der.c revision e46ca9aa7ac7fb0d486b2bdca760e288f76b160e
1/*-
2 * Copyright (c) 2016 Christos Zoulas
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
15 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
16 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
17 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
18 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
19 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
20 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
21 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
22 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
23 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
24 * POSSIBILITY OF SUCH DAMAGE.
25 */
26/*
27 * DER (Distinguished Encoding Rules) Parser
28 *
29 * Sources:
30 * https://en.wikipedia.org/wiki/X.690
31 * http://fm4dd.com/openssl/certexamples.htm
32 * http://blog.engelke.com/2014/10/17/parsing-ber-and-der-encoded-asn-1-objects/
33 */
34#ifndef TEST_DER
35#include "file.h"
36
37#ifndef lint
38FILE_RCSID("@(#)$File: der.c,v 1.6 2016/04/21 14:26:03 christos Exp $")
39#endif
40#endif
41
42#include <sys/types.h>
43#include <sys/stat.h>
44#include <sys/mman.h>
45
46#include <stdio.h>
47#include <fcntl.h>
48#include <stdlib.h>
49#include <string.h>
50#include <ctype.h>
51
52#ifndef TEST_DER
53#include "magic.h"
54#include "der.h"
55#else
56#include <err.h>
57#endif
58
59#define DER_BAD	((uint32_t)-1)
60
61#define DER_CLASS_UNIVERSAL	0
62#define	DER_CLASS_APPLICATION	1
63#define	DER_CLASS_CONTEXT	2
64#define	DER_CLASS_PRIVATE	3
65#ifdef DEBUG_DER
66static const char der_class[] = "UACP";
67#endif
68
69#define DER_TYPE_PRIMITIVE	0
70#define DER_TYPE_CONSTRUCTED	1
71#ifdef DEBUG_DER
72static const char der_type[] = "PC";
73#endif
74
75#define	DER_TAG_EOC			0x00
76#define	DER_TAG_BOOLEAN			0x01
77#define	DER_TAG_INTEGER			0x02
78#define	DER_TAG_BIT STRING		0x03
79#define	DER_TAG_OCTET_STRING		0x04
80#define	DER_TAG_NULL			0x05
81#define	DER_TAG_OBJECT_IDENTIFIER	0x06
82#define	DER_TAG_OBJECT_DESCRIPTOR	0x07
83#define	DER_TAG_EXTERNAL		0x08
84#define	DER_TAG_REAL			0x09
85#define	DER_TAG_ENUMERATED		0x0a
86#define	DER_TAG_EMBEDDED_PDV		0x0b
87#define	DER_TAG_UTF8_STRING		0x0c
88#define	DER_TAG_RELATIVE_OID		0x0d
89#define DER_TAG_RESERVED_1		0x0e
90#define DER_TAG_RESERVED_2		0x0f
91#define	DER_TAG_SEQUENCE		0x10
92#define	DER_TAG_SET			0x11
93#define	DER_TAG_NUMERIC_STRING		0x12
94#define	DER_TAG_PRINTABLE_STRING	0x13
95#define	DER_TAG_T61_STRING		0x14
96#define	DER_TAG_VIDEOTEX_STRING		0x15
97#define	DER_TAG_IA5_STRING		0x16
98#define	DER_TAG_UTCTIME			0x17
99#define	DER_TAG_GENERALIZED_TIME	0x18
100#define	DER_TAG_GRAPHIC_STRING		0x19
101#define	DER_TAG_VISIBLE_STRING		0x1a
102#define	DER_TAG_GENERAL_STRING		0x1b
103#define	DER_TAG_UNIVERSAL_STRING	0x1c
104#define	DER_TAG_CHARACTER_STRING	0x1d
105#define	DER_TAG_BMP_STRING		0x1e
106#define	DER_TAG_LONG			0x1f
107
108static const char *der__tag[] = {
109	"eoc", "bool", "int", "bit_str", "octet_str",
110	"null", "obj_id", "obj_desc", "ext", "real",
111	"enum", "embed", "utf8_str", "oid", "res1",
112	"res2", "seq", "set", "num_str", "prt_str",
113	"t61_str", "vid_str", "ia5_str", "utc_time",
114	"gen_time", "gr_str", "vis_str", "gen_str",
115	"char_str", "bmp_str", "long"
116};
117
118#ifdef DEBUG_DER
119#define DPRINTF(a) printf a
120#else
121#define DPRINTF(a)
122#endif
123
124#ifdef TEST_DER
125static uint8_t
126getclass(uint8_t c)
127{
128	return c >> 6;
129}
130
131static uint8_t
132gettype(uint8_t c)
133{
134	return (c >> 5) & 1;
135}
136#endif
137
138static uint32_t
139gettag(const uint8_t *c, size_t *p, size_t l)
140{
141	uint32_t tag;
142
143	if (*p >= l)
144		return DER_BAD;
145
146	tag = c[(*p)++] & 0x1f;
147
148	if (tag != 0x1f)
149		return tag;
150
151	if (*p >= l)
152		return DER_BAD;
153
154	while (c[*p] >= 0x80) {
155		tag = tag * 128 + c[(*p)++] - 0x80;
156		if (*p >= l)
157			return DER_BAD;
158	}
159	return tag;
160}
161
162static uint32_t
163getlength(const uint8_t *c, size_t *p, size_t l)
164{
165	uint8_t digits, i;
166	size_t len;
167
168	if (*p >= l)
169		return DER_BAD;
170
171	digits = c[(*p)++];
172
173        if ((digits & 0x80) == 0)
174		return digits;
175
176        digits &= 0x7f;
177	len = 0;
178
179	if (*p + digits >= l)
180		return DER_BAD;
181
182	for (i = 0; i < digits; i++)
183		len = (len << 8) | c[(*p)++];
184        return len;
185}
186
187static const char *
188der_tag(char *buf, size_t len, uint32_t tag)
189{
190	if (tag < DER_TAG_LONG)
191		strlcpy(buf, der__tag[tag], len);
192	else
193		snprintf(buf, len, "%#x", tag);
194	return buf;
195}
196
197#ifndef TEST_DER
198static int
199der_data(char *buf, size_t blen, uint32_t tag, const void *q, uint32_t len)
200{
201	const uint8_t *d = q;
202	switch (tag) {
203	case DER_TAG_PRINTABLE_STRING:
204	case DER_TAG_UTF8_STRING:
205	case DER_TAG_IA5_STRING:
206	case DER_TAG_UTCTIME:
207		return snprintf(buf, blen, "%.*s", len, (const char *)q);
208	default:
209		break;
210	}
211
212	for (uint32_t i = 0; i < len; i++) {
213		uint32_t z = i << 1;
214		if (z < blen - 2)
215			snprintf(buf + z, blen - z, "%.2x", d[i]);
216	}
217	return len * 2;
218}
219
220int32_t
221der_offs(struct magic_set *ms, struct magic *m, size_t nbytes)
222{
223	const uint8_t *b = CAST(const void *, ms->search.s);
224	size_t offs = 0, len = ms->search.rm_len ? ms->search.rm_len : nbytes;
225
226	if (gettag(b, &offs, len) == DER_BAD)
227		return -1;
228	DPRINTF(("%s1: %d %zu %u\n", __func__, ms->offset, offs, m->offset));
229
230	uint32_t tlen = getlength(b, &offs, len);
231	if (tlen == DER_BAD)
232		return -1;
233	DPRINTF(("%s2: %d %zu %u\n", __func__, ms->offset, offs, tlen));
234
235	offs += ms->offset + m->offset;
236	DPRINTF(("cont_level = %d\n", m->cont_level));
237#ifdef DEBUG_DER
238	for (size_t i = 0; i < m->cont_level; i++)
239		printf("cont_level[%zu] = %u\n", i, ms->c.li[i].off);
240#endif
241	if (m->cont_level != 0) {
242		if (offs + tlen > nbytes)
243			return DER_BAD;
244		ms->c.li[m->cont_level - 1].off = offs + tlen;
245		DPRINTF(("cont_level[%u] = %u\n", m->cont_level - 1,
246		    ms->c.li[m->cont_level - 1].off));
247	}
248	return offs;
249}
250
251int
252der_cmp(struct magic_set *ms, struct magic *m)
253{
254	const uint8_t *b = CAST(const void *, ms->search.s);
255	const char *s = m->value.s;
256	size_t offs = 0, len = ms->search.s_len;
257	uint32_t tag, tlen;
258	char buf[128];
259
260	tag = gettag(b, &offs, len);
261	if (tag == DER_BAD)
262		return -1;
263
264	tlen = getlength(b, &offs, len);
265	if (tlen == DER_BAD)
266		return -1;
267
268	der_tag(buf, sizeof(buf), tag);
269	if ((ms->flags & MAGIC_DEBUG) != 0)
270		fprintf(stderr, "%s: tag %p got=%s exp=%s\n", __func__, b,
271		    buf, s);
272	size_t slen = strlen(buf);
273
274	if (strncmp(buf, s, slen) != 0)
275		return 0;
276
277	s += slen;
278
279again:
280	switch (*s) {
281	case '\0':
282		return 1;
283	case '=':
284		s++;
285		goto val;
286	default:
287		if (!isdigit((unsigned char)*s))
288			return 0;
289
290		slen = 0;
291		do
292			slen = slen * 10 + *s - '0';
293		while (isdigit((unsigned char)*++s));
294		if ((ms->flags & MAGIC_DEBUG) != 0)
295			fprintf(stderr, "%s: len %zu %u\n", __func__,
296			    slen, tlen);
297		if (tlen != slen)
298			return 0;
299		goto again;
300	}
301val:
302	DPRINTF(("%s: before data %zu %u\n", __func__, offs, tlen));
303	der_data(buf, sizeof(buf), tag, b + offs, tlen);
304	if ((ms->flags & MAGIC_DEBUG) != 0)
305		fprintf(stderr, "%s: data %s %s\n", __func__, buf, s);
306	if (strcmp(buf, s) != 0 && strcmp("x", s) != 0)
307		return 0;
308	strlcpy(ms->ms_value.s, buf, sizeof(ms->ms_value.s));
309	return 1;
310}
311#endif
312
313#ifdef TEST_DER
314static void
315printtag(uint32_t tag, const void *q, uint32_t len)
316{
317	const uint8_t *d = q;
318	switch (tag) {
319	case DER_TAG_PRINTABLE_STRING:
320	case DER_TAG_UTF8_STRING:
321		printf("%.*s\n", len, (const char *)q);
322		return;
323	default:
324		break;
325	}
326
327	for (uint32_t i = 0; i < len; i++)
328		printf("%.2x", d[i]);
329	printf("\n");
330}
331
332static void
333printdata(size_t level, const void *v, size_t x, size_t l)
334{
335	const uint8_t *p = v, *ep = p + l;
336	size_t ox;
337	char buf[128];
338
339	while (p + x < ep) {
340		const uint8_t *q;
341		uint8_t c = getclass(p[x]);
342		uint8_t t = gettype(p[x]);
343		ox = x;
344		if (x != 0)
345		printf("%.2x %.2x %.2x\n", p[x - 1], p[x], p[x + 1]);
346		uint32_t tag = gettag(p, &x, ep - p + x);
347		if (p + x >= ep)
348			break;
349		uint32_t len = getlength(p, &x, ep - p + x);
350
351		printf("%zu %zu-%zu %c,%c,%s,%u:", level, ox, x,
352		    der_class[c], der_type[t],
353		    der_tag(buf, sizeof(buf), tag), len);
354		q = p + x;
355		if (p + len > ep)
356			errx(EXIT_FAILURE, "corrupt der");
357		printtag(tag, q, len);
358		if (t != DER_TYPE_PRIMITIVE)
359			printdata(level + 1, p, x, len + x);
360		x += len;
361	}
362}
363
364int
365main(int argc, char *argv[])
366{
367	int fd;
368	struct stat st;
369	size_t l;
370	void *p;
371
372	if ((fd = open(argv[1], O_RDONLY)) == -1)
373		err(EXIT_FAILURE, "open `%s'", argv[1]);
374	if (fstat(fd, &st) == -1)
375		err(EXIT_FAILURE, "stat `%s'", argv[1]);
376	l = (size_t)st.st_size;
377	if ((p = mmap(NULL, l, PROT_READ, MAP_FILE, fd, 0)) == MAP_FAILED)
378		err(EXIT_FAILURE, "mmap `%s'", argv[1]);
379
380	printdata(0, p, 0, l);
381	munmap(p, l);
382	return 0;
383}
384#endif
385