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afc2717e84
mbedtls/library/x509write_csr.c
Doru Gucea afc2717e84 Avoid stack-allocation of large memory buffers 
Using a stack-buffer with a size > 2K could easily produce a stack
overflow for an embedded device which has a limited stack size.
This commit dynamically allocates the large CSR buffer.

This commit avoids using a temporary buffer for storing the OIDs.
A single buffer is used:
a) OIDs are written backwards starting with the end of the buffer;
b) OIDs are memmove'd to the beginning of the buffer;
c) signature over this OIDs is computed and written backwards from the
end of the buffer;
d) the two memory regions are compacted.

Signed-off-by: Doru Gucea <doru-cristian.gucea@nxp.com>
2020-07-10 18:19:23 +00:00

364 lines
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/*
* X.509 Certificate Signing Request 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:
* - 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_CSR_WRITE_C)
#include "mbedtls/x509_csr.h"
#include "mbedtls/oid.h"
#include "mbedtls/asn1write.h"
#include "mbedtls/platform_util.h"
#include <string.h>
#include <stdlib.h>
#if defined(MBEDTLS_PEM_WRITE_C)
#include "mbedtls/pem.h"
#endif
/*
* 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
#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdlib.h>
#define mbedtls_calloc calloc
#define mbedtls_free free
#endif
void mbedtls_x509write_csr_init( mbedtls_x509write_csr *ctx )
{
memset( ctx, 0, sizeof( mbedtls_x509write_csr ) );
}
void mbedtls_x509write_csr_free( mbedtls_x509write_csr *ctx )
{
mbedtls_asn1_free_named_data_list( &ctx->subject );
mbedtls_asn1_free_named_data_list( &ctx->extensions );
mbedtls_platform_zeroize( ctx, sizeof( mbedtls_x509write_csr ) );
}
void mbedtls_x509write_csr_set_md_alg( mbedtls_x509write_csr *ctx, mbedtls_md_type_t md_alg )
{
ctx->md_alg = md_alg;
}
void mbedtls_x509write_csr_set_key( mbedtls_x509write_csr *ctx, mbedtls_pk_context *key )
{
ctx->key = key;
}
int mbedtls_x509write_csr_set_subject_name( mbedtls_x509write_csr *ctx,
const char *subject_name )
{
return mbedtls_x509_string_to_names( &ctx->subject, subject_name );
}
int mbedtls_x509write_csr_set_extension( mbedtls_x509write_csr *ctx,
const char *oid, size_t oid_len,
const unsigned char *val, size_t val_len )
{
return mbedtls_x509_set_extension( &ctx->extensions, oid, oid_len,
0, val, val_len );
}
static size_t csr_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_csr_set_key_usage( mbedtls_x509write_csr *ctx, unsigned char key_usage )
{
unsigned char buf[4];
unsigned char *c;
size_t unused_bits;
int ret;
c = buf + 4;
unused_bits = csr_get_unused_bits_for_named_bitstring( key_usage, 0 );
ret = mbedtls_asn1_write_bitstring( &c, buf, &key_usage, 8 - unused_bits );
if( ret < 0 )
return( ret );
else if( ret < 3 || ret > 4 )
return( MBEDTLS_ERR_X509_INVALID_FORMAT );
ret = mbedtls_x509write_csr_set_extension( ctx, MBEDTLS_OID_KEY_USAGE,
MBEDTLS_OID_SIZE( MBEDTLS_OID_KEY_USAGE ),
c, (size_t)ret );
if( ret != 0 )
return( ret );
return( 0 );
}
int mbedtls_x509write_csr_set_ns_cert_type( mbedtls_x509write_csr *ctx,
unsigned char ns_cert_type )
{
unsigned char buf[4];
unsigned char *c;
size_t unused_bits;
int ret;
c = buf + 4;
unused_bits = csr_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 < 0 )
return( ret );
else if( ret < 3 || ret > 4 )
return( ret );
ret = mbedtls_x509write_csr_set_extension( ctx, MBEDTLS_OID_NS_CERT_TYPE,
MBEDTLS_OID_SIZE( MBEDTLS_OID_NS_CERT_TYPE ),
c, (size_t)ret );
if( ret != 0 )
return( ret );
return( 0 );
}
static int x509write_csr_der_internal( mbedtls_x509write_csr *ctx,
unsigned char *buf,
size_t size, unsigned char *sig,
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];
size_t pub_len = 0, sig_and_oid_len = 0, sig_len;
size_t len = 0;
mbedtls_pk_type_t pk_alg;
/*
* Writing strategy:
* 1. start writing from the back of buf
* 2. sign the written data and place the signature at the start of buf
* 3. compact memory locations by moving the signature towards right
*/
c = buf + size;
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_extensions( &c, buf,
ctx->extensions ) );
if( 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 ) );
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_SET ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_oid( &c, buf,
MBEDTLS_OID_PKCS9_CSR_EXT_REQ,
MBEDTLS_OID_SIZE( MBEDTLS_OID_PKCS9_CSR_EXT_REQ ) ) );
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_CONSTRUCTED | MBEDTLS_ASN1_CONTEXT_SPECIFIC ) );
MBEDTLS_ASN1_CHK_ADD( pub_len, mbedtls_pk_write_pubkey_der( ctx->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 ) );
/*
* Version ::= INTEGER { v1(0), v2(1), v3(2) }
*/
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, buf, 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 ) );
/*
* Prepare signature
*/
ret = mbedtls_md( mbedtls_md_info_from_type( ctx->md_alg ), c, len, hash );
if( ret != 0 )
return( ret );
if( ( ret = mbedtls_pk_sign( ctx->key, ctx->md_alg, hash, 0, sig, &sig_len,
f_rng, p_rng ) ) != 0 )
{
return( ret );
}
if( mbedtls_pk_can_do( ctx->key, MBEDTLS_PK_RSA ) )
pk_alg = MBEDTLS_PK_RSA;
else if( mbedtls_pk_can_do( ctx->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 );
}
/* reserve space for the signature at the end of buf */
memmove( buf, c, len );
/* copy the signature */
c2 = buf + size;
MBEDTLS_ASN1_CHK_ADD( sig_and_oid_len, mbedtls_x509_write_sig( &c2,
buf + len, sig_oid, sig_oid_len, sig, sig_len ) );
/* compact oids and signature memory locations */
c2 -= len;
memmove( c2, buf, len );
len += sig_and_oid_len;
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c2, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c2, buf,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
memset( buf, 0, c2 - buf);
return( (int) len );
}
int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf,
size_t size,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret;
unsigned char *sig;
if( ( sig = mbedtls_calloc( 1, MBEDTLS_MPI_MAX_SIZE ) ) == NULL )
{
return( MBEDTLS_ERR_ASN1_ALLOC_FAILED );
}
ret = x509write_csr_der_internal( ctx, buf, size, sig, f_rng, p_rng );
mbedtls_free( sig );
return( ret );
}
#define PEM_BEGIN_CSR "-----BEGIN CERTIFICATE REQUEST-----\n"
#define PEM_END_CSR "-----END CERTIFICATE REQUEST-----\n"
#if defined(MBEDTLS_PEM_WRITE_C)
int mbedtls_x509write_csr_pem( mbedtls_x509write_csr *ctx, 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_csr_der( ctx, output_buf, sizeof(output_buf),
f_rng, p_rng ) ) < 0 )
{
return( ret );
}
if( ( ret = mbedtls_pem_write_buffer( PEM_BEGIN_CSR, PEM_END_CSR,
output_buf + sizeof(output_buf) - ret,
ret, buf, size, &olen ) ) != 0 )
{
return( ret );
}
return( 0 );
}
#endif /* MBEDTLS_PEM_WRITE_C */
#endif /* MBEDTLS_X509_CSR_WRITE_C */
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