1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* Large capacity key type
3 *
4 * Copyright (C) 2017-2020 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
5 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
6 * Written by David Howells (dhowells@redhat.com)
7 */
8
9 #define pr_fmt(fmt) "big_key: "fmt
10 #include <linux/init.h>
11 #include <linux/seq_file.h>
12 #include <linux/file.h>
13 #include <linux/shmem_fs.h>
14 #include <linux/err.h>
15 #include <linux/random.h>
16 #include <keys/user-type.h>
17 #include <keys/big_key-type.h>
18 #include <crypto/chacha20poly1305.h>
19
20 /*
21 * Layout of key payload words.
22 */
23 struct big_key_payload {
24 u8 *data;
25 struct path path;
26 size_t length;
27 };
28 #define to_big_key_payload(payload) \
29 (struct big_key_payload *)((payload).data)
30
31 /*
32 * If the data is under this limit, there's no point creating a shm file to
33 * hold it as the permanently resident metadata for the shmem fs will be at
34 * least as large as the data.
35 */
36 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
37
38 /*
39 * big_key defined keys take an arbitrary string as the description and an
40 * arbitrary blob of data as the payload
41 */
42 struct key_type key_type_big_key = {
43 .name = "big_key",
44 .preparse = big_key_preparse,
45 .free_preparse = big_key_free_preparse,
46 .instantiate = generic_key_instantiate,
47 .revoke = big_key_revoke,
48 .destroy = big_key_destroy,
49 .describe = big_key_describe,
50 .read = big_key_read,
51 .update = big_key_update,
52 };
53
54 /*
55 * Preparse a big key
56 */
big_key_preparse(struct key_preparsed_payload * prep)57 int big_key_preparse(struct key_preparsed_payload *prep)
58 {
59 struct big_key_payload *payload = to_big_key_payload(prep->payload);
60 struct file *file;
61 u8 *buf, *enckey;
62 ssize_t written;
63 size_t datalen = prep->datalen;
64 size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
65 int ret;
66
67 BUILD_BUG_ON(sizeof(*payload) != sizeof(prep->payload.data));
68
69 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
70 return -EINVAL;
71
72 /* Set an arbitrary quota */
73 prep->quotalen = 16;
74
75 payload->length = datalen;
76
77 if (datalen > BIG_KEY_FILE_THRESHOLD) {
78 /* Create a shmem file to store the data in. This will permit the data
79 * to be swapped out if needed.
80 *
81 * File content is stored encrypted with randomly generated key.
82 * Since the key is random for each file, we can set the nonce
83 * to zero, provided we never define a ->update() call.
84 */
85 loff_t pos = 0;
86
87 buf = kvmalloc(enclen, GFP_KERNEL);
88 if (!buf)
89 return -ENOMEM;
90
91 /* generate random key */
92 enckey = kmalloc(CHACHA20POLY1305_KEY_SIZE, GFP_KERNEL);
93 if (!enckey) {
94 ret = -ENOMEM;
95 goto error;
96 }
97 ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_KEY_SIZE);
98 if (unlikely(ret))
99 goto err_enckey;
100
101 /* encrypt data */
102 chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0,
103 0, enckey);
104
105 /* save aligned data to file */
106 file = shmem_kernel_file_setup("", enclen, 0);
107 if (IS_ERR(file)) {
108 ret = PTR_ERR(file);
109 goto err_enckey;
110 }
111
112 written = kernel_write(file, buf, enclen, &pos);
113 if (written != enclen) {
114 ret = written;
115 if (written >= 0)
116 ret = -EIO;
117 goto err_fput;
118 }
119
120 /* Pin the mount and dentry to the key so that we can open it again
121 * later
122 */
123 payload->data = enckey;
124 payload->path = file->f_path;
125 path_get(&payload->path);
126 fput(file);
127 kvfree_sensitive(buf, enclen);
128 } else {
129 /* Just store the data in a buffer */
130 void *data = kmalloc(datalen, GFP_KERNEL);
131
132 if (!data)
133 return -ENOMEM;
134
135 payload->data = data;
136 memcpy(data, prep->data, prep->datalen);
137 }
138 return 0;
139
140 err_fput:
141 fput(file);
142 err_enckey:
143 kfree_sensitive(enckey);
144 error:
145 kvfree_sensitive(buf, enclen);
146 return ret;
147 }
148
149 /*
150 * Clear preparsement.
151 */
big_key_free_preparse(struct key_preparsed_payload * prep)152 void big_key_free_preparse(struct key_preparsed_payload *prep)
153 {
154 struct big_key_payload *payload = to_big_key_payload(prep->payload);
155
156 if (prep->datalen > BIG_KEY_FILE_THRESHOLD)
157 path_put(&payload->path);
158 kfree_sensitive(payload->data);
159 }
160
161 /*
162 * dispose of the links from a revoked keyring
163 * - called with the key sem write-locked
164 */
big_key_revoke(struct key * key)165 void big_key_revoke(struct key *key)
166 {
167 struct big_key_payload *payload = to_big_key_payload(key->payload);
168
169 /* clear the quota */
170 key_payload_reserve(key, 0);
171 if (key_is_positive(key) && payload->length > BIG_KEY_FILE_THRESHOLD)
172 vfs_truncate(&payload->path, 0);
173 }
174
175 /*
176 * dispose of the data dangling from the corpse of a big_key key
177 */
big_key_destroy(struct key * key)178 void big_key_destroy(struct key *key)
179 {
180 struct big_key_payload *payload = to_big_key_payload(key->payload);
181
182 if (payload->length > BIG_KEY_FILE_THRESHOLD) {
183 path_put(&payload->path);
184 payload->path.mnt = NULL;
185 payload->path.dentry = NULL;
186 }
187 kfree_sensitive(payload->data);
188 payload->data = NULL;
189 }
190
191 /*
192 * Update a big key
193 */
big_key_update(struct key * key,struct key_preparsed_payload * prep)194 int big_key_update(struct key *key, struct key_preparsed_payload *prep)
195 {
196 int ret;
197
198 ret = key_payload_reserve(key, prep->datalen);
199 if (ret < 0)
200 return ret;
201
202 if (key_is_positive(key))
203 big_key_destroy(key);
204
205 return generic_key_instantiate(key, prep);
206 }
207
208 /*
209 * describe the big_key key
210 */
big_key_describe(const struct key * key,struct seq_file * m)211 void big_key_describe(const struct key *key, struct seq_file *m)
212 {
213 struct big_key_payload *payload = to_big_key_payload(key->payload);
214
215 seq_puts(m, key->description);
216
217 if (key_is_positive(key))
218 seq_printf(m, ": %zu [%s]",
219 payload->length,
220 payload->length > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
221 }
222
223 /*
224 * read the key data
225 * - the key's semaphore is read-locked
226 */
big_key_read(const struct key * key,char * buffer,size_t buflen)227 long big_key_read(const struct key *key, char *buffer, size_t buflen)
228 {
229 struct big_key_payload *payload = to_big_key_payload(key->payload);
230 size_t datalen = payload->length;
231 long ret;
232
233 if (!buffer || buflen < datalen)
234 return datalen;
235
236 if (datalen > BIG_KEY_FILE_THRESHOLD) {
237 struct file *file;
238 u8 *buf, *enckey = payload->data;
239 size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
240 loff_t pos = 0;
241
242 buf = kvmalloc(enclen, GFP_KERNEL);
243 if (!buf)
244 return -ENOMEM;
245
246 file = dentry_open(&payload->path, O_RDONLY, current_cred());
247 if (IS_ERR(file)) {
248 ret = PTR_ERR(file);
249 goto error;
250 }
251
252 /* read file to kernel and decrypt */
253 ret = kernel_read(file, buf, enclen, &pos);
254 if (ret != enclen) {
255 if (ret >= 0)
256 ret = -EIO;
257 goto err_fput;
258 }
259
260 ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0,
261 enckey) ? 0 : -EBADMSG;
262 if (unlikely(ret))
263 goto err_fput;
264
265 ret = datalen;
266
267 /* copy out decrypted data */
268 memcpy(buffer, buf, datalen);
269
270 err_fput:
271 fput(file);
272 error:
273 kvfree_sensitive(buf, enclen);
274 } else {
275 ret = datalen;
276 memcpy(buffer, payload->data, datalen);
277 }
278
279 return ret;
280 }
281
282 /*
283 * Register key type
284 */
big_key_init(void)285 static int __init big_key_init(void)
286 {
287 return register_key_type(&key_type_big_key);
288 }
289
290 late_initcall(big_key_init);
291
