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);
295