summaryrefslogtreecommitdiff
path: root/fs/crypto/keyinfo.c
blob: 82f0285f5d084934d0c13d98d684fbbd3f69f3ed (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
/*
 * key management facility for FS encryption support.
 *
 * Copyright (C) 2015, Google, Inc.
 *
 * This contains encryption key functions.
 *
 * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
 */

#include <keys/user-type.h>
#include <linux/scatterlist.h>
#include <linux/fscrypto.h>

static void derive_crypt_complete(struct crypto_async_request *req, int rc)
{
	struct fscrypt_completion_result *ecr = req->data;

	if (rc == -EINPROGRESS)
		return;

	ecr->res = rc;
	complete(&ecr->completion);
}

/**
 * derive_key_aes() - Derive a key using AES-128-ECB
 * @deriving_key: Encryption key used for derivation.
 * @source_key:   Source key to which to apply derivation.
 * @derived_key:  Derived key.
 *
 * Return: Zero on success; non-zero otherwise.
 */
static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
				u8 source_key[FS_AES_256_XTS_KEY_SIZE],
				u8 derived_key[FS_AES_256_XTS_KEY_SIZE])
{
	int res = 0;
	struct skcipher_request *req = NULL;
	DECLARE_FS_COMPLETION_RESULT(ecr);
	struct scatterlist src_sg, dst_sg;
	struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);

	if (IS_ERR(tfm)) {
		res = PTR_ERR(tfm);
		tfm = NULL;
		goto out;
	}
	crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
	req = skcipher_request_alloc(tfm, GFP_NOFS);
	if (!req) {
		res = -ENOMEM;
		goto out;
	}
	skcipher_request_set_callback(req,
			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
			derive_crypt_complete, &ecr);
	res = crypto_skcipher_setkey(tfm, deriving_key,
					FS_AES_128_ECB_KEY_SIZE);
	if (res < 0)
		goto out;

	sg_init_one(&src_sg, source_key, FS_AES_256_XTS_KEY_SIZE);
	sg_init_one(&dst_sg, derived_key, FS_AES_256_XTS_KEY_SIZE);
	skcipher_request_set_crypt(req, &src_sg, &dst_sg,
					FS_AES_256_XTS_KEY_SIZE, NULL);
	res = crypto_skcipher_encrypt(req);
	if (res == -EINPROGRESS || res == -EBUSY) {
		wait_for_completion(&ecr.completion);
		res = ecr.res;
	}
out:
	skcipher_request_free(req);
	crypto_free_skcipher(tfm);
	return res;
}

static int validate_user_key(struct fscrypt_info *crypt_info,
			struct fscrypt_context *ctx, u8 *raw_key,
			u8 *prefix, int prefix_size)
{
	u8 *full_key_descriptor;
	struct key *keyring_key;
	struct fscrypt_key *master_key;
	const struct user_key_payload *ukp;
	int full_key_len = prefix_size + (FS_KEY_DESCRIPTOR_SIZE * 2) + 1;
	int res;

	full_key_descriptor = kmalloc(full_key_len, GFP_NOFS);
	if (!full_key_descriptor)
		return -ENOMEM;

	memcpy(full_key_descriptor, prefix, prefix_size);
	sprintf(full_key_descriptor + prefix_size,
			"%*phN", FS_KEY_DESCRIPTOR_SIZE,
			ctx->master_key_descriptor);
	full_key_descriptor[full_key_len - 1] = '\0';
	keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
	kfree(full_key_descriptor);
	if (IS_ERR(keyring_key))
		return PTR_ERR(keyring_key);

	if (keyring_key->type != &key_type_logon) {
		printk_once(KERN_WARNING
				"%s: key type must be logon\n", __func__);
		res = -ENOKEY;
		goto out;
	}
	down_read(&keyring_key->sem);
	ukp = user_key_payload(keyring_key);
	if (ukp->datalen != sizeof(struct fscrypt_key)) {
		res = -EINVAL;
		up_read(&keyring_key->sem);
		goto out;
	}
	master_key = (struct fscrypt_key *)ukp->data;
	BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);

	if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
		printk_once(KERN_WARNING
				"%s: key size incorrect: %d\n",
				__func__, master_key->size);
		res = -ENOKEY;
		up_read(&keyring_key->sem);
		goto out;
	}
	res = derive_key_aes(ctx->nonce, master_key->raw, raw_key);
	up_read(&keyring_key->sem);
	if (res)
		goto out;

	crypt_info->ci_keyring_key = keyring_key;
	return 0;
out:
	key_put(keyring_key);
	return res;
}

static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode,
				 const char **cipher_str_ret, int *keysize_ret)
{
	if (S_ISREG(inode->i_mode)) {
		if (ci->ci_data_mode == FS_ENCRYPTION_MODE_AES_256_XTS) {
			*cipher_str_ret = "xts(aes)";
			*keysize_ret = FS_AES_256_XTS_KEY_SIZE;
			return 0;
		}
		pr_warn_once("fscrypto: unsupported contents encryption mode "
			     "%d for inode %lu\n",
			     ci->ci_data_mode, inode->i_ino);
		return -ENOKEY;
	}

	if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) {
		if (ci->ci_filename_mode == FS_ENCRYPTION_MODE_AES_256_CTS) {
			*cipher_str_ret = "cts(cbc(aes))";
			*keysize_ret = FS_AES_256_CTS_KEY_SIZE;
			return 0;
		}
		pr_warn_once("fscrypto: unsupported filenames encryption mode "
			     "%d for inode %lu\n",
			     ci->ci_filename_mode, inode->i_ino);
		return -ENOKEY;
	}

	pr_warn_once("fscrypto: unsupported file type %d for inode %lu\n",
		     (inode->i_mode & S_IFMT), inode->i_ino);
	return -ENOKEY;
}

static void put_crypt_info(struct fscrypt_info *ci)
{
	if (!ci)
		return;

	key_put(ci->ci_keyring_key);
	crypto_free_skcipher(ci->ci_ctfm);
	kmem_cache_free(fscrypt_info_cachep, ci);
}

int get_crypt_info(struct inode *inode)
{
	struct fscrypt_info *crypt_info;
	struct fscrypt_context ctx;
	struct crypto_skcipher *ctfm;
	const char *cipher_str;
	int keysize;
	u8 raw_key[FS_MAX_KEY_SIZE];
	int res;

	res = fscrypt_initialize();
	if (res)
		return res;

	if (!inode->i_sb->s_cop->get_context)
		return -EOPNOTSUPP;
retry:
	crypt_info = ACCESS_ONCE(inode->i_crypt_info);
	if (crypt_info) {
		if (!crypt_info->ci_keyring_key ||
				key_validate(crypt_info->ci_keyring_key) == 0)
			return 0;
		fscrypt_put_encryption_info(inode, crypt_info);
		goto retry;
	}

	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
	if (res < 0) {
		if (!fscrypt_dummy_context_enabled(inode))
			return res;
		ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
		ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
		ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
		ctx.flags = 0;
	} else if (res != sizeof(ctx)) {
		return -EINVAL;
	}

	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
		return -EINVAL;

	if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
		return -EINVAL;

	crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
	if (!crypt_info)
		return -ENOMEM;

	crypt_info->ci_flags = ctx.flags;
	crypt_info->ci_data_mode = ctx.contents_encryption_mode;
	crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
	crypt_info->ci_ctfm = NULL;
	crypt_info->ci_keyring_key = NULL;
	memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
				sizeof(crypt_info->ci_master_key));

	res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize);
	if (res)
		goto out;

	if (fscrypt_dummy_context_enabled(inode)) {
		memset(raw_key, 0x42, FS_AES_256_XTS_KEY_SIZE);
		goto got_key;
	}

	res = validate_user_key(crypt_info, &ctx, raw_key,
			FS_KEY_DESC_PREFIX, FS_KEY_DESC_PREFIX_SIZE);
	if (res && inode->i_sb->s_cop->key_prefix) {
		u8 *prefix = NULL;
		int prefix_size, res2;

		prefix_size = inode->i_sb->s_cop->key_prefix(inode, &prefix);
		res2 = validate_user_key(crypt_info, &ctx, raw_key,
							prefix, prefix_size);
		if (res2) {
			if (res2 == -ENOKEY)
				res = -ENOKEY;
			goto out;
		}
	} else if (res) {
		goto out;
	}
got_key:
	ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
	if (!ctfm || IS_ERR(ctfm)) {
		res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
		printk(KERN_DEBUG
		       "%s: error %d (inode %u) allocating crypto tfm\n",
		       __func__, res, (unsigned) inode->i_ino);
		goto out;
	}
	crypt_info->ci_ctfm = ctfm;
	crypto_skcipher_clear_flags(ctfm, ~0);
	crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
	res = crypto_skcipher_setkey(ctfm, raw_key, keysize);
	if (res)
		goto out;

	memzero_explicit(raw_key, sizeof(raw_key));
	if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) != NULL) {
		put_crypt_info(crypt_info);
		goto retry;
	}
	return 0;

out:
	if (res == -ENOKEY)
		res = 0;
	put_crypt_info(crypt_info);
	memzero_explicit(raw_key, sizeof(raw_key));
	return res;
}

void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
{
	struct fscrypt_info *prev;

	if (ci == NULL)
		ci = ACCESS_ONCE(inode->i_crypt_info);
	if (ci == NULL)
		return;

	prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
	if (prev != ci)
		return;

	put_crypt_info(ci);
}
EXPORT_SYMBOL(fscrypt_put_encryption_info);

int fscrypt_get_encryption_info(struct inode *inode)
{
	struct fscrypt_info *ci = inode->i_crypt_info;

	if (!ci ||
		(ci->ci_keyring_key &&
		 (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
					       (1 << KEY_FLAG_REVOKED) |
					       (1 << KEY_FLAG_DEAD)))))
		return get_crypt_info(inode);
	return 0;
}
EXPORT_SYMBOL(fscrypt_get_encryption_info);