ima: do not send field length to userspace for digest of ima template

This patch defines a new value for the 'ima_show_type' enumerator
(IMA_SHOW_BINARY_NO_FIELD_LEN) to prevent that the field length
is transmitted through the 'binary_runtime_measurements' interface
for the digest field of the 'ima' template.

Fixes commit: 3ce1217 ima: define template fields library and new helpers

Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
index 6d66ad6..c38adcc 100644
--- a/security/integrity/ima/ima_template_lib.c
+++ b/security/integrity/ima/ima_template_lib.c
@@ -109,9 +109,12 @@
 					  enum data_formats datafmt,
 					  struct ima_field_data *field_data)
 {
-	ima_putc(m, &field_data->len, sizeof(u32));
+	if (show != IMA_SHOW_BINARY_NO_FIELD_LEN)
+		ima_putc(m, &field_data->len, sizeof(u32));
+
 	if (!field_data->len)
 		return;
+
 	ima_putc(m, field_data->data, field_data->len);
 }
 
@@ -125,6 +128,7 @@
 		ima_show_template_data_ascii(m, show, datafmt, field_data);
 		break;
 	case IMA_SHOW_BINARY:
+	case IMA_SHOW_BINARY_NO_FIELD_LEN:
 		ima_show_template_data_binary(m, show, datafmt, field_data);
 		break;
 	default: