From: Nick Porter <nick@portercomputing.co.uk>
Date: Tue, 15 Sep 2020 12:00:14 +0000 (+0100)
Subject: Determine the address to be used to identify client subnet
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=aedfb5d3bddad5036f2c19dc0c7b177fb4acdb7a;p=thirdparty%2Ffreeradius-server.git

Determine the address to be used to identify client subnet

After parsing the DHCP packet, check Relay-Link-Selection option,
Subnet-Selection-Option option then giaddr and finally ciaddr to
determine address to lookup client's subnet.
---

diff --git a/src/protocols/dhcpv4/attrs.h b/src/protocols/dhcpv4/attrs.h
index 6a0686b8e87..f05fbe211a2 100644
--- a/src/protocols/dhcpv4/attrs.h
+++ b/src/protocols/dhcpv4/attrs.h
@@ -49,3 +49,6 @@ extern fr_dict_attr_t const *attr_dhcp_message_type;
 extern fr_dict_attr_t const *attr_dhcp_parameter_request_list;
 extern fr_dict_attr_t const *attr_dhcp_overload;
 extern fr_dict_attr_t const *attr_dhcp_vendor_class_identifier;
+extern fr_dict_attr_t const *attr_dhcp_relay_link_selection;
+extern fr_dict_attr_t const *attr_dhcp_subnet_selection_option;
+extern fr_dict_attr_t const *attr_dhcp_network_ip_address;
diff --git a/src/protocols/dhcpv4/base.c b/src/protocols/dhcpv4/base.c
index e1e7b7d56b1..080e4f22b6d 100644
--- a/src/protocols/dhcpv4/base.c
+++ b/src/protocols/dhcpv4/base.c
@@ -66,6 +66,9 @@ fr_dict_attr_t const *attr_dhcp_message_type;
 fr_dict_attr_t const *attr_dhcp_parameter_request_list;
 fr_dict_attr_t const *attr_dhcp_overload;
 fr_dict_attr_t const *attr_dhcp_vendor_class_identifier;
+fr_dict_attr_t const *attr_dhcp_relay_link_selection;
+fr_dict_attr_t const *attr_dhcp_subnet_selection_option;
+fr_dict_attr_t const *attr_dhcp_network_ip_address;
 
 extern fr_dict_attr_autoload_t dhcpv4_dict_attr[];
 fr_dict_attr_autoload_t dhcpv4_dict_attr[] = {
@@ -89,6 +92,9 @@ fr_dict_attr_autoload_t dhcpv4_dict_attr[] = {
 	{ .out = &attr_dhcp_parameter_request_list, .name = "DHCP-Parameter-Request-List", .type = FR_TYPE_UINT8, .dict = &dict_dhcpv4 },
 	{ .out = &attr_dhcp_overload, .name = "DHCP-Overload", .type = FR_TYPE_UINT8, .dict = &dict_dhcpv4 },
 	{ .out = &attr_dhcp_vendor_class_identifier, .name = "DHCP-Vendor-Class-Identifier", .type = FR_TYPE_OCTETS, .dict = &dict_dhcpv4 },
+	{ .out = &attr_dhcp_relay_link_selection, .name = "DHCP-Relay-Link-Selection", .type = FR_TYPE_IPV4_ADDR, .dict = &dict_dhcpv4 },
+	{ .out = &attr_dhcp_subnet_selection_option, .name = "DHCP-Subnet-Selection-Option", .type = FR_TYPE_IPV4_ADDR, .dict = &dict_dhcpv4 },
+	{ .out = &attr_dhcp_network_ip_address, .name = "DHCP-Network-IP-Address", .type = FR_TYPE_IPV4_ADDR, .dict = &dict_dhcpv4 },
 	{ NULL }
 };
 
diff --git a/src/protocols/dhcpv4/packet.c b/src/protocols/dhcpv4/packet.c
index d8dd63ff6cc..2bd1f504de2 100644
--- a/src/protocols/dhcpv4/packet.c
+++ b/src/protocols/dhcpv4/packet.c
@@ -110,7 +110,7 @@ int fr_dhcpv4_decode(TALLOC_CTX *ctx, uint8_t const *data, size_t data_len, VALU
 	uint32_t	giaddr;
 	fr_cursor_t	cursor;
 	VALUE_PAIR	*head = NULL, *vp;
-	VALUE_PAIR	*maxms, *mtu;
+	VALUE_PAIR	*maxms, *mtu, *netaddr;
 
 	fr_cursor_init(&cursor, &head);
 
@@ -298,6 +298,46 @@ int fr_dhcpv4_decode(TALLOC_CTX *ctx, uint8_t const *data, size_t data_len, VALU
 		}
 	}
 
+	/*
+	 *	Determine the address to use in looking up which subnet the
+	 *	client belongs to based on packet data.  The sequence here
+	 *	is based on ISC DHCP behaviour and RFCs 3527 and 3011.  We
+	 *	store the found address in an internal attribute of
+	 *	DHCP-Network-IP-Address.
+	 */
+	vp = fr_pair_afrom_da(ctx, attr_dhcp_network_ip_address);
+	/*
+	 *	First look for Relay-Link-Selection
+	 */
+	netaddr = fr_pair_find_by_da(head, attr_dhcp_relay_link_selection);
+	if (!netaddr) {
+		/*
+		 *	Next try Subnet-Selection-Option
+		 */
+		netaddr = fr_pair_find_by_da(head, attr_dhcp_subnet_selection_option);
+	}
+	if (!netaddr) {
+		if (giaddr != htonl(INADDR_ANY)) {
+			/*
+			 *	Gateway address is set - use that one
+			 */
+			fr_value_box_from_network(vp, &vp->data, vp->vp_type, vp->da,
+						  data + 24, 4, true);
+		} else {
+			/*
+			 *	else, store client address whatever it is
+			 */
+			fr_value_box_from_network(vp, &vp->data, vp->vp_type, vp->da,
+						  data + 12, 4, true);
+		}
+	} else {
+		/*
+		 *	Store whichever address we found from options
+		 */
+		fr_value_box_copy(vp, &vp->data, &netaddr->data);
+	}
+	fr_cursor_append(&cursor, vp);
+
 	/*
 	 *	Client can request a LARGER size, but not a smaller
 	 *	one.  They also cannot request a size larger than MTU.