summaryrefslogtreecommitdiff
path: root/lib/asn1_encoder.c
blob: 27bbe891714f914cadcec73d9407687c7ef2a405 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Simple encoder primitives for ASN.1 BER/DER/CER
 *
 * Copyright (C) 2019 James.Bottomley@HansenPartnership.com
 */

#include <linux/asn1_encoder.h>
#include <linux/bug.h>
#include <linux/string.h>
#include <linux/module.h>

/**
 * asn1_encode_integer() - encode positive integer to ASN.1
 * @data:	pointer to the pointer to the data
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @integer:	integer to be encoded
 *
 * This is a simplified encoder: it only currently does
 * positive integers, but it should be simple enough to add the
 * negative case if a use comes along.
 */
unsigned char *
asn1_encode_integer(unsigned char *data, const unsigned char *end_data,
		    s64 integer)
{
	int data_len = end_data - data;
	unsigned char *d = &data[2];
	bool found = false;
	int i;

	if (WARN(integer < 0,
		 "BUG: integer encode only supports positive integers"))
		return ERR_PTR(-EINVAL);

	if (IS_ERR(data))
		return data;

	/* need at least 3 bytes for tag, length and integer encoding */
	if (data_len < 3)
		return ERR_PTR(-EINVAL);

	/* remaining length where at d (the start of the integer encoding) */
	data_len -= 2;

	data[0] = _tag(UNIV, PRIM, INT);
	if (integer == 0) {
		*d++ = 0;
		goto out;
	}

	for (i = sizeof(integer); i > 0 ; i--) {
		int byte = integer >> (8 * (i - 1));

		if (!found && byte == 0)
			continue;

		/*
		 * for a positive number the first byte must have bit
		 * 7 clear in two's complement (otherwise it's a
		 * negative number) so prepend a leading zero if
		 * that's not the case
		 */
		if (!found && (byte & 0x80)) {
			/*
			 * no check needed here, we already know we
			 * have len >= 1
			 */
			*d++ = 0;
			data_len--;
		}

		found = true;
		if (data_len == 0)
			return ERR_PTR(-EINVAL);

		*d++ = byte;
		data_len--;
	}

 out:
	data[1] = d - data - 2;

	return d;
}
EXPORT_SYMBOL_GPL(asn1_encode_integer);

/* calculate the base 128 digit values setting the top bit of the first octet */
static int asn1_encode_oid_digit(unsigned char **_data, int *data_len, u32 oid)
{
	unsigned char *data = *_data;
	int start = 7 + 7 + 7 + 7;
	int ret = 0;

	if (*data_len < 1)
		return -EINVAL;

	/* quick case */
	if (oid == 0) {
		*data++ = 0x80;
		(*data_len)--;
		goto out;
	}

	while (oid >> start == 0)
		start -= 7;

	while (start > 0 && *data_len > 0) {
		u8 byte;

		byte = oid >> start;
		oid = oid - (byte << start);
		start -= 7;
		byte |= 0x80;
		*data++ = byte;
		(*data_len)--;
	}

	if (*data_len > 0) {
		*data++ = oid;
		(*data_len)--;
	} else {
		ret = -EINVAL;
	}

 out:
	*_data = data;
	return ret;
}

/**
 * asn1_encode_oid() - encode an oid to ASN.1
 * @data:	position to begin encoding at
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @oid:	array of oids
 * @oid_len:	length of oid array
 *
 * this encodes an OID up to ASN.1 when presented as an array of OID values
 */
unsigned char *
asn1_encode_oid(unsigned char *data, const unsigned char *end_data,
		u32 oid[], int oid_len)
{
	int data_len = end_data - data;
	unsigned char *d = data + 2;
	int i, ret;

	if (WARN(oid_len < 2, "OID must have at least two elements"))
		return ERR_PTR(-EINVAL);

	if (WARN(oid_len > 32, "OID is too large"))
		return ERR_PTR(-EINVAL);

	if (IS_ERR(data))
		return data;


	/* need at least 3 bytes for tag, length and OID encoding */
	if (data_len < 3)
		return ERR_PTR(-EINVAL);

	data[0] = _tag(UNIV, PRIM, OID);
	*d++ = oid[0] * 40 + oid[1];

	data_len -= 3;

	ret = 0;

	for (i = 2; i < oid_len; i++) {
		ret = asn1_encode_oid_digit(&d, &data_len, oid[i]);
		if (ret < 0)
			return ERR_PTR(ret);
	}

	data[1] = d - data - 2;

	return d;
}
EXPORT_SYMBOL_GPL(asn1_encode_oid);

/**
 * asn1_encode_length() - encode a length to follow an ASN.1 tag
 * @data: pointer to encode at
 * @data_len: pointer to remaining length (adjusted by routine)
 * @len: length to encode
 *
 * This routine can encode lengths up to 65535 using the ASN.1 rules.
 * It will accept a negative length and place a zero length tag
 * instead (to keep the ASN.1 valid).  This convention allows other
 * encoder primitives to accept negative lengths as singalling the
 * sequence will be re-encoded when the length is known.
 */
static int asn1_encode_length(unsigned char **data, int *data_len, int len)
{
	if (*data_len < 1)
		return -EINVAL;

	if (len < 0) {
		*((*data)++) = 0;
		(*data_len)--;
		return 0;
	}

	if (len <= 0x7f) {
		*((*data)++) = len;
		(*data_len)--;
		return 0;
	}

	if (*data_len < 2)
		return -EINVAL;

	if (len <= 0xff) {
		*((*data)++) = 0x81;
		*((*data)++) = len & 0xff;
		*data_len -= 2;
		return 0;
	}

	if (*data_len < 3)
		return -EINVAL;

	if (len <= 0xffff) {
		*((*data)++) = 0x82;
		*((*data)++) = (len >> 8) & 0xff;
		*((*data)++) = len & 0xff;
		*data_len -= 3;
		return 0;
	}

	if (WARN(len > 0xffffff, "ASN.1 length can't be > 0xffffff"))
		return -EINVAL;

	if (*data_len < 4)
		return -EINVAL;
	*((*data)++) = 0x83;
	*((*data)++) = (len >> 16) & 0xff;
	*((*data)++) = (len >> 8) & 0xff;
	*((*data)++) = len & 0xff;
	*data_len -= 4;

	return 0;
}

/**
 * asn1_encode_tag() - add a tag for optional or explicit value
 * @data:	pointer to place tag at
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @tag:	tag to be placed
 * @string:	the data to be tagged
 * @len:	the length of the data to be tagged
 *
 * Note this currently only handles short form tags < 31.
 *
 * Standard usage is to pass in a @tag, @string and @length and the
 * @string will be ASN.1 encoded with @tag and placed into @data.  If
 * the encoding would put data past @end_data then an error is
 * returned, otherwise a pointer to a position one beyond the encoding
 * is returned.
 *
 * To encode in place pass a NULL @string and -1 for @len and the
 * maximum allowable beginning and end of the data; all this will do
 * is add the current maximum length and update the data pointer to
 * the place where the tag contents should be placed is returned.  The
 * data should be copied in by the calling routine which should then
 * repeat the prior statement but now with the known length.  In order
 * to avoid having to keep both before and after pointers, the repeat
 * expects to be called with @data pointing to where the first encode
 * returned it and still NULL for @string but the real length in @len.
 */
unsigned char *
asn1_encode_tag(unsigned char *data, const unsigned char *end_data,
		u32 tag, const unsigned char *string, int len)
{
	int data_len = end_data - data;
	int ret;

	if (WARN(tag > 30, "ASN.1 tag can't be > 30"))
		return ERR_PTR(-EINVAL);

	if (!string && WARN(len > 127,
			    "BUG: recode tag is too big (>127)"))
		return ERR_PTR(-EINVAL);

	if (IS_ERR(data))
		return data;

	if (!string && len > 0) {
		/*
		 * we're recoding, so move back to the start of the
		 * tag and install a dummy length because the real
		 * data_len should be NULL
		 */
		data -= 2;
		data_len = 2;
	}

	if (data_len < 2)
		return ERR_PTR(-EINVAL);

	*(data++) = _tagn(CONT, CONS, tag);
	data_len--;
	ret = asn1_encode_length(&data, &data_len, len);
	if (ret < 0)
		return ERR_PTR(ret);

	if (!string)
		return data;

	if (data_len < len)
		return ERR_PTR(-EINVAL);

	memcpy(data, string, len);
	data += len;

	return data;
}
EXPORT_SYMBOL_GPL(asn1_encode_tag);

/**
 * asn1_encode_octet_string() - encode an ASN.1 OCTET STRING
 * @data:	pointer to encode at
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @string:	string to be encoded
 * @len:	length of string
 *
 * Note ASN.1 octet strings may contain zeros, so the length is obligatory.
 */
unsigned char *
asn1_encode_octet_string(unsigned char *data,
			 const unsigned char *end_data,
			 const unsigned char *string, u32 len)
{
	int data_len = end_data - data;
	int ret;

	if (IS_ERR(data))
		return data;

	/* need minimum of 2 bytes for tag and length of zero length string */
	if (data_len < 2)
		return ERR_PTR(-EINVAL);

	*(data++) = _tag(UNIV, PRIM, OTS);
	data_len--;

	ret = asn1_encode_length(&data, &data_len, len);
	if (ret)
		return ERR_PTR(ret);

	if (data_len < len)
		return ERR_PTR(-EINVAL);

	memcpy(data, string, len);
	data += len;

	return data;
}
EXPORT_SYMBOL_GPL(asn1_encode_octet_string);

/**
 * asn1_encode_sequence() - wrap a byte stream in an ASN.1 SEQUENCE
 * @data:	pointer to encode at
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @seq:	data to be encoded as a sequence
 * @len:	length of the data to be encoded as a sequence
 *
 * Fill in a sequence.  To encode in place, pass NULL for @seq and -1
 * for @len; then call again once the length is known (still with NULL
 * for @seq). In order to avoid having to keep both before and after
 * pointers, the repeat expects to be called with @data pointing to
 * where the first encode placed it.
 */
unsigned char *
asn1_encode_sequence(unsigned char *data, const unsigned char *end_data,
		     const unsigned char *seq, int len)
{
	int data_len = end_data - data;
	int ret;

	if (!seq && WARN(len > 127,
			 "BUG: recode sequence is too big (>127)"))
		return ERR_PTR(-EINVAL);

	if (IS_ERR(data))
		return data;

	if (!seq && len >= 0) {
		/*
		 * we're recoding, so move back to the start of the
		 * sequence and install a dummy length because the
		 * real length should be NULL
		 */
		data -= 2;
		data_len = 2;
	}

	if (data_len < 2)
		return ERR_PTR(-EINVAL);

	*(data++) = _tag(UNIV, CONS, SEQ);
	data_len--;

	ret = asn1_encode_length(&data, &data_len, len);
	if (ret)
		return ERR_PTR(ret);

	if (!seq)
		return data;

	if (data_len < len)
		return ERR_PTR(-EINVAL);

	memcpy(data, seq, len);
	data += len;

	return data;
}
EXPORT_SYMBOL_GPL(asn1_encode_sequence);

/**
 * asn1_encode_boolean() - encode a boolean value to ASN.1
 * @data:	pointer to encode at
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @val:	the boolean true/false value
 */
unsigned char *
asn1_encode_boolean(unsigned char *data, const unsigned char *end_data,
		    bool val)
{
	int data_len = end_data - data;

	if (IS_ERR(data))
		return data;

	/* booleans are 3 bytes: tag, length == 1 and value == 0 or 1 */
	if (data_len < 3)
		return ERR_PTR(-EINVAL);

	*(data++) = _tag(UNIV, PRIM, BOOL);
	data_len--;

	asn1_encode_length(&data, &data_len, 1);

	if (val)
		*(data++) = 1;
	else
		*(data++) = 0;

	return data;
}
EXPORT_SYMBOL_GPL(asn1_encode_boolean);

MODULE_LICENSE("GPL");