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mbedtls/library/x509write_crt.c
Hanno Becker eeea9ead3c Perform CRT writing in-place on the output buffer 
The CRT writing routine mbedtls_x509write_crt_der() prepares the TBS
(to-be-signed) part of the CRT in a temporary stack-allocated buffer,
copying it to the actual output buffer at the end of the routine.

This comes at the cost of a very large stack buffer. Moreover, its size
must be hardcoded to an upper bound for the lengths of all CRTs to be
written through the routine. So far, this upper bound was set to 2Kb, which
isn't sufficient some larger certificates, as was reported e.g. in #2631.

This commit fixes this by changing mbedtls_x509write_crt_der() to write
the certificate in-place in the output buffer, thereby avoiding the use
of a statically sized stack buffer for the TBS.

Fixes #2631.
2020-07-10 17:51:54 +00:00

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/*
* X.509 certificate writing
*
* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
*
* This file is provided under the Apache License 2.0, or the
* GNU General Public License v2.0 or later.
*
* **********
* Apache License 2.0:
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* **********
*
* **********
* GNU General Public License v2.0 or later:
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*
* **********
*
* This file is part of mbed TLS (https://tls.mbed.org)
*/
/*
* References:
* - certificates: RFC 5280, updated by RFC 6818
* - CSRs: PKCS#10 v1.7 aka RFC 2986
* - attributes: PKCS#9 v2.0 aka RFC 2985
*/
#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
#if defined(MBEDTLS_X509_CRT_WRITE_C)
#include "mbedtls/x509_crt.h"
#include "mbedtls/oid.h"
#include "mbedtls/asn1write.h"
#include "mbedtls/sha1.h"
#include "mbedtls/platform_util.h"
#include <string.h>
#if defined(MBEDTLS_PEM_WRITE_C)
#include "mbedtls/pem.h"
#endif /* MBEDTLS_PEM_WRITE_C */
/*
* For the currently used signature algorithms the buffer to store any signature
* must be at least of size MAX(MBEDTLS_ECDSA_MAX_LEN, MBEDTLS_MPI_MAX_SIZE)
*/
#if MBEDTLS_ECDSA_MAX_LEN > MBEDTLS_MPI_MAX_SIZE
#define SIGNATURE_MAX_SIZE MBEDTLS_ECDSA_MAX_LEN
#else
#define SIGNATURE_MAX_SIZE MBEDTLS_MPI_MAX_SIZE
#endif
void mbedtls_x509write_crt_init( mbedtls_x509write_cert *ctx )
{
memset( ctx, 0, sizeof( mbedtls_x509write_cert ) );
mbedtls_mpi_init( &ctx->serial );
ctx->version = MBEDTLS_X509_CRT_VERSION_3;
}
void mbedtls_x509write_crt_free( mbedtls_x509write_cert *ctx )
{
mbedtls_mpi_free( &ctx->serial );
mbedtls_asn1_free_named_data_list( &ctx->subject );
mbedtls_asn1_free_named_data_list( &ctx->issuer );
mbedtls_asn1_free_named_data_list( &ctx->extensions );
mbedtls_platform_zeroize( ctx, sizeof( mbedtls_x509write_cert ) );
}
void mbedtls_x509write_crt_set_version( mbedtls_x509write_cert *ctx,
int version )
{
ctx->version = version;
}
void mbedtls_x509write_crt_set_md_alg( mbedtls_x509write_cert *ctx,
mbedtls_md_type_t md_alg )
{
ctx->md_alg = md_alg;
}
void mbedtls_x509write_crt_set_subject_key( mbedtls_x509write_cert *ctx,
mbedtls_pk_context *key )
{
ctx->subject_key = key;
}
void mbedtls_x509write_crt_set_issuer_key( mbedtls_x509write_cert *ctx,
mbedtls_pk_context *key )
{
ctx->issuer_key = key;
}
int mbedtls_x509write_crt_set_subject_name( mbedtls_x509write_cert *ctx,
const char *subject_name )
{
return mbedtls_x509_string_to_names( &ctx->subject, subject_name );
}
int mbedtls_x509write_crt_set_issuer_name( mbedtls_x509write_cert *ctx,
const char *issuer_name )
{
return mbedtls_x509_string_to_names( &ctx->issuer, issuer_name );
}
int mbedtls_x509write_crt_set_serial( mbedtls_x509write_cert *ctx,
const mbedtls_mpi *serial )
{
int ret;
if( ( ret = mbedtls_mpi_copy( &ctx->serial, serial ) ) != 0 )
return( ret );
return( 0 );
}
int mbedtls_x509write_crt_set_validity( mbedtls_x509write_cert *ctx,
const char *not_before,
const char *not_after )
{
if( strlen( not_before ) != MBEDTLS_X509_RFC5280_UTC_TIME_LEN - 1 ||
strlen( not_after ) != MBEDTLS_X509_RFC5280_UTC_TIME_LEN - 1 )
{
return( MBEDTLS_ERR_X509_BAD_INPUT_DATA );
}
strncpy( ctx->not_before, not_before, MBEDTLS_X509_RFC5280_UTC_TIME_LEN );
strncpy( ctx->not_after , not_after , MBEDTLS_X509_RFC5280_UTC_TIME_LEN );
ctx->not_before[MBEDTLS_X509_RFC5280_UTC_TIME_LEN - 1] = 'Z';
ctx->not_after[MBEDTLS_X509_RFC5280_UTC_TIME_LEN - 1] = 'Z';
return( 0 );
}
int mbedtls_x509write_crt_set_extension( mbedtls_x509write_cert *ctx,
const char *oid, size_t oid_len,
int critical,
const unsigned char *val, size_t val_len )
{
return( mbedtls_x509_set_extension( &ctx->extensions, oid, oid_len,
critical, val, val_len ) );
}
int mbedtls_x509write_crt_set_basic_constraints( mbedtls_x509write_cert *ctx,
int is_ca, int max_pathlen )
{
int ret;
unsigned char buf[9];
unsigned char *c = buf + sizeof(buf);
size_t len = 0;
memset( buf, 0, sizeof(buf) );
if( is_ca && max_pathlen > 127 )
return( MBEDTLS_ERR_X509_BAD_INPUT_DATA );
if( is_ca )
{
if( max_pathlen >= 0 )
{
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, buf,
max_pathlen ) );
}
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_bool( &c, buf, 1 ) );
}
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, buf,
MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE ) );
return(
mbedtls_x509write_crt_set_extension( ctx, MBEDTLS_OID_BASIC_CONSTRAINTS,
MBEDTLS_OID_SIZE( MBEDTLS_OID_BASIC_CONSTRAINTS ),
0, buf + sizeof(buf) - len, len ) );
}
#if defined(MBEDTLS_SHA1_C)
int mbedtls_x509write_crt_set_subject_key_identifier( mbedtls_x509write_cert *ctx )
{
int ret;
unsigned char buf[MBEDTLS_MPI_MAX_SIZE * 2 + 20]; /* tag, length + 2xMPI */
unsigned char *c = buf + sizeof(buf);
size_t len = 0;
memset( buf, 0, sizeof(buf) );
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_pk_write_pubkey( &c, buf, ctx->subject_key ) );
ret = mbedtls_sha1_ret( buf + sizeof( buf ) - len, len,
buf + sizeof( buf ) - 20 );
if( ret != 0 )
return( ret );
c = buf + sizeof( buf ) - 20;
len = 20;
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_asn1_write_tag( &c, buf, MBEDTLS_ASN1_OCTET_STRING ) );
return mbedtls_x509write_crt_set_extension( ctx,
MBEDTLS_OID_SUBJECT_KEY_IDENTIFIER,
MBEDTLS_OID_SIZE( MBEDTLS_OID_SUBJECT_KEY_IDENTIFIER ),
0, buf + sizeof(buf) - len, len );
}
int mbedtls_x509write_crt_set_authority_key_identifier( mbedtls_x509write_cert *ctx )
{
int ret;
unsigned char buf[MBEDTLS_MPI_MAX_SIZE * 2 + 20]; /* tag, length + 2xMPI */
unsigned char *c = buf + sizeof( buf );
size_t len = 0;
memset( buf, 0, sizeof(buf) );
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_pk_write_pubkey( &c, buf, ctx->issuer_key ) );
ret = mbedtls_sha1_ret( buf + sizeof( buf ) - len, len,
buf + sizeof( buf ) - 20 );
if( ret != 0 )
return( ret );
c = buf + sizeof( buf ) - 20;
len = 20;
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_asn1_write_tag( &c, buf, MBEDTLS_ASN1_CONTEXT_SPECIFIC | 0 ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_asn1_write_tag( &c, buf,
MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE ) );
return mbedtls_x509write_crt_set_extension(
ctx, MBEDTLS_OID_AUTHORITY_KEY_IDENTIFIER,
MBEDTLS_OID_SIZE( MBEDTLS_OID_AUTHORITY_KEY_IDENTIFIER ),
0, buf + sizeof( buf ) - len, len );
}
#endif /* MBEDTLS_SHA1_C */
static size_t crt_get_unused_bits_for_named_bitstring( unsigned char bitstring,
size_t bit_offset )
{
size_t unused_bits;
/* Count the unused bits removing trailing 0s */
for( unused_bits = bit_offset; unused_bits < 8; unused_bits++ )
if( ( ( bitstring >> unused_bits ) & 0x1 ) != 0 )
break;
return( unused_bits );
}
int mbedtls_x509write_crt_set_key_usage( mbedtls_x509write_cert *ctx,
unsigned int key_usage )
{
unsigned char buf[4], ku;
unsigned char *c;
int ret;
size_t unused_bits;
const unsigned int allowed_bits = MBEDTLS_X509_KU_DIGITAL_SIGNATURE |
MBEDTLS_X509_KU_NON_REPUDIATION |
MBEDTLS_X509_KU_KEY_ENCIPHERMENT |
MBEDTLS_X509_KU_DATA_ENCIPHERMENT |
MBEDTLS_X509_KU_KEY_AGREEMENT |
MBEDTLS_X509_KU_KEY_CERT_SIGN |
MBEDTLS_X509_KU_CRL_SIGN;
/* Check that nothing other than the allowed flags is set */
if( ( key_usage & ~allowed_bits ) != 0 )
return( MBEDTLS_ERR_X509_FEATURE_UNAVAILABLE );
c = buf + 4;
ku = (unsigned char)key_usage;
unused_bits = crt_get_unused_bits_for_named_bitstring( ku, 1 );
ret = mbedtls_asn1_write_bitstring( &c, buf, &ku, 8 - unused_bits );
if( ret < 0 )
return( ret );
else if( ret < 3 || ret > 4 )
return( MBEDTLS_ERR_X509_INVALID_FORMAT );
ret = mbedtls_x509write_crt_set_extension( ctx, MBEDTLS_OID_KEY_USAGE,
MBEDTLS_OID_SIZE( MBEDTLS_OID_KEY_USAGE ),
1, c, (size_t)ret );
if( ret != 0 )
return( ret );
return( 0 );
}
int mbedtls_x509write_crt_set_ns_cert_type( mbedtls_x509write_cert *ctx,
unsigned char ns_cert_type )
{
unsigned char buf[4];
unsigned char *c;
size_t unused_bits;
int ret;
c = buf + 4;
unused_bits = crt_get_unused_bits_for_named_bitstring( ns_cert_type, 0 );
ret = mbedtls_asn1_write_bitstring( &c,
buf,
&ns_cert_type,
8 - unused_bits );
if( ret < 3 || ret > 4 )
return( ret );
ret = mbedtls_x509write_crt_set_extension( ctx, MBEDTLS_OID_NS_CERT_TYPE,
MBEDTLS_OID_SIZE( MBEDTLS_OID_NS_CERT_TYPE ),
0, c, (size_t)ret );
if( ret != 0 )
return( ret );
return( 0 );
}
static int x509_write_time( unsigned char **p, unsigned char *start,
const char *t, size_t size )
{
int ret;
size_t len = 0;
/*
* write MBEDTLS_ASN1_UTC_TIME if year < 2050 (2 bytes shorter)
*/
if( t[0] == '2' && t[1] == '0' && t[2] < '5' )
{
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start,
(const unsigned char *) t + 2,
size - 2 ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start,
MBEDTLS_ASN1_UTC_TIME ) );
}
else
{
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start,
(const unsigned char *) t,
size ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start,
MBEDTLS_ASN1_GENERALIZED_TIME ) );
}
return( (int) len );
}
int mbedtls_x509write_crt_der( mbedtls_x509write_cert *ctx,
unsigned char *buf, size_t size,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret;
const char *sig_oid;
size_t sig_oid_len = 0;
unsigned char *c, *c2;
unsigned char hash[64];
unsigned char sig[SIGNATURE_MAX_SIZE];
size_t sub_len = 0, pub_len = 0, sig_and_oid_len = 0, sig_len;
size_t len = 0;
mbedtls_pk_type_t pk_alg;
/*
* Prepare data to be signed at the end of the target buffer
*/
c = buf + size;
/* Signature algorithm needed in TBS, and later for actual signature */
/* There's no direct way of extracting a signature algorithm
* (represented as an element of mbedtls_pk_type_t) from a PK instance. */
if( mbedtls_pk_can_do( ctx->issuer_key, MBEDTLS_PK_RSA ) )
pk_alg = MBEDTLS_PK_RSA;
else if( mbedtls_pk_can_do( ctx->issuer_key, MBEDTLS_PK_ECDSA ) )
pk_alg = MBEDTLS_PK_ECDSA;
else
return( MBEDTLS_ERR_X509_INVALID_ALG );
if( ( ret = mbedtls_oid_get_oid_by_sig_alg( pk_alg, ctx->md_alg,
&sig_oid, &sig_oid_len ) ) != 0 )
{
return( ret );
}
/*
* Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension
*/
/* Only for v3 */
if( ctx->version == MBEDTLS_X509_CRT_VERSION_3 )
{
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_x509_write_extensions( &c,
buf, ctx->extensions ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_asn1_write_tag( &c, buf,
MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_asn1_write_tag( &c, buf,
MBEDTLS_ASN1_CONTEXT_SPECIFIC |
MBEDTLS_ASN1_CONSTRUCTED | 3 ) );
}
/*
* SubjectPublicKeyInfo
*/
MBEDTLS_ASN1_CHK_ADD( pub_len,
mbedtls_pk_write_pubkey_der( ctx->subject_key,
buf, c - buf ) );
c -= pub_len;
len += pub_len;
/*
* Subject ::= Name
*/
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_x509_write_names( &c, buf,
ctx->subject ) );
/*
* Validity ::= SEQUENCE {
* notBefore Time,
* notAfter Time }
*/
sub_len = 0;
MBEDTLS_ASN1_CHK_ADD( sub_len,
x509_write_time( &c, buf, ctx->not_after,
MBEDTLS_X509_RFC5280_UTC_TIME_LEN ) );
MBEDTLS_ASN1_CHK_ADD( sub_len,
x509_write_time( &c, buf, ctx->not_before,
MBEDTLS_X509_RFC5280_UTC_TIME_LEN ) );
len += sub_len;
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, sub_len ) );
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_asn1_write_tag( &c, buf,
MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE ) );
/*
* Issuer ::= Name
*/
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_names( &c, buf,
ctx->issuer ) );
/*
* Signature ::= AlgorithmIdentifier
*/
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_asn1_write_algorithm_identifier( &c, buf,
sig_oid, strlen( sig_oid ), 0 ) );
/*
* Serial ::= INTEGER
*/
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_mpi( &c, buf,
&ctx->serial ) );
/*
* Version ::= INTEGER { v1(0), v2(1), v3(2) }
*/
/* Can be omitted for v1 */
if( ctx->version != MBEDTLS_X509_CRT_VERSION_1 )
{
sub_len = 0;
MBEDTLS_ASN1_CHK_ADD( sub_len,
mbedtls_asn1_write_int( &c, buf, ctx->version ) );
len += sub_len;
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_asn1_write_len( &c, buf, sub_len ) );
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_asn1_write_tag( &c, buf,
MBEDTLS_ASN1_CONTEXT_SPECIFIC |
MBEDTLS_ASN1_CONSTRUCTED | 0 ) );
}
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len,
mbedtls_asn1_write_tag( &c, buf, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE ) );
/*
* Make signature
*/
/* Compute hash of CRT. */
if( ( ret = mbedtls_md( mbedtls_md_info_from_type( ctx->md_alg ), c,
len, hash ) ) != 0 )
{
return( ret );
}
if( ( ret = mbedtls_pk_sign( ctx->issuer_key, ctx->md_alg,
hash, 0, sig, &sig_len,
f_rng, p_rng ) ) != 0 )
{
return( ret );
}
/* Move CRT to the front of the buffer to have space
* for the signature. */
memmove( buf, c, len );
c = buf + len;
/* Add signature at the end of the buffer,
* making sure that it doesn't underflow
* into the CRT buffer. */
c2 = buf + size;
MBEDTLS_ASN1_CHK_ADD( sig_and_oid_len, mbedtls_x509_write_sig( &c2, c,
sig_oid, sig_oid_len, sig, sig_len ) );
/*
* Memory layout after this step:
*
* buf c=buf+len c2 buf+size
* [CRT0,...,CRTn, UNUSED, ..., UNUSED, SIG0, ..., SIGm]
*/
/* Move raw CRT to just before the signature. */
c = c2 - len;
memmove( c, buf, len );
len += sig_and_oid_len;
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, buf,
MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE ) );
return( (int) len );
}
#define PEM_BEGIN_CRT "-----BEGIN CERTIFICATE-----\n"
#define PEM_END_CRT "-----END CERTIFICATE-----\n"
#if defined(MBEDTLS_PEM_WRITE_C)
int mbedtls_x509write_crt_pem( mbedtls_x509write_cert *crt,
unsigned char *buf, size_t size,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret;
unsigned char output_buf[4096];
size_t olen = 0;
if( ( ret = mbedtls_x509write_crt_der( crt, output_buf, sizeof(output_buf),
f_rng, p_rng ) ) < 0 )
{
return( ret );
}
if( ( ret = mbedtls_pem_write_buffer( PEM_BEGIN_CRT, PEM_END_CRT,
output_buf + sizeof(output_buf) - ret,
ret, buf, size, &olen ) ) != 0 )
{
return( ret );
}
return( 0 );
}
#endif /* MBEDTLS_PEM_WRITE_C */
#endif /* MBEDTLS_X509_CRT_WRITE_C */
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