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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/* Large capacity key type
2 *
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)
6 *
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.
11 */
12
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>
25
26struct big_key_buf {
27 unsigned int nr_pages;
28 void *virt;
29 struct scatterlist *sg;
30 struct page *pages[];
31};
32
33/*
34 * Layout of key payload words.
35 */
36enum {
37 big_key_data,
38 big_key_path,
39 big_key_path_2nd_part,
40 big_key_len,
41};
42
43/*
44 * Crypto operation with big_key data
45 */
46enum big_key_op {
47 BIG_KEY_ENC,
48 BIG_KEY_DEC,
49};
50
51/*
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.
55 */
56#define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
57
58/*
59 * Key size for big_key data encryption
60 */
61#define ENC_KEY_SIZE 32
62
63/*
64 * Authentication tag length
65 */
66#define ENC_AUTHTAG_SIZE 16
67
68/*
69 * big_key defined keys take an arbitrary string as the description and an
70 * arbitrary blob of data as the payload
71 */
72struct key_type key_type_big_key = {
73 .name = "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,
80 .read = big_key_read,
81 /* no ->update(); don't add it without changing big_key_crypt() nonce */
82};
83
84/*
85 * Crypto names for big_key data authenticated encryption
86 */
87static const char big_key_alg_name[] = "gcm(aes)";
88
89/*
90 * Crypto algorithms for big_key data authenticated encryption
91 */
92static struct crypto_aead *big_key_aead;
93
94/*
95 * Since changing the key affects the entire object, we need a mutex.
96 */
97static DEFINE_MUTEX(big_key_aead_lock);
98
99/*
100 * Encrypt/decrypt big_key data
101 */
102static int big_key_crypt(enum big_key_op op, struct big_key_buf *buf, size_t datalen, u8 *key)
103{
104 int ret;
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.
111 */
112 u8 zero_nonce[crypto_aead_ivsize(big_key_aead)];
113
114 aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL);
115 if (!aead_req)
116 return -ENOMEM;
117
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);
122
123 mutex_lock(&big_key_aead_lock);
124 if (crypto_aead_setkey(big_key_aead, key, ENC_KEY_SIZE)) {
125 ret = -EAGAIN;
126 goto error;
127 }
128 if (op == BIG_KEY_ENC)
129 ret = crypto_aead_encrypt(aead_req);
130 else
131 ret = crypto_aead_decrypt(aead_req);
132error:
133 mutex_unlock(&big_key_aead_lock);
134 aead_request_free(aead_req);
135 return ret;
136}
137
138/*
139 * Free up the buffer.
140 */
141static void big_key_free_buffer(struct big_key_buf *buf)
142{
143 unsigned int i;
144
145 if (buf->virt) {
146 memset(buf->virt, 0, buf->nr_pages * PAGE_SIZE);
147 vunmap(buf->virt);
148 }
149
150 for (i = 0; i < buf->nr_pages; i++)
151 if (buf->pages[i])
152 __free_page(buf->pages[i]);
153
154 kfree(buf);
155}
156
157/*
158 * Allocate a buffer consisting of a set of pages with a virtual mapping
159 * applied over them.
160 */
161static void *big_key_alloc_buffer(size_t len)
162{
163 struct big_key_buf *buf;
164 unsigned int npg = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
165 unsigned int i, l;
166
167 buf = kzalloc(sizeof(struct big_key_buf) +
168 sizeof(struct page) * npg +
169 sizeof(struct scatterlist) * npg,
170 GFP_KERNEL);
171 if (!buf)
172 return NULL;
173
174 buf->nr_pages = npg;
175 buf->sg = (void *)(buf->pages + npg);
176 sg_init_table(buf->sg, npg);
177
178 for (i = 0; i < buf->nr_pages; i++) {
179 buf->pages[i] = alloc_page(GFP_KERNEL);
180 if (!buf->pages[i])
181 goto nomem;
182
183 l = min_t(size_t, len, PAGE_SIZE);
184 sg_set_page(&buf->sg[i], buf->pages[i], l, 0);
185 len -= l;
186 }
187
188 buf->virt = vmap(buf->pages, buf->nr_pages, VM_MAP, PAGE_KERNEL);
189 if (!buf->virt)
190 goto nomem;
191
192 return buf;
193
194nomem:
195 big_key_free_buffer(buf);
196 return NULL;
197}
198
199/*
200 * Preparse a big key
201 */
202int big_key_preparse(struct key_preparsed_payload *prep)
203{
204 struct big_key_buf *buf;
205 struct path *path = (struct path *)&prep->payload.data[big_key_path];
206 struct file *file;
207 u8 *enckey;
208 ssize_t written;
209 size_t datalen = prep->datalen, enclen = datalen + ENC_AUTHTAG_SIZE;
210 int ret;
211
212 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
213 return -EINVAL;
214
215 /* Set an arbitrary quota */
216 prep->quotalen = 16;
217
218 prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
219
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.
223 *
224 * File content is stored encrypted with randomly generated key.
225 */
226 loff_t pos = 0;
227
228 buf = big_key_alloc_buffer(enclen);
229 if (!buf)
230 return -ENOMEM;
231 memcpy(buf->virt, prep->data, datalen);
232
233 /* generate random key */
234 enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
235 if (!enckey) {
236 ret = -ENOMEM;
237 goto error;
238 }
239 ret = get_random_bytes_wait(enckey, ENC_KEY_SIZE);
240 if (unlikely(ret))
241 goto err_enckey;
242
243 /* encrypt aligned data */
244 ret = big_key_crypt(BIG_KEY_ENC, buf, datalen, enckey);
245 if (ret)
246 goto err_enckey;
247
248 /* save aligned data to file */
249 file = shmem_kernel_file_setup("", enclen, 0);
250 if (IS_ERR(file)) {
251 ret = PTR_ERR(file);
252 goto err_enckey;
253 }
254
255 written = kernel_write(file, buf->virt, enclen, &pos);
256 if (written != enclen) {
257 ret = written;
258 if (written >= 0)
259 ret = -ENOMEM;
260 goto err_fput;
261 }
262
263 /* Pin the mount and dentry to the key so that we can open it again
264 * later
265 */
266 prep->payload.data[big_key_data] = enckey;
267 *path = file->f_path;
268 path_get(path);
269 fput(file);
270 big_key_free_buffer(buf);
271 } else {
272 /* Just store the data in a buffer */
273 void *data = kmalloc(datalen, GFP_KERNEL);
274
275 if (!data)
276 return -ENOMEM;
277
278 prep->payload.data[big_key_data] = data;
279 memcpy(data, prep->data, prep->datalen);
280 }
281 return 0;
282
283err_fput:
284 fput(file);
285err_enckey:
286 kzfree(enckey);
287error:
288 big_key_free_buffer(buf);
289 return ret;
290}
291
292/*
293 * Clear preparsement.
294 */
295void big_key_free_preparse(struct key_preparsed_payload *prep)
296{
297 if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
298 struct path *path = (struct path *)&prep->payload.data[big_key_path];
299
300 path_put(path);
301 }
302 kzfree(prep->payload.data[big_key_data]);
303}
304
305/*
306 * dispose of the links from a revoked keyring
307 * - called with the key sem write-locked
308 */
309void big_key_revoke(struct key *key)
310{
311 struct path *path = (struct path *)&key->payload.data[big_key_path];
312
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);
318}
319
320/*
321 * dispose of the data dangling from the corpse of a big_key key
322 */
323void big_key_destroy(struct key *key)
324{
325 size_t datalen = (size_t)key->payload.data[big_key_len];
326
327 if (datalen > BIG_KEY_FILE_THRESHOLD) {
328 struct path *path = (struct path *)&key->payload.data[big_key_path];
329
330 path_put(path);
331 path->mnt = NULL;
332 path->dentry = NULL;
333 }
334 kzfree(key->payload.data[big_key_data]);
335 key->payload.data[big_key_data] = NULL;
336}
337
338/*
339 * describe the big_key key
340 */
341void big_key_describe(const struct key *key, struct seq_file *m)
342{
343 size_t datalen = (size_t)key->payload.data[big_key_len];
344
345 seq_puts(m, key->description);
346
347 if (key_is_positive(key))
348 seq_printf(m, ": %zu [%s]",
349 datalen,
350 datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
351}
352
353/*
354 * read the key data
355 * - the key's semaphore is read-locked
356 */
357long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
358{
359 size_t datalen = (size_t)key->payload.data[big_key_len];
360 long ret;
361
362 if (!buffer || buflen < datalen)
363 return datalen;
364
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];
368 struct file *file;
369 u8 *enckey = (u8 *)key->payload.data[big_key_data];
370 size_t enclen = datalen + ENC_AUTHTAG_SIZE;
371 loff_t pos = 0;
372
373 buf = big_key_alloc_buffer(enclen);
374 if (!buf)
375 return -ENOMEM;
376
377 file = dentry_open(path, O_RDONLY, current_cred());
378 if (IS_ERR(file)) {
379 ret = PTR_ERR(file);
380 goto error;
381 }
382
383 /* read file to kernel and decrypt */
384 ret = kernel_read(file, buf->virt, enclen, &pos);
385 if (ret >= 0 && ret != enclen) {
386 ret = -EIO;
387 goto err_fput;
388 }
389
390 ret = big_key_crypt(BIG_KEY_DEC, buf, enclen, enckey);
391 if (ret)
392 goto err_fput;
393
394 ret = datalen;
395
396 /* copy decrypted data to user */
397 if (copy_to_user(buffer, buf->virt, datalen) != 0)
398 ret = -EFAULT;
399
400err_fput:
401 fput(file);
402error:
403 big_key_free_buffer(buf);
404 } else {
405 ret = datalen;
406 if (copy_to_user(buffer, key->payload.data[big_key_data],
407 datalen) != 0)
408 ret = -EFAULT;
409 }
410
411 return ret;
412}
413
414/*
415 * Register key type
416 */
417static int __init big_key_init(void)
418{
419 int ret;
420
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);
426 return ret;
427 }
428 ret = crypto_aead_setauthsize(big_key_aead, ENC_AUTHTAG_SIZE);
429 if (ret < 0) {
430 pr_err("Can't set crypto auth tag len: %d\n", ret);
431 goto free_aead;
432 }
433
434 ret = register_key_type(&key_type_big_key);
435 if (ret < 0) {
436 pr_err("Can't register type: %d\n", ret);
437 goto free_aead;
438 }
439
440 return 0;
441
442free_aead:
443 crypto_free_aead(big_key_aead);
444 return ret;
445}
446
447late_initcall(big_key_init);