1/*
2 * linux/fs/ext4/crypto_key.c
3 *
4 * Copyright (C) 2015, Google, Inc.
5 *
6 * This contains encryption key functions for ext4
7 *
8 * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
9 */
10
11#include <keys/encrypted-type.h>
12#include <keys/user-type.h>
13#include <linux/random.h>
14#include <linux/scatterlist.h>
15#include <uapi/linux/keyctl.h>
16
17#include "ext4.h"
18#include "xattr.h"
19
20static void derive_crypt_complete(struct crypto_async_request *req, int rc)
21{
22	struct ext4_completion_result *ecr = req->data;
23
24	if (rc == -EINPROGRESS)
25		return;
26
27	ecr->res = rc;
28	complete(&ecr->completion);
29}
30
31/**
32 * ext4_derive_key_aes() - Derive a key using AES-128-ECB
33 * @deriving_key: Encryption key used for derivatio.
34 * @source_key:   Source key to which to apply derivation.
35 * @derived_key:  Derived key.
36 *
37 * Return: Zero on success; non-zero otherwise.
38 */
39static int ext4_derive_key_aes(char deriving_key[EXT4_AES_128_ECB_KEY_SIZE],
40			       char source_key[EXT4_AES_256_XTS_KEY_SIZE],
41			       char derived_key[EXT4_AES_256_XTS_KEY_SIZE])
42{
43	int res = 0;
44	struct ablkcipher_request *req = NULL;
45	DECLARE_EXT4_COMPLETION_RESULT(ecr);
46	struct scatterlist src_sg, dst_sg;
47	struct crypto_ablkcipher *tfm = crypto_alloc_ablkcipher("ecb(aes)", 0,
48								0);
49
50	if (IS_ERR(tfm)) {
51		res = PTR_ERR(tfm);
52		tfm = NULL;
53		goto out;
54	}
55	crypto_ablkcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
56	req = ablkcipher_request_alloc(tfm, GFP_NOFS);
57	if (!req) {
58		res = -ENOMEM;
59		goto out;
60	}
61	ablkcipher_request_set_callback(req,
62			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
63			derive_crypt_complete, &ecr);
64	res = crypto_ablkcipher_setkey(tfm, deriving_key,
65				       EXT4_AES_128_ECB_KEY_SIZE);
66	if (res < 0)
67		goto out;
68	sg_init_one(&src_sg, source_key, EXT4_AES_256_XTS_KEY_SIZE);
69	sg_init_one(&dst_sg, derived_key, EXT4_AES_256_XTS_KEY_SIZE);
70	ablkcipher_request_set_crypt(req, &src_sg, &dst_sg,
71				     EXT4_AES_256_XTS_KEY_SIZE, NULL);
72	res = crypto_ablkcipher_encrypt(req);
73	if (res == -EINPROGRESS || res == -EBUSY) {
74		BUG_ON(req->base.data != &ecr);
75		wait_for_completion(&ecr.completion);
76		res = ecr.res;
77	}
78
79out:
80	if (req)
81		ablkcipher_request_free(req);
82	if (tfm)
83		crypto_free_ablkcipher(tfm);
84	return res;
85}
86
87/**
88 * ext4_generate_encryption_key() - generates an encryption key
89 * @inode: The inode to generate the encryption key for.
90 */
91int ext4_generate_encryption_key(struct inode *inode)
92{
93	struct ext4_inode_info *ei = EXT4_I(inode);
94	struct ext4_encryption_key *crypt_key = &ei->i_encryption_key;
95	char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
96				 (EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1];
97	struct key *keyring_key = NULL;
98	struct ext4_encryption_key *master_key;
99	struct ext4_encryption_context ctx;
100	struct user_key_payload *ukp;
101	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
102	int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
103				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
104				 &ctx, sizeof(ctx));
105
106	if (res != sizeof(ctx)) {
107		if (res > 0)
108			res = -EINVAL;
109		goto out;
110	}
111	res = 0;
112
113	ei->i_crypt_policy_flags = ctx.flags;
114	if (S_ISREG(inode->i_mode))
115		crypt_key->mode = ctx.contents_encryption_mode;
116	else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
117		crypt_key->mode = ctx.filenames_encryption_mode;
118	else {
119		printk(KERN_ERR "ext4 crypto: Unsupported inode type.\n");
120		BUG();
121	}
122	crypt_key->size = ext4_encryption_key_size(crypt_key->mode);
123	BUG_ON(!crypt_key->size);
124	if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
125		memset(crypt_key->raw, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
126		goto out;
127	}
128	memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
129	       EXT4_KEY_DESC_PREFIX_SIZE);
130	sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
131		"%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
132		ctx.master_key_descriptor);
133	full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
134			    (2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
135	keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
136	if (IS_ERR(keyring_key)) {
137		res = PTR_ERR(keyring_key);
138		keyring_key = NULL;
139		goto out;
140	}
141	BUG_ON(keyring_key->type != &key_type_logon);
142	ukp = ((struct user_key_payload *)keyring_key->payload.data);
143	if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
144		res = -EINVAL;
145		goto out;
146	}
147	master_key = (struct ext4_encryption_key *)ukp->data;
148	BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
149		     EXT4_KEY_DERIVATION_NONCE_SIZE);
150	BUG_ON(master_key->size != EXT4_AES_256_XTS_KEY_SIZE);
151	res = ext4_derive_key_aes(ctx.nonce, master_key->raw, crypt_key->raw);
152out:
153	if (keyring_key)
154		key_put(keyring_key);
155	if (res < 0)
156		crypt_key->mode = EXT4_ENCRYPTION_MODE_INVALID;
157	return res;
158}
159
160int ext4_has_encryption_key(struct inode *inode)
161{
162	struct ext4_inode_info *ei = EXT4_I(inode);
163	struct ext4_encryption_key *crypt_key = &ei->i_encryption_key;
164
165	return (crypt_key->mode != EXT4_ENCRYPTION_MODE_INVALID);
166}
167