tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1/*
2 * key management facility for FS encryption support.
3 *
4 * Copyright (C) 2015, Google, Inc.
5 *
6 * This contains encryption key functions.
7 *
8 * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
9 */
10
11#include <keys/user-type.h>
12#include <linux/scatterlist.h>
13#include "fscrypt_private.h"
14
15static void derive_crypt_complete(struct crypto_async_request *req, int rc)
16{
17 struct fscrypt_completion_result *ecr = req->data;
18
19 if (rc == -EINPROGRESS)
20 return;
21
22 ecr->res = rc;
23 complete(&ecr->completion);
24}
25
26/**
27 * derive_key_aes() - Derive a key using AES-128-ECB
28 * @deriving_key: Encryption key used for derivation.
29 * @source_key: Source key to which to apply derivation.
30 * @derived_key: Derived key.
31 *
32 * Return: Zero on success; non-zero otherwise.
33 */
34static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
35 u8 source_key[FS_AES_256_XTS_KEY_SIZE],
36 u8 derived_key[FS_AES_256_XTS_KEY_SIZE])
37{
38 int res = 0;
39 struct skcipher_request *req = NULL;
40 DECLARE_FS_COMPLETION_RESULT(ecr);
41 struct scatterlist src_sg, dst_sg;
42 struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
43
44 if (IS_ERR(tfm)) {
45 res = PTR_ERR(tfm);
46 tfm = NULL;
47 goto out;
48 }
49 crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
50 req = skcipher_request_alloc(tfm, GFP_NOFS);
51 if (!req) {
52 res = -ENOMEM;
53 goto out;
54 }
55 skcipher_request_set_callback(req,
56 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
57 derive_crypt_complete, &ecr);
58 res = crypto_skcipher_setkey(tfm, deriving_key,
59 FS_AES_128_ECB_KEY_SIZE);
60 if (res < 0)
61 goto out;
62
63 sg_init_one(&src_sg, source_key, FS_AES_256_XTS_KEY_SIZE);
64 sg_init_one(&dst_sg, derived_key, FS_AES_256_XTS_KEY_SIZE);
65 skcipher_request_set_crypt(req, &src_sg, &dst_sg,
66 FS_AES_256_XTS_KEY_SIZE, NULL);
67 res = crypto_skcipher_encrypt(req);
68 if (res == -EINPROGRESS || res == -EBUSY) {
69 wait_for_completion(&ecr.completion);
70 res = ecr.res;
71 }
72out:
73 skcipher_request_free(req);
74 crypto_free_skcipher(tfm);
75 return res;
76}
77
78static int validate_user_key(struct fscrypt_info *crypt_info,
79 struct fscrypt_context *ctx, u8 *raw_key,
80 const char *prefix)
81{
82 char *description;
83 struct key *keyring_key;
84 struct fscrypt_key *master_key;
85 const struct user_key_payload *ukp;
86 int res;
87
88 description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
89 FS_KEY_DESCRIPTOR_SIZE,
90 ctx->master_key_descriptor);
91 if (!description)
92 return -ENOMEM;
93
94 keyring_key = request_key(&key_type_logon, description, NULL);
95 kfree(description);
96 if (IS_ERR(keyring_key))
97 return PTR_ERR(keyring_key);
98 down_read(&keyring_key->sem);
99
100 if (keyring_key->type != &key_type_logon) {
101 printk_once(KERN_WARNING
102 "%s: key type must be logon\n", __func__);
103 res = -ENOKEY;
104 goto out;
105 }
106 ukp = user_key_payload_locked(keyring_key);
107 if (ukp->datalen != sizeof(struct fscrypt_key)) {
108 res = -EINVAL;
109 goto out;
110 }
111 master_key = (struct fscrypt_key *)ukp->data;
112 BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
113
114 if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
115 printk_once(KERN_WARNING
116 "%s: key size incorrect: %d\n",
117 __func__, master_key->size);
118 res = -ENOKEY;
119 goto out;
120 }
121 res = derive_key_aes(ctx->nonce, master_key->raw, raw_key);
122out:
123 up_read(&keyring_key->sem);
124 key_put(keyring_key);
125 return res;
126}
127
128static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode,
129 const char **cipher_str_ret, int *keysize_ret)
130{
131 if (S_ISREG(inode->i_mode)) {
132 if (ci->ci_data_mode == FS_ENCRYPTION_MODE_AES_256_XTS) {
133 *cipher_str_ret = "xts(aes)";
134 *keysize_ret = FS_AES_256_XTS_KEY_SIZE;
135 return 0;
136 }
137 pr_warn_once("fscrypto: unsupported contents encryption mode "
138 "%d for inode %lu\n",
139 ci->ci_data_mode, inode->i_ino);
140 return -ENOKEY;
141 }
142
143 if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) {
144 if (ci->ci_filename_mode == FS_ENCRYPTION_MODE_AES_256_CTS) {
145 *cipher_str_ret = "cts(cbc(aes))";
146 *keysize_ret = FS_AES_256_CTS_KEY_SIZE;
147 return 0;
148 }
149 pr_warn_once("fscrypto: unsupported filenames encryption mode "
150 "%d for inode %lu\n",
151 ci->ci_filename_mode, inode->i_ino);
152 return -ENOKEY;
153 }
154
155 pr_warn_once("fscrypto: unsupported file type %d for inode %lu\n",
156 (inode->i_mode & S_IFMT), inode->i_ino);
157 return -ENOKEY;
158}
159
160static void put_crypt_info(struct fscrypt_info *ci)
161{
162 if (!ci)
163 return;
164
165 crypto_free_skcipher(ci->ci_ctfm);
166 kmem_cache_free(fscrypt_info_cachep, ci);
167}
168
169int fscrypt_get_encryption_info(struct inode *inode)
170{
171 struct fscrypt_info *crypt_info;
172 struct fscrypt_context ctx;
173 struct crypto_skcipher *ctfm;
174 const char *cipher_str;
175 int keysize;
176 u8 *raw_key = NULL;
177 int res;
178
179 if (inode->i_crypt_info)
180 return 0;
181
182 res = fscrypt_initialize(inode->i_sb->s_cop->flags);
183 if (res)
184 return res;
185
186 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
187 if (res < 0) {
188 if (!fscrypt_dummy_context_enabled(inode) ||
189 inode->i_sb->s_cop->is_encrypted(inode))
190 return res;
191 /* Fake up a context for an unencrypted directory */
192 memset(&ctx, 0, sizeof(ctx));
193 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
194 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
195 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
196 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
197 } else if (res != sizeof(ctx)) {
198 return -EINVAL;
199 }
200
201 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
202 return -EINVAL;
203
204 if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
205 return -EINVAL;
206
207 crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
208 if (!crypt_info)
209 return -ENOMEM;
210
211 crypt_info->ci_flags = ctx.flags;
212 crypt_info->ci_data_mode = ctx.contents_encryption_mode;
213 crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
214 crypt_info->ci_ctfm = NULL;
215 memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
216 sizeof(crypt_info->ci_master_key));
217
218 res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize);
219 if (res)
220 goto out;
221
222 /*
223 * This cannot be a stack buffer because it is passed to the scatterlist
224 * crypto API as part of key derivation.
225 */
226 res = -ENOMEM;
227 raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS);
228 if (!raw_key)
229 goto out;
230
231 res = validate_user_key(crypt_info, &ctx, raw_key, FS_KEY_DESC_PREFIX);
232 if (res && inode->i_sb->s_cop->key_prefix) {
233 int res2 = validate_user_key(crypt_info, &ctx, raw_key,
234 inode->i_sb->s_cop->key_prefix);
235 if (res2) {
236 if (res2 == -ENOKEY)
237 res = -ENOKEY;
238 goto out;
239 }
240 } else if (res) {
241 goto out;
242 }
243 ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
244 if (!ctfm || IS_ERR(ctfm)) {
245 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
246 printk(KERN_DEBUG
247 "%s: error %d (inode %u) allocating crypto tfm\n",
248 __func__, res, (unsigned) inode->i_ino);
249 goto out;
250 }
251 crypt_info->ci_ctfm = ctfm;
252 crypto_skcipher_clear_flags(ctfm, ~0);
253 crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
254 res = crypto_skcipher_setkey(ctfm, raw_key, keysize);
255 if (res)
256 goto out;
257
258 if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL)
259 crypt_info = NULL;
260out:
261 if (res == -ENOKEY)
262 res = 0;
263 put_crypt_info(crypt_info);
264 kzfree(raw_key);
265 return res;
266}
267EXPORT_SYMBOL(fscrypt_get_encryption_info);
268
269void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
270{
271 struct fscrypt_info *prev;
272
273 if (ci == NULL)
274 ci = ACCESS_ONCE(inode->i_crypt_info);
275 if (ci == NULL)
276 return;
277
278 prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
279 if (prev != ci)
280 return;
281
282 put_crypt_info(ci);
283}
284EXPORT_SYMBOL(fscrypt_put_encryption_info);