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 enum {
24 big_key_data,
25 big_key_path,
26 big_key_path_2nd_part,
27 big_key_len,
28 };
29
30 /*
31 * If the data is under this limit, there's no point creating a shm file to
32 * hold it as the permanently resident metadata for the shmem fs will be at
33 * least as large as the data.
34 */
35 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
36
37 /*
38 * big_key defined keys take an arbitrary string as the description and an
39 * arbitrary blob of data as the payload
40 */
41 struct key_type key_type_big_key = {
42 .name = "big_key",
43 .preparse = big_key_preparse,
44 .free_preparse = big_key_free_preparse,
45 .instantiate = generic_key_instantiate,
46 .revoke = big_key_revoke,
47 .destroy = big_key_destroy,
48 .describe = big_key_describe,
49 .read = big_key_read,
50 .update = big_key_update,
51 };
52
53 /*
54 * Preparse a big key
55 */
big_key_preparse(struct key_preparsed_payload * prep)56 int big_key_preparse(struct key_preparsed_payload *prep)
57 {
58 struct path *path = (struct path *)&prep->payload.data[big_key_path];
59 struct file *file;
60 u8 *buf, *enckey;
61 ssize_t written;
62 size_t datalen = prep->datalen;
63 size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
64 int ret;
65
66 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
67 return -EINVAL;
68
69 /* Set an arbitrary quota */
70 prep->quotalen = 16;
71
72 prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
73
74 if (datalen > BIG_KEY_FILE_THRESHOLD) {
75 /* Create a shmem file to store the data in. This will permit the data
76 * to be swapped out if needed.
77 *
78 * File content is stored encrypted with randomly generated key.
79 * Since the key is random for each file, we can set the nonce
80 * to zero, provided we never define a ->update() call.
81 */
82 loff_t pos = 0;
83
84 buf = kvmalloc(enclen, GFP_KERNEL);
85 if (!buf)
86 return -ENOMEM;
87
88 /* generate random key */
89 enckey = kmalloc(CHACHA20POLY1305_KEY_SIZE, GFP_KERNEL);
90 if (!enckey) {
91 ret = -ENOMEM;
92 goto error;
93 }
94 ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_KEY_SIZE);
95 if (unlikely(ret))
96 goto err_enckey;
97
98 /* encrypt data */
99 chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0,
100 0, enckey);
101
102 /* save aligned data to file */
103 file = shmem_kernel_file_setup("", enclen, 0);
104 if (IS_ERR(file)) {
105 ret = PTR_ERR(file);
106 goto err_enckey;
107 }
108
109 written = kernel_write(file, buf, enclen, &pos);
110 if (written != enclen) {
111 ret = written;
112 if (written >= 0)
113 ret = -EIO;
114 goto err_fput;
115 }
116
117 /* Pin the mount and dentry to the key so that we can open it again
118 * later
119 */
120 prep->payload.data[big_key_data] = enckey;
121 *path = file->f_path;
122 path_get(path);
123 fput(file);
124 kvfree_sensitive(buf, enclen);
125 } else {
126 /* Just store the data in a buffer */
127 void *data = kmalloc(datalen, GFP_KERNEL);
128
129 if (!data)
130 return -ENOMEM;
131
132 prep->payload.data[big_key_data] = data;
133 memcpy(data, prep->data, prep->datalen);
134 }
135 return 0;
136
137 err_fput:
138 fput(file);
139 err_enckey:
140 kfree_sensitive(enckey);
141 error:
142 kvfree_sensitive(buf, enclen);
143 return ret;
144 }
145
146 /*
147 * Clear preparsement.
148 */
big_key_free_preparse(struct key_preparsed_payload * prep)149 void big_key_free_preparse(struct key_preparsed_payload *prep)
150 {
151 if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
152 struct path *path = (struct path *)&prep->payload.data[big_key_path];
153
154 path_put(path);
155 }
156 kfree_sensitive(prep->payload.data[big_key_data]);
157 }
158
159 /*
160 * dispose of the links from a revoked keyring
161 * - called with the key sem write-locked
162 */
big_key_revoke(struct key * key)163 void big_key_revoke(struct key *key)
164 {
165 struct path *path = (struct path *)&key->payload.data[big_key_path];
166
167 /* clear the quota */
168 key_payload_reserve(key, 0);
169 if (key_is_positive(key) &&
170 (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
171 vfs_truncate(path, 0);
172 }
173
174 /*
175 * dispose of the data dangling from the corpse of a big_key key
176 */
big_key_destroy(struct key * key)177 void big_key_destroy(struct key *key)
178 {
179 size_t datalen = (size_t)key->payload.data[big_key_len];
180
181 if (datalen > BIG_KEY_FILE_THRESHOLD) {
182 struct path *path = (struct path *)&key->payload.data[big_key_path];
183
184 path_put(path);
185 path->mnt = NULL;
186 path->dentry = NULL;
187 }
188 kfree_sensitive(key->payload.data[big_key_data]);
189 key->payload.data[big_key_data] = NULL;
190 }
191
192 /*
193 * Update a big key
194 */
big_key_update(struct key * key,struct key_preparsed_payload * prep)195 int big_key_update(struct key *key, struct key_preparsed_payload *prep)
196 {
197 int ret;
198
199 ret = key_payload_reserve(key, prep->datalen);
200 if (ret < 0)
201 return ret;
202
203 if (key_is_positive(key))
204 big_key_destroy(key);
205
206 return generic_key_instantiate(key, prep);
207 }
208
209 /*
210 * describe the big_key key
211 */
big_key_describe(const struct key * key,struct seq_file * m)212 void big_key_describe(const struct key *key, struct seq_file *m)
213 {
214 size_t datalen = (size_t)key->payload.data[big_key_len];
215
216 seq_puts(m, key->description);
217
218 if (key_is_positive(key))
219 seq_printf(m, ": %zu [%s]",
220 datalen,
221 datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
222 }
223
224 /*
225 * read the key data
226 * - the key's semaphore is read-locked
227 */
big_key_read(const struct key * key,char * buffer,size_t buflen)228 long big_key_read(const struct key *key, char *buffer, size_t buflen)
229 {
230 size_t datalen = (size_t)key->payload.data[big_key_len];
231 long ret;
232
233 if (!buffer || buflen < datalen)
234 return datalen;
235
236 if (datalen > BIG_KEY_FILE_THRESHOLD) {
237 struct path *path = (struct path *)&key->payload.data[big_key_path];
238 struct file *file;
239 u8 *buf, *enckey = (u8 *)key->payload.data[big_key_data];
240 size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
241 loff_t pos = 0;
242
243 buf = kvmalloc(enclen, GFP_KERNEL);
244 if (!buf)
245 return -ENOMEM;
246
247 file = dentry_open(path, O_RDONLY, current_cred());
248 if (IS_ERR(file)) {
249 ret = PTR_ERR(file);
250 goto error;
251 }
252
253 /* read file to kernel and decrypt */
254 ret = kernel_read(file, buf, enclen, &pos);
255 if (ret != enclen) {
256 if (ret >= 0)
257 ret = -EIO;
258 goto err_fput;
259 }
260
261 ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0,
262 enckey) ? 0 : -EBADMSG;
263 if (unlikely(ret))
264 goto err_fput;
265
266 ret = datalen;
267
268 /* copy out decrypted data */
269 memcpy(buffer, buf, datalen);
270
271 err_fput:
272 fput(file);
273 error:
274 kvfree_sensitive(buf, enclen);
275 } else {
276 ret = datalen;
277 memcpy(buffer, key->payload.data[big_key_data], datalen);
278 }
279
280 return ret;
281 }
282
283 /*
284 * Register key type
285 */
big_key_init(void)286 static int __init big_key_init(void)
287 {
288 return register_key_type(&key_type_big_key);
289 }
290
291 late_initcall(big_key_init);
292