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);
291