core/rdisc: add autoconf addresses as /64 (instead of /128)

This feature needs support from the kernel and libnl.

If there is no system support, NM acts as before, adding the
autoconf address as /128. It does so, to prevent the kernel
from adding a route for this prefix. With system support, we
add the address as /64 and set the flag IFA_F_NOPREFIXROUTE.

https://bugzilla.redhat.com/show_bug.cgi?id=1044590
https://bugzilla.redhat.com/show_bug.cgi?id=1045118

Signed-off-by: Thomas Haller <thaller@redhat.com>

1 files changed, 27 insertions, 1 deletions

diff --git a/src/devices/nm-device.c b/src/devices/nm-device.c
index 90ffff4b32..c6581b4b61 100644
--- a/src/devices/nm-device.c
+++ b/src/devices/nm-device.c
@@ -36,6 +36,7 @@
 #include <arpa/inet.h>
 #include <fcntl.h>
 #include <linux/if.h>
+#include <netlink/route/addr.h>
 
 #include "libgsystem.h"
 #include "nm-glib-compat.h"
@@ -74,6 +75,11 @@
 #include "nm-device-bond.h"
 #include "nm-device-team.h"
 
+/* workaround for older libnl version, that does not define this flag. */
+#ifndef IFA_F_NOPREFIXROUTE
+#define IFA_F_NOPREFIXROUTE 0x200
+#endif
+
 static void impl_device_disconnect (NMDevice *device, DBusGMethodInvocation *context);
 
 #include "nm-device-glue.h"
@@ -3313,6 +3319,25 @@ rdisc_config_changed (NMRDisc *rdisc, NMRDiscConfigMap changed, NMDevice *device
 	NMConnection *connection;
 	int i;
 	NMDeviceStateReason reason;
+	static int system_support = -1;
+	guint ifa_flags;
+
+	if (system_support == -1) {
+		/*
+		 * Check, if both libnl and the kernel are recent enough,
+		 * to help user space handling RA. If it's not supported,
+		 * we must add autoconf addresses as /128.
+		 * The reason for /128 is to prevent the kernel from adding
+		 * a prefix route for this address.
+		 **/
+		system_support = nm_platform_check_support_libnl_extended_ifa_flags () &&
+		                 nm_platform_check_support_kernel_extended_ifa_flags ();
+	}
+
+	/* without system_support, this flag will be ignored.
+	 * Still, we set it (why not?).
+	 **/
+	ifa_flags = IFA_F_NOPREFIXROUTE;
 
 	g_return_if_fail (priv->act_request);
 	connection = nm_device_get_connection (device);
@@ -3346,11 +3371,12 @@ rdisc_config_changed (NMRDisc *rdisc, NMRDiscConfigMap changed, NMDevice *device
 
 			memset (&address, 0, sizeof (address));
 			address.address = discovered_address->address;
-			address.plen = 128;
+			address.plen = system_support ? 64 : 128;
 			address.timestamp = discovered_address->timestamp;
 			address.lifetime = discovered_address->lifetime;
 			address.preferred = discovered_address->preferred;
 			address.source = NM_PLATFORM_SOURCE_RDISC;
+			address.flags = ifa_flags;
 
 			nm_ip6_config_add_address (priv->ac_ip6_config, &address);
 		}