networkd: add preferred source to dhcp4 gateway route

This makes DHCPv4 and IPv4LL coexist peacefully.

[tomegun: apply to both the dhcp routes, use in_addr_is_null() rather than a
separate variable to indicate when prefsrc should be applied]

3 files changed, 34 insertions, 0 deletions

diff --git a/src/network/networkd-dhcp4.c b/src/network/networkd-dhcp4.c
index 5e4ff2b80b..b87fa73082 100644
--- a/src/network/networkd-dhcp4.c
+++ b/src/network/networkd-dhcp4.c
@@ -67,9 +67,18 @@ static int link_set_dhcp_routes(Link *link) {
                 return r;
         }
         if (r >= 0) {
+                struct in_addr address;
                 _cleanup_route_free_ Route *route = NULL;
                 _cleanup_route_free_ Route *route_gw = NULL;
 
+                r = sd_dhcp_lease_get_address(link->dhcp_lease, &address);
+                if (r < 0) {
+                        log_warning_link(link,
+                                         "DHCP error: could not get address: %s",
+                                         strerror(-r));
+                        return r;
+                }
+
                 r = route_new_dynamic(&route, RTPROT_DHCP);
                 if (r < 0) {
                         log_error_link(link,
@@ -92,6 +101,7 @@ static int link_set_dhcp_routes(Link *link) {
                 route_gw->family = AF_INET;
                 route_gw->dst_addr.in = gateway;
                 route_gw->dst_prefixlen = 32;
+                route_gw->prefsrc_addr.in = address;
                 route_gw->scope = RT_SCOPE_LINK;
                 route_gw->metrics = DHCP_ROUTE_METRIC;
 
@@ -107,6 +117,7 @@ static int link_set_dhcp_routes(Link *link) {
 
                 route->family = AF_INET;
                 route->in_addr.in = gateway;
+                route->prefsrc_addr.in = address;
                 route->metrics = DHCP_ROUTE_METRIC;
 
                 r = route_configure(route, link, &dhcp4_route_handler);
diff --git a/src/network/networkd-route.c b/src/network/networkd-route.c
index aead4fbb9e..10d8cd902a 100644
--- a/src/network/networkd-route.c
+++ b/src/network/networkd-route.c
@@ -144,6 +144,17 @@ int route_drop(Route *route, Link *link,
                 }
         }
 
+        if (!in_addr_is_null(route->family, &route->prefsrc_addr)) {
+                if (route->family == AF_INET)
+                        r = sd_rtnl_message_append_in_addr(req, RTA_PREFSRC, &route->prefsrc_addr.in);
+                else if (route->family == AF_INET6)
+                        r = sd_rtnl_message_append_in6_addr(req, RTA_PREFSRC, &route->prefsrc_addr.in6);
+                if (r < 0) {
+                        log_error("Could not append RTA_PREFSRC attribute: %s", strerror(-r));
+                        return r;
+                }
+        }
+
         r = sd_rtnl_message_route_set_scope(req, route->scope);
         if (r < 0) {
                 log_error("Could not set scope: %s", strerror(-r));
@@ -218,6 +229,17 @@ int route_configure(Route *route, Link *link,
                 }
         }
 
+        if (!in_addr_is_null(route->family, &route->prefsrc_addr)) {
+                if (route->family == AF_INET)
+                        r = sd_rtnl_message_append_in_addr(req, RTA_PREFSRC, &route->prefsrc_addr.in);
+                else if (route->family == AF_INET6)
+                        r = sd_rtnl_message_append_in6_addr(req, RTA_PREFSRC, &route->prefsrc_addr.in6);
+                if (r < 0) {
+                        log_error("Could not append RTA_PREFSRC attribute: %s", strerror(-r));
+                        return r;
+                }
+        }
+
         r = sd_rtnl_message_route_set_scope(req, route->scope);
         if (r < 0) {
                 log_error("Could not set scope: %s", strerror(-r));
diff --git a/src/network/networkd.h b/src/network/networkd.h
index ab5df1aa3c..c6e6b22c38 100644
--- a/src/network/networkd.h
+++ b/src/network/networkd.h
@@ -150,6 +150,7 @@ struct Route {
 
         union in_addr_union in_addr;
         union in_addr_union dst_addr;
+        union in_addr_union prefsrc_addr;
 
         LIST_FIELDS(Route, routes);
 };