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/* Copyright (c) 2014, Google Inc.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
#include <openssl/bytestring.h>
#include <string.h>
#include "internal.h"
/* kMaxDepth is a just a sanity limit. The code should be such that the length
* of the input being processes always decreases. None the less, a very large
* input could otherwise cause the stack to overflow. */
static const unsigned kMaxDepth = 2048;
/* cbs_find_ber walks an ASN.1 structure in |orig_in| and sets |*ber_found|
* depending on whether an indefinite length element was found. The value of
* |in| is not changed. It returns one on success (i.e. |*ber_found| was set)
* and zero on error. */
static int cbs_find_ber(CBS *orig_in, char *ber_found, unsigned depth) {
CBS in;
if (depth > kMaxDepth) {
return 0;
}
CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in));
*ber_found = 0;
while (CBS_len(&in) > 0) {
CBS contents;
unsigned tag;
size_t header_len;
if (!CBS_get_any_ber_asn1_element(&in, &contents, &tag, &header_len)) {
return 0;
}
if (CBS_len(&contents) == header_len &&
header_len > 0 &&
CBS_data(&contents)[header_len-1] == 0x80) {
*ber_found = 1;
return 1;
}
if (tag & CBS_ASN1_CONSTRUCTED) {
if (!CBS_skip(&contents, header_len) ||
!cbs_find_ber(&contents, ber_found, depth + 1)) {
return 0;
}
}
}
return 1;
}
/* is_primitive_type returns true if |tag| likely a primitive type. Normally
* one can just test the "constructed" bit in the tag but, in BER, even
* primitive tags can have the constructed bit if they have indefinite
* length. */
static char is_primitive_type(unsigned tag) {
return (tag & 0xc0) == 0 &&
(tag & 0x1f) != (CBS_ASN1_SEQUENCE & 0x1f) &&
(tag & 0x1f) != (CBS_ASN1_SET & 0x1f);
}
/* is_eoc returns true if |header_len| and |contents|, as returned by
* |CBS_get_any_ber_asn1_element|, indicate an "end of contents" (EOC) value. */
static char is_eoc(size_t header_len, CBS *contents) {
return header_len == 2 && CBS_len(contents) == 2 &&
memcmp(CBS_data(contents), "\x00\x00", 2) == 0;
}
/* cbs_convert_ber reads BER data from |in| and writes DER data to |out|. If
* |squash_header| is set then the top-level of elements from |in| will not
* have their headers written. This is used when concatenating the fragments of
* an indefinite length, primitive value. If |looking_for_eoc| is set then any
* EOC elements found will cause the function to return after consuming it.
* It returns one on success and zero on error. */
static int cbs_convert_ber(CBS *in, CBB *out, char squash_header,
char looking_for_eoc, unsigned depth) {
if (depth > kMaxDepth) {
return 0;
}
while (CBS_len(in) > 0) {
CBS contents;
unsigned tag;
size_t header_len;
CBB *out_contents, out_contents_storage;
if (!CBS_get_any_ber_asn1_element(in, &contents, &tag, &header_len)) {
return 0;
}
out_contents = out;
if (CBS_len(&contents) == header_len) {
if (is_eoc(header_len, &contents)) {
return looking_for_eoc;
}
if (header_len > 0 && CBS_data(&contents)[header_len - 1] == 0x80) {
/* This is an indefinite length element. If it's a SEQUENCE or SET then
* we just need to write the out the contents as normal, but with a
* concrete length prefix.
*
* If it's a something else then the contents will be a series of BER
* elements of the same type which need to be concatenated. */
const char context_specific = (tag & 0xc0) == 0x80;
char squash_child_headers = is_primitive_type(tag);
/* This is a hack, but it sufficies to handle NSS's output. If we find
* an indefinite length, context-specific tag with a definite, primtive
* tag inside it, then we assume that the context-specific tag is
* implicit and the tags within are fragments of a primitive type that
* need to be concatenated. */
if (context_specific && (tag & CBS_ASN1_CONSTRUCTED)) {
CBS in_copy, inner_contents;
unsigned inner_tag;
size_t inner_header_len;
CBS_init(&in_copy, CBS_data(in), CBS_len(in));
if (!CBS_get_any_ber_asn1_element(&in_copy, &inner_contents,
&inner_tag, &inner_header_len)) {
return 0;
}
if (CBS_len(&inner_contents) > inner_header_len &&
is_primitive_type(inner_tag)) {
squash_child_headers = 1;
}
}
if (!squash_header) {
unsigned out_tag = tag;
if (squash_child_headers) {
out_tag &= ~CBS_ASN1_CONSTRUCTED;
}
if (!CBB_add_asn1(out, &out_contents_storage, out_tag)) {
return 0;
}
out_contents = &out_contents_storage;
}
if (!cbs_convert_ber(in, out_contents,
squash_child_headers,
1 /* looking for eoc */, depth + 1)) {
return 0;
}
if (out_contents != out && !CBB_flush(out)) {
return 0;
}
continue;
}
}
if (!squash_header) {
if (!CBB_add_asn1(out, &out_contents_storage, tag)) {
return 0;
}
out_contents = &out_contents_storage;
}
if (!CBS_skip(&contents, header_len)) {
return 0;
}
if (tag & CBS_ASN1_CONSTRUCTED) {
if (!cbs_convert_ber(&contents, out_contents, 0 /* don't squash header */,
0 /* not looking for eoc */, depth + 1)) {
return 0;
}
} else {
if (!CBB_add_bytes(out_contents, CBS_data(&contents),
CBS_len(&contents))) {
return 0;
}
}
if (out_contents != out && !CBB_flush(out)) {
return 0;
}
}
return looking_for_eoc == 0;
}
int CBS_asn1_ber_to_der(CBS *in, uint8_t **out, size_t *out_len) {
CBB cbb;
/* First, do a quick walk to find any indefinite-length elements. Most of the
* time we hope that there aren't any and thus we can quickly return. */
char conversion_needed;
if (!cbs_find_ber(in, &conversion_needed, 0)) {
return 0;
}
if (!conversion_needed) {
*out = NULL;
*out_len = 0;
return 1;
}
if (!CBB_init(&cbb, CBS_len(in))) {
return 0;
}
if (!cbs_convert_ber(in, &cbb, 0, 0, 0)) {
CBB_cleanup(&cbb);
return 0;
}
return CBB_finish(&cbb, out, out_len);
}
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