1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Simple encoder primitives for ASN.1 BER/DER/CER
4 *
5 * Copyright (C) 2019 James.Bottomley@HansenPartnership.com
6 */
7
8 #include <linux/asn1_encoder.h>
9 #include <linux/bug.h>
10 #include <linux/string.h>
11 #include <linux/module.h>
12
13 /**
14 * asn1_encode_integer() - encode positive integer to ASN.1
15 * @data: pointer to the pointer to the data
16 * @end_data: end of data pointer, points one beyond last usable byte in @data
17 * @integer: integer to be encoded
18 *
19 * This is a simplified encoder: it only currently does
20 * positive integers, but it should be simple enough to add the
21 * negative case if a use comes along.
22 */
23 unsigned char *
24 asn1_encode_integer(unsigned char *data, const unsigned char *end_data,
25 s64 integer)
26 {
27 int data_len = end_data - data;
28 unsigned char *d = &data[2];
29 bool found = false;
30 int i;
31
32 if (WARN(integer < 0,
33 "BUG: integer encode only supports positive integers"))
34 return ERR_PTR(-EINVAL);
35
36 if (IS_ERR(data))
37 return data;
38
39 /* need at least 3 bytes for tag, length and integer encoding */
40 if (data_len < 3)
41 return ERR_PTR(-EINVAL);
42
43 /* remaining length where at d (the start of the integer encoding) */
44 data_len -= 2;
45
46 data[0] = _tag(UNIV, PRIM, INT);
47 if (integer == 0) {
48 *d++ = 0;
49 goto out;
50 }
51
52 for (i = sizeof(integer); i > 0 ; i--) {
53 int byte = integer >> (8 * (i - 1));
54
55 if (!found && byte == 0)
56 continue;
57
58 /*
59 * for a positive number the first byte must have bit
60 * 7 clear in two's complement (otherwise it's a
61 * negative number) so prepend a leading zero if
62 * that's not the case
63 */
64 if (!found && (byte & 0x80)) {
65 /*
66 * no check needed here, we already know we
67 * have len >= 1
68 */
69 *d++ = 0;
70 data_len--;
71 }
72
73 found = true;
74 if (data_len == 0)
75 return ERR_PTR(-EINVAL);
76
77 *d++ = byte;
78 data_len--;
79 }
80
81 out:
82 data[1] = d - data - 2;
83
84 return d;
85 }
86 EXPORT_SYMBOL_GPL(asn1_encode_integer);
87
88 /* calculate the base 128 digit values setting the top bit of the first octet */
89 static int asn1_encode_oid_digit(unsigned char **_data, int *data_len, u32 oid)
90 {
91 unsigned char *data = *_data;
92 int start = 7 + 7 + 7 + 7;
93 int ret = 0;
94
95 if (*data_len < 1)
96 return -EINVAL;
97
98 /* quick case */
99 if (oid == 0) {
100 *data++ = 0x80;
101 (*data_len)--;
102 goto out;
103 }
104
105 while (oid >> start == 0)
106 start -= 7;
107
108 while (start > 0 && *data_len > 0) {
109 u8 byte;
110
111 byte = oid >> start;
112 oid = oid - (byte << start);
113 start -= 7;
114 byte |= 0x80;
115 *data++ = byte;
116 (*data_len)--;
117 }
118
119 if (*data_len > 0) {
120 *data++ = oid;
121 (*data_len)--;
122 } else {
123 ret = -EINVAL;
124 }
125
126 out:
127 *_data = data;
128 return ret;
129 }
130
131 /**
132 * asn1_encode_oid() - encode an oid to ASN.1
133 * @data: position to begin encoding at
134 * @end_data: end of data pointer, points one beyond last usable byte in @data
135 * @oid: array of oids
136 * @oid_len: length of oid array
137 *
138 * this encodes an OID up to ASN.1 when presented as an array of OID values
139 */
140 unsigned char *
141 asn1_encode_oid(unsigned char *data, const unsigned char *end_data,
142 u32 oid[], int oid_len)
143 {
144 int data_len = end_data - data;
145 unsigned char *d = data + 2;
146 int i, ret;
147
148 if (WARN(oid_len < 2, "OID must have at least two elements"))
149 return ERR_PTR(-EINVAL);
150
151 if (WARN(oid_len > 32, "OID is too large"))
152 return ERR_PTR(-EINVAL);
153
154 if (IS_ERR(data))
155 return data;
156
157
158 /* need at least 3 bytes for tag, length and OID encoding */
159 if (data_len < 3)
160 return ERR_PTR(-EINVAL);
161
162 data[0] = _tag(UNIV, PRIM, OID);
163 *d++ = oid[0] * 40 + oid[1];
164
165 data_len -= 3;
166
167 for (i = 2; i < oid_len; i++) {
168 ret = asn1_encode_oid_digit(&d, &data_len, oid[i]);
169 if (ret < 0)
170 return ERR_PTR(ret);
171 }
172
173 data[1] = d - data - 2;
174
175 return d;
176 }
177 EXPORT_SYMBOL_GPL(asn1_encode_oid);
178
179 /**
180 * asn1_encode_length() - encode a length to follow an ASN.1 tag
181 * @data: pointer to encode at
182 * @data_len: pointer to remaining length (adjusted by routine)
183 * @len: length to encode
184 *
185 * This routine can encode lengths up to 65535 using the ASN.1 rules.
186 * It will accept a negative length and place a zero length tag
187 * instead (to keep the ASN.1 valid). This convention allows other
188 * encoder primitives to accept negative lengths as singalling the
189 * sequence will be re-encoded when the length is known.
190 */
191 static int asn1_encode_length(unsigned char **data, int *data_len, int len)
192 {
193 if (*data_len < 1)
194 return -EINVAL;
195
196 if (len < 0) {
197 *((*data)++) = 0;
198 (*data_len)--;
199 return 0;
200 }
201
202 if (len <= 0x7f) {
203 *((*data)++) = len;
204 (*data_len)--;
205 return 0;
206 }
207
208 if (*data_len < 2)
209 return -EINVAL;
210
211 if (len <= 0xff) {
212 *((*data)++) = 0x81;
213 *((*data)++) = len & 0xff;
214 *data_len -= 2;
215 return 0;
216 }
217
218 if (*data_len < 3)
219 return -EINVAL;
220
221 if (len <= 0xffff) {
222 *((*data)++) = 0x82;
223 *((*data)++) = (len >> 8) & 0xff;
224 *((*data)++) = len & 0xff;
225 *data_len -= 3;
226 return 0;
227 }
228
229 if (WARN(len > 0xffffff, "ASN.1 length can't be > 0xffffff"))
230 return -EINVAL;
231
232 if (*data_len < 4)
233 return -EINVAL;
234 *((*data)++) = 0x83;
235 *((*data)++) = (len >> 16) & 0xff;
236 *((*data)++) = (len >> 8) & 0xff;
237 *((*data)++) = len & 0xff;
238 *data_len -= 4;
239
240 return 0;
241 }
242
243 /**
244 * asn1_encode_tag() - add a tag for optional or explicit value
245 * @data: pointer to place tag at
246 * @end_data: end of data pointer, points one beyond last usable byte in @data
247 * @tag: tag to be placed
248 * @string: the data to be tagged
249 * @len: the length of the data to be tagged
250 *
251 * Note this currently only handles short form tags < 31.
252 *
253 * Standard usage is to pass in a @tag, @string and @length and the
254 * @string will be ASN.1 encoded with @tag and placed into @data. If
255 * the encoding would put data past @end_data then an error is
256 * returned, otherwise a pointer to a position one beyond the encoding
257 * is returned.
258 *
259 * To encode in place pass a NULL @string and -1 for @len and the
260 * maximum allowable beginning and end of the data; all this will do
261 * is add the current maximum length and update the data pointer to
262 * the place where the tag contents should be placed is returned. The
263 * data should be copied in by the calling routine which should then
264 * repeat the prior statement but now with the known length. In order
265 * to avoid having to keep both before and after pointers, the repeat
266 * expects to be called with @data pointing to where the first encode
267 * returned it and still NULL for @string but the real length in @len.
268 */
269 unsigned char *
270 asn1_encode_tag(unsigned char *data, const unsigned char *end_data,
271 u32 tag, const unsigned char *string, int len)
272 {
273 int data_len = end_data - data;
274 int ret;
275
276 if (WARN(tag > 30, "ASN.1 tag can't be > 30"))
277 return ERR_PTR(-EINVAL);
278
279 if (!string && WARN(len > 127,
280 "BUG: recode tag is too big (>127)"))
281 return ERR_PTR(-EINVAL);
282
283 if (IS_ERR(data))
284 return data;
285
286 if (!string && len > 0) {
287 /*
288 * we're recoding, so move back to the start of the
289 * tag and install a dummy length because the real
290 * data_len should be NULL
291 */
292 data -= 2;
293 data_len = 2;
294 }
295
296 if (data_len < 2)
297 return ERR_PTR(-EINVAL);
298
299 *(data++) = _tagn(CONT, CONS, tag);
300 data_len--;
301 ret = asn1_encode_length(&data, &data_len, len);
302 if (ret < 0)
303 return ERR_PTR(ret);
304
305 if (!string)
306 return data;
307
308 if (data_len < len)
309 return ERR_PTR(-EINVAL);
310
311 memcpy(data, string, len);
312 data += len;
313
314 return data;
315 }
316 EXPORT_SYMBOL_GPL(asn1_encode_tag);
317
318 /**
319 * asn1_encode_octet_string() - encode an ASN.1 OCTET STRING
320 * @data: pointer to encode at
321 * @end_data: end of data pointer, points one beyond last usable byte in @data
322 * @string: string to be encoded
323 * @len: length of string
324 *
325 * Note ASN.1 octet strings may contain zeros, so the length is obligatory.
326 */
327 unsigned char *
328 asn1_encode_octet_string(unsigned char *data,
329 const unsigned char *end_data,
330 const unsigned char *string, u32 len)
331 {
332 int data_len = end_data - data;
333 int ret;
334
335 if (IS_ERR(data))
336 return data;
337
338 /* need minimum of 2 bytes for tag and length of zero length string */
339 if (data_len < 2)
340 return ERR_PTR(-EINVAL);
341
342 *(data++) = _tag(UNIV, PRIM, OTS);
343 data_len--;
344
345 ret = asn1_encode_length(&data, &data_len, len);
346 if (ret)
347 return ERR_PTR(ret);
348
349 if (data_len < len)
350 return ERR_PTR(-EINVAL);
351
352 memcpy(data, string, len);
353 data += len;
354
355 return data;
356 }
357 EXPORT_SYMBOL_GPL(asn1_encode_octet_string);
358
359 /**
360 * asn1_encode_sequence() - wrap a byte stream in an ASN.1 SEQUENCE
361 * @data: pointer to encode at
362 * @end_data: end of data pointer, points one beyond last usable byte in @data
363 * @seq: data to be encoded as a sequence
364 * @len: length of the data to be encoded as a sequence
365 *
366 * Fill in a sequence. To encode in place, pass NULL for @seq and -1
367 * for @len; then call again once the length is known (still with NULL
368 * for @seq). In order to avoid having to keep both before and after
369 * pointers, the repeat expects to be called with @data pointing to
370 * where the first encode placed it.
371 */
372 unsigned char *
373 asn1_encode_sequence(unsigned char *data, const unsigned char *end_data,
374 const unsigned char *seq, int len)
375 {
376 int data_len = end_data - data;
377 int ret;
378
379 if (!seq && WARN(len > 127,
380 "BUG: recode sequence is too big (>127)"))
381 return ERR_PTR(-EINVAL);
382
383 if (IS_ERR(data))
384 return data;
385
386 if (!seq && len >= 0) {
387 /*
388 * we're recoding, so move back to the start of the
389 * sequence and install a dummy length because the
390 * real length should be NULL
391 */
392 data -= 2;
393 data_len = 2;
394 }
395
396 if (data_len < 2)
397 return ERR_PTR(-EINVAL);
398
399 *(data++) = _tag(UNIV, CONS, SEQ);
400 data_len--;
401
402 ret = asn1_encode_length(&data, &data_len, len);
403 if (ret)
404 return ERR_PTR(ret);
405
406 if (!seq)
407 return data;
408
409 if (data_len < len)
410 return ERR_PTR(-EINVAL);
411
412 memcpy(data, seq, len);
413 data += len;
414
415 return data;
416 }
417 EXPORT_SYMBOL_GPL(asn1_encode_sequence);
418
419 /**
420 * asn1_encode_boolean() - encode a boolean value to ASN.1
421 * @data: pointer to encode at
422 * @end_data: end of data pointer, points one beyond last usable byte in @data
423 * @val: the boolean true/false value
424 */
425 unsigned char *
426 asn1_encode_boolean(unsigned char *data, const unsigned char *end_data,
427 bool val)
428 {
429 int data_len = end_data - data;
430
431 if (IS_ERR(data))
432 return data;
433
434 /* booleans are 3 bytes: tag, length == 1 and value == 0 or 1 */
435 if (data_len < 3)
436 return ERR_PTR(-EINVAL);
437
438 *(data++) = _tag(UNIV, PRIM, BOOL);
439 data_len--;
440
441 asn1_encode_length(&data, &data_len, 1);
442
443 if (val)
444 *(data++) = 1;
445 else
446 *(data++) = 0;
447
448 return data;
449 }
450 EXPORT_SYMBOL_GPL(asn1_encode_boolean);
451
452 MODULE_DESCRIPTION("Simple encoder primitives for ASN.1 BER/DER/CER");
453 MODULE_LICENSE("GPL");
454
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