child-cfg: Add method to select a security label

src/libcharon/config/child_cfg.c

@@ -544,6 +544,85 @@ METHOD(child_cfg_t, get_label_mode, sec_label_mode_t,
 	return this->label_mode;
 }
 
+METHOD(child_cfg_t, select_label, bool,
+	private_child_cfg_t *this, linked_list_t *labels, bool log,
+	sec_label_t **label, bool *exact_out)
+{
+	enumerator_t *enumerator;
+	sec_label_t *current, *match = NULL;
+	bool exact = FALSE;
+
+	if (labels && labels->get_count(labels))
+	{
+		if (!this->label)
+		{
+			DBG2(DBG_CFG, "peer proposed a security label, but none expected");
+			return FALSE;
+		}
+		if (log)
+		{
+			DBG2(DBG_CFG, "selecting security label matching '%s':",
+				 this->label->get_string(this->label));
+		}
+		enumerator = labels->create_enumerator(labels);
+		while (enumerator->enumerate(enumerator, &current))
+		{
+			if (this->label->equals(this->label, current))
+			{
+				if (log)
+				{
+					DBG2(DBG_CFG, " %s => matches exactly",
+						 current->get_string(current));
+				}
+				match = current;
+				exact = TRUE;
+				break;
+			}
+			else if (this->label_mode == SEC_LABEL_MODE_SELINUX &&
+					 this->label->matches(this->label, current))
+			{
+				if (log)
+				{
+					DBG2(DBG_CFG, " %s => matches%s",
+						 current->get_string(current), match ? ", ignored" : "");
+				}
+				/* return the first match if we don't find an exact one */
+				if (!match)
+				{
+					match = current;
+				}
+			}
+			else if (log)
+			{
+				DBG2(DBG_CFG, " %s => no match", current->get_string(current));
+			}
+		}
+		enumerator->destroy(enumerator);
+		if (!match)
+		{
+			DBG2(DBG_CFG, "none of the proposed security labels match the "
+				 "configured label '%s'", this->label->get_string(this->label));
+			return FALSE;
+		}
+	}
+	else if (this->label)
+	{
+		DBG2(DBG_CFG, "peer didn't propose any security labels, we expect one "
+			 "matching '%s'", this->label->get_string(this->label));
+		return FALSE;
+	}
+
+	if (label)
+	{
+		*label = match;
+	}
+	if (exact_out)
+	{
+		*exact_out = exact;
+	}
+	return TRUE;
+}
+
 METHOD(child_cfg_t, get_tfc, uint32_t,
 	private_child_cfg_t *this)
 {
@@ -686,6 +765,7 @@ child_cfg_t *child_cfg_create(char *name, child_cfg_create_t *data)
 			.get_set_mark = _get_set_mark,
 			.get_label = _get_label,
 			.get_label_mode = _get_label_mode,
+			.select_label = _select_label,
 			.get_tfc = _get_tfc,
 			.get_manual_prio = _get_manual_prio,
 			.get_interface = _get_interface,

src/libcharon/config/child_cfg.h

@@ -261,6 +261,27 @@ struct child_cfg_t {
 	 */
 	sec_label_mode_t (*get_label_mode)(child_cfg_t *this);
 
+	/**
+	 * Select a security label from the given list that matches the configured
+	 * label.
+	 *
+	 * This fails under the following conditions:
+	 * - a label is configured but no labels are provided
+	 * - no label is configured but at least one label is provided
+	 * - the configured and provided labels don't match
+	 *
+	 * If no label is configured and none are provided, that's considered a
+	 * success and label will be set to NULL.
+	 *
+	 * @param labels		list of labels to match
+	 * @param log			FALSE to avoid logging details about the selection
+	 * @param label[out]	selected label or NULL if no label necessary
+	 * @param exact[out]	TRUE if there was an exact match
+	 * @return				FALSE on failure
+	 */
+	bool (*select_label)(child_cfg_t *this, linked_list_t *labels, bool log,
+						 sec_label_t **label, bool *exact);
+
 	/**
 	 * Get the TFC padding value to use for CHILD_SA.
 	 *