child-sa: Move unique mark allocation to a separate helper function

This aligns the code with unique interface ID allocation, which uses a helper
function for the same purpose and mechanic as well.

src/libstrongswan/ipsec/ipsec_types.c

@@ -150,6 +150,34 @@ bool mark_from_string(const char *value, mark_op_t ops, mark_t *mark)
 	return TRUE;
 }
 
+/*
+ * Described in header
+ */
+void allocate_unique_marks(uint32_t *in, uint32_t *out)
+{
+	static refcount_t unique_mark = 0;
+
+	if (MARK_IS_UNIQUE(*in) || MARK_IS_UNIQUE(*out))
+	{
+		refcount_t mark = 0;
+		bool unique_dir = *in == MARK_UNIQUE_DIR ||
+						  *out == MARK_UNIQUE_DIR;
+
+		if (!unique_dir)
+		{
+			mark = ref_get(&unique_mark);
+		}
+		if (MARK_IS_UNIQUE(*in))
+		{
+			*in = unique_dir ? ref_get(&unique_mark) : mark;
+		}
+		if (MARK_IS_UNIQUE(*out))
+		{
+			*out = unique_dir ? ref_get(&unique_mark) : mark;
+		}
+	}
+}
+
 /*
  * Described in header
  */

src/libstrongswan/ipsec/ipsec_types.h

@@ -242,6 +242,18 @@ enum mark_op_t {
  */
 bool mark_from_string(const char *value, mark_op_t ops, mark_t *mark);
 
+/**
+ * Allocate up to two unique marks depending on the given values.
+ *
+ * If the given values are MARK_UNIQUE, the values get replaced by a single
+ * unique mark. If the given values are MARK_UNIQUE_DIR, the values get
+ * replaced by a single unique mark for each direction.
+ *
+ * @param[out] in	inbound interface ID
+ * @param[out] out	outbound interface ID
+ */
+void allocate_unique_marks(uint32_t *in, uint32_t *out);
+
 /**
  * Special interface ID values to allocate a unique ID for each CHILD_SA/dir
  */