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1/* Large capacity key type
2 *
3 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
5 *
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.
10 */
11
12#include <linux/init.h>
13#include <linux/seq_file.h>
14#include <linux/file.h>
15#include <linux/shmem_fs.h>
16#include <linux/err.h>
17#include <keys/user-type.h>
18#include <keys/big_key-type.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};
51
52/*
53 * Preparse a big key
54 */
55int big_key_preparse(struct key_preparsed_payload *prep)
56{
57 struct path *path = (struct path *)&prep->payload.data[big_key_path];
58 struct file *file;
59 ssize_t written;
60 size_t datalen = prep->datalen;
61 int ret;
62
63 ret = -EINVAL;
64 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
65 goto error;
66
67 /* Set an arbitrary quota */
68 prep->quotalen = 16;
69
70 prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
71
72 if (datalen > BIG_KEY_FILE_THRESHOLD) {
73 /* Create a shmem file to store the data in. This will permit the data
74 * to be swapped out if needed.
75 *
76 * TODO: Encrypt the stored data with a temporary key.
77 */
78 file = shmem_kernel_file_setup("", datalen, 0);
79 if (IS_ERR(file)) {
80 ret = PTR_ERR(file);
81 goto error;
82 }
83
84 written = kernel_write(file, prep->data, prep->datalen, 0);
85 if (written != datalen) {
86 ret = written;
87 if (written >= 0)
88 ret = -ENOMEM;
89 goto err_fput;
90 }
91
92 /* Pin the mount and dentry to the key so that we can open it again
93 * later
94 */
95 *path = file->f_path;
96 path_get(path);
97 fput(file);
98 } else {
99 /* Just store the data in a buffer */
100 void *data = kmalloc(datalen, GFP_KERNEL);
101 if (!data)
102 return -ENOMEM;
103
104 prep->payload.data[big_key_data] = data;
105 memcpy(data, prep->data, prep->datalen);
106 }
107 return 0;
108
109err_fput:
110 fput(file);
111error:
112 return ret;
113}
114
115/*
116 * Clear preparsement.
117 */
118void big_key_free_preparse(struct key_preparsed_payload *prep)
119{
120 if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
121 struct path *path = (struct path *)&prep->payload.data[big_key_path];
122 path_put(path);
123 } else {
124 kfree(prep->payload.data[big_key_data]);
125 }
126}
127
128/*
129 * dispose of the links from a revoked keyring
130 * - called with the key sem write-locked
131 */
132void big_key_revoke(struct key *key)
133{
134 struct path *path = (struct path *)&key->payload.data[big_key_path];
135
136 /* clear the quota */
137 key_payload_reserve(key, 0);
138 if (key_is_instantiated(key) &&
139 (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
140 vfs_truncate(path, 0);
141}
142
143/*
144 * dispose of the data dangling from the corpse of a big_key key
145 */
146void big_key_destroy(struct key *key)
147{
148 size_t datalen = (size_t)key->payload.data[big_key_len];
149
150 if (datalen) {
151 struct path *path = (struct path *)&key->payload.data[big_key_path];
152 path_put(path);
153 path->mnt = NULL;
154 path->dentry = NULL;
155 } else {
156 kfree(key->payload.data[big_key_data]);
157 key->payload.data[big_key_data] = NULL;
158 }
159}
160
161/*
162 * describe the big_key key
163 */
164void big_key_describe(const struct key *key, struct seq_file *m)
165{
166 size_t datalen = (size_t)key->payload.data[big_key_len];
167
168 seq_puts(m, key->description);
169
170 if (key_is_instantiated(key))
171 seq_printf(m, ": %zu [%s]",
172 datalen,
173 datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
174}
175
176/*
177 * read the key data
178 * - the key's semaphore is read-locked
179 */
180long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
181{
182 size_t datalen = (size_t)key->payload.data[big_key_len];
183 long ret;
184
185 if (!buffer || buflen < datalen)
186 return datalen;
187
188 if (datalen > BIG_KEY_FILE_THRESHOLD) {
189 struct path *path = (struct path *)&key->payload.data[big_key_path];
190 struct file *file;
191 loff_t pos;
192
193 file = dentry_open(path, O_RDONLY, current_cred());
194 if (IS_ERR(file))
195 return PTR_ERR(file);
196
197 pos = 0;
198 ret = vfs_read(file, buffer, datalen, &pos);
199 fput(file);
200 if (ret >= 0 && ret != datalen)
201 ret = -EIO;
202 } else {
203 ret = datalen;
204 if (copy_to_user(buffer, key->payload.data[big_key_data],
205 datalen) != 0)
206 ret = -EFAULT;
207 }
208
209 return ret;
210}
211
212static int __init big_key_init(void)
213{
214 return register_key_type(&key_type_big_key);
215}
216device_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);