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ext4 crypto: add encryption key management facilities
Signed-off-by: Michael Halcrow <mhalcrow@google.com> Signed-off-by: Ildar Muslukhov <muslukhovi@gmail.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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‎fs/ext4/Makefile

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -12,4 +12,4 @@ ext4-y := balloc.o bitmap.o dir.o file.o fsync.o ialloc.o inode.o page-io.o \
1212

1313
ext4-$(CONFIG_EXT4_FS_POSIX_ACL) += acl.o
1414
ext4-$(CONFIG_EXT4_FS_SECURITY) += xattr_security.o
15-
ext4-$(CONFIG_EXT4_FS_ENCRYPTION) += crypto_policy.o crypto.o
15+
ext4-$(CONFIG_EXT4_FS_ENCRYPTION) += crypto_policy.o crypto.o crypto_key.o

‎fs/ext4/crypto_key.c

Lines changed: 162 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,162 @@
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+
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+
*
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* Return: Zero on success; non-zero otherwise.
38+
*/
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+
*/
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+
int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
102+
EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
103+
&ctx, sizeof(ctx));
104+
105+
if (res != sizeof(ctx)) {
106+
if (res > 0)
107+
res = -EINVAL;
108+
goto out;
109+
}
110+
res = 0;
111+
112+
memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
113+
EXT4_KEY_DESC_PREFIX_SIZE);
114+
sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
115+
"%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
116+
ctx.master_key_descriptor);
117+
full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
118+
(2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
119+
keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
120+
if (IS_ERR(keyring_key)) {
121+
res = PTR_ERR(keyring_key);
122+
keyring_key = NULL;
123+
goto out;
124+
}
125+
BUG_ON(keyring_key->type != &key_type_logon);
126+
ukp = ((struct user_key_payload *)keyring_key->payload.data);
127+
if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
128+
res = -EINVAL;
129+
goto out;
130+
}
131+
master_key = (struct ext4_encryption_key *)ukp->data;
132+
133+
if (S_ISREG(inode->i_mode))
134+
crypt_key->mode = ctx.contents_encryption_mode;
135+
else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
136+
crypt_key->mode = ctx.filenames_encryption_mode;
137+
else {
138+
printk(KERN_ERR "ext4 crypto: Unsupported inode type.\n");
139+
BUG();
140+
}
141+
crypt_key->size = ext4_encryption_key_size(crypt_key->mode);
142+
BUG_ON(!crypt_key->size);
143+
BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
144+
EXT4_KEY_DERIVATION_NONCE_SIZE);
145+
BUG_ON(master_key->size != EXT4_AES_256_XTS_KEY_SIZE);
146+
BUG_ON(crypt_key->size < EXT4_AES_256_CBC_KEY_SIZE);
147+
res = ext4_derive_key_aes(ctx.nonce, master_key->raw, crypt_key->raw);
148+
out:
149+
if (keyring_key)
150+
key_put(keyring_key);
151+
if (res < 0)
152+
crypt_key->mode = EXT4_ENCRYPTION_MODE_INVALID;
153+
return res;
154+
}
155+
156+
int ext4_has_encryption_key(struct inode *inode)
157+
{
158+
struct ext4_inode_info *ei = EXT4_I(inode);
159+
struct ext4_encryption_key *crypt_key = &ei->i_encryption_key;
160+
161+
return (crypt_key->mode != EXT4_ENCRYPTION_MODE_INVALID);
162+
}

‎fs/ext4/ext4.h

Lines changed: 13 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2078,6 +2078,19 @@ static inline int ext4_sb_has_crypto(struct super_block *sb)
20782078
}
20792079
#endif
20802080

2081+
/* crypto_key.c */
2082+
int ext4_generate_encryption_key(struct inode *inode);
2083+
2084+
#ifdef CONFIG_EXT4_FS_ENCRYPTION
2085+
int ext4_has_encryption_key(struct inode *inode);
2086+
#else
2087+
static inline int ext4_has_encryption_key(struct inode *inode)
2088+
{
2089+
return 0;
2090+
}
2091+
#endif
2092+
2093+
20812094
/* dir.c */
20822095
extern int __ext4_check_dir_entry(const char *, unsigned int, struct inode *,
20832096
struct file *,

‎fs/ext4/ext4_crypto.h

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -55,6 +55,9 @@ struct ext4_encryption_context {
5555
#define EXT4_AES_256_XTS_KEY_SIZE 64
5656
#define EXT4_MAX_KEY_SIZE 64
5757

58+
#define EXT4_KEY_DESC_PREFIX "ext4:"
59+
#define EXT4_KEY_DESC_PREFIX_SIZE 5
60+
5861
struct ext4_encryption_key {
5962
uint32_t mode;
6063
char raw[EXT4_MAX_KEY_SIZE];

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