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Merge pull request #3464 from CodeMonkeyLeet/csr_heap_alloc

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Dynamically allocate requested CSR write buffer size
This commit is contained in:
Manuel Pégourié-Gonnard 2020-07-10 10:57:22 +02:00 committed by GitHub
commit d4d6ad0363
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 103 additions and 41 deletions
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4
ChangeLog.d/x509write_csr_heap_alloc.txt Normal file
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@ -0,0 +1,4 @@
Changes
* Reduce the stack consumption of mbedtls_x509write_csr_der() which
previously could lead to stack overflow on constrained devices.
Contributed by Doru Gucea and Simon Leet in #3464.

132
library/x509write_csr.c
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@ -46,6 +46,14 @@
#include "mbedtls/pem.h" #include "mbedtls/pem.h"
#endif #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 ) void mbedtls_x509write_csr_init( mbedtls_x509write_csr *ctx )
{ {
memset( ctx, 0, sizeof( mbedtls_x509write_csr ) ); memset( ctx, 0, sizeof( mbedtls_x509write_csr ) );
@ -126,7 +134,10 @@ int mbedtls_x509write_csr_set_ns_cert_type( mbedtls_x509write_csr *ctx,
return( 0 ); return( 0 );
} }
int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf, size_t size, 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), int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng ) void *p_rng )
{ {
@ -135,8 +146,6 @@ int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf, s
size_t sig_oid_len = 0; size_t sig_oid_len = 0;
unsigned char *c, *c2; unsigned char *c, *c2;
unsigned char hash[64]; unsigned char hash[64];
unsigned char sig[MBEDTLS_PK_SIGNATURE_MAX_SIZE];
unsigned char tmp_buf[2048];
size_t pub_len = 0, sig_and_oid_len = 0, sig_len; size_t pub_len = 0, sig_and_oid_len = 0, sig_len;
size_t len = 0; size_t len = 0;
mbedtls_pk_type_t pk_alg; mbedtls_pk_type_t pk_alg;
@ -145,56 +154,69 @@ int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf, s
size_t hash_len; size_t hash_len;
psa_algorithm_t hash_alg = mbedtls_psa_translate_md( ctx->md_alg ); psa_algorithm_t hash_alg = mbedtls_psa_translate_md( ctx->md_alg );
#endif /* MBEDTLS_USE_PSA_CRYPTO */ #endif /* MBEDTLS_USE_PSA_CRYPTO */
/*
* Prepare data to be signed in tmp_buf
*/
c = tmp_buf + sizeof( tmp_buf );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_extensions( &c, tmp_buf, ctx->extensions ) ); /* Write the CSR backwards starting from the end of buf */
c = buf + size;
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_extensions( &c, buf,
ctx->extensions ) );
if( len ) if( len )
{ {
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) ); MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CHK_ADD( len,
MBEDTLS_ASN1_SEQUENCE ) ); mbedtls_asn1_write_tag(
&c, buf,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) ); MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CHK_ADD( len,
MBEDTLS_ASN1_SET ) ); mbedtls_asn1_write_tag(
&c, buf,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SET ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_oid( &c, tmp_buf, MBEDTLS_OID_PKCS9_CSR_EXT_REQ, 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_OID_SIZE( MBEDTLS_OID_PKCS9_CSR_EXT_REQ ) ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) ); MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CHK_ADD( len,
MBEDTLS_ASN1_SEQUENCE ) ); mbedtls_asn1_write_tag(
&c, buf,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
} }
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) ); MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CHK_ADD( len,
MBEDTLS_ASN1_CONTEXT_SPECIFIC ) ); 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, MBEDTLS_ASN1_CHK_ADD( pub_len, mbedtls_pk_write_pubkey_der( ctx->key,
tmp_buf, c - tmp_buf ) ); buf, c - buf ) );
c -= pub_len; c -= pub_len;
len += pub_len; len += pub_len;
/* /*
* Subject ::= Name * Subject ::= Name
*/ */
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_names( &c, tmp_buf, ctx->subject ) ); MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_names( &c, buf,
ctx->subject ) );
/* /*
* Version ::= INTEGER { v1(0), v2(1), v3(2) } * Version ::= INTEGER { v1(0), v2(1), v3(2) }
*/ */
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, tmp_buf, 0 ) ); MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, buf, 0 ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) ); MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CHK_ADD( len,
MBEDTLS_ASN1_SEQUENCE ) ); mbedtls_asn1_write_tag(
&c, buf,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
/* /*
* Prepare signature * Sign the written CSR data into the sig buffer
* Note: hash errors can happen only after an internal error * Note: hash errors can happen only after an internal error
*/ */
#if defined(MBEDTLS_USE_PSA_CRYPTO) #if defined(MBEDTLS_USE_PSA_CRYPTO)
@ -234,26 +256,62 @@ int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf, s
} }
/* /*
* Write data to output buffer * Move the written CSR data to the start of buf to create space for
* writing the signature into buf.
*/
memmove( buf, c, len );
/*
* Write sig and its OID into buf backwards from the end of buf.
* Note: mbedtls_x509_write_sig will check for c2 - ( buf + len ) < sig_len
* and return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL if needed.
*/ */
c2 = buf + size; c2 = buf + size;
MBEDTLS_ASN1_CHK_ADD( sig_and_oid_len, mbedtls_x509_write_sig( &c2, buf, MBEDTLS_ASN1_CHK_ADD( sig_and_oid_len,
sig_oid, sig_oid_len, sig, sig_len ) ); mbedtls_x509_write_sig( &c2, buf + len, sig_oid, sig_oid_len,
sig, sig_len ) );
if( len > (size_t)( c2 - buf ) )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
/*
* Compact the space between the CSR data and signature by moving the
* CSR data to the start of the signature.
*/
c2 -= len; c2 -= len;
memcpy( c2, c, len ); memmove( c2, buf, len );
/* ASN encode the total size and tag the CSR data with it. */
len += sig_and_oid_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_len( &c2, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c2, buf, MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CHK_ADD( len,
MBEDTLS_ASN1_SEQUENCE ) ); mbedtls_asn1_write_tag(
&c2, buf,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
/* Zero the unused bytes at the start of buf */
memset( buf, 0, c2 - buf);
return( (int) len ); 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_PK_SIGNATURE_MAX_SIZE ) ) == NULL )
{
return( MBEDTLS_ERR_X509_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_BEGIN_CSR "-----BEGIN CERTIFICATE REQUEST-----\n"
#define PEM_END_CSR "-----END CERTIFICATE REQUEST-----\n" #define PEM_END_CSR "-----END CERTIFICATE REQUEST-----\n"