mirror of
https://github.com/yuzu-emu/mbedtls.git
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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>
This commit is contained in:
Doru Gucea
Simon Leet
parent
a586099fd3
commit
afc2717e84
@ -81,6 +81,14 @@
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#define SIGNATURE_MAX_SIZE MBEDTLS_MPI_MAX_SIZE
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#endif
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#if defined(MBEDTLS_PLATFORM_C)
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#include "mbedtls/platform.h"
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#else
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#include <stdlib.h>
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#define mbedtls_calloc calloc
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#define mbedtls_free free
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#endif
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void mbedtls_x509write_csr_init( mbedtls_x509write_csr *ctx )
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{
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memset( ctx, 0, sizeof( mbedtls_x509write_csr ) );
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@ -187,68 +195,74 @@ int mbedtls_x509write_csr_set_ns_cert_type( mbedtls_x509write_csr *ctx,
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return( 0 );
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}
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int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf, size_t size,
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int (*f_rng)(void *, unsigned char *, size_t),
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void *p_rng )
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static int x509write_csr_der_internal( mbedtls_x509write_csr *ctx,
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unsigned char *buf,
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size_t size, unsigned char *sig,
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int (*f_rng)(void *, unsigned char *, size_t),
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void *p_rng )
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{
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int ret;
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const char *sig_oid;
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size_t sig_oid_len = 0;
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unsigned char *c, *c2;
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unsigned char hash[64];
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unsigned char sig[SIGNATURE_MAX_SIZE];
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unsigned char tmp_buf[2048];
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size_t pub_len = 0, sig_and_oid_len = 0, sig_len;
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size_t len = 0;
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mbedtls_pk_type_t pk_alg;
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/*
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* Prepare data to be signed in tmp_buf
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* Writing strategy:
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* 1. start writing from the back of buf
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* 2. sign the written data and place the signature at the start of buf
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* 3. compact memory locations by moving the signature towards right
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*/
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c = tmp_buf + sizeof( tmp_buf );
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c = buf + size;
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_extensions( &c, tmp_buf, ctx->extensions ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_extensions( &c, buf,
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ctx->extensions ) );
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if( len )
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{
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED |
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MBEDTLS_ASN1_SEQUENCE ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, buf,
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MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED |
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MBEDTLS_ASN1_SET ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, buf,
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MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SET ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_oid( &c, tmp_buf, MBEDTLS_OID_PKCS9_CSR_EXT_REQ,
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MBEDTLS_OID_SIZE( MBEDTLS_OID_PKCS9_CSR_EXT_REQ ) ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_oid( &c, buf,
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MBEDTLS_OID_PKCS9_CSR_EXT_REQ,
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MBEDTLS_OID_SIZE( MBEDTLS_OID_PKCS9_CSR_EXT_REQ ) ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED |
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MBEDTLS_ASN1_SEQUENCE ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, buf,
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MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
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}
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED |
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MBEDTLS_ASN1_CONTEXT_SPECIFIC ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, buf,
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MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CONTEXT_SPECIFIC ) );
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MBEDTLS_ASN1_CHK_ADD( pub_len, mbedtls_pk_write_pubkey_der( ctx->key,
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tmp_buf, c - tmp_buf ) );
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buf, c - buf ) );
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c -= pub_len;
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len += pub_len;
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/*
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* Subject ::= Name
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*/
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_names( &c, tmp_buf, ctx->subject ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_names( &c, buf,
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ctx->subject ) );
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/*
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* Version ::= INTEGER { v1(0), v2(1), v3(2) }
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*/
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, tmp_buf, 0 ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, buf, 0 ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED |
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MBEDTLS_ASN1_SEQUENCE ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, buf,
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MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
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/*
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* Prepare signature
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@ -271,32 +285,52 @@ int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf, s
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return( MBEDTLS_ERR_X509_INVALID_ALG );
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if( ( ret = mbedtls_oid_get_oid_by_sig_alg( pk_alg, ctx->md_alg,
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&sig_oid, &sig_oid_len ) ) != 0 )
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&sig_oid, &sig_oid_len ) ) != 0 )
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{
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return( ret );
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}
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/*
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* Write data to output buffer
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*/
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/* reserve space for the signature at the end of buf */
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memmove( buf, c, len );
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/* copy the signature */
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c2 = buf + size;
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MBEDTLS_ASN1_CHK_ADD( sig_and_oid_len, mbedtls_x509_write_sig( &c2, buf,
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sig_oid, sig_oid_len, sig, sig_len ) );
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if( len > (size_t)( c2 - buf ) )
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return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
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MBEDTLS_ASN1_CHK_ADD( sig_and_oid_len, mbedtls_x509_write_sig( &c2,
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buf + len, sig_oid, sig_oid_len, sig, sig_len ) );
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/* compact oids and signature memory locations */
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c2 -= len;
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memcpy( c2, c, len );
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memmove( c2, buf, len );
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len += sig_and_oid_len;
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c2, buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c2, buf, MBEDTLS_ASN1_CONSTRUCTED |
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MBEDTLS_ASN1_SEQUENCE ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c2, buf,
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MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
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memset( buf, 0, c2 - buf);
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return( (int) len );
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}
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int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf,
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size_t size,
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int (*f_rng)(void *, unsigned char *, size_t),
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void *p_rng )
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{
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int ret;
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unsigned char *sig;
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if( ( sig = mbedtls_calloc( 1, MBEDTLS_MPI_MAX_SIZE ) ) == NULL )
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{
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return( MBEDTLS_ERR_ASN1_ALLOC_FAILED );
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}
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ret = x509write_csr_der_internal( ctx, buf, size, sig, f_rng, p_rng );
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mbedtls_free( sig );
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return( ret );
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}
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#define PEM_BEGIN_CSR "-----BEGIN CERTIFICATE REQUEST-----\n"
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#define PEM_END_CSR "-----END CERTIFICATE REQUEST-----\n"
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