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Safer buffer comparisons in the SSL modules

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Manuel Pégourié-Gonnard 2013-10-28 13:46:11 +01:00 committed by Paul Bakker
parent 291f9af935
commit 31ff1d2e4f
4 changed files with 41 additions and 17 deletions
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14
include/polarssl/ssl.h
View file

@ -1565,6 +1565,20 @@ static inline x509_crt *ssl_own_cert( ssl_context *ssl )
}
#endif /* POLARSSL_X509_CRT_PARSE_C */
/* constant-time buffer comparison */
static inline int safer_memcmp( const void *a, const void *b, size_t n )
{
size_t i;
const unsigned char *A = (const unsigned char *) a;
const unsigned char *B = (const unsigned char *) b;
unsigned char diff = 0;
for( i = 0; i < n; i++ )
diff |= A[i] ^ B[i];
return( diff );
}
#ifdef __cplusplus
}
#endif

8
library/ssl_cli.c
View file

@ -628,11 +628,13 @@ static int ssl_parse_renegotiation_info( ssl_context *ssl,
}
else
{
/* Check verify-data in constant-time. The length OTOH is no secret */
if( len != 1 + ssl->verify_data_len * 2 ||
buf[0] != ssl->verify_data_len * 2 ||
memcmp( buf + 1, ssl->own_verify_data, ssl->verify_data_len ) != 0 ||
memcmp( buf + 1 + ssl->verify_data_len,
ssl->peer_verify_data, ssl->verify_data_len ) != 0 )
safer_memcmp( buf + 1,
ssl->own_verify_data, ssl->verify_data_len ) != 0 ||
safer_memcmp( buf + 1 + ssl->verify_data_len,
ssl->peer_verify_data, ssl->verify_data_len ) != 0 )
{
SSL_DEBUG_MSG( 1, ( "non-matching renegotiated connection field" ) );

32
library/ssl_srv.c
View file

@ -254,7 +254,7 @@ static int ssl_parse_ticket( ssl_context *ssl,
unsigned char *mac;
unsigned char computed_mac[32];
size_t enc_len, clear_len, i;
unsigned char pad_len;
unsigned char pad_len, diff;
SSL_DEBUG_BUF( 3, "session ticket structure", buf, len );
@ -267,19 +267,23 @@ static int ssl_parse_ticket( ssl_context *ssl,
if( len != enc_len + 66 )
return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
/* Check name */
if( memcmp( key_name, ssl->ticket_keys->key_name, 16 ) != 0 )
return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
/* Check name, in constant time though it's not a big secret */
diff = 0;
for( i = 0; i < 16; i++ )
diff |= key_name[i] ^ ssl->ticket_keys->key_name[i];
/* don't return yet, check the MAC anyway */
/* Check mac */
/* Check mac, with constant-time buffer comparison */
sha256_hmac( ssl->ticket_keys->mac_key, 16, buf, len - 32,
computed_mac, 0 );
ret = 0;
for( i = 0; i < 32; i++ )
if( mac[i] != computed_mac[i] )
ret = POLARSSL_ERR_SSL_INVALID_MAC;
if( ret != 0 )
return( ret );
diff |= mac[i] ^ computed_mac[i];
/* Now return if ticket is not authentic, since we want to avoid
* decrypting arbitrary attacker-chosen data */
if( diff != 0 )
return( POLARSSL_ERR_SSL_INVALID_MAC );
/* Decrypt */
if( ( ret = aes_crypt_cbc( &ssl->ticket_keys->dec, AES_DECRYPT,
@ -428,9 +432,11 @@ static int ssl_parse_renegotiation_info( ssl_context *ssl,
}
else
{
/* Check verify-data in constant-time. The length OTOH is no secret */
if( len != 1 + ssl->verify_data_len ||
buf[0] != ssl->verify_data_len ||
memcmp( buf + 1, ssl->peer_verify_data, ssl->verify_data_len ) != 0 )
safer_memcmp( buf + 1, ssl->peer_verify_data,
ssl->verify_data_len ) != 0 )
{
SSL_DEBUG_MSG( 1, ( "non-matching renegotiated connection field" ) );
@ -2408,8 +2414,10 @@ static int ssl_parse_client_psk_identity( ssl_context *ssl, unsigned char **p,
if( ret == 0 )
{
/* Identity is not a big secret since clients send it in the clear,
* but treat it carefully anyway, just in case */
if( n != ssl->psk_identity_len ||
memcmp( ssl->psk_identity, *p, n ) != 0 )
safer_memcmp( ssl->psk_identity, *p, n ) != 0 )
{
ret = POLARSSL_ERR_SSL_UNKNOWN_IDENTITY;
}

4
library/ssl_tls.c
View file

@ -1711,7 +1711,7 @@ static int ssl_decrypt_buf( ssl_context *ssl )
SSL_DEBUG_BUF( 4, "computed mac", ssl->in_msg + ssl->in_msglen,
ssl->transform_in->maclen );
if( memcmp( tmp, ssl->in_msg + ssl->in_msglen,
if( safer_memcmp( tmp, ssl->in_msg + ssl->in_msglen,
ssl->transform_in->maclen ) != 0 )
{
#if defined(POLARSSL_SSL_DEBUG_ALL)
@ -3192,7 +3192,7 @@ int ssl_parse_finished( ssl_context *ssl )
return( POLARSSL_ERR_SSL_BAD_HS_FINISHED );
}
if( memcmp( ssl->in_msg + 4, buf, hash_len ) != 0 )
if( safer_memcmp( ssl->in_msg + 4, buf, hash_len ) != 0 )
{
SSL_DEBUG_MSG( 1, ( "bad finished message" ) );
return( POLARSSL_ERR_SSL_BAD_HS_FINISHED );