xref: /linux/security/keys/big_key.c (revision e58e871becec2d3b04ed91c0c16fe8deac9c9dfa) 
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 #define pr_fmt(fmt) "big_key: "fmt
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 <linux/scatterlist.h>
19 #include <keys/user-type.h>
20 #include <keys/big_key-type.h>
21 #include <crypto/rng.h>
22 #include <crypto/skcipher.h>
23 
24 /*
25  * Layout of key payload words.
26  */
27 enum {
28 	big_key_data,
29 	big_key_path,
30 	big_key_path_2nd_part,
31 	big_key_len,
32 };
33 
34 /*
35  * Crypto operation with big_key data
36  */
37 enum big_key_op {
38 	BIG_KEY_ENC,
39 	BIG_KEY_DEC,
40 };
41 
42 /*
43  * If the data is under this limit, there's no point creating a shm file to
44  * hold it as the permanently resident metadata for the shmem fs will be at
45  * least as large as the data.
46  */
47 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
48 
49 /*
50  * Key size for big_key data encryption
51  */
52 #define ENC_KEY_SIZE	16
53 
54 /*
55  * big_key defined keys take an arbitrary string as the description and an
56  * arbitrary blob of data as the payload
57  */
58 struct key_type key_type_big_key = {
59 	.name			= "big_key",
60 	.preparse		= big_key_preparse,
61 	.free_preparse		= big_key_free_preparse,
62 	.instantiate		= generic_key_instantiate,
63 	.revoke			= big_key_revoke,
64 	.destroy		= big_key_destroy,
65 	.describe		= big_key_describe,
66 	.read			= big_key_read,
67 };
68 
69 /*
70  * Crypto names for big_key data encryption
71  */
72 static const char big_key_rng_name[] = "stdrng";
73 static const char big_key_alg_name[] = "ecb(aes)";
74 
75 /*
76  * Crypto algorithms for big_key data encryption
77  */
78 static struct crypto_rng *big_key_rng;
79 static struct crypto_skcipher *big_key_skcipher;
80 
81 /*
82  * Generate random key to encrypt big_key data
83  */
84 static inline int big_key_gen_enckey(u8 *key)
85 {
86 	return crypto_rng_get_bytes(big_key_rng, key, ENC_KEY_SIZE);
87 }
88 
89 /*
90  * Encrypt/decrypt big_key data
91  */
92 static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key)
93 {
94 	int ret = -EINVAL;
95 	struct scatterlist sgio;
96 	SKCIPHER_REQUEST_ON_STACK(req, big_key_skcipher);
97 
98 	if (crypto_skcipher_setkey(big_key_skcipher, key, ENC_KEY_SIZE)) {
99 		ret = -EAGAIN;
100 		goto error;
101 	}
102 
103 	skcipher_request_set_tfm(req, big_key_skcipher);
104 	skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP,
105 				      NULL, NULL);
106 
107 	sg_init_one(&sgio, data, datalen);
108 	skcipher_request_set_crypt(req, &sgio, &sgio, datalen, NULL);
109 
110 	if (op == BIG_KEY_ENC)
111 		ret = crypto_skcipher_encrypt(req);
112 	else
113 		ret = crypto_skcipher_decrypt(req);
114 
115 	skcipher_request_zero(req);
116 
117 error:
118 	return ret;
119 }
120 
121 /*
122  * Preparse a big key
123  */
124 int big_key_preparse(struct key_preparsed_payload *prep)
125 {
126 	struct path *path = (struct path *)&prep->payload.data[big_key_path];
127 	struct file *file;
128 	u8 *enckey;
129 	u8 *data = NULL;
130 	ssize_t written;
131 	size_t datalen = prep->datalen;
132 	int ret;
133 
134 	ret = -EINVAL;
135 	if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
136 		goto error;
137 
138 	/* Set an arbitrary quota */
139 	prep->quotalen = 16;
140 
141 	prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
142 
143 	if (datalen > BIG_KEY_FILE_THRESHOLD) {
144 		/* Create a shmem file to store the data in.  This will permit the data
145 		 * to be swapped out if needed.
146 		 *
147 		 * File content is stored encrypted with randomly generated key.
148 		 */
149 		size_t enclen = ALIGN(datalen, crypto_skcipher_blocksize(big_key_skcipher));
150 
151 		/* prepare aligned data to encrypt */
152 		data = kmalloc(enclen, GFP_KERNEL);
153 		if (!data)
154 			return -ENOMEM;
155 
156 		memcpy(data, prep->data, datalen);
157 		memset(data + datalen, 0x00, enclen - datalen);
158 
159 		/* generate random key */
160 		enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
161 		if (!enckey) {
162 			ret = -ENOMEM;
163 			goto error;
164 		}
165 
166 		ret = big_key_gen_enckey(enckey);
167 		if (ret)
168 			goto err_enckey;
169 
170 		/* encrypt aligned data */
171 		ret = big_key_crypt(BIG_KEY_ENC, data, enclen, enckey);
172 		if (ret)
173 			goto err_enckey;
174 
175 		/* save aligned data to file */
176 		file = shmem_kernel_file_setup("", enclen, 0);
177 		if (IS_ERR(file)) {
178 			ret = PTR_ERR(file);
179 			goto err_enckey;
180 		}
181 
182 		written = kernel_write(file, data, enclen, 0);
183 		if (written != enclen) {
184 			ret = written;
185 			if (written >= 0)
186 				ret = -ENOMEM;
187 			goto err_fput;
188 		}
189 
190 		/* Pin the mount and dentry to the key so that we can open it again
191 		 * later
192 		 */
193 		prep->payload.data[big_key_data] = enckey;
194 		*path = file->f_path;
195 		path_get(path);
196 		fput(file);
197 		kfree(data);
198 	} else {
199 		/* Just store the data in a buffer */
200 		void *data = kmalloc(datalen, GFP_KERNEL);
201 
202 		if (!data)
203 			return -ENOMEM;
204 
205 		prep->payload.data[big_key_data] = data;
206 		memcpy(data, prep->data, prep->datalen);
207 	}
208 	return 0;
209 
210 err_fput:
211 	fput(file);
212 err_enckey:
213 	kfree(enckey);
214 error:
215 	kfree(data);
216 	return ret;
217 }
218 
219 /*
220  * Clear preparsement.
221  */
222 void big_key_free_preparse(struct key_preparsed_payload *prep)
223 {
224 	if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
225 		struct path *path = (struct path *)&prep->payload.data[big_key_path];
226 
227 		path_put(path);
228 	}
229 	kfree(prep->payload.data[big_key_data]);
230 }
231 
232 /*
233  * dispose of the links from a revoked keyring
234  * - called with the key sem write-locked
235  */
236 void big_key_revoke(struct key *key)
237 {
238 	struct path *path = (struct path *)&key->payload.data[big_key_path];
239 
240 	/* clear the quota */
241 	key_payload_reserve(key, 0);
242 	if (key_is_instantiated(key) &&
243 	    (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
244 		vfs_truncate(path, 0);
245 }
246 
247 /*
248  * dispose of the data dangling from the corpse of a big_key key
249  */
250 void big_key_destroy(struct key *key)
251 {
252 	size_t datalen = (size_t)key->payload.data[big_key_len];
253 
254 	if (datalen > BIG_KEY_FILE_THRESHOLD) {
255 		struct path *path = (struct path *)&key->payload.data[big_key_path];
256 
257 		path_put(path);
258 		path->mnt = NULL;
259 		path->dentry = NULL;
260 	}
261 	kfree(key->payload.data[big_key_data]);
262 	key->payload.data[big_key_data] = NULL;
263 }
264 
265 /*
266  * describe the big_key key
267  */
268 void big_key_describe(const struct key *key, struct seq_file *m)
269 {
270 	size_t datalen = (size_t)key->payload.data[big_key_len];
271 
272 	seq_puts(m, key->description);
273 
274 	if (key_is_instantiated(key))
275 		seq_printf(m, ": %zu [%s]",
276 			   datalen,
277 			   datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
278 }
279 
280 /*
281  * read the key data
282  * - the key's semaphore is read-locked
283  */
284 long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
285 {
286 	size_t datalen = (size_t)key->payload.data[big_key_len];
287 	long ret;
288 
289 	if (!buffer || buflen < datalen)
290 		return datalen;
291 
292 	if (datalen > BIG_KEY_FILE_THRESHOLD) {
293 		struct path *path = (struct path *)&key->payload.data[big_key_path];
294 		struct file *file;
295 		u8 *data;
296 		u8 *enckey = (u8 *)key->payload.data[big_key_data];
297 		size_t enclen = ALIGN(datalen, crypto_skcipher_blocksize(big_key_skcipher));
298 
299 		data = kmalloc(enclen, GFP_KERNEL);
300 		if (!data)
301 			return -ENOMEM;
302 
303 		file = dentry_open(path, O_RDONLY, current_cred());
304 		if (IS_ERR(file)) {
305 			ret = PTR_ERR(file);
306 			goto error;
307 		}
308 
309 		/* read file to kernel and decrypt */
310 		ret = kernel_read(file, 0, data, enclen);
311 		if (ret >= 0 && ret != enclen) {
312 			ret = -EIO;
313 			goto err_fput;
314 		}
315 
316 		ret = big_key_crypt(BIG_KEY_DEC, data, enclen, enckey);
317 		if (ret)
318 			goto err_fput;
319 
320 		ret = datalen;
321 
322 		/* copy decrypted data to user */
323 		if (copy_to_user(buffer, data, datalen) != 0)
324 			ret = -EFAULT;
325 
326 err_fput:
327 		fput(file);
328 error:
329 		kfree(data);
330 	} else {
331 		ret = datalen;
332 		if (copy_to_user(buffer, key->payload.data[big_key_data],
333 				 datalen) != 0)
334 			ret = -EFAULT;
335 	}
336 
337 	return ret;
338 }
339 
340 /*
341  * Register key type
342  */
343 static int __init big_key_init(void)
344 {
345 	struct crypto_skcipher *cipher;
346 	struct crypto_rng *rng;
347 	int ret;
348 
349 	rng = crypto_alloc_rng(big_key_rng_name, 0, 0);
350 	if (IS_ERR(rng)) {
351 		pr_err("Can't alloc rng: %ld\n", PTR_ERR(rng));
352 		return PTR_ERR(rng);
353 	}
354 
355 	big_key_rng = rng;
356 
357 	/* seed RNG */
358 	ret = crypto_rng_reset(rng, NULL, crypto_rng_seedsize(rng));
359 	if (ret) {
360 		pr_err("Can't reset rng: %d\n", ret);
361 		goto error_rng;
362 	}
363 
364 	/* init block cipher */
365 	cipher = crypto_alloc_skcipher(big_key_alg_name, 0, CRYPTO_ALG_ASYNC);
366 	if (IS_ERR(cipher)) {
367 		ret = PTR_ERR(cipher);
368 		pr_err("Can't alloc crypto: %d\n", ret);
369 		goto error_rng;
370 	}
371 
372 	big_key_skcipher = cipher;
373 
374 	ret = register_key_type(&key_type_big_key);
375 	if (ret < 0) {
376 		pr_err("Can't register type: %d\n", ret);
377 		goto error_cipher;
378 	}
379 
380 	return 0;
381 
382 error_cipher:
383 	crypto_free_skcipher(big_key_skcipher);
384 error_rng:
385 	crypto_free_rng(big_key_rng);
386 	return ret;
387 }
388 
389 late_initcall(big_key_init);
390