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
ext4_free_crypt_info(struct ext4_crypt_info * ci)87 void ext4_free_crypt_info(struct ext4_crypt_info *ci)
88 {
89 if (!ci)
90 return;
91
92 if (ci->ci_keyring_key)
93 key_put(ci->ci_keyring_key);
94 crypto_free_ablkcipher(ci->ci_ctfm);
95 kmem_cache_free(ext4_crypt_info_cachep, ci);
96 }
97
ext4_free_encryption_info(struct inode * inode,struct ext4_crypt_info * ci)98 void ext4_free_encryption_info(struct inode *inode,
99 struct ext4_crypt_info *ci)
100 {
101 struct ext4_inode_info *ei = EXT4_I(inode);
102 struct ext4_crypt_info *prev;
103
104 if (ci == NULL)
105 ci = ACCESS_ONCE(ei->i_crypt_info);
106 if (ci == NULL)
107 return;
108 prev = cmpxchg(&ei->i_crypt_info, ci, NULL);
109 if (prev != ci)
110 return;
111
112 ext4_free_crypt_info(ci);
113 }
114
_ext4_get_encryption_info(struct inode * inode)115 int _ext4_get_encryption_info(struct inode *inode)
116 {
117 struct ext4_inode_info *ei = EXT4_I(inode);
118 struct ext4_crypt_info *crypt_info;
119 char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
120 (EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1];
121 struct key *keyring_key = NULL;
122 struct ext4_encryption_key *master_key;
123 struct ext4_encryption_context ctx;
124 struct user_key_payload *ukp;
125 struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
126 struct crypto_ablkcipher *ctfm;
127 const char *cipher_str;
128 char raw_key[EXT4_MAX_KEY_SIZE];
129 char mode;
130 int res;
131
132 if (!ext4_read_workqueue) {
133 res = ext4_init_crypto();
134 if (res)
135 return res;
136 }
137
138 retry:
139 crypt_info = ACCESS_ONCE(ei->i_crypt_info);
140 if (crypt_info) {
141 if (!crypt_info->ci_keyring_key ||
142 key_validate(crypt_info->ci_keyring_key) == 0)
143 return 0;
144 ext4_free_encryption_info(inode, crypt_info);
145 goto retry;
146 }
147
148 res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
149 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
150 &ctx, sizeof(ctx));
151 if (res < 0) {
152 if (!DUMMY_ENCRYPTION_ENABLED(sbi))
153 return res;
154 ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
155 ctx.filenames_encryption_mode =
156 EXT4_ENCRYPTION_MODE_AES_256_CTS;
157 ctx.flags = 0;
158 } else if (res != sizeof(ctx))
159 return -EINVAL;
160 res = 0;
161
162 crypt_info = kmem_cache_alloc(ext4_crypt_info_cachep, GFP_KERNEL);
163 if (!crypt_info)
164 return -ENOMEM;
165
166 crypt_info->ci_flags = ctx.flags;
167 crypt_info->ci_data_mode = ctx.contents_encryption_mode;
168 crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
169 crypt_info->ci_ctfm = NULL;
170 crypt_info->ci_keyring_key = NULL;
171 memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
172 sizeof(crypt_info->ci_master_key));
173 if (S_ISREG(inode->i_mode))
174 mode = crypt_info->ci_data_mode;
175 else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
176 mode = crypt_info->ci_filename_mode;
177 else
178 BUG();
179 switch (mode) {
180 case EXT4_ENCRYPTION_MODE_AES_256_XTS:
181 cipher_str = "xts(aes)";
182 break;
183 case EXT4_ENCRYPTION_MODE_AES_256_CTS:
184 cipher_str = "cts(cbc(aes))";
185 break;
186 default:
187 printk_once(KERN_WARNING
188 "ext4: unsupported key mode %d (ino %u)\n",
189 mode, (unsigned) inode->i_ino);
190 res = -ENOKEY;
191 goto out;
192 }
193 if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
194 memset(raw_key, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
195 goto got_key;
196 }
197 memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
198 EXT4_KEY_DESC_PREFIX_SIZE);
199 sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
200 "%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
201 ctx.master_key_descriptor);
202 full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
203 (2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
204 keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
205 if (IS_ERR(keyring_key)) {
206 res = PTR_ERR(keyring_key);
207 keyring_key = NULL;
208 goto out;
209 }
210 crypt_info->ci_keyring_key = keyring_key;
211 BUG_ON(keyring_key->type != &key_type_logon);
212 ukp = ((struct user_key_payload *)keyring_key->payload.data);
213 if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
214 res = -EINVAL;
215 goto out;
216 }
217 master_key = (struct ext4_encryption_key *)ukp->data;
218 BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
219 EXT4_KEY_DERIVATION_NONCE_SIZE);
220 BUG_ON(master_key->size != EXT4_AES_256_XTS_KEY_SIZE);
221 res = ext4_derive_key_aes(ctx.nonce, master_key->raw,
222 raw_key);
223 got_key:
224 ctfm = crypto_alloc_ablkcipher(cipher_str, 0, 0);
225 if (!ctfm || IS_ERR(ctfm)) {
226 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
227 printk(KERN_DEBUG
228 "%s: error %d (inode %u) allocating crypto tfm\n",
229 __func__, res, (unsigned) inode->i_ino);
230 goto out;
231 }
232 crypt_info->ci_ctfm = ctfm;
233 crypto_ablkcipher_clear_flags(ctfm, ~0);
234 crypto_tfm_set_flags(crypto_ablkcipher_tfm(ctfm),
235 CRYPTO_TFM_REQ_WEAK_KEY);
236 res = crypto_ablkcipher_setkey(ctfm, raw_key,
237 ext4_encryption_key_size(mode));
238 if (res)
239 goto out;
240 memset(raw_key, 0, sizeof(raw_key));
241 if (cmpxchg(&ei->i_crypt_info, NULL, crypt_info) != NULL) {
242 ext4_free_crypt_info(crypt_info);
243 goto retry;
244 }
245 return 0;
246
247 out:
248 if (res == -ENOKEY)
249 res = 0;
250 ext4_free_crypt_info(crypt_info);
251 memset(raw_key, 0, sizeof(raw_key));
252 return res;
253 }
254
ext4_has_encryption_key(struct inode * inode)255 int ext4_has_encryption_key(struct inode *inode)
256 {
257 struct ext4_inode_info *ei = EXT4_I(inode);
258
259 return (ei->i_crypt_info != NULL);
260 }
261