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(error: -EINVAL); |
35 | |
36 | if (IS_ERR(ptr: 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(error: -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(error: -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(error: -EINVAL); |
150 | |
151 | if (WARN(oid_len > 32, "OID is too large" )) |
152 | return ERR_PTR(error: -EINVAL); |
153 | |
154 | if (IS_ERR(ptr: 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(error: -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(data: &d, data_len: &data_len, oid: oid[i]); |
169 | if (ret < 0) |
170 | return ERR_PTR(error: 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(error: -EINVAL); |
278 | |
279 | if (!string && WARN(len > 127, |
280 | "BUG: recode tag is too big (>127)" )) |
281 | return ERR_PTR(error: -EINVAL); |
282 | |
283 | if (IS_ERR(ptr: 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(error: -EINVAL); |
298 | |
299 | *(data++) = _tagn(CONT, CONS, tag); |
300 | data_len--; |
301 | ret = asn1_encode_length(data: &data, data_len: &data_len, len); |
302 | if (ret < 0) |
303 | return ERR_PTR(error: ret); |
304 | |
305 | if (!string) |
306 | return data; |
307 | |
308 | if (data_len < len) |
309 | return ERR_PTR(error: -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(ptr: 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(error: -EINVAL); |
341 | |
342 | *(data++) = _tag(UNIV, PRIM, OTS); |
343 | data_len--; |
344 | |
345 | ret = asn1_encode_length(data: &data, data_len: &data_len, len); |
346 | if (ret) |
347 | return ERR_PTR(error: ret); |
348 | |
349 | if (data_len < len) |
350 | return ERR_PTR(error: -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(error: -EINVAL); |
382 | |
383 | if (IS_ERR(ptr: 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(error: -EINVAL); |
398 | |
399 | *(data++) = _tag(UNIV, CONS, SEQ); |
400 | data_len--; |
401 | |
402 | ret = asn1_encode_length(data: &data, data_len: &data_len, len); |
403 | if (ret) |
404 | return ERR_PTR(error: ret); |
405 | |
406 | if (!seq) |
407 | return data; |
408 | |
409 | if (data_len < len) |
410 | return ERR_PTR(error: -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(ptr: 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(error: -EINVAL); |
437 | |
438 | *(data++) = _tag(UNIV, PRIM, BOOL); |
439 | data_len--; |
440 | |
441 | asn1_encode_length(data: &data, data_len: &data_len, 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_LICENSE("GPL" ); |
453 | |