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		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
137err_fput:
138	fput(file);
139err_enckey:
140	kfree_sensitive(enckey);
141error:
142	kvfree_sensitive(buf, enclen);
143	return ret;
144}
145
146/*
147 * Clear preparsement.
148 */
149void 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 */
163void 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 */
177void 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 */
195int 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 */
212void 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 */
228long 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
271err_fput:
272		fput(file);
273error:
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 */
286static int __init big_key_init(void)
287{
288	return register_key_type(&key_type_big_key);
289}
290
291late_initcall(big_key_init);