode))
60 return -EPERM;
61
62 return 0;
63}
64EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
65
66int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
67 struct inode *new_dir, struct dentry *new_dentry,
68 unsigned int flags)
69{
70 int err;
71
72 err = fscrypt_require_key(old_dir);
73 if (err)
74 return err;
75
76 err = fscrypt_require_key(new_dir);
77 if (err)
78 return err;
79
80 if (old_dir != new_dir) {
81 if (IS_ENCRYPTED(new_dir) &&
82 !fscrypt_has_permitted_context(new_dir,
83 d_inode(old_dentry)))
84 return -EPERM;
85
86 if ((flags & RENAME_EXCHANGE) &&
87 IS_ENCRYPTED(old_dir) &&
88 !fscrypt_has_permitted_context(old_dir,
89 d_inode(new_dentry)))
90 return -EPERM;
91 }
92 return 0;
93}
94EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);
95
96int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry)
97{
98 int err = fscrypt_get_encryption_info(dir);
99
100 if (err)
101 return err;
102
103 if (fscrypt_has_encryption_key(dir)) {
104 spin_lock(&dentry->d_lock);
105 dentry->d_flags |= DCACHE_ENCRYPTED_WITH_KEY;
106 spin_unlock(&dentry->d_lock);
107 }
108
109 d_set_d_op(dentry, &fscrypt_d_ops);
110 return 0;
111}
112EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
113
114int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
115 unsigned int max_len,
116 struct fscrypt_str *disk_link)
117{
118 int err;
119
120 /*
121 * To calculate the size of the encrypted symlink target we need to know
122 * the amount of NUL padding, which is determined by the flags set in
123 * the encryption policy which will be inherited from the directory.
124 * The easiest way to get access to this is to just load the directory's
125 * fscrypt_info, since we'll need it to create the dir_entry anyway.
126 *
127 * Note: in test_dummy_encryption mode, @dir may be unencrypted.
128 */
129 err = fscrypt_get_encryption_info(dir);
130 if (err)
131 return err;
132 if (!fscrypt_has_encryption_key(dir))
133 return -ENOKEY;
134
135 /*
136 * Calculate the size of the encrypted symlink and verify it won't
137 * exceed max_len. Note that for historical reasons, encrypted symlink
138 * targets are prefixed with the ciphertext length, despite this
139 * actually being redundant with i_size. This decreases by 2 bytes the
140 * longest symlink target we can accept.
141 *
142 * We could recover 1 byte by not counting a null terminator, but
143 * counting it (even though it is meaningless for ciphertext) is simpler
144 * for now since filesystems will assume it is there and subtract it.
145 */
146 if (!fscrypt_fname_encrypted_size(dir, len,
147 max_len - sizeof(struct fscrypt_symlink_data),
148 &disk_link->len))
149 return -ENAMETOOLONG;
150 disk_link->len += sizeof(struct fscrypt_symlink_data);
151
152 disk_link->name = NULL;
153 return 0;
154}
155EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink);
156
157int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
158 unsigned int len, struct fscrypt_str *disk_link)
159{
160 int err;
161 struct qstr iname = QSTR_INIT(target, len);
162 struct fscrypt_symlink_data *sd;
163 unsigned int ciphertext_len;
164
165 err = fscrypt_require_key(inode);
166 if (err)
167 return err;
168
169 if (disk_link->name) {
170 /* filesystem-provided buffer */
171 sd = (struct fscrypt_symlink_data *)disk_link->name;
172 } else {
173 sd = kmalloc(disk_link->len, GFP_NOFS);
174 if (!sd)
175 return -ENOMEM;
176 }
177 ciphertext_len = disk_link->len - sizeof(*sd);
178 sd->len = cpu_to_le16(ciphertext_len);
179
180 err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len);
181 if (err) {
182 if (!disk_link->name)
183 kfree(sd);
184 return err;
185 }
186 /*
187 * Null-terminating the ciphertext doesn't make sense, but we still
188 * count the null terminator in the length, so we might as well
189 * initialize it just in case the filesystem writes it out.
190 */
191 sd->encrypted_path[ciphertext_len] = '\0';
192
193 if (!disk_link->name)
194 disk_link->name = (unsigned char *)sd;
195 return 0;
196}
197EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
198
199/**
200 * fscrypt_get_symlink - get the target of an encrypted symlink
201 * @inode: the symlink inode
202 * @caddr: the on-disk contents of the symlink
203 * @max_size: size of @caddr buffer
204 * @done: if successful, will be set up to free the returned target
205 *
206 * If the symlink's encryption key is available, we decrypt its target.
207 * Otherwise, we encode its target for presentation.
208 *
209 * This may sleep, so the filesystem must have dropped out of RCU mode already.
210 *
211 * Return: the presentable symlink target or an ERR_PTR()
212 */
213const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
214 unsigned int max_size,
215 struct delayed_call *done)
216{
217 const struct fscrypt_symlink_data *sd;
218 struct fscrypt_str cstr, pstr;
219 int err;
220
221 /* This is for encrypted symlinks only */
222 if (WARN_ON(!IS_ENCRYPTED(inode)))
223 return ERR_PTR(-EINVAL);
224
225 /*
226 * Try to set up the symlink's encryption key, but we can continue
227 * regardless of whether the key is available or not.
228 */
229 err = fscrypt_get_encryption_info(inode);
230 if (err)
231 return ERR_PTR(err);
232
233 /*
234 * For historical reasons, encrypted symlink targets are prefixed with
235 * the ciphertext length, even though this is redundant with i_size.
236 */
237
238 if (max_size < sizeof(*sd))
239 return ERR_PTR(-EUCLEAN);
240 sd = caddr;
241 cstr.name = (unsigned char *)sd->encrypted_path;
242 cstr.len = le16_to_cpu(sd->len);
243
244 if (cstr.len == 0)
245 return ERR_PTR(-EUCLEAN);
246
247 if (cstr.len + sizeof(*sd) - 1 > max_size)
248 return ERR_PTR(-EUCLEAN);
249
250 err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);
251 if (err)
252 return ERR_PTR(err);
253
254 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
255 if (err)
256 goto err_kfree;
257
258 err = -EUCLEAN;
259 if (pstr.name[0] == '\0')
260 goto err_kfree;
261
262 pstr.name[pstr.len] = '\0';
263 set_delayed_call(done, kfree_link, pstr.name);
264 return pstr.name;
265
266err_kfree:
267 kfree(pstr.name);
268 return ERR_PTR(err);
269}
270EXPORT_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 int err;
58
59 err = fscrypt_require_key(dir);
60 if (err)
61 return err;
62
63 /* ... in case we looked up ciphertext name before key was added */
64 if (dentry->d_flags & DCACHE_ENCRYPTED_NAME)
65 return -ENOKEY;
66
67 if (!fscrypt_has_permitted_context(dir, inode))
68 return -EXDEV;
69
70 return 0;
71}
72EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
73
74int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
75 struct inode *new_dir, struct dentry *new_dentry,
76 unsigned int flags)
77{
78 int err;
79
80 err = fscrypt_require_key(old_dir);
81 if (err)
82 return err;
83
84 err = fscrypt_require_key(new_dir);
85 if (err)
86 return err;
87
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)
91 return -ENOKEY;
92
93 if (old_dir != new_dir) {
94 if (IS_ENCRYPTED(new_dir) &&
95 !fscrypt_has_permitted_context(new_dir,
96 d_inode(old_dentry)))
97 return -EXDEV;
98
99 if ((flags & RENAME_EXCHANGE) &&
100 IS_ENCRYPTED(old_dir) &&
101 !fscrypt_has_permitted_context(old_dir,
102 d_inode(new_dentry)))
103 return -EXDEV;
104 }
105 return 0;
106}
107EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);
108
109int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
110 struct fscrypt_name *fname)
111{
112 int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname);
113
114 if (err && err != -ENOENT)
115 return err;
116
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);
122 }
123 return err;
124}
125EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
126
127/**
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
132 *
133 * The caller should be holding i_rwsem for write.
134 *
135 * Return: 0 on success; -errno if the flags change isn't allowed or if
136 * another error occurs.
137 */
138int fscrypt_prepare_setflags(struct inode *inode,
139 unsigned int oldflags, unsigned int flags)
140{
141 struct fscrypt_info *ci;
142 struct fscrypt_master_key *mk;
143 int err;
144
145 /*
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.
149 */
150 if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) {
151 err = fscrypt_require_key(inode);
152 if (err)
153 return err;
154 ci = inode->i_crypt_info;
155 if (ci->ci_policy.version != FSCRYPT_POLICY_V2)
156 return -EINVAL;
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);
161 else
162 err = -ENOKEY;
163 up_read(&mk->mk_secret_sem);
164 return err;
165 }
166 return 0;
167}
168
169int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
170 unsigned int max_len,
171 struct fscrypt_str *disk_link)
172{
173 int err;
174
175 /*
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.
181 *
182 * Note: in test_dummy_encryption mode, @dir may be unencrypted.
183 */
184 err = fscrypt_get_encryption_info(dir);
185 if (err)
186 return err;
187 if (!fscrypt_has_encryption_key(dir))
188 return -ENOKEY;
189
190 /*
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.
196 *
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.
200 */
201 if (!fscrypt_fname_encrypted_size(dir, len,
202 max_len - sizeof(struct fscrypt_symlink_data),
203 &disk_link->len))
204 return -ENAMETOOLONG;
205 disk_link->len += sizeof(struct fscrypt_symlink_data);
206
207 disk_link->name = NULL;
208 return 0;
209}
210EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink);
211
212int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
213 unsigned int len, struct fscrypt_str *disk_link)
214{
215 int err;
216 struct qstr iname = QSTR_INIT(target, len);
217 struct fscrypt_symlink_data *sd;
218 unsigned int ciphertext_len;
219
220 err = fscrypt_require_key(inode);
221 if (err)
222 return err;
223
224 if (disk_link->name) {
225 /* filesystem-provided buffer */
226 sd = (struct fscrypt_symlink_data *)disk_link->name;
227 } else {
228 sd = kmalloc(disk_link->len, GFP_NOFS);
229 if (!sd)
230 return -ENOMEM;
231 }
232 ciphertext_len = disk_link->len - sizeof(*sd);
233 sd->len = cpu_to_le16(ciphertext_len);
234
235 err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path,
236 ciphertext_len);
237 if (err)
238 goto err_free_sd;
239
240 /*
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.
244 */
245 sd->encrypted_path[ciphertext_len] = '\0';
246
247 /* Cache the plaintext symlink target for later use by get_link() */
248 err = -ENOMEM;
249 inode->i_link = kmemdup(target, len + 1, GFP_NOFS);
250 if (!inode->i_link)
251 goto err_free_sd;
252
253 if (!disk_link->name)
254 disk_link->name = (unsigned char *)sd;
255 return 0;
256
257err_free_sd:
258 if (!disk_link->name)
259 kfree(sd);
260 return err;
261}
262EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
263
264/**
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
270 *
271 * If the symlink's encryption key is available, we decrypt its target.
272 * Otherwise, we encode its target for presentation.
273 *
274 * This may sleep, so the filesystem must have dropped out of RCU mode already.
275 *
276 * Return: the presentable symlink target or an ERR_PTR()
277 */
278const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
279 unsigned int max_size,
280 struct delayed_call *done)
281{
282 const struct fscrypt_symlink_data *sd;
283 struct fscrypt_str cstr, pstr;
284 bool has_key;
285 int err;
286
287 /* This is for encrypted symlinks only */
288 if (WARN_ON(!IS_ENCRYPTED(inode)))
289 return ERR_PTR(-EINVAL);
290
291 /* If the decrypted target is already cached, just return it. */
292 pstr.name = READ_ONCE(inode->i_link);
293 if (pstr.name)
294 return pstr.name;
295
296 /*
297 * Try to set up the symlink's encryption key, but we can continue
298 * regardless of whether the key is available or not.
299 */
300 err = fscrypt_get_encryption_info(inode);
301 if (err)
302 return ERR_PTR(err);
303 has_key = fscrypt_has_encryption_key(inode);
304
305 /*
306 * For historical reasons, encrypted symlink targets are prefixed with
307 * the ciphertext length, even though this is redundant with i_size.
308 */
309
310 if (max_size < sizeof(*sd))
311 return ERR_PTR(-EUCLEAN);
312 sd = caddr;
313 cstr.name = (unsigned char *)sd->encrypted_path;
314 cstr.len = le16_to_cpu(sd->len);
315
316 if (cstr.len == 0)
317 return ERR_PTR(-EUCLEAN);
318
319 if (cstr.len + sizeof(*sd) - 1 > max_size)
320 return ERR_PTR(-EUCLEAN);
321
322 err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);
323 if (err)
324 return ERR_PTR(err);
325
326 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
327 if (err)
328 goto err_kfree;
329
330 err = -EUCLEAN;
331 if (pstr.name[0] == '\0')
332 goto err_kfree;
333
334 pstr.name[pstr.len] = '\0';
335
336 /*
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.
341 */
342 if (!has_key ||
343 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL)
344 set_delayed_call(done, kfree_link, pstr.name);
345
346 return pstr.name;
347
348err_kfree:
349 kfree(pstr.name);
350 return ERR_PTR(err);
351}
352EXPORT_SYMBOL_GPL(fscrypt_get_symlink);