1 /* Large capacity key type
3 * Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
4 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public Licence
9 * as published by the Free Software Foundation; either version
10 * 2 of the Licence, or (at your option) any later version.
13 #define pr_fmt(fmt) "big_key: "fmt
14 #include <linux/init.h>
15 #include <linux/seq_file.h>
16 #include <linux/file.h>
17 #include <linux/shmem_fs.h>
18 #include <linux/err.h>
19 #include <linux/scatterlist.h>
20 #include <linux/random.h>
21 #include <linux/vmalloc.h>
22 #include <keys/user-type.h>
23 #include <keys/big_key-type.h>
24 #include <crypto/aead.h>
27 unsigned int nr_pages;
29 struct scatterlist *sg;
34 * Layout of key payload words.
39 big_key_path_2nd_part,
44 * Crypto operation with big_key data
52 * If the data is under this limit, there's no point creating a shm file to
53 * hold it as the permanently resident metadata for the shmem fs will be at
54 * least as large as the data.
56 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
59 * Key size for big_key data encryption
61 #define ENC_KEY_SIZE 32
64 * Authentication tag length
66 #define ENC_AUTHTAG_SIZE 16
69 * big_key defined keys take an arbitrary string as the description and an
70 * arbitrary blob of data as the payload
72 struct key_type key_type_big_key = {
74 .preparse = big_key_preparse,
75 .free_preparse = big_key_free_preparse,
76 .instantiate = generic_key_instantiate,
77 .revoke = big_key_revoke,
78 .destroy = big_key_destroy,
79 .describe = big_key_describe,
81 /* no ->update(); don't add it without changing big_key_crypt() nonce */
85 * Crypto names for big_key data authenticated encryption
87 static const char big_key_alg_name[] = "gcm(aes)";
90 * Crypto algorithms for big_key data authenticated encryption
92 static struct crypto_aead *big_key_aead;
95 * Since changing the key affects the entire object, we need a mutex.
97 static DEFINE_MUTEX(big_key_aead_lock);
100 * Encrypt/decrypt big_key data
102 static int big_key_crypt(enum big_key_op op, struct big_key_buf *buf, size_t datalen, u8 *key)
105 struct aead_request *aead_req;
106 /* We always use a zero nonce. The reason we can get away with this is
107 * because we're using a different randomly generated key for every
108 * different encryption. Notably, too, key_type_big_key doesn't define
109 * an .update function, so there's no chance we'll wind up reusing the
110 * key to encrypt updated data. Simply put: one key, one encryption.
112 u8 zero_nonce[crypto_aead_ivsize(big_key_aead)];
114 aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL);
118 memset(zero_nonce, 0, sizeof(zero_nonce));
119 aead_request_set_crypt(aead_req, buf->sg, buf->sg, datalen, zero_nonce);
120 aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
121 aead_request_set_ad(aead_req, 0);
123 mutex_lock(&big_key_aead_lock);
124 if (crypto_aead_setkey(big_key_aead, key, ENC_KEY_SIZE)) {
128 if (op == BIG_KEY_ENC)
129 ret = crypto_aead_encrypt(aead_req);
131 ret = crypto_aead_decrypt(aead_req);
133 mutex_unlock(&big_key_aead_lock);
134 aead_request_free(aead_req);
139 * Free up the buffer.
141 static void big_key_free_buffer(struct big_key_buf *buf)
146 memset(buf->virt, 0, buf->nr_pages * PAGE_SIZE);
150 for (i = 0; i < buf->nr_pages; i++)
152 __free_page(buf->pages[i]);
158 * Allocate a buffer consisting of a set of pages with a virtual mapping
161 static void *big_key_alloc_buffer(size_t len)
163 struct big_key_buf *buf;
164 unsigned int npg = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
167 buf = kzalloc(sizeof(struct big_key_buf) +
168 sizeof(struct page) * npg +
169 sizeof(struct scatterlist) * npg,
175 buf->sg = (void *)(buf->pages + npg);
176 sg_init_table(buf->sg, npg);
178 for (i = 0; i < buf->nr_pages; i++) {
179 buf->pages[i] = alloc_page(GFP_KERNEL);
183 l = min_t(size_t, len, PAGE_SIZE);
184 sg_set_page(&buf->sg[i], buf->pages[i], l, 0);
188 buf->virt = vmap(buf->pages, buf->nr_pages, VM_MAP, PAGE_KERNEL);
195 big_key_free_buffer(buf);
202 int big_key_preparse(struct key_preparsed_payload *prep)
204 struct big_key_buf *buf;
205 struct path *path = (struct path *)&prep->payload.data[big_key_path];
209 size_t datalen = prep->datalen, enclen = datalen + ENC_AUTHTAG_SIZE;
212 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
215 /* Set an arbitrary quota */
218 prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
220 if (datalen > BIG_KEY_FILE_THRESHOLD) {
221 /* Create a shmem file to store the data in. This will permit the data
222 * to be swapped out if needed.
224 * File content is stored encrypted with randomly generated key.
228 buf = big_key_alloc_buffer(enclen);
231 memcpy(buf->virt, prep->data, datalen);
233 /* generate random key */
234 enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
239 ret = get_random_bytes_wait(enckey, ENC_KEY_SIZE);
243 /* encrypt aligned data */
244 ret = big_key_crypt(BIG_KEY_ENC, buf, datalen, enckey);
248 /* save aligned data to file */
249 file = shmem_kernel_file_setup("", enclen, 0);
255 written = kernel_write(file, buf->virt, enclen, &pos);
256 if (written != enclen) {
263 /* Pin the mount and dentry to the key so that we can open it again
266 prep->payload.data[big_key_data] = enckey;
267 *path = file->f_path;
270 big_key_free_buffer(buf);
272 /* Just store the data in a buffer */
273 void *data = kmalloc(datalen, GFP_KERNEL);
278 prep->payload.data[big_key_data] = data;
279 memcpy(data, prep->data, prep->datalen);
288 big_key_free_buffer(buf);
293 * Clear preparsement.
295 void big_key_free_preparse(struct key_preparsed_payload *prep)
297 if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
298 struct path *path = (struct path *)&prep->payload.data[big_key_path];
302 kzfree(prep->payload.data[big_key_data]);
306 * dispose of the links from a revoked keyring
307 * - called with the key sem write-locked
309 void big_key_revoke(struct key *key)
311 struct path *path = (struct path *)&key->payload.data[big_key_path];
313 /* clear the quota */
314 key_payload_reserve(key, 0);
315 if (key_is_positive(key) &&
316 (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
317 vfs_truncate(path, 0);
321 * dispose of the data dangling from the corpse of a big_key key
323 void big_key_destroy(struct key *key)
325 size_t datalen = (size_t)key->payload.data[big_key_len];
327 if (datalen > BIG_KEY_FILE_THRESHOLD) {
328 struct path *path = (struct path *)&key->payload.data[big_key_path];
334 kzfree(key->payload.data[big_key_data]);
335 key->payload.data[big_key_data] = NULL;
339 * describe the big_key key
341 void big_key_describe(const struct key *key, struct seq_file *m)
343 size_t datalen = (size_t)key->payload.data[big_key_len];
345 seq_puts(m, key->description);
347 if (key_is_positive(key))
348 seq_printf(m, ": %zu [%s]",
350 datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
355 * - the key's semaphore is read-locked
357 long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
359 size_t datalen = (size_t)key->payload.data[big_key_len];
362 if (!buffer || buflen < datalen)
365 if (datalen > BIG_KEY_FILE_THRESHOLD) {
366 struct big_key_buf *buf;
367 struct path *path = (struct path *)&key->payload.data[big_key_path];
369 u8 *enckey = (u8 *)key->payload.data[big_key_data];
370 size_t enclen = datalen + ENC_AUTHTAG_SIZE;
373 buf = big_key_alloc_buffer(enclen);
377 file = dentry_open(path, O_RDONLY, current_cred());
383 /* read file to kernel and decrypt */
384 ret = kernel_read(file, buf->virt, enclen, &pos);
385 if (ret >= 0 && ret != enclen) {
390 ret = big_key_crypt(BIG_KEY_DEC, buf, enclen, enckey);
396 /* copy decrypted data to user */
397 if (copy_to_user(buffer, buf->virt, datalen) != 0)
403 big_key_free_buffer(buf);
406 if (copy_to_user(buffer, key->payload.data[big_key_data],
417 static int __init big_key_init(void)
421 /* init block cipher */
422 big_key_aead = crypto_alloc_aead(big_key_alg_name, 0, CRYPTO_ALG_ASYNC);
423 if (IS_ERR(big_key_aead)) {
424 ret = PTR_ERR(big_key_aead);
425 pr_err("Can't alloc crypto: %d\n", ret);
428 ret = crypto_aead_setauthsize(big_key_aead, ENC_AUTHTAG_SIZE);
430 pr_err("Can't set crypto auth tag len: %d\n", ret);
434 ret = register_key_type(&key_type_big_key);
436 pr_err("Can't register type: %d\n", ret);
443 crypto_free_aead(big_key_aead);
447 late_initcall(big_key_init);