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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 */
23enum {
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 */
41struct 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 */
56int 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 memzero_explicit(buf, enclen);
125 kvfree(buf);
126 } else {
127 /* Just store the data in a buffer */
128 void *data = kmalloc(datalen, GFP_KERNEL);
129
130 if (!data)
131 return -ENOMEM;
132
133 prep->payload.data[big_key_data] = data;
134 memcpy(data, prep->data, prep->datalen);
135 }
136 return 0;
137
138err_fput:
139 fput(file);
140err_enckey:
141 kfree_sensitive(enckey);
142error:
143 memzero_explicit(buf, enclen);
144 kvfree(buf);
145 return ret;
146}
147
148/*
149 * Clear preparsement.
150 */
151void big_key_free_preparse(struct key_preparsed_payload *prep)
152{
153 if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
154 struct path *path = (struct path *)&prep->payload.data[big_key_path];
155
156 path_put(path);
157 }
158 kfree_sensitive(prep->payload.data[big_key_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 path *path = (struct path *)&key->payload.data[big_key_path];
168
169 /* clear the quota */
170 key_payload_reserve(key, 0);
171 if (key_is_positive(key) &&
172 (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
173 vfs_truncate(path, 0);
174}
175
176/*
177 * dispose of the data dangling from the corpse of a big_key key
178 */
179void big_key_destroy(struct key *key)
180{
181 size_t datalen = (size_t)key->payload.data[big_key_len];
182
183 if (datalen > BIG_KEY_FILE_THRESHOLD) {
184 struct path *path = (struct path *)&key->payload.data[big_key_path];
185
186 path_put(path);
187 path->mnt = NULL;
188 path->dentry = NULL;
189 }
190 kfree_sensitive(key->payload.data[big_key_data]);
191 key->payload.data[big_key_data] = NULL;
192}
193
194/*
195 * Update a big key
196 */
197int big_key_update(struct key *key, struct key_preparsed_payload *prep)
198{
199 int ret;
200
201 ret = key_payload_reserve(key, prep->datalen);
202 if (ret < 0)
203 return ret;
204
205 if (key_is_positive(key))
206 big_key_destroy(key);
207
208 return generic_key_instantiate(key, prep);
209}
210
211/*
212 * describe the big_key key
213 */
214void big_key_describe(const struct key *key, struct seq_file *m)
215{
216 size_t datalen = (size_t)key->payload.data[big_key_len];
217
218 seq_puts(m, key->description);
219
220 if (key_is_positive(key))
221 seq_printf(m, ": %zu [%s]",
222 datalen,
223 datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
224}
225
226/*
227 * read the key data
228 * - the key's semaphore is read-locked
229 */
230long big_key_read(const struct key *key, char *buffer, size_t buflen)
231{
232 size_t datalen = (size_t)key->payload.data[big_key_len];
233 long ret;
234
235 if (!buffer || buflen < datalen)
236 return datalen;
237
238 if (datalen > BIG_KEY_FILE_THRESHOLD) {
239 struct path *path = (struct path *)&key->payload.data[big_key_path];
240 struct file *file;
241 u8 *buf, *enckey = (u8 *)key->payload.data[big_key_data];
242 size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
243 loff_t pos = 0;
244
245 buf = kvmalloc(enclen, GFP_KERNEL);
246 if (!buf)
247 return -ENOMEM;
248
249 file = dentry_open(path, O_RDONLY, current_cred());
250 if (IS_ERR(file)) {
251 ret = PTR_ERR(file);
252 goto error;
253 }
254
255 /* read file to kernel and decrypt */
256 ret = kernel_read(file, buf, enclen, &pos);
257 if (ret != enclen) {
258 if (ret >= 0)
259 ret = -EIO;
260 goto err_fput;
261 }
262
263 ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0,
264 enckey) ? 0 : -EBADMSG;
265 if (unlikely(ret))
266 goto err_fput;
267
268 ret = datalen;
269
270 /* copy out decrypted data */
271 memcpy(buffer, buf, datalen);
272
273err_fput:
274 fput(file);
275error:
276 memzero_explicit(buf, enclen);
277 kvfree(buf);
278 } else {
279 ret = datalen;
280 memcpy(buffer, key->payload.data[big_key_data], datalen);
281 }
282
283 return ret;
284}
285
286/*
287 * Register key type
288 */
289static int __init big_key_init(void)
290{
291 return register_key_type(&key_type_big_key);
292}
293
294late_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/init.h>
13#include <linux/seq_file.h>
14#include <linux/file.h>
15#include <linux/shmem_fs.h>
16#include <linux/err.h>
17#include <keys/user-type.h>
18#include <keys/big_key-type.h>
19
20/*
21 * Layout of key payload words.
22 */
23enum {
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 */
41struct 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};
51
52/*
53 * Preparse a big key
54 */
55int big_key_preparse(struct key_preparsed_payload *prep)
56{
57 struct path *path = (struct path *)&prep->payload.data[big_key_path];
58 struct file *file;
59 ssize_t written;
60 size_t datalen = prep->datalen;
61 int ret;
62
63 ret = -EINVAL;
64 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
65 goto error;
66
67 /* Set an arbitrary quota */
68 prep->quotalen = 16;
69
70 prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
71
72 if (datalen > BIG_KEY_FILE_THRESHOLD) {
73 /* Create a shmem file to store the data in. This will permit the data
74 * to be swapped out if needed.
75 *
76 * TODO: Encrypt the stored data with a temporary key.
77 */
78 file = shmem_kernel_file_setup("", datalen, 0);
79 if (IS_ERR(file)) {
80 ret = PTR_ERR(file);
81 goto error;
82 }
83
84 written = kernel_write(file, prep->data, prep->datalen, 0);
85 if (written != datalen) {
86 ret = written;
87 if (written >= 0)
88 ret = -ENOMEM;
89 goto err_fput;
90 }
91
92 /* Pin the mount and dentry to the key so that we can open it again
93 * later
94 */
95 *path = file->f_path;
96 path_get(path);
97 fput(file);
98 } else {
99 /* Just store the data in a buffer */
100 void *data = kmalloc(datalen, GFP_KERNEL);
101 if (!data)
102 return -ENOMEM;
103
104 prep->payload.data[big_key_data] = data;
105 memcpy(data, prep->data, prep->datalen);
106 }
107 return 0;
108
109err_fput:
110 fput(file);
111error:
112 return ret;
113}
114
115/*
116 * Clear preparsement.
117 */
118void big_key_free_preparse(struct key_preparsed_payload *prep)
119{
120 if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
121 struct path *path = (struct path *)&prep->payload.data[big_key_path];
122 path_put(path);
123 } else {
124 kfree(prep->payload.data[big_key_data]);
125 }
126}
127
128/*
129 * dispose of the links from a revoked keyring
130 * - called with the key sem write-locked
131 */
132void big_key_revoke(struct key *key)
133{
134 struct path *path = (struct path *)&key->payload.data[big_key_path];
135
136 /* clear the quota */
137 key_payload_reserve(key, 0);
138 if (key_is_instantiated(key) &&
139 (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
140 vfs_truncate(path, 0);
141}
142
143/*
144 * dispose of the data dangling from the corpse of a big_key key
145 */
146void big_key_destroy(struct key *key)
147{
148 size_t datalen = (size_t)key->payload.data[big_key_len];
149
150 if (datalen) {
151 struct path *path = (struct path *)&key->payload.data[big_key_path];
152 path_put(path);
153 path->mnt = NULL;
154 path->dentry = NULL;
155 } else {
156 kfree(key->payload.data[big_key_data]);
157 key->payload.data[big_key_data] = NULL;
158 }
159}
160
161/*
162 * describe the big_key key
163 */
164void big_key_describe(const struct key *key, struct seq_file *m)
165{
166 size_t datalen = (size_t)key->payload.data[big_key_len];
167
168 seq_puts(m, key->description);
169
170 if (key_is_instantiated(key))
171 seq_printf(m, ": %zu [%s]",
172 datalen,
173 datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
174}
175
176/*
177 * read the key data
178 * - the key's semaphore is read-locked
179 */
180long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
181{
182 size_t datalen = (size_t)key->payload.data[big_key_len];
183 long ret;
184
185 if (!buffer || buflen < datalen)
186 return datalen;
187
188 if (datalen > BIG_KEY_FILE_THRESHOLD) {
189 struct path *path = (struct path *)&key->payload.data[big_key_path];
190 struct file *file;
191 loff_t pos;
192
193 file = dentry_open(path, O_RDONLY, current_cred());
194 if (IS_ERR(file))
195 return PTR_ERR(file);
196
197 pos = 0;
198 ret = vfs_read(file, buffer, datalen, &pos);
199 fput(file);
200 if (ret >= 0 && ret != datalen)
201 ret = -EIO;
202 } else {
203 ret = datalen;
204 if (copy_to_user(buffer, key->payload.data[big_key_data],
205 datalen) != 0)
206 ret = -EFAULT;
207 }
208
209 return ret;
210}
211
212static int __init big_key_init(void)
213{
214 return register_key_type(&key_type_big_key);
215}
216device_initcall(big_key_init);