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
derive_crypt_complete(struct crypto_async_request * req,int rc)20 static 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 */
ext4_derive_key_aes(char deriving_key[EXT4_AES_128_ECB_KEY_SIZE],char source_key[EXT4_AES_256_XTS_KEY_SIZE],char derived_key[EXT4_AES_256_XTS_KEY_SIZE])39 static 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
79 out:
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 */
ext4_generate_encryption_key(struct inode * inode)91 int 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);
152 out:
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
ext4_has_encryption_key(struct inode * inode)160 int 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