270 lines
7.2 KiB
C
270 lines
7.2 KiB
C
/* $OpenBSD: bs_ber.c,v 1.11 2021/05/16 10:58:27 jsing Exp $ */
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/*
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* Copyright (c) 2014, Google Inc.
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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#include <string.h>
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#include "bytestring.h"
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/*
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* kMaxDepth is a just a sanity limit. The code should be such that the length
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* of the input being processes always decreases. None the less, a very large
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* input could otherwise cause the stack to overflow.
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*/
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static const unsigned int kMaxDepth = 2048;
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/* Non-strict version that allows a relaxed DER with indefinite form. */
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static int
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cbs_nonstrict_get_any_asn1_element(CBS *cbs, CBS *out, unsigned int *out_tag,
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size_t *out_header_len)
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{
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return cbs_get_any_asn1_element_internal(cbs, out,
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out_tag, out_header_len, 0);
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}
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/*
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* cbs_find_indefinite walks an ASN.1 structure in |orig_in| and sets
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* |*indefinite_found| depending on whether an indefinite length element was
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* found. The value of |orig_in| is not modified.
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*
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* Returns one on success (i.e. |*indefinite_found| was set) and zero on error.
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*/
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static int
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cbs_find_indefinite(const CBS *orig_in, char *indefinite_found,
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unsigned int depth)
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{
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CBS in;
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if (depth > kMaxDepth)
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return 0;
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CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in));
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while (CBS_len(&in) > 0) {
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CBS contents;
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unsigned int tag;
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size_t header_len;
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if (!cbs_nonstrict_get_any_asn1_element(&in, &contents, &tag,
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&header_len))
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return 0;
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/* Indefinite form not allowed by DER. */
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if (CBS_len(&contents) == header_len && header_len > 0 &&
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CBS_data(&contents)[header_len - 1] == 0x80) {
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*indefinite_found = 1;
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return 1;
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}
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if (tag & CBS_ASN1_CONSTRUCTED) {
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if (!CBS_skip(&contents, header_len) ||
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!cbs_find_indefinite(&contents, indefinite_found,
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depth + 1))
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return 0;
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}
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}
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*indefinite_found = 0;
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return 1;
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}
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/*
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* is_primitive_type returns true if |tag| likely a primitive type. Normally
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* one can just test the "constructed" bit in the tag but, in BER, even
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* primitive tags can have the constructed bit if they have indefinite
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* length.
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*/
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static char
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is_primitive_type(unsigned int tag)
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{
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return (tag & 0xc0) == 0 &&
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(tag & 0x1f) != (CBS_ASN1_SEQUENCE & 0x1f) &&
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(tag & 0x1f) != (CBS_ASN1_SET & 0x1f);
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}
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/*
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* is_eoc returns true if |header_len| and |contents|, as returned by
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* |cbs_nonstrict_get_any_asn1_element|, indicate an "end of contents" (EOC)
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* value.
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*/
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static char
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is_eoc(size_t header_len, CBS *contents)
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{
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const unsigned char eoc[] = {0x0, 0x0};
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return header_len == 2 && CBS_mem_equal(contents, eoc, 2);
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}
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/*
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* cbs_convert_indefinite reads data with DER encoding (but relaxed to allow
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* indefinite form) from |in| and writes definite form DER data to |out|. If
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* |squash_header| is set then the top-level of elements from |in| will not
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* have their headers written. This is used when concatenating the fragments of
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* an indefinite length, primitive value. If |looking_for_eoc| is set then any
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* EOC elements found will cause the function to return after consuming it.
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* It returns one on success and zero on error.
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*/
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static int
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cbs_convert_indefinite(CBS *in, CBB *out, char squash_header,
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char looking_for_eoc, unsigned int depth)
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{
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if (depth > kMaxDepth)
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return 0;
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while (CBS_len(in) > 0) {
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CBS contents;
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unsigned int tag;
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size_t header_len;
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CBB *out_contents, out_contents_storage;
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if (!cbs_nonstrict_get_any_asn1_element(in, &contents, &tag,
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&header_len))
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return 0;
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out_contents = out;
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if (CBS_len(&contents) == header_len) {
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if (is_eoc(header_len, &contents))
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return looking_for_eoc;
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if (header_len > 0 &&
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CBS_data(&contents)[header_len - 1] == 0x80) {
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/*
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* This is an indefinite length element. If
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* it's a SEQUENCE or SET then we just need to
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* write the out the contents as normal, but
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* with a concrete length prefix.
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*
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* If it's a something else then the contents
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* will be a series of DER elements of the same
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* type which need to be concatenated.
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*/
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const char context_specific = (tag & 0xc0)
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== 0x80;
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char squash_child_headers =
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is_primitive_type(tag);
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/*
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* This is a hack, but it sufficies to handle
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* NSS's output. If we find an indefinite
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* length, context-specific tag with a definite,
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* primtive tag inside it, then we assume that
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* the context-specific tag is implicit and the
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* tags within are fragments of a primitive type
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* that need to be concatenated.
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*/
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if (context_specific &&
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(tag & CBS_ASN1_CONSTRUCTED)) {
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CBS in_copy, inner_contents;
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unsigned int inner_tag;
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size_t inner_header_len;
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CBS_init(&in_copy, CBS_data(in),
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CBS_len(in));
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if (!cbs_nonstrict_get_any_asn1_element(
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&in_copy, &inner_contents,
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&inner_tag, &inner_header_len))
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return 0;
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if (CBS_len(&inner_contents) >
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inner_header_len &&
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is_primitive_type(inner_tag))
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squash_child_headers = 1;
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}
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if (!squash_header) {
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unsigned int out_tag = tag;
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if (squash_child_headers)
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out_tag &=
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~CBS_ASN1_CONSTRUCTED;
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if (!CBB_add_asn1(out,
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&out_contents_storage, out_tag))
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return 0;
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out_contents = &out_contents_storage;
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}
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if (!cbs_convert_indefinite(in, out_contents,
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squash_child_headers,
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1 /* looking for eoc */, depth + 1))
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return 0;
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if (out_contents != out && !CBB_flush(out))
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return 0;
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continue;
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}
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}
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if (!squash_header) {
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if (!CBB_add_asn1(out, &out_contents_storage, tag))
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return 0;
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out_contents = &out_contents_storage;
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}
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if (!CBS_skip(&contents, header_len))
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return 0;
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if (tag & CBS_ASN1_CONSTRUCTED) {
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if (!cbs_convert_indefinite(&contents, out_contents,
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0 /* don't squash header */,
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0 /* not looking for eoc */, depth + 1))
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return 0;
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} else {
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if (!CBB_add_bytes(out_contents, CBS_data(&contents),
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CBS_len(&contents)))
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return 0;
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}
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if (out_contents != out && !CBB_flush(out))
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return 0;
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}
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return looking_for_eoc == 0;
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}
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int
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CBS_asn1_indefinite_to_definite(CBS *in, uint8_t **out, size_t *out_len)
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{
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CBB cbb;
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/*
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* First, do a quick walk to find any indefinite-length elements. Most
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* of the time we hope that there aren't any and thus we can quickly
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* return.
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*/
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char conversion_needed;
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if (!cbs_find_indefinite(in, &conversion_needed, 0))
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return 0;
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if (!conversion_needed) {
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*out = NULL;
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*out_len = 0;
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return 1;
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}
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if (!CBB_init(&cbb, CBS_len(in)))
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return 0;
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if (!cbs_convert_indefinite(in, &cbb, 0, 0, 0)) {
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CBB_cleanup(&cbb);
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return 0;
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}
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return CBB_finish(&cbb, out, out_len);
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}
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