networkd: use VRFs routing table for DHCP routes

When an interface has been enslaved to a VRF the received routes should
be added to the VRFs RT instead of the main table.

This change modifies the default behaviour of routes in the case where a
network belongs to an VRF.  When the user does not configure a
`DHCP.RouteTable` in a `systemd.network` file and the interface belongs
to a VRF, the VRFs routing table is used instead of RT_TABLE_MAIN.

When the user has configured a custom routing table for DHCP the VRFs
table is ignored and the users preference takes precedence.

src/network/networkd-dhcp4.c

@@ -23,6 +23,7 @@
 #include "alloc-util.h"
 #include "dhcp-lease-internal.h"
 #include "hostname-util.h"
+#include "netdev/vrf.h"
 #include "network-internal.h"
 #include "networkd-link.h"
 #include "networkd-manager.h"
@@ -69,6 +70,7 @@ static int link_set_dhcp_routes(Link *link) {
         struct in_addr gateway, address;
         _cleanup_free_ sd_dhcp_route **static_routes = NULL;
         int r, n, i;
+        uint32_t table;
 
         assert(link);
 
@@ -81,6 +83,12 @@ static int link_set_dhcp_routes(Link *link) {
         if (!link->network->dhcp_use_routes)
                 return 0;
 
+        /* When the interface is part of an VRF use the VRFs routing table, unless
+         * there is a another table specified. */
+        table = link->network->dhcp_route_table;
+        if (!link->network->dhcp_route_table_set && link->network->vrf != NULL)
+                table = VRF(link->network->vrf)->table;
+
         r = sd_dhcp_lease_get_address(link->dhcp_lease, &address);
         if (r < 0)
                 return log_link_warning_errno(link, r, "DHCP error: could not get address: %m");
@@ -113,7 +121,7 @@ static int link_set_dhcp_routes(Link *link) {
                 route_gw->scope = RT_SCOPE_LINK;
                 route_gw->protocol = RTPROT_DHCP;
                 route_gw->priority = link->network->dhcp_route_metric;
-                route_gw->table = link->network->dhcp_route_table;
+                route_gw->table = table;
 
                 r = route_configure(route_gw, link, dhcp4_route_handler);
                 if (r < 0)
@@ -125,7 +133,7 @@ static int link_set_dhcp_routes(Link *link) {
                 route->gw.in = gateway;
                 route->prefsrc.in = address;
                 route->priority = link->network->dhcp_route_metric;
-                route->table = link->network->dhcp_route_table;
+                route->table = table;
 
                 r = route_configure(route, link, dhcp4_route_handler);
                 if (r < 0) {
@@ -156,7 +164,7 @@ static int link_set_dhcp_routes(Link *link) {
                 assert_se(sd_dhcp_route_get_destination(static_routes[i], &route->dst.in) >= 0);
                 assert_se(sd_dhcp_route_get_destination_prefix_length(static_routes[i], &route->dst_prefixlen) >= 0);
                 route->priority = link->network->dhcp_route_metric;
-                route->table = link->network->dhcp_route_table;
+                route->table = table;
                 route->scope = route_scope_from_address(route, &address);
 
                 r = route_configure(route, link, dhcp4_route_handler);

src/network/networkd-network-gperf.gperf

@@ -110,7 +110,7 @@ DHCP.VendorClassIdentifier,             config_parse_string,
 DHCP.DUIDType,                          config_parse_duid_type,                         0,                             offsetof(Network, duid.type)
 DHCP.DUIDRawData,                       config_parse_duid_rawdata,                      0,                             offsetof(Network, duid)
 DHCP.RouteMetric,                       config_parse_unsigned,                          0,                             offsetof(Network, dhcp_route_metric)
-DHCP.RouteTable,                        config_parse_dhcp_route_table,                  0,                             offsetof(Network, dhcp_route_table)
+DHCP.RouteTable,                        config_parse_dhcp_route_table,                  0,                             0
 DHCP.UseTimezone,                       config_parse_bool,                              0,                             offsetof(Network, dhcp_use_timezone)
 DHCP.IAID,                              config_parse_iaid,                              0,                             offsetof(Network, iaid)
 DHCP.ListenPort,                        config_parse_uint16,                            0,                             offsetof(Network, dhcp_client_port)

src/network/networkd-network.c

@@ -212,6 +212,7 @@ static int network_load_one(Manager *manager, const char *filename) {
         /* NOTE: this var might be overwrite by network_apply_anonymize_if_set */
         network->dhcp_client_identifier = DHCP_CLIENT_ID_DUID;
         network->dhcp_route_table = RT_TABLE_MAIN;
+        network->dhcp_route_table_set = false;
         /* NOTE: the following vars were not set to any default,
          * even if they are commented in the man?
          * These vars might be overwriten by network_apply_anonymize_if_set */
@@ -1339,6 +1340,7 @@ int config_parse_dhcp_route_table(const char *unit,
                                   const char *rvalue,
                                   void *data,
                                   void *userdata) {
+        Network *network = data;
         uint32_t rt;
         int r;
 
@@ -1354,7 +1356,8 @@ int config_parse_dhcp_route_table(const char *unit,
                 return 0;
         }
 
-        *((uint32_t *)data) = rt;
+        network->dhcp_route_table = rt;
+        network->dhcp_route_table_set = true;
 
         return 0;
 }

src/network/networkd-network.h

@@ -138,6 +138,7 @@ struct Network {
         bool dhcp_use_routes;
         bool dhcp_use_timezone;
         bool dhcp_use_hostname;
+        bool dhcp_route_table_set;
         DHCPUseDomains dhcp_use_domains;
 
         /* DHCP Server Support */