audit: allow not equal op for audit by executable

Current implementation of auditing by executable name only implements
the 'equal' operator. This patch extends it to also support the 'not
equal' operator.

See: https://github.com/linux-audit/audit-kernel/issues/53

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/auditfilter.c

@@ -426,7 +426,7 @@ static int audit_field_valid(struct audit_entry *entry, struct audit_field *f)
 			return -EINVAL;
 		break;
 	case AUDIT_EXE:
-		if (f->op != Audit_equal)
+		if (f->op != Audit_not_equal && f->op != Audit_equal)
 			return -EINVAL;
 		if (entry->rule.listnr != AUDIT_FILTER_EXIT)
 			return -EINVAL;

kernel/auditsc.c

@@ -471,6 +471,8 @@ static int audit_filter_rules(struct task_struct *tsk,
 			break;
 		case AUDIT_EXE:
 			result = audit_exe_compare(tsk, rule->exe);
+			if (f->op == Audit_not_equal)
+				result = !result;
 			break;
 		case AUDIT_UID:
 			result = audit_uid_comparator(cred->uid, f->op, f->uid);