xref: /openbsd/lib/libcrypto/bytestring/bs_cbb.c (revision 5a38ef86) 
1 /*	$OpenBSD: bs_cbb.c,v 1.2 2021/12/15 18:02:39 jsing Exp $	*/
2 /*
3  * Copyright (c) 2014, Google Inc.
4  *
5  * Permission to use, copy, modify, and/or distribute this software for any
6  * purpose with or without fee is hereby granted, provided that the above
7  * copyright notice and this permission notice appear in all copies.
8  *
9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
12  * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
14  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
15  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16  */
17 
18 #include <stdlib.h>
19 #include <string.h>
20 
21 #include "bytestring.h"
22 
23 #define CBB_INITIAL_SIZE 64
24 
25 static int
26 cbb_init(CBB *cbb, uint8_t *buf, size_t cap)
27 {
28 	struct cbb_buffer_st *base;
29 
30 	if ((base = calloc(1, sizeof(struct cbb_buffer_st))) == NULL)
31 		return 0;
32 
33 	base->buf = buf;
34 	base->len = 0;
35 	base->cap = cap;
36 	base->can_resize = 1;
37 
38 	cbb->base = base;
39 	cbb->is_top_level = 1;
40 
41 	return 1;
42 }
43 
44 int
45 CBB_init(CBB *cbb, size_t initial_capacity)
46 {
47 	uint8_t *buf = NULL;
48 
49 	memset(cbb, 0, sizeof(*cbb));
50 
51 	if (initial_capacity == 0)
52 		initial_capacity = CBB_INITIAL_SIZE;
53 
54 	if ((buf = calloc(1, initial_capacity)) == NULL)
55 		return 0;
56 
57 	if (!cbb_init(cbb, buf, initial_capacity)) {
58 		free(buf);
59 		return 0;
60 	}
61 
62 	return 1;
63 }
64 
65 int
66 CBB_init_fixed(CBB *cbb, uint8_t *buf, size_t len)
67 {
68 	memset(cbb, 0, sizeof(*cbb));
69 
70 	if (!cbb_init(cbb, buf, len))
71 		return 0;
72 
73 	cbb->base->can_resize = 0;
74 
75 	return 1;
76 }
77 
78 void
79 CBB_cleanup(CBB *cbb)
80 {
81 	if (cbb->base) {
82 		if (cbb->base->can_resize)
83 			freezero(cbb->base->buf, cbb->base->cap);
84 		free(cbb->base);
85 	}
86 	cbb->base = NULL;
87 	cbb->child = NULL;
88 }
89 
90 static int
91 cbb_buffer_add(struct cbb_buffer_st *base, uint8_t **out, size_t len)
92 {
93 	size_t newlen;
94 
95 	if (base == NULL)
96 		return 0;
97 
98 	newlen = base->len + len;
99 	if (newlen < base->len)
100 		/* Overflow */
101 		return 0;
102 
103 	if (newlen > base->cap) {
104 		size_t newcap = base->cap * 2;
105 		uint8_t *newbuf;
106 
107 		if (!base->can_resize)
108 			return 0;
109 
110 		if (newcap < base->cap || newcap < newlen)
111 			newcap = newlen;
112 
113 		newbuf = recallocarray(base->buf, base->cap, newcap, 1);
114 		if (newbuf == NULL)
115 			return 0;
116 
117 		base->buf = newbuf;
118 		base->cap = newcap;
119 	}
120 
121 	if (out)
122 		*out = base->buf + base->len;
123 
124 	base->len = newlen;
125 	return 1;
126 }
127 
128 static int
129 cbb_add_u(CBB *cbb, uint32_t v, size_t len_len)
130 {
131 	uint8_t *buf;
132 	size_t i;
133 
134 	if (len_len == 0)
135 		return 1;
136 
137 	if (len_len > 4)
138 		return 0;
139 
140 	if (!CBB_flush(cbb) || !cbb_buffer_add(cbb->base, &buf, len_len))
141 		return 0;
142 
143 	for (i = len_len - 1; i < len_len; i--) {
144 		buf[i] = v;
145 		v >>= 8;
146 	}
147 	return 1;
148 }
149 
150 int
151 CBB_finish(CBB *cbb, uint8_t **out_data, size_t *out_len)
152 {
153 	if (!cbb->is_top_level)
154 		return 0;
155 
156 	if (!CBB_flush(cbb))
157 		return 0;
158 
159 	if (cbb->base->can_resize && (out_data == NULL || out_len == NULL))
160 		/*
161 		 * |out_data| and |out_len| can only be NULL if the CBB is
162 		 * fixed.
163 		 */
164 		return 0;
165 
166 	if (out_data != NULL)
167 		*out_data = cbb->base->buf;
168 
169 	if (out_len != NULL)
170 		*out_len = cbb->base->len;
171 
172 	cbb->base->buf = NULL;
173 	CBB_cleanup(cbb);
174 	return 1;
175 }
176 
177 /*
178  * CBB_flush recurses and then writes out any pending length prefix. The current
179  * length of the underlying base is taken to be the length of the
180  * length-prefixed data.
181  */
182 int
183 CBB_flush(CBB *cbb)
184 {
185 	size_t child_start, i, len;
186 
187 	if (cbb->base == NULL)
188 		return 0;
189 
190 	if (cbb->child == NULL || cbb->pending_len_len == 0)
191 		return 1;
192 
193 	child_start = cbb->offset + cbb->pending_len_len;
194 
195 	if (!CBB_flush(cbb->child) || child_start < cbb->offset ||
196 	    cbb->base->len < child_start)
197 		return 0;
198 
199 	len = cbb->base->len - child_start;
200 
201 	if (cbb->pending_is_asn1) {
202 		/*
203 		 * For ASN.1, we assumed that we were using short form which
204 		 * only requires a single byte for the length octet.
205 		 *
206 		 * If it turns out that we need long form, we have to move
207 		 * the contents along in order to make space for more length
208 		 * octets.
209 		 */
210 		size_t len_len = 1;  /* total number of length octets */
211 		uint8_t initial_length_byte;
212 
213 		/* We already wrote 1 byte for the length. */
214 		if (cbb->pending_len_len != 1)
215 			return 0;
216 
217 		/* Check for long form */
218 		if (len > 0xfffffffe)
219 			return 0;	/* 0xffffffff is reserved */
220 		else if (len > 0xffffff)
221 			len_len = 5;
222 		else if (len > 0xffff)
223 			len_len = 4;
224 		else if (len > 0xff)
225 			len_len = 3;
226 		else if (len > 0x7f)
227 			len_len = 2;
228 
229 		if (len_len == 1) {
230 			/* For short form, the initial byte is the length. */
231 			initial_length_byte = len;
232 			len = 0;
233 
234 		} else {
235 			/*
236 			 * For long form, the initial byte is the number of
237 			 * subsequent length octets (plus bit 8 set).
238 			 */
239 			initial_length_byte = 0x80 | (len_len - 1);
240 
241 			/*
242 			 * We need to move the contents along in order to make
243 			 * space for the long form length octets.
244 			 */
245 			size_t extra_bytes = len_len - 1;
246 			if (!cbb_buffer_add(cbb->base, NULL, extra_bytes))
247 				return 0;
248 
249 			memmove(cbb->base->buf + child_start + extra_bytes,
250 			    cbb->base->buf + child_start, len);
251 		}
252 		cbb->base->buf[cbb->offset++] = initial_length_byte;
253 		cbb->pending_len_len = len_len - 1;
254 	}
255 
256 	for (i = cbb->pending_len_len - 1; i < cbb->pending_len_len; i--) {
257 		cbb->base->buf[cbb->offset + i] = len;
258 		len >>= 8;
259 	}
260 	if (len != 0)
261 		return 0;
262 
263 	cbb->child->base = NULL;
264 	cbb->child = NULL;
265 	cbb->pending_len_len = 0;
266 	cbb->pending_is_asn1 = 0;
267 	cbb->offset = 0;
268 
269 	return 1;
270 }
271 
272 void
273 CBB_discard_child(CBB *cbb)
274 {
275 	if (cbb->child == NULL)
276 		return;
277 
278 	cbb->base->len = cbb->offset;
279 
280 	cbb->child->base = NULL;
281 	cbb->child = NULL;
282 	cbb->pending_len_len = 0;
283 	cbb->pending_is_asn1 = 0;
284 	cbb->offset = 0;
285 }
286 
287 static int
288 cbb_add_length_prefixed(CBB *cbb, CBB *out_contents, size_t len_len)
289 {
290 	uint8_t *prefix_bytes;
291 
292 	if (!CBB_flush(cbb))
293 		return 0;
294 
295 	cbb->offset = cbb->base->len;
296 	if (!cbb_buffer_add(cbb->base, &prefix_bytes, len_len))
297 		return 0;
298 
299 	memset(prefix_bytes, 0, len_len);
300 	memset(out_contents, 0, sizeof(CBB));
301 	out_contents->base = cbb->base;
302 	cbb->child = out_contents;
303 	cbb->pending_len_len = len_len;
304 	cbb->pending_is_asn1 = 0;
305 
306 	return 1;
307 }
308 
309 int
310 CBB_add_u8_length_prefixed(CBB *cbb, CBB *out_contents)
311 {
312 	return cbb_add_length_prefixed(cbb, out_contents, 1);
313 }
314 
315 int
316 CBB_add_u16_length_prefixed(CBB *cbb, CBB *out_contents)
317 {
318 	return cbb_add_length_prefixed(cbb, out_contents, 2);
319 }
320 
321 int
322 CBB_add_u24_length_prefixed(CBB *cbb, CBB *out_contents)
323 {
324 	return cbb_add_length_prefixed(cbb, out_contents, 3);
325 }
326 
327 int
328 CBB_add_asn1(CBB *cbb, CBB *out_contents, unsigned int tag)
329 {
330 	if (tag > UINT8_MAX)
331 		return 0;
332 
333 	/* Long form identifier octets are not supported. */
334 	if ((tag & 0x1f) == 0x1f)
335 		return 0;
336 
337 	/* Short-form identifier octet only needs a single byte */
338 	if (!CBB_flush(cbb) || !CBB_add_u8(cbb, tag))
339 		return 0;
340 
341 	/*
342 	 * Add 1 byte to cover the short-form length octet case.  If it turns
343 	 * out we need long-form, it will be extended later.
344 	 */
345 	cbb->offset = cbb->base->len;
346 	if (!CBB_add_u8(cbb, 0))
347 		return 0;
348 
349 	memset(out_contents, 0, sizeof(CBB));
350 	out_contents->base = cbb->base;
351 	cbb->child = out_contents;
352 	cbb->pending_len_len = 1;
353 	cbb->pending_is_asn1 = 1;
354 
355 	return 1;
356 }
357 
358 int
359 CBB_add_bytes(CBB *cbb, const uint8_t *data, size_t len)
360 {
361 	uint8_t *dest;
362 
363 	if (!CBB_flush(cbb) || !cbb_buffer_add(cbb->base, &dest, len))
364 		return 0;
365 
366 	memcpy(dest, data, len);
367 	return 1;
368 }
369 
370 int
371 CBB_add_space(CBB *cbb, uint8_t **out_data, size_t len)
372 {
373 	if (!CBB_flush(cbb) || !cbb_buffer_add(cbb->base, out_data, len))
374 		return 0;
375 
376 	memset(*out_data, 0, len);
377 	return 1;
378 }
379 
380 int
381 CBB_add_u8(CBB *cbb, size_t value)
382 {
383 	if (value > UINT8_MAX)
384 		return 0;
385 
386 	return cbb_add_u(cbb, (uint32_t)value, 1);
387 }
388 
389 int
390 CBB_add_u16(CBB *cbb, size_t value)
391 {
392 	if (value > UINT16_MAX)
393 		return 0;
394 
395 	return cbb_add_u(cbb, (uint32_t)value, 2);
396 }
397 
398 int
399 CBB_add_u24(CBB *cbb, size_t value)
400 {
401 	if (value > 0xffffffUL)
402 		return 0;
403 
404 	return cbb_add_u(cbb, (uint32_t)value, 3);
405 }
406 
407 int
408 CBB_add_u32(CBB *cbb, size_t value)
409 {
410 	if (value > 0xffffffffUL)
411 		return 0;
412 
413 	return cbb_add_u(cbb, (uint32_t)value, 4);
414 }
415 
416 int
417 CBB_add_asn1_uint64(CBB *cbb, uint64_t value)
418 {
419 	CBB child;
420 	size_t i;
421 	int started = 0;
422 
423 	if (!CBB_add_asn1(cbb, &child, CBS_ASN1_INTEGER))
424 		return 0;
425 
426 	for (i = 0; i < 8; i++) {
427 		uint8_t byte = (value >> 8 * (7 - i)) & 0xff;
428 
429 		/*
430 		 * ASN.1 restriction: first 9 bits cannot be all zeroes or
431 		 * all ones.  Since this function only encodes unsigned
432 		 * integers, the only concerns are not encoding leading
433 		 * zeros and adding a padding byte if necessary.
434 		 *
435 		 * In practice, this means:
436 		 * 1) Skip leading octets of all zero bits in the value
437 		 * 2) After skipping the leading zero octets, if the next 9
438 		 *    bits are all ones, add an all zero prefix octet (and
439 		 *    set the high bit of the prefix octet if negative).
440 		 *
441 		 * Additionally, for an unsigned value, add an all zero
442 		 * prefix if the high bit of the first octet would be one.
443 		 */
444 		if (!started) {
445 			if (byte == 0)
446 				/* Don't encode leading zeros. */
447 				continue;
448 
449 			/*
450 			 * If the high bit is set, add a padding byte to make it
451 			 * unsigned.
452 			 */
453 			if ((byte & 0x80) && !CBB_add_u8(&child, 0))
454 				return 0;
455 
456 			started = 1;
457 		}
458 		if (!CBB_add_u8(&child, byte))
459 			return 0;
460 	}
461 
462 	/* 0 is encoded as a single 0, not the empty string. */
463 	if (!started && !CBB_add_u8(&child, 0))
464 		return 0;
465 
466 	return CBB_flush(cbb);
467 }
468