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Reject invalid CCS records early

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This commit moves the length and content check for CCS messages to
the function mbedtls_ssl_handle_message_type() which is called after
a record has been deprotected.

Previously, these checks were performed in the function
mbedtls_ssl_parse_change_cipher_spec(); however, now that
the arrival of out-of-order CCS messages is remembered
as a boolean flag, the check also has to happen when this
flag is set. Moving the length and content check to
mbedtls_ssl_handle_message_type() allows to treat both
checks uniformly.
This commit is contained in:
Hanno Becker 2018-08-21 14:57:46 +01:00
parent 4cb782d2f6
commit e678eaa93e
1 changed files with 30 additions and 19 deletions
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49
library/ssl_tls.c
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@ -4476,6 +4476,7 @@ static int ssl_buffer_message( mbedtls_ssl_context *ssl )
{
case MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC:
MBEDTLS_SSL_DEBUG_MSG( 2, ( "Remember CCS message" ) );
hs->buffering.seen_ccs = 1;
break;
@ -4986,23 +4987,38 @@ int mbedtls_ssl_handle_message_type( mbedtls_ssl_context *ssl )
}
}
#if defined(MBEDTLS_SSL_PROTO_DTLS)
/* Drop unexpected ChangeCipherSpec messages */
if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
ssl->in_msgtype == MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC &&
ssl->state != MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC &&
ssl->state != MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC )
if( ssl->in_msgtype == MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC )
{
if( ssl->handshake == NULL )
if( ssl->in_msglen != 1 )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "dropping ChangeCipherSpec outside handshake" ) );
return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid CCS message, len: %d",
ssl->in_msglen ) );
return( MBEDTLS_ERR_SSL_INVALID_RECORD );
}
MBEDTLS_SSL_DEBUG_MSG( 1, ( "received out-of-order ChangeCipherSpec - remember" ) );
return( MBEDTLS_ERR_SSL_EARLY_MESSAGE );
}
if( ssl->in_msg[0] != 1 )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid CCS message, content: %02x",
ssl->in_msg[0] ) );
return( MBEDTLS_ERR_SSL_INVALID_RECORD );
}
#if defined(MBEDTLS_SSL_PROTO_DTLS)
if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
ssl->state != MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC &&
ssl->state != MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC )
{
if( ssl->handshake == NULL )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "dropping ChangeCipherSpec outside handshake" ) );
return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
}
MBEDTLS_SSL_DEBUG_MSG( 1, ( "received out-of-order ChangeCipherSpec - remember" ) );
return( MBEDTLS_ERR_SSL_EARLY_MESSAGE );
}
#endif
}
if( ssl->in_msgtype == MBEDTLS_SSL_MSG_ALERT )
{
@ -5718,13 +5734,8 @@ int mbedtls_ssl_parse_change_cipher_spec( mbedtls_ssl_context *ssl )
return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
}
if( ssl->in_msglen != 1 || ssl->in_msg[0] != 1 )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad change cipher spec message" ) );
mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
return( MBEDTLS_ERR_SSL_BAD_HS_CHANGE_CIPHER_SPEC );
}
/* CCS records are only accepted if they have length 1 and content '1',
* so we don't need to check this here. */
/*
* Switch to our negotiated transform and session parameters for inbound