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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 "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);