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/* $OpenBSD: bs_ber.c,v 1.2 2021/12/15 18:02:39 jsing Exp $ */
/*
* 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 <string.h>
#include "bytestring.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 int kMaxDepth = 2048;
/* Non-strict version that allows a relaxed DER with indefinite form. */
static int
cbs_nonstrict_get_any_asn1_element(CBS *cbs, CBS *out, unsigned int *out_tag,
size_t *out_header_len)
{
return cbs_get_any_asn1_element_internal(cbs, out,
out_tag, out_header_len, 0);
}
/*
* cbs_find_indefinite walks an ASN.1 structure in |orig_in| and sets
* |*indefinite_found| depending on whether an indefinite length element was
* found. The value of |orig_in| is not modified.
*
* Returns one on success (i.e. |*indefinite_found| was set) and zero on error.
*/
static int
cbs_find_indefinite(const CBS *orig_in, char *indefinite_found,
unsigned int depth)
{
CBS in;
if (depth > kMaxDepth)
return 0;
CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in));
while (CBS_len(&in) > 0) {
CBS contents;
unsigned int tag;
size_t header_len;
if (!cbs_nonstrict_get_any_asn1_element(&in, &contents, &tag,
&header_len))
return 0;
/* Indefinite form not allowed by DER. */
if (CBS_len(&contents) == header_len && header_len > 0 &&
CBS_data(&contents)[header_len - 1] == 0x80) {
*indefinite_found = 1;
return 1;
}
if (tag & CBS_ASN1_CONSTRUCTED) {
if (!CBS_skip(&contents, header_len) ||
!cbs_find_indefinite(&contents, indefinite_found,
depth + 1))
return 0;
}
}
*indefinite_found = 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 int 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_nonstrict_get_any_asn1_element|, indicate an "end of contents" (EOC)
* value.
*/
static char
is_eoc(size_t header_len, CBS *contents)
{
const unsigned char eoc[] = {0x0, 0x0};
return header_len == 2 && CBS_mem_equal(contents, eoc, 2);
}
/*
* cbs_convert_indefinite reads data with DER encoding (but relaxed to allow
* indefinite form) from |in| and writes definite form 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_indefinite(CBS *in, CBB *out, char squash_header,
char looking_for_eoc, unsigned int depth)
{
if (depth > kMaxDepth)
return 0;
while (CBS_len(in) > 0) {
CBS contents;
unsigned int tag;
size_t header_len;
CBB *out_contents, out_contents_storage;
if (!cbs_nonstrict_get_any_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 DER 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 int inner_tag;
size_t inner_header_len;
CBS_init(&in_copy, CBS_data(in),
CBS_len(in));
if (!cbs_nonstrict_get_any_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 int 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_indefinite(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_indefinite(&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_indefinite_to_definite(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_indefinite(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_indefinite(in, &cbb, 0, 0, 0)) {
CBB_cleanup(&cbb);
return 0;
}
return CBB_finish(&cbb, out, out_len);
}
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