1 /* Copyright (c) 2014, Google Inc. 2 * 3 * Permission to use, copy, modify, and/or distribute this software for any 4 * purpose with or without fee is hereby granted, provided that the above 5 * copyright notice and this permission notice appear in all copies. 6 * 7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY 10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION 12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN 13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ 14 15 #include <openssl/bytestring.h> 16 17 #include <string.h> 18 19 #include "internal.h" 20 21 22 /* kMaxDepth is a just a sanity limit. The code should be such that the length 23 * of the input being processes always decreases. None the less, a very large 24 * input could otherwise cause the stack to overflow. */ 25 static const unsigned kMaxDepth = 2048; 26 27 /* cbs_find_ber walks an ASN.1 structure in |orig_in| and sets |*ber_found| 28 * depending on whether an indefinite length element was found. The value of 29 * |in| is not changed. It returns one on success (i.e. |*ber_found| was set) 30 * and zero on error. */ 31 static int cbs_find_ber(CBS *orig_in, char *ber_found, unsigned depth) { 32 CBS in; 33 34 if (depth > kMaxDepth) { 35 return 0; 36 } 37 38 CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in)); 39 *ber_found = 0; 40 41 while (CBS_len(&in) > 0) { 42 CBS contents; 43 unsigned tag; 44 size_t header_len; 45 46 if (!CBS_get_any_ber_asn1_element(&in, &contents, &tag, &header_len)) { 47 return 0; 48 } 49 if (CBS_len(&contents) == header_len && 50 header_len > 0 && 51 CBS_data(&contents)[header_len-1] == 0x80) { 52 *ber_found = 1; 53 return 1; 54 } 55 if (tag & CBS_ASN1_CONSTRUCTED) { 56 if (!CBS_skip(&contents, header_len) || 57 !cbs_find_ber(&contents, ber_found, depth + 1)) { 58 return 0; 59 } 60 } 61 } 62 63 return 1; 64 } 65 66 /* is_primitive_type returns true if |tag| likely a primitive type. Normally 67 * one can just test the "constructed" bit in the tag but, in BER, even 68 * primitive tags can have the constructed bit if they have indefinite 69 * length. */ 70 static char is_primitive_type(unsigned tag) { 71 return (tag & 0xc0) == 0 && 72 (tag & 0x1f) != (CBS_ASN1_SEQUENCE & 0x1f) && 73 (tag & 0x1f) != (CBS_ASN1_SET & 0x1f); 74 } 75 76 /* is_eoc returns true if |header_len| and |contents|, as returned by 77 * |CBS_get_any_ber_asn1_element|, indicate an "end of contents" (EOC) value. */ 78 static char is_eoc(size_t header_len, CBS *contents) { 79 return header_len == 2 && CBS_len(contents) == 2 && 80 memcmp(CBS_data(contents), "\x00\x00", 2) == 0; 81 } 82 83 /* cbs_convert_ber reads BER data from |in| and writes DER data to |out|. If 84 * |squash_header| is set then the top-level of elements from |in| will not 85 * have their headers written. This is used when concatenating the fragments of 86 * an indefinite length, primitive value. If |looking_for_eoc| is set then any 87 * EOC elements found will cause the function to return after consuming it. 88 * It returns one on success and zero on error. */ 89 static int cbs_convert_ber(CBS *in, CBB *out, char squash_header, 90 char looking_for_eoc, unsigned depth) { 91 if (depth > kMaxDepth) { 92 return 0; 93 } 94 95 while (CBS_len(in) > 0) { 96 CBS contents; 97 unsigned tag; 98 size_t header_len; 99 CBB *out_contents, out_contents_storage; 100 101 if (!CBS_get_any_ber_asn1_element(in, &contents, &tag, &header_len)) { 102 return 0; 103 } 104 out_contents = out; 105 106 if (CBS_len(&contents) == header_len) { 107 if (is_eoc(header_len, &contents)) { 108 return looking_for_eoc; 109 } 110 111 if (header_len > 0 && CBS_data(&contents)[header_len - 1] == 0x80) { 112 /* This is an indefinite length element. If it's a SEQUENCE or SET then 113 * we just need to write the out the contents as normal, but with a 114 * concrete length prefix. 115 * 116 * If it's a something else then the contents will be a series of BER 117 * elements of the same type which need to be concatenated. */ 118 const char context_specific = (tag & 0xc0) == 0x80; 119 char squash_child_headers = is_primitive_type(tag); 120 121 /* This is a hack, but it sufficies to handle NSS's output. If we find 122 * an indefinite length, context-specific tag with a definite, primitive 123 * tag inside it, then we assume that the context-specific tag is 124 * implicit and the tags within are fragments of a primitive type that 125 * need to be concatenated. */ 126 if (context_specific && (tag & CBS_ASN1_CONSTRUCTED)) { 127 CBS in_copy, inner_contents; 128 unsigned inner_tag; 129 size_t inner_header_len; 130 131 CBS_init(&in_copy, CBS_data(in), CBS_len(in)); 132 if (!CBS_get_any_ber_asn1_element(&in_copy, &inner_contents, 133 &inner_tag, &inner_header_len)) { 134 return 0; 135 } 136 if (CBS_len(&inner_contents) > inner_header_len && 137 is_primitive_type(inner_tag)) { 138 squash_child_headers = 1; 139 } 140 } 141 142 if (!squash_header) { 143 unsigned out_tag = tag; 144 if (squash_child_headers) { 145 out_tag &= ~CBS_ASN1_CONSTRUCTED; 146 } 147 if (!CBB_add_asn1(out, &out_contents_storage, out_tag)) { 148 return 0; 149 } 150 out_contents = &out_contents_storage; 151 } 152 153 if (!cbs_convert_ber(in, out_contents, 154 squash_child_headers, 155 1 /* looking for eoc */, depth + 1)) { 156 return 0; 157 } 158 if (out_contents != out && !CBB_flush(out)) { 159 return 0; 160 } 161 continue; 162 } 163 } 164 165 if (!squash_header) { 166 if (!CBB_add_asn1(out, &out_contents_storage, tag)) { 167 return 0; 168 } 169 out_contents = &out_contents_storage; 170 } 171 172 if (!CBS_skip(&contents, header_len)) { 173 return 0; 174 } 175 176 if (tag & CBS_ASN1_CONSTRUCTED) { 177 if (!cbs_convert_ber(&contents, out_contents, 0 /* don't squash header */, 178 0 /* not looking for eoc */, depth + 1)) { 179 return 0; 180 } 181 } else { 182 if (!CBB_add_bytes(out_contents, CBS_data(&contents), 183 CBS_len(&contents))) { 184 return 0; 185 } 186 } 187 188 if (out_contents != out && !CBB_flush(out)) { 189 return 0; 190 } 191 } 192 193 return looking_for_eoc == 0; 194 } 195 196 int CBS_asn1_ber_to_der(CBS *in, uint8_t **out, size_t *out_len) { 197 CBB cbb; 198 199 /* First, do a quick walk to find any indefinite-length elements. Most of the 200 * time we hope that there aren't any and thus we can quickly return. */ 201 char conversion_needed; 202 if (!cbs_find_ber(in, &conversion_needed, 0)) { 203 return 0; 204 } 205 206 if (!conversion_needed) { 207 *out = NULL; 208 *out_len = 0; 209 return 1; 210 } 211 212 if (!CBB_init(&cbb, CBS_len(in))) { 213 return 0; 214 } 215 if (!cbs_convert_ber(in, &cbb, 0, 0, 0)) { 216 CBB_cleanup(&cbb); 217 return 0; 218 } 219 220 return CBB_finish(&cbb, out, out_len); 221 } 222
