Loading...
1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Large capacity key type
3 *
4 * Copyright (C) 2017-2020 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
5 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
6 * Written by David Howells (dhowells@redhat.com)
7 */
8
9#define pr_fmt(fmt) "big_key: "fmt
10#include <linux/init.h>
11#include <linux/seq_file.h>
12#include <linux/file.h>
13#include <linux/shmem_fs.h>
14#include <linux/err.h>
15#include <linux/random.h>
16#include <keys/user-type.h>
17#include <keys/big_key-type.h>
18#include <crypto/chacha20poly1305.h>
19
20/*
21 * Layout of key payload words.
22 */
23struct big_key_payload {
24 u8 *data;
25 struct path path;
26 size_t length;
27};
28#define to_big_key_payload(payload) \
29 (struct big_key_payload *)((payload).data)
30
31/*
32 * If the data is under this limit, there's no point creating a shm file to
33 * hold it as the permanently resident metadata for the shmem fs will be at
34 * least as large as the data.
35 */
36#define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
37
38/*
39 * big_key defined keys take an arbitrary string as the description and an
40 * arbitrary blob of data as the payload
41 */
42struct key_type key_type_big_key = {
43 .name = "big_key",
44 .preparse = big_key_preparse,
45 .free_preparse = big_key_free_preparse,
46 .instantiate = generic_key_instantiate,
47 .revoke = big_key_revoke,
48 .destroy = big_key_destroy,
49 .describe = big_key_describe,
50 .read = big_key_read,
51 .update = big_key_update,
52};
53
54/*
55 * Preparse a big key
56 */
57int big_key_preparse(struct key_preparsed_payload *prep)
58{
59 struct big_key_payload *payload = to_big_key_payload(prep->payload);
60 struct file *file;
61 u8 *buf, *enckey;
62 ssize_t written;
63 size_t datalen = prep->datalen;
64 size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
65 int ret;
66
67 BUILD_BUG_ON(sizeof(*payload) != sizeof(prep->payload.data));
68
69 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
70 return -EINVAL;
71
72 /* Set an arbitrary quota */
73 prep->quotalen = 16;
74
75 payload->length = datalen;
76
77 if (datalen > BIG_KEY_FILE_THRESHOLD) {
78 /* Create a shmem file to store the data in. This will permit the data
79 * to be swapped out if needed.
80 *
81 * File content is stored encrypted with randomly generated key.
82 * Since the key is random for each file, we can set the nonce
83 * to zero, provided we never define a ->update() call.
84 */
85 loff_t pos = 0;
86
87 buf = kvmalloc(enclen, GFP_KERNEL);
88 if (!buf)
89 return -ENOMEM;
90
91 /* generate random key */
92 enckey = kmalloc(CHACHA20POLY1305_KEY_SIZE, GFP_KERNEL);
93 if (!enckey) {
94 ret = -ENOMEM;
95 goto error;
96 }
97 ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_KEY_SIZE);
98 if (unlikely(ret))
99 goto err_enckey;
100
101 /* encrypt data */
102 chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0,
103 0, enckey);
104
105 /* save aligned data to file */
106 file = shmem_kernel_file_setup("", enclen, 0);
107 if (IS_ERR(file)) {
108 ret = PTR_ERR(file);
109 goto err_enckey;
110 }
111
112 written = kernel_write(file, buf, enclen, &pos);
113 if (written != enclen) {
114 ret = written;
115 if (written >= 0)
116 ret = -EIO;
117 goto err_fput;
118 }
119
120 /* Pin the mount and dentry to the key so that we can open it again
121 * later
122 */
123 payload->data = enckey;
124 payload->path = file->f_path;
125 path_get(&payload->path);
126 fput(file);
127 kvfree_sensitive(buf, enclen);
128 } else {
129 /* Just store the data in a buffer */
130 void *data = kmalloc(datalen, GFP_KERNEL);
131
132 if (!data)
133 return -ENOMEM;
134
135 payload->data = data;
136 memcpy(data, prep->data, prep->datalen);
137 }
138 return 0;
139
140err_fput:
141 fput(file);
142err_enckey:
143 kfree_sensitive(enckey);
144error:
145 kvfree_sensitive(buf, enclen);
146 return ret;
147}
148
149/*
150 * Clear preparsement.
151 */
152void big_key_free_preparse(struct key_preparsed_payload *prep)
153{
154 struct big_key_payload *payload = to_big_key_payload(prep->payload);
155
156 if (prep->datalen > BIG_KEY_FILE_THRESHOLD)
157 path_put(&payload->path);
158 kfree_sensitive(payload->data);
159}
160
161/*
162 * dispose of the links from a revoked keyring
163 * - called with the key sem write-locked
164 */
165void big_key_revoke(struct key *key)
166{
167 struct big_key_payload *payload = to_big_key_payload(key->payload);
168
169 /* clear the quota */
170 key_payload_reserve(key, 0);
171 if (key_is_positive(key) && payload->length > BIG_KEY_FILE_THRESHOLD)
172 vfs_truncate(&payload->path, 0);
173}
174
175/*
176 * dispose of the data dangling from the corpse of a big_key key
177 */
178void big_key_destroy(struct key *key)
179{
180 struct big_key_payload *payload = to_big_key_payload(key->payload);
181
182 if (payload->length > BIG_KEY_FILE_THRESHOLD) {
183 path_put(&payload->path);
184 payload->path.mnt = NULL;
185 payload->path.dentry = NULL;
186 }
187 kfree_sensitive(payload->data);
188 payload->data = NULL;
189}
190
191/*
192 * Update a big key
193 */
194int big_key_update(struct key *key, struct key_preparsed_payload *prep)
195{
196 int ret;
197
198 ret = key_payload_reserve(key, prep->datalen);
199 if (ret < 0)
200 return ret;
201
202 if (key_is_positive(key))
203 big_key_destroy(key);
204
205 return generic_key_instantiate(key, prep);
206}
207
208/*
209 * describe the big_key key
210 */
211void big_key_describe(const struct key *key, struct seq_file *m)
212{
213 struct big_key_payload *payload = to_big_key_payload(key->payload);
214
215 seq_puts(m, key->description);
216
217 if (key_is_positive(key))
218 seq_printf(m, ": %zu [%s]",
219 payload->length,
220 payload->length > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
221}
222
223/*
224 * read the key data
225 * - the key's semaphore is read-locked
226 */
227long big_key_read(const struct key *key, char *buffer, size_t buflen)
228{
229 struct big_key_payload *payload = to_big_key_payload(key->payload);
230 size_t datalen = payload->length;
231 long ret;
232
233 if (!buffer || buflen < datalen)
234 return datalen;
235
236 if (datalen > BIG_KEY_FILE_THRESHOLD) {
237 struct file *file;
238 u8 *buf, *enckey = payload->data;
239 size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
240 loff_t pos = 0;
241
242 buf = kvmalloc(enclen, GFP_KERNEL);
243 if (!buf)
244 return -ENOMEM;
245
246 file = dentry_open(&payload->path, O_RDONLY, current_cred());
247 if (IS_ERR(file)) {
248 ret = PTR_ERR(file);
249 goto error;
250 }
251
252 /* read file to kernel and decrypt */
253 ret = kernel_read(file, buf, enclen, &pos);
254 if (ret != enclen) {
255 if (ret >= 0)
256 ret = -EIO;
257 goto err_fput;
258 }
259
260 ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0,
261 enckey) ? 0 : -EBADMSG;
262 if (unlikely(ret))
263 goto err_fput;
264
265 ret = datalen;
266
267 /* copy out decrypted data */
268 memcpy(buffer, buf, datalen);
269
270err_fput:
271 fput(file);
272error:
273 kvfree_sensitive(buf, enclen);
274 } else {
275 ret = datalen;
276 memcpy(buffer, payload->data, datalen);
277 }
278
279 return ret;
280}
281
282/*
283 * Register key type
284 */
285static int __init big_key_init(void)
286{
287 return register_key_type(&key_type_big_key);
288}
289
290late_initcall(big_key_init);
1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Large capacity key type
3 *
4 * Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
5 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
6 * Written by David Howells (dhowells@redhat.com)
7 */
8
9#define pr_fmt(fmt) "big_key: "fmt
10#include <linux/init.h>
11#include <linux/seq_file.h>
12#include <linux/file.h>
13#include <linux/shmem_fs.h>
14#include <linux/err.h>
15#include <linux/scatterlist.h>
16#include <linux/random.h>
17#include <linux/vmalloc.h>
18#include <keys/user-type.h>
19#include <keys/big_key-type.h>
20#include <crypto/aead.h>
21#include <crypto/gcm.h>
22
23struct big_key_buf {
24 unsigned int nr_pages;
25 void *virt;
26 struct scatterlist *sg;
27 struct page *pages[];
28};
29
30/*
31 * Layout of key payload words.
32 */
33enum {
34 big_key_data,
35 big_key_path,
36 big_key_path_2nd_part,
37 big_key_len,
38};
39
40/*
41 * Crypto operation with big_key data
42 */
43enum big_key_op {
44 BIG_KEY_ENC,
45 BIG_KEY_DEC,
46};
47
48/*
49 * If the data is under this limit, there's no point creating a shm file to
50 * hold it as the permanently resident metadata for the shmem fs will be at
51 * least as large as the data.
52 */
53#define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
54
55/*
56 * Key size for big_key data encryption
57 */
58#define ENC_KEY_SIZE 32
59
60/*
61 * Authentication tag length
62 */
63#define ENC_AUTHTAG_SIZE 16
64
65/*
66 * big_key defined keys take an arbitrary string as the description and an
67 * arbitrary blob of data as the payload
68 */
69struct key_type key_type_big_key = {
70 .name = "big_key",
71 .preparse = big_key_preparse,
72 .free_preparse = big_key_free_preparse,
73 .instantiate = generic_key_instantiate,
74 .revoke = big_key_revoke,
75 .destroy = big_key_destroy,
76 .describe = big_key_describe,
77 .read = big_key_read,
78 /* no ->update(); don't add it without changing big_key_crypt() nonce */
79};
80
81/*
82 * Crypto names for big_key data authenticated encryption
83 */
84static const char big_key_alg_name[] = "gcm(aes)";
85#define BIG_KEY_IV_SIZE GCM_AES_IV_SIZE
86
87/*
88 * Crypto algorithms for big_key data authenticated encryption
89 */
90static struct crypto_aead *big_key_aead;
91
92/*
93 * Since changing the key affects the entire object, we need a mutex.
94 */
95static DEFINE_MUTEX(big_key_aead_lock);
96
97/*
98 * Encrypt/decrypt big_key data
99 */
100static int big_key_crypt(enum big_key_op op, struct big_key_buf *buf, size_t datalen, u8 *key)
101{
102 int ret;
103 struct aead_request *aead_req;
104 /* We always use a zero nonce. The reason we can get away with this is
105 * because we're using a different randomly generated key for every
106 * different encryption. Notably, too, key_type_big_key doesn't define
107 * an .update function, so there's no chance we'll wind up reusing the
108 * key to encrypt updated data. Simply put: one key, one encryption.
109 */
110 u8 zero_nonce[BIG_KEY_IV_SIZE];
111
112 aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL);
113 if (!aead_req)
114 return -ENOMEM;
115
116 memset(zero_nonce, 0, sizeof(zero_nonce));
117 aead_request_set_crypt(aead_req, buf->sg, buf->sg, datalen, zero_nonce);
118 aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
119 aead_request_set_ad(aead_req, 0);
120
121 mutex_lock(&big_key_aead_lock);
122 if (crypto_aead_setkey(big_key_aead, key, ENC_KEY_SIZE)) {
123 ret = -EAGAIN;
124 goto error;
125 }
126 if (op == BIG_KEY_ENC)
127 ret = crypto_aead_encrypt(aead_req);
128 else
129 ret = crypto_aead_decrypt(aead_req);
130error:
131 mutex_unlock(&big_key_aead_lock);
132 aead_request_free(aead_req);
133 return ret;
134}
135
136/*
137 * Free up the buffer.
138 */
139static void big_key_free_buffer(struct big_key_buf *buf)
140{
141 unsigned int i;
142
143 if (buf->virt) {
144 memset(buf->virt, 0, buf->nr_pages * PAGE_SIZE);
145 vunmap(buf->virt);
146 }
147
148 for (i = 0; i < buf->nr_pages; i++)
149 if (buf->pages[i])
150 __free_page(buf->pages[i]);
151
152 kfree(buf);
153}
154
155/*
156 * Allocate a buffer consisting of a set of pages with a virtual mapping
157 * applied over them.
158 */
159static void *big_key_alloc_buffer(size_t len)
160{
161 struct big_key_buf *buf;
162 unsigned int npg = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
163 unsigned int i, l;
164
165 buf = kzalloc(sizeof(struct big_key_buf) +
166 sizeof(struct page) * npg +
167 sizeof(struct scatterlist) * npg,
168 GFP_KERNEL);
169 if (!buf)
170 return NULL;
171
172 buf->nr_pages = npg;
173 buf->sg = (void *)(buf->pages + npg);
174 sg_init_table(buf->sg, npg);
175
176 for (i = 0; i < buf->nr_pages; i++) {
177 buf->pages[i] = alloc_page(GFP_KERNEL);
178 if (!buf->pages[i])
179 goto nomem;
180
181 l = min_t(size_t, len, PAGE_SIZE);
182 sg_set_page(&buf->sg[i], buf->pages[i], l, 0);
183 len -= l;
184 }
185
186 buf->virt = vmap(buf->pages, buf->nr_pages, VM_MAP, PAGE_KERNEL);
187 if (!buf->virt)
188 goto nomem;
189
190 return buf;
191
192nomem:
193 big_key_free_buffer(buf);
194 return NULL;
195}
196
197/*
198 * Preparse a big key
199 */
200int big_key_preparse(struct key_preparsed_payload *prep)
201{
202 struct big_key_buf *buf;
203 struct path *path = (struct path *)&prep->payload.data[big_key_path];
204 struct file *file;
205 u8 *enckey;
206 ssize_t written;
207 size_t datalen = prep->datalen, enclen = datalen + ENC_AUTHTAG_SIZE;
208 int ret;
209
210 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
211 return -EINVAL;
212
213 /* Set an arbitrary quota */
214 prep->quotalen = 16;
215
216 prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
217
218 if (datalen > BIG_KEY_FILE_THRESHOLD) {
219 /* Create a shmem file to store the data in. This will permit the data
220 * to be swapped out if needed.
221 *
222 * File content is stored encrypted with randomly generated key.
223 */
224 loff_t pos = 0;
225
226 buf = big_key_alloc_buffer(enclen);
227 if (!buf)
228 return -ENOMEM;
229 memcpy(buf->virt, prep->data, datalen);
230
231 /* generate random key */
232 enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
233 if (!enckey) {
234 ret = -ENOMEM;
235 goto error;
236 }
237 ret = get_random_bytes_wait(enckey, ENC_KEY_SIZE);
238 if (unlikely(ret))
239 goto err_enckey;
240
241 /* encrypt aligned data */
242 ret = big_key_crypt(BIG_KEY_ENC, buf, datalen, enckey);
243 if (ret)
244 goto err_enckey;
245
246 /* save aligned data to file */
247 file = shmem_kernel_file_setup("", enclen, 0);
248 if (IS_ERR(file)) {
249 ret = PTR_ERR(file);
250 goto err_enckey;
251 }
252
253 written = kernel_write(file, buf->virt, enclen, &pos);
254 if (written != enclen) {
255 ret = written;
256 if (written >= 0)
257 ret = -ENOMEM;
258 goto err_fput;
259 }
260
261 /* Pin the mount and dentry to the key so that we can open it again
262 * later
263 */
264 prep->payload.data[big_key_data] = enckey;
265 *path = file->f_path;
266 path_get(path);
267 fput(file);
268 big_key_free_buffer(buf);
269 } else {
270 /* Just store the data in a buffer */
271 void *data = kmalloc(datalen, GFP_KERNEL);
272
273 if (!data)
274 return -ENOMEM;
275
276 prep->payload.data[big_key_data] = data;
277 memcpy(data, prep->data, prep->datalen);
278 }
279 return 0;
280
281err_fput:
282 fput(file);
283err_enckey:
284 kzfree(enckey);
285error:
286 big_key_free_buffer(buf);
287 return ret;
288}
289
290/*
291 * Clear preparsement.
292 */
293void big_key_free_preparse(struct key_preparsed_payload *prep)
294{
295 if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
296 struct path *path = (struct path *)&prep->payload.data[big_key_path];
297
298 path_put(path);
299 }
300 kzfree(prep->payload.data[big_key_data]);
301}
302
303/*
304 * dispose of the links from a revoked keyring
305 * - called with the key sem write-locked
306 */
307void big_key_revoke(struct key *key)
308{
309 struct path *path = (struct path *)&key->payload.data[big_key_path];
310
311 /* clear the quota */
312 key_payload_reserve(key, 0);
313 if (key_is_positive(key) &&
314 (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
315 vfs_truncate(path, 0);
316}
317
318/*
319 * dispose of the data dangling from the corpse of a big_key key
320 */
321void big_key_destroy(struct key *key)
322{
323 size_t datalen = (size_t)key->payload.data[big_key_len];
324
325 if (datalen > BIG_KEY_FILE_THRESHOLD) {
326 struct path *path = (struct path *)&key->payload.data[big_key_path];
327
328 path_put(path);
329 path->mnt = NULL;
330 path->dentry = NULL;
331 }
332 kzfree(key->payload.data[big_key_data]);
333 key->payload.data[big_key_data] = NULL;
334}
335
336/*
337 * describe the big_key key
338 */
339void big_key_describe(const struct key *key, struct seq_file *m)
340{
341 size_t datalen = (size_t)key->payload.data[big_key_len];
342
343 seq_puts(m, key->description);
344
345 if (key_is_positive(key))
346 seq_printf(m, ": %zu [%s]",
347 datalen,
348 datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
349}
350
351/*
352 * read the key data
353 * - the key's semaphore is read-locked
354 */
355long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
356{
357 size_t datalen = (size_t)key->payload.data[big_key_len];
358 long ret;
359
360 if (!buffer || buflen < datalen)
361 return datalen;
362
363 if (datalen > BIG_KEY_FILE_THRESHOLD) {
364 struct big_key_buf *buf;
365 struct path *path = (struct path *)&key->payload.data[big_key_path];
366 struct file *file;
367 u8 *enckey = (u8 *)key->payload.data[big_key_data];
368 size_t enclen = datalen + ENC_AUTHTAG_SIZE;
369 loff_t pos = 0;
370
371 buf = big_key_alloc_buffer(enclen);
372 if (!buf)
373 return -ENOMEM;
374
375 file = dentry_open(path, O_RDONLY, current_cred());
376 if (IS_ERR(file)) {
377 ret = PTR_ERR(file);
378 goto error;
379 }
380
381 /* read file to kernel and decrypt */
382 ret = kernel_read(file, buf->virt, enclen, &pos);
383 if (ret >= 0 && ret != enclen) {
384 ret = -EIO;
385 goto err_fput;
386 }
387
388 ret = big_key_crypt(BIG_KEY_DEC, buf, enclen, enckey);
389 if (ret)
390 goto err_fput;
391
392 ret = datalen;
393
394 /* copy decrypted data to user */
395 if (copy_to_user(buffer, buf->virt, datalen) != 0)
396 ret = -EFAULT;
397
398err_fput:
399 fput(file);
400error:
401 big_key_free_buffer(buf);
402 } else {
403 ret = datalen;
404 if (copy_to_user(buffer, key->payload.data[big_key_data],
405 datalen) != 0)
406 ret = -EFAULT;
407 }
408
409 return ret;
410}
411
412/*
413 * Register key type
414 */
415static int __init big_key_init(void)
416{
417 int ret;
418
419 /* init block cipher */
420 big_key_aead = crypto_alloc_aead(big_key_alg_name, 0, CRYPTO_ALG_ASYNC);
421 if (IS_ERR(big_key_aead)) {
422 ret = PTR_ERR(big_key_aead);
423 pr_err("Can't alloc crypto: %d\n", ret);
424 return ret;
425 }
426
427 if (unlikely(crypto_aead_ivsize(big_key_aead) != BIG_KEY_IV_SIZE)) {
428 WARN(1, "big key algorithm changed?");
429 ret = -EINVAL;
430 goto free_aead;
431 }
432
433 ret = crypto_aead_setauthsize(big_key_aead, ENC_AUTHTAG_SIZE);
434 if (ret < 0) {
435 pr_err("Can't set crypto auth tag len: %d\n", ret);
436 goto free_aead;
437 }
438
439 ret = register_key_type(&key_type_big_key);
440 if (ret < 0) {
441 pr_err("Can't register type: %d\n", ret);
442 goto free_aead;
443 }
444
445 return 0;
446
447free_aead:
448 crypto_free_aead(big_key_aead);
449 return ret;
450}
451
452late_initcall(big_key_init);