2 * key management facility for FS encryption support.
4 * Copyright (C) 2015, Google, Inc.
6 * This contains encryption key functions.
8 * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
11 #include <keys/user-type.h>
12 #include <linux/scatterlist.h>
13 #include "fscrypt_private.h"
15 static void derive_crypt_complete(struct crypto_async_request *req, int rc)
17 struct fscrypt_completion_result *ecr = req->data;
19 if (rc == -EINPROGRESS)
23 complete(&ecr->completion);
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.
32 * Return: Zero on success; non-zero otherwise.
34 static 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])
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);
49 crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
50 req = skcipher_request_alloc(tfm, GFP_NOFS);
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);
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);
73 skcipher_request_free(req);
74 crypto_free_skcipher(tfm);
78 static int validate_user_key(struct fscrypt_info *crypt_info,
79 struct fscrypt_context *ctx, u8 *raw_key,
80 u8 *prefix, int prefix_size)
82 u8 *full_key_descriptor;
83 struct key *keyring_key;
84 struct fscrypt_key *master_key;
85 const struct user_key_payload *ukp;
86 int full_key_len = prefix_size + (FS_KEY_DESCRIPTOR_SIZE * 2) + 1;
89 full_key_descriptor = kmalloc(full_key_len, GFP_NOFS);
90 if (!full_key_descriptor)
93 memcpy(full_key_descriptor, prefix, prefix_size);
94 sprintf(full_key_descriptor + prefix_size,
95 "%*phN", FS_KEY_DESCRIPTOR_SIZE,
96 ctx->master_key_descriptor);
97 full_key_descriptor[full_key_len - 1] = '\0';
98 keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
99 kfree(full_key_descriptor);
100 if (IS_ERR(keyring_key))
101 return PTR_ERR(keyring_key);
103 if (keyring_key->type != &key_type_logon) {
104 printk_once(KERN_WARNING
105 "%s: key type must be logon\n", __func__);
109 down_read(&keyring_key->sem);
110 ukp = user_key_payload(keyring_key);
111 if (ukp->datalen != sizeof(struct fscrypt_key)) {
113 up_read(&keyring_key->sem);
116 master_key = (struct fscrypt_key *)ukp->data;
117 BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
119 if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
120 printk_once(KERN_WARNING
121 "%s: key size incorrect: %d\n",
122 __func__, master_key->size);
124 up_read(&keyring_key->sem);
127 res = derive_key_aes(ctx->nonce, master_key->raw, raw_key);
128 up_read(&keyring_key->sem);
132 crypt_info->ci_keyring_key = keyring_key;
135 key_put(keyring_key);
139 static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode,
140 const char **cipher_str_ret, int *keysize_ret)
142 if (S_ISREG(inode->i_mode)) {
143 if (ci->ci_data_mode == FS_ENCRYPTION_MODE_AES_256_XTS) {
144 *cipher_str_ret = "xts(aes)";
145 *keysize_ret = FS_AES_256_XTS_KEY_SIZE;
148 pr_warn_once("fscrypto: unsupported contents encryption mode "
149 "%d for inode %lu\n",
150 ci->ci_data_mode, inode->i_ino);
154 if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) {
155 if (ci->ci_filename_mode == FS_ENCRYPTION_MODE_AES_256_CTS) {
156 *cipher_str_ret = "cts(cbc(aes))";
157 *keysize_ret = FS_AES_256_CTS_KEY_SIZE;
160 pr_warn_once("fscrypto: unsupported filenames encryption mode "
161 "%d for inode %lu\n",
162 ci->ci_filename_mode, inode->i_ino);
166 pr_warn_once("fscrypto: unsupported file type %d for inode %lu\n",
167 (inode->i_mode & S_IFMT), inode->i_ino);
171 static void put_crypt_info(struct fscrypt_info *ci)
176 key_put(ci->ci_keyring_key);
177 crypto_free_skcipher(ci->ci_ctfm);
178 kmem_cache_free(fscrypt_info_cachep, ci);
181 int fscrypt_get_crypt_info(struct inode *inode)
183 struct fscrypt_info *crypt_info;
184 struct fscrypt_context ctx;
185 struct crypto_skcipher *ctfm;
186 const char *cipher_str;
191 res = fscrypt_initialize(inode->i_sb->s_cop->flags);
195 if (!inode->i_sb->s_cop->get_context)
198 crypt_info = ACCESS_ONCE(inode->i_crypt_info);
200 if (!crypt_info->ci_keyring_key ||
201 key_validate(crypt_info->ci_keyring_key) == 0)
203 fscrypt_put_encryption_info(inode, crypt_info);
207 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
209 if (!fscrypt_dummy_context_enabled(inode))
211 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
212 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
213 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
215 } else if (res != sizeof(ctx)) {
219 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
222 if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
225 crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
229 crypt_info->ci_flags = ctx.flags;
230 crypt_info->ci_data_mode = ctx.contents_encryption_mode;
231 crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
232 crypt_info->ci_ctfm = NULL;
233 crypt_info->ci_keyring_key = NULL;
234 memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
235 sizeof(crypt_info->ci_master_key));
237 res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize);
242 * This cannot be a stack buffer because it is passed to the scatterlist
243 * crypto API as part of key derivation.
246 raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS);
250 if (fscrypt_dummy_context_enabled(inode)) {
251 memset(raw_key, 0x42, FS_AES_256_XTS_KEY_SIZE);
255 res = validate_user_key(crypt_info, &ctx, raw_key,
256 FS_KEY_DESC_PREFIX, FS_KEY_DESC_PREFIX_SIZE);
257 if (res && inode->i_sb->s_cop->key_prefix) {
259 int prefix_size, res2;
261 prefix_size = inode->i_sb->s_cop->key_prefix(inode, &prefix);
262 res2 = validate_user_key(crypt_info, &ctx, raw_key,
263 prefix, prefix_size);
273 ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
274 if (!ctfm || IS_ERR(ctfm)) {
275 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
277 "%s: error %d (inode %u) allocating crypto tfm\n",
278 __func__, res, (unsigned) inode->i_ino);
281 crypt_info->ci_ctfm = ctfm;
282 crypto_skcipher_clear_flags(ctfm, ~0);
283 crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
284 res = crypto_skcipher_setkey(ctfm, raw_key, keysize);
290 if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) != NULL) {
291 put_crypt_info(crypt_info);
299 put_crypt_info(crypt_info);
304 void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
306 struct fscrypt_info *prev;
309 ci = ACCESS_ONCE(inode->i_crypt_info);
313 prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
319 EXPORT_SYMBOL(fscrypt_put_encryption_info);
321 int fscrypt_get_encryption_info(struct inode *inode)
323 struct fscrypt_info *ci = inode->i_crypt_info;
326 (ci->ci_keyring_key &&
327 (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
328 (1 << KEY_FLAG_REVOKED) |
329 (1 << KEY_FLAG_DEAD)))))
330 return fscrypt_get_crypt_info(inode);
333 EXPORT_SYMBOL(fscrypt_get_encryption_info);