summaryrefslogtreecommitdiffstats
path: root/src/ber_tlv_length.c
blob: b87e75e0469887ee7d06bfb5f83b99b8120a5374 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
/*-
 * Copyright (c) 2003, 2004 Lev Walkin <vlm@lionet.info>. All rights reserved.
 * Redistribution and modifications are permitted subject to BSD license.
 */
#include <asn_internal.h>
#include <ber_tlv_length.h>
#include <ber_tlv_tag.h>

ssize_t
ber_fetch_length(int _is_constructed, const void *bufptr, size_t size,
		ber_tlv_len_t *len_r) {
	const uint8_t *buf = (const uint8_t *)bufptr;
	unsigned oct;

	if(size == 0)
		return 0;	/* Want more */

	oct = *(const uint8_t *)buf;
	if((oct & 0x80) == 0) {
		/*
		 * Short definite length.
		 */
		*len_r = oct;	/* & 0x7F */
		return 1;
	} else {
		ber_tlv_len_t len;
		size_t skipped;

		if(_is_constructed && oct == 0x80) {
			*len_r = -1;	/* Indefinite length */
			return 1;
		}

		if(oct == 0xff) {
			/* Reserved in standard for future use. */
			return -1;
		}

		oct &= 0x7F;	/* Leave only the 7 LS bits */
		for(len = 0, buf++, skipped = 1;
			oct && (++skipped <= size); buf++, oct--) {

			len = (len << 8) | *buf;
			if(len < 0
			|| (len >> ((8 * sizeof(len)) - 8) && oct > 1)) {
				/*
				 * Too large length value.
				 */
				return -1;
			}
		}

		if(oct == 0) {
			ber_tlv_len_t lenplusepsilon = (size_t)len + 1024;
			/*
			 * Here length may be very close or equal to 2G.
			 * However, the arithmetics used in some decoders
			 * may add some (small) quantities to the length,
			 * to check the resulting value against some limits.
			 * This may result in integer wrap-around, which
			 * we try to avoid by checking it earlier here.
			 */
			if(lenplusepsilon < 0) {
				/* Too large length value */
				return -1;
			}

			*len_r = len;
			return skipped;
		}

		return 0;	/* Want more */
	}

}

ssize_t
ber_skip_length(asn_codec_ctx_t *opt_codec_ctx,
		int _is_constructed, const void *ptr, size_t size) {
	ber_tlv_len_t vlen;	/* Length of V in TLV */
	ssize_t tl;		/* Length of L in TLV */
	ssize_t ll;		/* Length of L in TLV */
	size_t skip;

	/*
	 * Make sure we didn't exceed the maximum stack size.
	 */
	if(_ASN_STACK_OVERFLOW_CHECK(opt_codec_ctx))
		return -1;

	/*
	 * Determine the size of L in TLV.
	 */
	ll = ber_fetch_length(_is_constructed, ptr, size, &vlen);
	if(ll <= 0) return ll;

	/*
	 * Definite length.
	 */
	if(vlen >= 0) {
		skip = ll + vlen;
		if(skip > size)
			return 0;	/* Want more */
		return skip;
	}

	/*
	 * Indefinite length!
	 */
	ASN_DEBUG("Skipping indefinite length");
	for(skip = ll, ptr = ((const char *)ptr) + ll, size -= ll;;) {
		ber_tlv_tag_t tag;

		/* Fetch the tag */
		tl = ber_fetch_tag(ptr, size, &tag);
		if(tl <= 0) return tl;

		ll = ber_skip_length(opt_codec_ctx,
			BER_TLV_CONSTRUCTED(ptr),
			((const char *)ptr) + tl, size - tl);
		if(ll <= 0) return ll;

		skip += tl + ll;

		/*
		 * This may be the end of the indefinite length structure,
		 * two consecutive 0 octets.
		 * Check if it is true.
		 */
		if(((const uint8_t *)ptr)[0] == 0
		&& ((const uint8_t *)ptr)[1] == 0)
			return skip;

		ptr = ((const char *)ptr) + tl + ll;
		size -= tl + ll;
 	}

	/* UNREACHABLE */
}

size_t
der_tlv_length_serialize(ber_tlv_len_t len, void *bufp, size_t size) {
	size_t required_size;	/* Size of len encoding */
	uint8_t *buf = (uint8_t *)bufp;
	uint8_t *end;
	size_t i;

	if(len <= 127) {
		/* Encoded in 1 octet */
		if(size) *buf = (uint8_t)len;
		return 1;
	}

	/*
	 * Compute the size of the subsequent bytes.
	 */
	for(required_size = 1, i = 8; i < 8 * sizeof(len); i += 8) {
		if(len >> i)
			required_size++;
		else
			break;
	}

	if(size <= required_size)
		return required_size + 1;

	*buf++ = (uint8_t)(0x80 | required_size);  /* Length of the encoding */

	/*
	 * Produce the len encoding, space permitting.
	 */
	end = buf + required_size;
	for(i -= 8; buf < end; i -= 8, buf++)
		*buf = (uint8_t)(len >> i);

	return required_size + 1;
}