Disable debug messages that can introduce a timing side channel.

Introduced the POLARSSL_SSL_DEBUG_ALL flag to enable all these debug
messages in case somebody does want to see the reason checks fail.

ChangeLog

@@ -3,6 +3,8 @@ PolarSSL ChangeLog
 = Development
 Changes
    * Allow enabling of dummy error_strerror() to support some use-cases
+   * Debug messages about padding errors during SSL message decryption are
+     disabled by default and can be enabled with POLARSSL_SSL_DEBUG_ALL 
 
 Security
    * Removed timing differences during SSL message decryption in

include/polarssl/config.h

@@ -238,6 +238,22 @@
  */
 #define POLARSSL_SELF_TEST
 
+/**
+ * \def POLARSSL_SSL_DEBUG_ALL
+ *
+ * Enable the debug messages in SSL module for all issues.
+ * Debug messages have been disabled in some places to prevent timing
+ * attacks due to (unbalanced) debugging function calls.
+ *
+ * If you need all error reporting you should enable this during debugging,
+ * but remove this for production servers that should log as well.
+ *
+ * Uncomment this macro to report all debug messages on errors introducing
+ * a timing side-channel.
+ *
+#define POLARSSL_SSL_DEBUG_ALL
+ */
+
 /**
  * \def POLARSSL_SSL_HW_RECORD_ACCEL
  *

library/ssl_tls.c

@@ -1403,9 +1403,10 @@ static int ssl_decrypt_buf( ssl_context *ssl )
 
         if( ssl->in_msglen < ssl->transform_in->maclen + padlen )
         {
+#if defined(POLARSSL_SSL_DEBUG_ALL)
             SSL_DEBUG_MSG( 1, ( "msglen (%d) < maclen (%d) + padlen (%d)",
                         ssl->in_msglen, ssl->transform_in->maclen, padlen ) );
-
+#endif
             padlen = 0;
             fake_padlen = 256;
             correct = 0;
@@ -1415,9 +1416,11 @@ static int ssl_decrypt_buf( ssl_context *ssl )
         {
             if( padlen > ssl->transform_in->ivlen )
             {
+#if defined(POLARSSL_SSL_DEBUG_ALL)
                 SSL_DEBUG_MSG( 1, ( "bad padding length: is %d, "
                                     "should be no more than %d",
                                padlen, ssl->transform_in->ivlen ) );
+#endif
                 correct = 0;
             }
         }
@@ -1443,8 +1446,10 @@ static int ssl_decrypt_buf( ssl_context *ssl )
                 else
                     minlen = 1;
             }
+#if defined(POLARSSL_SSL_DEBUG_ALL)
             if( padlen > 0 && correct == 0)
                 SSL_DEBUG_MSG( 1, ( "bad padding byte detected" ) );
+#endif
         }
     }