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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 */
23enum {
24 big_key_data,
25 big_key_path,
26 big_key_path_2nd_part,
27 big_key_len,
28};
29
30/*
31 * If the data is under this limit, there's no point creating a shm file to
32 * hold it as the permanently resident metadata for the shmem fs will be at
33 * least as large as the data.
34 */
35#define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
36
37/*
38 * big_key defined keys take an arbitrary string as the description and an
39 * arbitrary blob of data as the payload
40 */
41struct key_type key_type_big_key = {
42 .name = "big_key",
43 .preparse = big_key_preparse,
44 .free_preparse = big_key_free_preparse,
45 .instantiate = generic_key_instantiate,
46 .revoke = big_key_revoke,
47 .destroy = big_key_destroy,
48 .describe = big_key_describe,
49 .read = big_key_read,
50 .update = big_key_update,
51};
52
53/*
54 * Preparse a big key
55 */
56int big_key_preparse(struct key_preparsed_payload *prep)
57{
58 struct path *path = (struct path *)&prep->payload.data[big_key_path];
59 struct file *file;
60 u8 *buf, *enckey;
61 ssize_t written;
62 size_t datalen = prep->datalen;
63 size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
64 int ret;
65
66 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
67 return -EINVAL;
68
69 /* Set an arbitrary quota */
70 prep->quotalen = 16;
71
72 prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
73
74 if (datalen > BIG_KEY_FILE_THRESHOLD) {
75 /* Create a shmem file to store the data in. This will permit the data
76 * to be swapped out if needed.
77 *
78 * File content is stored encrypted with randomly generated key.
79 * Since the key is random for each file, we can set the nonce
80 * to zero, provided we never define a ->update() call.
81 */
82 loff_t pos = 0;
83
84 buf = kvmalloc(enclen, GFP_KERNEL);
85 if (!buf)
86 return -ENOMEM;
87
88 /* generate random key */
89 enckey = kmalloc(CHACHA20POLY1305_KEY_SIZE, GFP_KERNEL);
90 if (!enckey) {
91 ret = -ENOMEM;
92 goto error;
93 }
94 ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_KEY_SIZE);
95 if (unlikely(ret))
96 goto err_enckey;
97
98 /* encrypt data */
99 chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0,
100 0, enckey);
101
102 /* save aligned data to file */
103 file = shmem_kernel_file_setup("", enclen, 0);
104 if (IS_ERR(file)) {
105 ret = PTR_ERR(file);
106 goto err_enckey;
107 }
108
109 written = kernel_write(file, buf, enclen, &pos);
110 if (written != enclen) {
111 ret = written;
112 if (written >= 0)
113 ret = -EIO;
114 goto err_fput;
115 }
116
117 /* Pin the mount and dentry to the key so that we can open it again
118 * later
119 */
120 prep->payload.data[big_key_data] = enckey;
121 *path = file->f_path;
122 path_get(path);
123 fput(file);
124 kvfree_sensitive(buf, enclen);
125 } else {
126 /* Just store the data in a buffer */
127 void *data = kmalloc(datalen, GFP_KERNEL);
128
129 if (!data)
130 return -ENOMEM;
131
132 prep->payload.data[big_key_data] = data;
133 memcpy(data, prep->data, prep->datalen);
134 }
135 return 0;
136
137err_fput:
138 fput(file);
139err_enckey:
140 kfree_sensitive(enckey);
141error:
142 kvfree_sensitive(buf, enclen);
143 return ret;
144}
145
146/*
147 * Clear preparsement.
148 */
149void big_key_free_preparse(struct key_preparsed_payload *prep)
150{
151 if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
152 struct path *path = (struct path *)&prep->payload.data[big_key_path];
153
154 path_put(path);
155 }
156 kfree_sensitive(prep->payload.data[big_key_data]);
157}
158
159/*
160 * dispose of the links from a revoked keyring
161 * - called with the key sem write-locked
162 */
163void big_key_revoke(struct key *key)
164{
165 struct path *path = (struct path *)&key->payload.data[big_key_path];
166
167 /* clear the quota */
168 key_payload_reserve(key, 0);
169 if (key_is_positive(key) &&
170 (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
171 vfs_truncate(path, 0);
172}
173
174/*
175 * dispose of the data dangling from the corpse of a big_key key
176 */
177void big_key_destroy(struct key *key)
178{
179 size_t datalen = (size_t)key->payload.data[big_key_len];
180
181 if (datalen > BIG_KEY_FILE_THRESHOLD) {
182 struct path *path = (struct path *)&key->payload.data[big_key_path];
183
184 path_put(path);
185 path->mnt = NULL;
186 path->dentry = NULL;
187 }
188 kfree_sensitive(key->payload.data[big_key_data]);
189 key->payload.data[big_key_data] = NULL;
190}
191
192/*
193 * Update a big key
194 */
195int big_key_update(struct key *key, struct key_preparsed_payload *prep)
196{
197 int ret;
198
199 ret = key_payload_reserve(key, prep->datalen);
200 if (ret < 0)
201 return ret;
202
203 if (key_is_positive(key))
204 big_key_destroy(key);
205
206 return generic_key_instantiate(key, prep);
207}
208
209/*
210 * describe the big_key key
211 */
212void big_key_describe(const struct key *key, struct seq_file *m)
213{
214 size_t datalen = (size_t)key->payload.data[big_key_len];
215
216 seq_puts(m, key->description);
217
218 if (key_is_positive(key))
219 seq_printf(m, ": %zu [%s]",
220 datalen,
221 datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
222}
223
224/*
225 * read the key data
226 * - the key's semaphore is read-locked
227 */
228long big_key_read(const struct key *key, char *buffer, size_t buflen)
229{
230 size_t datalen = (size_t)key->payload.data[big_key_len];
231 long ret;
232
233 if (!buffer || buflen < datalen)
234 return datalen;
235
236 if (datalen > BIG_KEY_FILE_THRESHOLD) {
237 struct path *path = (struct path *)&key->payload.data[big_key_path];
238 struct file *file;
239 u8 *buf, *enckey = (u8 *)key->payload.data[big_key_data];
240 size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
241 loff_t pos = 0;
242
243 buf = kvmalloc(enclen, GFP_KERNEL);
244 if (!buf)
245 return -ENOMEM;
246
247 file = dentry_open(path, O_RDONLY, current_cred());
248 if (IS_ERR(file)) {
249 ret = PTR_ERR(file);
250 goto error;
251 }
252
253 /* read file to kernel and decrypt */
254 ret = kernel_read(file, buf, enclen, &pos);
255 if (ret != enclen) {
256 if (ret >= 0)
257 ret = -EIO;
258 goto err_fput;
259 }
260
261 ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0,
262 enckey) ? 0 : -EBADMSG;
263 if (unlikely(ret))
264 goto err_fput;
265
266 ret = datalen;
267
268 /* copy out decrypted data */
269 memcpy(buffer, buf, datalen);
270
271err_fput:
272 fput(file);
273error:
274 kvfree_sensitive(buf, enclen);
275 } else {
276 ret = datalen;
277 memcpy(buffer, key->payload.data[big_key_data], datalen);
278 }
279
280 return ret;
281}
282
283/*
284 * Register key type
285 */
286static int __init big_key_init(void)
287{
288 return register_key_type(&key_type_big_key);
289}
290
291late_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);