1 /* Large capacity key type
3 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public Licence
8 * as published by the Free Software Foundation; either version
9 * 2 of the Licence, or (at your option) any later version.
12 #define pr_fmt(fmt) "big_key: "fmt
13 #include <linux/init.h>
14 #include <linux/seq_file.h>
15 #include <linux/file.h>
16 #include <linux/shmem_fs.h>
17 #include <linux/err.h>
18 #include <linux/scatterlist.h>
19 #include <keys/user-type.h>
20 #include <keys/big_key-type.h>
21 #include <crypto/rng.h>
22 #include <crypto/skcipher.h>
25 * Layout of key payload words.
30 big_key_path_2nd_part,
35 * Crypto operation with big_key data
43 * If the data is under this limit, there's no point creating a shm file to
44 * hold it as the permanently resident metadata for the shmem fs will be at
45 * least as large as the data.
47 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
50 * Key size for big_key data encryption
52 #define ENC_KEY_SIZE 16
55 * big_key defined keys take an arbitrary string as the description and an
56 * arbitrary blob of data as the payload
58 struct key_type key_type_big_key = {
60 .preparse = big_key_preparse,
61 .free_preparse = big_key_free_preparse,
62 .instantiate = generic_key_instantiate,
63 .revoke = big_key_revoke,
64 .destroy = big_key_destroy,
65 .describe = big_key_describe,
70 * Crypto names for big_key data encryption
72 static const char big_key_rng_name[] = "stdrng";
73 static const char big_key_alg_name[] = "ecb(aes)";
76 * Crypto algorithms for big_key data encryption
78 static struct crypto_rng *big_key_rng;
79 static struct crypto_skcipher *big_key_skcipher;
82 * Generate random key to encrypt big_key data
84 static inline int big_key_gen_enckey(u8 *key)
86 return crypto_rng_get_bytes(big_key_rng, key, ENC_KEY_SIZE);
90 * Encrypt/decrypt big_key data
92 static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key)
95 struct scatterlist sgio;
96 SKCIPHER_REQUEST_ON_STACK(req, big_key_skcipher);
98 if (crypto_skcipher_setkey(big_key_skcipher, key, ENC_KEY_SIZE)) {
103 skcipher_request_set_tfm(req, big_key_skcipher);
104 skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP,
107 sg_init_one(&sgio, data, datalen);
108 skcipher_request_set_crypt(req, &sgio, &sgio, datalen, NULL);
110 if (op == BIG_KEY_ENC)
111 ret = crypto_skcipher_encrypt(req);
113 ret = crypto_skcipher_decrypt(req);
115 skcipher_request_zero(req);
124 int big_key_preparse(struct key_preparsed_payload *prep)
126 struct path *path = (struct path *)&prep->payload.data[big_key_path];
131 size_t datalen = prep->datalen;
135 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
138 /* Set an arbitrary quota */
141 prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
143 if (datalen > BIG_KEY_FILE_THRESHOLD) {
144 /* Create a shmem file to store the data in. This will permit the data
145 * to be swapped out if needed.
147 * File content is stored encrypted with randomly generated key.
149 size_t enclen = ALIGN(datalen, crypto_skcipher_blocksize(big_key_skcipher));
151 /* prepare aligned data to encrypt */
152 data = kmalloc(enclen, GFP_KERNEL);
156 memcpy(data, prep->data, datalen);
157 memset(data + datalen, 0x00, enclen - datalen);
159 /* generate random key */
160 enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
166 ret = big_key_gen_enckey(enckey);
170 /* encrypt aligned data */
171 ret = big_key_crypt(BIG_KEY_ENC, data, enclen, enckey);
175 /* save aligned data to file */
176 file = shmem_kernel_file_setup("", enclen, 0);
182 written = kernel_write(file, data, enclen, 0);
183 if (written != enclen) {
190 /* Pin the mount and dentry to the key so that we can open it again
193 prep->payload.data[big_key_data] = enckey;
194 *path = file->f_path;
199 /* Just store the data in a buffer */
200 void *data = kmalloc(datalen, GFP_KERNEL);
205 prep->payload.data[big_key_data] = data;
206 memcpy(data, prep->data, prep->datalen);
220 * Clear preparsement.
222 void big_key_free_preparse(struct key_preparsed_payload *prep)
224 if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
225 struct path *path = (struct path *)&prep->payload.data[big_key_path];
229 kfree(prep->payload.data[big_key_data]);
233 * dispose of the links from a revoked keyring
234 * - called with the key sem write-locked
236 void big_key_revoke(struct key *key)
238 struct path *path = (struct path *)&key->payload.data[big_key_path];
240 /* clear the quota */
241 key_payload_reserve(key, 0);
242 if (key_is_instantiated(key) &&
243 (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
244 vfs_truncate(path, 0);
248 * dispose of the data dangling from the corpse of a big_key key
250 void big_key_destroy(struct key *key)
252 size_t datalen = (size_t)key->payload.data[big_key_len];
254 if (datalen > BIG_KEY_FILE_THRESHOLD) {
255 struct path *path = (struct path *)&key->payload.data[big_key_path];
261 kfree(key->payload.data[big_key_data]);
262 key->payload.data[big_key_data] = NULL;
266 * describe the big_key key
268 void big_key_describe(const struct key *key, struct seq_file *m)
270 size_t datalen = (size_t)key->payload.data[big_key_len];
272 seq_puts(m, key->description);
274 if (key_is_instantiated(key))
275 seq_printf(m, ": %zu [%s]",
277 datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
282 * - the key's semaphore is read-locked
284 long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
286 size_t datalen = (size_t)key->payload.data[big_key_len];
289 if (!buffer || buflen < datalen)
292 if (datalen > BIG_KEY_FILE_THRESHOLD) {
293 struct path *path = (struct path *)&key->payload.data[big_key_path];
296 u8 *enckey = (u8 *)key->payload.data[big_key_data];
297 size_t enclen = ALIGN(datalen, crypto_skcipher_blocksize(big_key_skcipher));
299 data = kmalloc(enclen, GFP_KERNEL);
303 file = dentry_open(path, O_RDONLY, current_cred());
309 /* read file to kernel and decrypt */
310 ret = kernel_read(file, 0, data, enclen);
311 if (ret >= 0 && ret != enclen) {
316 ret = big_key_crypt(BIG_KEY_DEC, data, enclen, enckey);
322 /* copy decrypted data to user */
323 if (copy_to_user(buffer, data, datalen) != 0)
332 if (copy_to_user(buffer, key->payload.data[big_key_data],
343 static int __init big_key_init(void)
345 struct crypto_skcipher *cipher;
346 struct crypto_rng *rng;
349 rng = crypto_alloc_rng(big_key_rng_name, 0, 0);
351 pr_err("Can't alloc rng: %ld\n", PTR_ERR(rng));
358 ret = crypto_rng_reset(rng, NULL, crypto_rng_seedsize(rng));
360 pr_err("Can't reset rng: %d\n", ret);
364 /* init block cipher */
365 cipher = crypto_alloc_skcipher(big_key_alg_name, 0, CRYPTO_ALG_ASYNC);
366 if (IS_ERR(cipher)) {
367 ret = PTR_ERR(cipher);
368 pr_err("Can't alloc crypto: %d\n", ret);
372 big_key_skcipher = cipher;
374 ret = register_key_type(&key_type_big_key);
376 pr_err("Can't register type: %d\n", ret);
383 crypto_free_skcipher(big_key_skcipher);
385 crypto_free_rng(big_key_rng);
389 late_initcall(big_key_init);