ext4 crypto: add encryption key management facilities
[linux-3.10.git] / fs / ext4 / crypto_key.c
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  *
37  * 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 }