From bed605f5bd8524779b3cf3d3e02baf06a76f4054 Mon Sep 17 00:00:00 2001

From: Beniamino Galvani <bgalvani@redhat.com>

Date: Wed, 10 May 2017 16:17:48 +0200

Subject: [PATCH] dhcp: don't add route to DHCP4 server

This basically reverts commit 31fe84e46773 "core: Add host route for

DHCP4 server if outside assigned subnet (bgo #721767)" because the

additional route added by NM does more harm than good.

First, the code does not consider routes pushed by the server and thus

it can add a route conflicting with the ones from the network

administrator.

Second, there is no specification on what a DHCP client should do when

the server is not reachable via unicast, and adding arbitrary logic

into the client is likely to break things in specific cases. If

network administrators want to make the DHCP server reachable from a

client in a different subnet, they should push proper routes with the

lease.

In any case, if the DHCP server is not reachable through unicast,

before the lease expiration (after timeout T2) the client will resort

to broadcast and so there won't be any network disruption; the renewal

will only happen at a later time.

Fixes: 31fe84e467732463eabc8f70c2a419008e7a227c

https://bugzilla.redhat.com/show_bug.cgi?id=1448987

(cherry picked from commit 36e97f5d7beba7ab5446c2b7c6c22523b1bca476)

(cherry picked from commit cbf5a776f72d1895405b71f45a74cf4fe9046dae)

---

 src/dhcp/nm-dhcp-utils.c | 37 -------------------------------------

 1 file changed, 37 deletions(-)

diff --git a/src/dhcp/nm-dhcp-utils.c b/src/dhcp/nm-dhcp-utils.c

index e020ca3..e55a21b 100644

--- a/src/dhcp/nm-dhcp-utils.c

+++ b/src/dhcp/nm-dhcp-utils.c

@@ -450,43 +450,6 @@ nm_dhcp_utils_ip4_config_from_options (int ifindex,

 		}

 	}

-	/*

-	 * RFC 2132, section 9.7

-	 *   DHCP clients use the contents of the 'server identifier' field

-	 *   as the destination address for any DHCP messages unicast to

-	 *   the DHCP server.

-	 *

-	 * Some ISP's provide leases from central servers that are on

-	 * different subnets that the address offered.  If the host

-	 * does not configure the interface as the default route, the

-	 * dhcp server may not be reachable via unicast, and a host

-	 * specific route is needed.

-	 **/

-	str = g_hash_table_lookup (options, "dhcp_server_identifier");

-	if (str) {

-		if (inet_pton (AF_INET, str, &tmp_addr) > 0) {

-

-			_LOG2I (LOGD_DHCP4, iface, "  server identifier %s", str);

-			if (   nm_utils_ip4_address_clear_host_address(tmp_addr, address.plen) != nm_utils_ip4_address_clear_host_address(address.address, address.plen)

-			    && !nm_ip4_config_get_direct_route_for_host (ip4_config, tmp_addr)) {

-				/* DHCP server not on assigned subnet and the no direct route was returned. Add route */

-				NMPlatformIP4Route route = { 0 };

-

-				route.network = tmp_addr;

-				route.plen = 32;

-				/* this will be a device route if gwaddr is 0 */

-				route.gateway = gwaddr;

-				route.rt_source = NM_IP_CONFIG_SOURCE_DHCP;

-				route.metric = priority;

-				nm_ip4_config_add_route (ip4_config, &route);

-				_LOG2D (LOGD_IP, iface, "adding route for server identifier: %s",

-				        nm_platform_ip4_route_to_string (&route, NULL, 0));

-			}

-		}

-		else

-			_LOG2W (LOGD_DHCP4, iface, "ignoring invalid server identifier '%s'", str);

-	}

-

 	str = g_hash_table_lookup (options, "dhcp_lease_time");

 	if (str) {

 		address.lifetime = address.preferred = strtoul (str, NULL, 10);

-- 

2.9.3