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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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32
library/ssl_srv.c
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@ -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;
}