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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 */
23struct 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 */
42struct 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 */
57int 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
140err_fput:
141 fput(file);
142err_enckey:
143 kfree_sensitive(enckey);
144error:
145 kvfree_sensitive(buf, enclen);
146 return ret;
147}
148
149/*
150 * Clear preparsement.
151 */
152void 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 */
165void 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 */
178void 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 */
194int 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 */
211void 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 */
227long 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
270err_fput:
271 fput(file);
272error:
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 */
285static int __init big_key_init(void)
286{
287 return register_key_type(&key_type_big_key);
288}
289
290late_initcall(big_key_init);
1/* Large capacity key type
2 *
3 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public Licence
8 * as published by the Free Software Foundation; either version
9 * 2 of the Licence, or (at your option) any later version.
10 */
11
12#include <linux/module.h>
13#include <linux/init.h>
14#include <linux/seq_file.h>
15#include <linux/file.h>
16#include <linux/shmem_fs.h>
17#include <linux/err.h>
18#include <keys/user-type.h>
19#include <keys/big_key-type.h>
20
21MODULE_LICENSE("GPL");
22
23/*
24 * If the data is under this limit, there's no point creating a shm file to
25 * hold it as the permanently resident metadata for the shmem fs will be at
26 * least as large as the data.
27 */
28#define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
29
30/*
31 * big_key defined keys take an arbitrary string as the description and an
32 * arbitrary blob of data as the payload
33 */
34struct key_type key_type_big_key = {
35 .name = "big_key",
36 .def_lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
37 .instantiate = big_key_instantiate,
38 .match = user_match,
39 .revoke = big_key_revoke,
40 .destroy = big_key_destroy,
41 .describe = big_key_describe,
42 .read = big_key_read,
43};
44
45/*
46 * Instantiate a big key
47 */
48int big_key_instantiate(struct key *key, struct key_preparsed_payload *prep)
49{
50 struct path *path = (struct path *)&key->payload.data2;
51 struct file *file;
52 ssize_t written;
53 size_t datalen = prep->datalen;
54 int ret;
55
56 ret = -EINVAL;
57 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
58 goto error;
59
60 /* Set an arbitrary quota */
61 ret = key_payload_reserve(key, 16);
62 if (ret < 0)
63 goto error;
64
65 key->type_data.x[1] = datalen;
66
67 if (datalen > BIG_KEY_FILE_THRESHOLD) {
68 /* Create a shmem file to store the data in. This will permit the data
69 * to be swapped out if needed.
70 *
71 * TODO: Encrypt the stored data with a temporary key.
72 */
73 file = shmem_kernel_file_setup("", datalen, 0);
74 if (IS_ERR(file)) {
75 ret = PTR_ERR(file);
76 goto err_quota;
77 }
78
79 written = kernel_write(file, prep->data, prep->datalen, 0);
80 if (written != datalen) {
81 ret = written;
82 if (written >= 0)
83 ret = -ENOMEM;
84 goto err_fput;
85 }
86
87 /* Pin the mount and dentry to the key so that we can open it again
88 * later
89 */
90 *path = file->f_path;
91 path_get(path);
92 fput(file);
93 } else {
94 /* Just store the data in a buffer */
95 void *data = kmalloc(datalen, GFP_KERNEL);
96 if (!data) {
97 ret = -ENOMEM;
98 goto err_quota;
99 }
100
101 key->payload.data = memcpy(data, prep->data, prep->datalen);
102 }
103 return 0;
104
105err_fput:
106 fput(file);
107err_quota:
108 key_payload_reserve(key, 0);
109error:
110 return ret;
111}
112
113/*
114 * dispose of the links from a revoked keyring
115 * - called with the key sem write-locked
116 */
117void big_key_revoke(struct key *key)
118{
119 struct path *path = (struct path *)&key->payload.data2;
120
121 /* clear the quota */
122 key_payload_reserve(key, 0);
123 if (key_is_instantiated(key) && key->type_data.x[1] > BIG_KEY_FILE_THRESHOLD)
124 vfs_truncate(path, 0);
125}
126
127/*
128 * dispose of the data dangling from the corpse of a big_key key
129 */
130void big_key_destroy(struct key *key)
131{
132 if (key->type_data.x[1] > BIG_KEY_FILE_THRESHOLD) {
133 struct path *path = (struct path *)&key->payload.data2;
134 path_put(path);
135 path->mnt = NULL;
136 path->dentry = NULL;
137 } else {
138 kfree(key->payload.data);
139 key->payload.data = NULL;
140 }
141}
142
143/*
144 * describe the big_key key
145 */
146void big_key_describe(const struct key *key, struct seq_file *m)
147{
148 unsigned long datalen = key->type_data.x[1];
149
150 seq_puts(m, key->description);
151
152 if (key_is_instantiated(key))
153 seq_printf(m, ": %lu [%s]",
154 datalen,
155 datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
156}
157
158/*
159 * read the key data
160 * - the key's semaphore is read-locked
161 */
162long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
163{
164 unsigned long datalen = key->type_data.x[1];
165 long ret;
166
167 if (!buffer || buflen < datalen)
168 return datalen;
169
170 if (datalen > BIG_KEY_FILE_THRESHOLD) {
171 struct path *path = (struct path *)&key->payload.data2;
172 struct file *file;
173 loff_t pos;
174
175 file = dentry_open(path, O_RDONLY, current_cred());
176 if (IS_ERR(file))
177 return PTR_ERR(file);
178
179 pos = 0;
180 ret = vfs_read(file, buffer, datalen, &pos);
181 fput(file);
182 if (ret >= 0 && ret != datalen)
183 ret = -EIO;
184 } else {
185 ret = datalen;
186 if (copy_to_user(buffer, key->payload.data, datalen) != 0)
187 ret = -EFAULT;
188 }
189
190 return ret;
191}
192
193/*
194 * Module stuff
195 */
196static int __init big_key_init(void)
197{
198 return register_key_type(&key_type_big_key);
199}
200
201static void __exit big_key_cleanup(void)
202{
203 unregister_key_type(&key_type_big_key);
204}
205
206module_init(big_key_init);
207module_exit(big_key_cleanup);