xref: /openbsd/lib/libssl/bs_cbb.c (revision 09467b48) 
1 /*	$OpenBSD: bs_cbb.c,v 1.22 2020/03/13 15:54:34 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 #include <stdlib.h>
18 #include <string.h>
19 
20 #include <openssl/opensslconf.h>
21 
22 #include "bytestring.h"
23 
24 #define CBB_INITIAL_SIZE 64
25 
26 static int
27 cbb_init(CBB *cbb, uint8_t *buf, size_t cap)
28 {
29 	struct cbb_buffer_st *base;
30 
31 	if ((base = calloc(1, sizeof(struct cbb_buffer_st))) == NULL)
32 		return 0;
33 
34 	base->buf = buf;
35 	base->len = 0;
36 	base->cap = cap;
37 	base->can_resize = 1;
38 
39 	cbb->base = base;
40 	cbb->is_top_level = 1;
41 
42 	return 1;
43 }
44 
45 int
46 CBB_init(CBB *cbb, size_t initial_capacity)
47 {
48 	uint8_t *buf = NULL;
49 
50 	memset(cbb, 0, sizeof(*cbb));
51 
52 	if (initial_capacity == 0)
53 		initial_capacity = CBB_INITIAL_SIZE;
54 
55 	if ((buf = calloc(1, initial_capacity)) == NULL)
56 		return 0;
57 
58 	if (!cbb_init(cbb, buf, initial_capacity)) {
59 		free(buf);
60 		return 0;
61 	}
62 
63 	return 1;
64 }
65 
66 int
67 CBB_init_fixed(CBB *cbb, uint8_t *buf, size_t len)
68 {
69 	memset(cbb, 0, sizeof(*cbb));
70 
71 	if (!cbb_init(cbb, buf, len))
72 		return 0;
73 
74 	cbb->base->can_resize = 0;
75 
76 	return 1;
77 }
78 
79 void
80 CBB_cleanup(CBB *cbb)
81 {
82 	if (cbb->base) {
83 		if (cbb->base->can_resize)
84 			freezero(cbb->base->buf, cbb->base->cap);
85 		free(cbb->base);
86 	}
87 	cbb->base = NULL;
88 	cbb->child = NULL;
89 }
90 
91 static int
92 cbb_buffer_add(struct cbb_buffer_st *base, uint8_t **out, size_t len)
93 {
94 	size_t newlen;
95 
96 	if (base == NULL)
97 		return 0;
98 
99 	newlen = base->len + len;
100 	if (newlen < base->len)
101 		/* Overflow */
102 		return 0;
103 
104 	if (newlen > base->cap) {
105 		size_t newcap = base->cap * 2;
106 		uint8_t *newbuf;
107 
108 		if (!base->can_resize)
109 			return 0;
110 
111 		if (newcap < base->cap || newcap < newlen)
112 			newcap = newlen;
113 
114 		newbuf = recallocarray(base->buf, base->cap, newcap, 1);
115 		if (newbuf == NULL)
116 			return 0;
117 
118 		base->buf = newbuf;
119 		base->cap = newcap;
120 	}
121 
122 	if (out)
123 		*out = base->buf + base->len;
124 
125 	base->len = newlen;
126 	return 1;
127 }
128 
129 static int
130 cbb_add_u(CBB *cbb, uint32_t v, size_t len_len)
131 {
132 	uint8_t *buf;
133 	size_t i;
134 
135 	if (len_len == 0)
136 		return 1;
137 
138 	if (len_len > 4)
139 		return 0;
140 
141 	if (!CBB_flush(cbb) || !cbb_buffer_add(cbb->base, &buf, len_len))
142 		return 0;
143 
144 	for (i = len_len - 1; i < len_len; i--) {
145 		buf[i] = v;
146 		v >>= 8;
147 	}
148 	return 1;
149 }
150 
151 int
152 CBB_finish(CBB *cbb, uint8_t **out_data, size_t *out_len)
153 {
154 	if (!cbb->is_top_level)
155 		return 0;
156 
157 	if (!CBB_flush(cbb))
158 		return 0;
159 
160 	if (cbb->base->can_resize && (out_data == NULL || out_len == NULL))
161 		/*
162 		 * |out_data| and |out_len| can only be NULL if the CBB is
163 		 * fixed.
164 		 */
165 		return 0;
166 
167 	if (out_data != NULL)
168 		*out_data = cbb->base->buf;
169 
170 	if (out_len != NULL)
171 		*out_len = cbb->base->len;
172 
173 	cbb->base->buf = NULL;
174 	CBB_cleanup(cbb);
175 	return 1;
176 }
177 
178 /*
179  * CBB_flush recurses and then writes out any pending length prefix. The current
180  * length of the underlying base is taken to be the length of the
181  * length-prefixed data.
182  */
183 int
184 CBB_flush(CBB *cbb)
185 {
186 	size_t child_start, i, len;
187 
188 	if (cbb->base == NULL)
189 		return 0;
190 
191 	if (cbb->child == NULL || cbb->pending_len_len == 0)
192 		return 1;
193 
194 	child_start = cbb->offset + cbb->pending_len_len;
195 
196 	if (!CBB_flush(cbb->child) || child_start < cbb->offset ||
197 	    cbb->base->len < child_start)
198 		return 0;
199 
200 	len = cbb->base->len - child_start;
201 
202 	if (cbb->pending_is_asn1) {
203 		/*
204 		 * For ASN.1, we assumed that we were using short form which
205 		 * only requires a single byte for the length octet.
206 		 *
207 		 * If it turns out that we need long form, we have to move
208 		 * the contents along in order to make space for more length
209 		 * octets.
210 		 */
211 		size_t len_len = 1;  /* total number of length octets */
212 		uint8_t initial_length_byte;
213 
214 		/* We already wrote 1 byte for the length. */
215 		if (cbb->pending_len_len != 1)
216 			return 0;
217 
218 		/* Check for long form */
219 		if (len > 0xfffffffe)
220 			return 0;	/* 0xffffffff is reserved */
221 		else if (len > 0xffffff)
222 			len_len = 5;
223 		else if (len > 0xffff)
224 			len_len = 4;
225 		else if (len > 0xff)
226 			len_len = 3;
227 		else if (len > 0x7f)
228 			len_len = 2;
229 
230 		if (len_len == 1) {
231 			/* For short form, the initial byte is the length. */
232 			initial_length_byte = len;
233 			len = 0;
234 
235 		} else {
236 			/*
237 			 * For long form, the initial byte is the number of
238 			 * subsequent length octets (plus bit 8 set).
239 			 */
240 			initial_length_byte = 0x80 | (len_len - 1);
241 
242 			/*
243 			 * We need to move the contents along in order to make
244 			 * space for the long form length octets.
245 			 */
246 			size_t extra_bytes = len_len - 1;
247 			if (!cbb_buffer_add(cbb->base, NULL, extra_bytes))
248 				return 0;
249 
250 			memmove(cbb->base->buf + child_start + extra_bytes,
251 			    cbb->base->buf + child_start, len);
252 		}
253 		cbb->base->buf[cbb->offset++] = initial_length_byte;
254 		cbb->pending_len_len = len_len - 1;
255 	}
256 
257 	for (i = cbb->pending_len_len - 1; i < cbb->pending_len_len; i--) {
258 		cbb->base->buf[cbb->offset + i] = len;
259 		len >>= 8;
260 	}
261 	if (len != 0)
262 		return 0;
263 
264 	cbb->child->base = NULL;
265 	cbb->child = NULL;
266 	cbb->pending_len_len = 0;
267 	cbb->pending_is_asn1 = 0;
268 	cbb->offset = 0;
269 
270 	return 1;
271 }
272 
273 void
274 CBB_discard_child(CBB *cbb)
275 {
276 	if (cbb->child == NULL)
277 		return;
278 
279 	cbb->base->len = cbb->offset;
280 
281 	cbb->child->base = NULL;
282 	cbb->child = NULL;
283 	cbb->pending_len_len = 0;
284 	cbb->pending_is_asn1 = 0;
285 	cbb->offset = 0;
286 }
287 
288 static int
289 cbb_add_length_prefixed(CBB *cbb, CBB *out_contents, size_t len_len)
290 {
291 	uint8_t *prefix_bytes;
292 
293 	if (!CBB_flush(cbb))
294 		return 0;
295 
296 	cbb->offset = cbb->base->len;
297 	if (!cbb_buffer_add(cbb->base, &prefix_bytes, len_len))
298 		return 0;
299 
300 	memset(prefix_bytes, 0, len_len);
301 	memset(out_contents, 0, sizeof(CBB));
302 	out_contents->base = cbb->base;
303 	cbb->child = out_contents;
304 	cbb->pending_len_len = len_len;
305 	cbb->pending_is_asn1 = 0;
306 
307 	return 1;
308 }
309 
310 int
311 CBB_add_u8_length_prefixed(CBB *cbb, CBB *out_contents)
312 {
313 	return cbb_add_length_prefixed(cbb, out_contents, 1);
314 }
315 
316 int
317 CBB_add_u16_length_prefixed(CBB *cbb, CBB *out_contents)
318 {
319 	return cbb_add_length_prefixed(cbb, out_contents, 2);
320 }
321 
322 int
323 CBB_add_u24_length_prefixed(CBB *cbb, CBB *out_contents)
324 {
325 	return cbb_add_length_prefixed(cbb, out_contents, 3);
326 }
327 
328 int
329 CBB_add_asn1(CBB *cbb, CBB *out_contents, unsigned int tag)
330 {
331 	if (tag > UINT8_MAX)
332 		return 0;
333 
334 	/* Long form identifier octets are not supported. */
335 	if ((tag & 0x1f) == 0x1f)
336 		return 0;
337 
338 	/* Short-form identifier octet only needs a single byte */
339 	if (!CBB_flush(cbb) || !CBB_add_u8(cbb, tag))
340 		return 0;
341 
342 	/*
343 	 * Add 1 byte to cover the short-form length octet case.  If it turns
344 	 * out we need long-form, it will be extended later.
345 	 */
346 	cbb->offset = cbb->base->len;
347 	if (!CBB_add_u8(cbb, 0))
348 		return 0;
349 
350 	memset(out_contents, 0, sizeof(CBB));
351 	out_contents->base = cbb->base;
352 	cbb->child = out_contents;
353 	cbb->pending_len_len = 1;
354 	cbb->pending_is_asn1 = 1;
355 
356 	return 1;
357 }
358 
359 int
360 CBB_add_bytes(CBB *cbb, const uint8_t *data, size_t len)
361 {
362 	uint8_t *dest;
363 
364 	if (!CBB_add_space(cbb, &dest, len))
365 		return 0;
366 
367 	memcpy(dest, data, len);
368 	return 1;
369 }
370 
371 int
372 CBB_add_space(CBB *cbb, uint8_t **out_data, size_t len)
373 {
374 	if (!CBB_flush(cbb) || !cbb_buffer_add(cbb->base, out_data, len))
375 		return 0;
376 
377 	memset(*out_data, 0, len);
378 	return 1;
379 }
380 
381 int
382 CBB_add_u8(CBB *cbb, size_t value)
383 {
384 	if (value > UINT8_MAX)
385 		return 0;
386 
387 	return cbb_add_u(cbb, (uint32_t)value, 1);
388 }
389 
390 int
391 CBB_add_u16(CBB *cbb, size_t value)
392 {
393 	if (value > UINT16_MAX)
394 		return 0;
395 
396 	return cbb_add_u(cbb, (uint32_t)value, 2);
397 }
398 
399 int
400 CBB_add_u24(CBB *cbb, size_t value)
401 {
402 	if (value > 0xffffffUL)
403 		return 0;
404 
405 	return cbb_add_u(cbb, (uint32_t)value, 3);
406 }
407 
408 int
409 CBB_add_u32(CBB *cbb, size_t value)
410 {
411 	if (value > 0xffffffffUL)
412 		return 0;
413 
414 	return cbb_add_u(cbb, (uint32_t)value, 4);
415 }
416 
417 int
418 CBB_add_asn1_uint64(CBB *cbb, uint64_t value)
419 {
420 	CBB child;
421 	size_t i;
422 	int started = 0;
423 
424 	if (!CBB_add_asn1(cbb, &child, CBS_ASN1_INTEGER))
425 		return 0;
426 
427 	for (i = 0; i < 8; i++) {
428 		uint8_t byte = (value >> 8 * (7 - i)) & 0xff;
429 
430 		/*
431 		 * ASN.1 restriction: first 9 bits cannot be all zeroes or
432 		 * all ones.  Since this function only encodes unsigned
433 		 * integers, the only concerns are not encoding leading
434 		 * zeros and adding a padding byte if necessary.
435 		 *
436 		 * In practice, this means:
437 		 * 1) Skip leading octets of all zero bits in the value
438 		 * 2) After skipping the leading zero octets, if the next 9
439 		 *    bits are all ones, add an all zero prefix octet (and
440 		 *    set the high bit of the prefix octet if negative).
441 		 *
442 		 * Additionally, for an unsigned value, add an all zero
443 		 * prefix if the high bit of the first octet would be one.
444 		 */
445 		if (!started) {
446 			if (byte == 0)
447 				/* Don't encode leading zeros. */
448 				continue;
449 
450 			/*
451 			 * If the high bit is set, add a padding byte to make it
452 			 * unsigned.
453 			 */
454 			if ((byte & 0x80) && !CBB_add_u8(&child, 0))
455 				return 0;
456 
457 			started = 1;
458 		}
459 		if (!CBB_add_u8(&child, byte))
460 			return 0;
461 	}
462 
463 	/* 0 is encoded as a single 0, not the empty string. */
464 	if (!started && !CBB_add_u8(&child, 0))
465 		return 0;
466 
467 	return CBB_flush(cbb);
468 }
469