platform: preserve IPv6 multicast route added by kernelbg/ipv6-multicast-route-rh2004212

Kernels < 5.11 add a route like:

  unicast ff00::/8 dev $IFACE proto boot scope global metric 256 pref medium

to allow sending and receiving IPv6 multicast traffic. Ensure it's not
removed it when we do a route sync in mode ALL.

In kernel 5.11 there were commits:

  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ceed9038b2783d14e0422bdc6fd04f70580efb4c
  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a826b04303a40d52439aa141035fca5654ccaccd

After those the route looks like

  multicast ff00::/8 dev $IFACE proto kernel metric 256 pref medium

As NM ignores routes with rtm_type multicast, the code in this commit
is not needed on newer kernels.

https://bugzilla.redhat.com/show_bug.cgi?id=2004212
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/984

1 files changed, 39 insertions, 0 deletions

diff --git a/src/libnm-platform/nm-platform.c b/src/libnm-platform/nm-platform.c
index e65e47041e..fb9dcf50b8 100644
--- a/src/libnm-platform/nm-platform.c
+++ b/src/libnm-platform/nm-platform.c
@@ -4288,6 +4288,7 @@ nm_platform_ip_route_get_prune_list(NMPlatform *           self,
     CList *                      iter;
     NMPlatformIP4Route           rt_local4;
     NMPlatformIP6Route           rt_local6;
+    NMPlatformIP6Route           rt_mcast6;
     const NMPlatformLink *       pllink;
     const NMPlatformLnkVrf *     lnk_vrf;
     guint32                      local_table;
@@ -4312,6 +4313,7 @@ nm_platform_ip_route_get_prune_list(NMPlatform *           self,
 
     rt_local4.plen = 0;
     rt_local6.plen = 0;
+    rt_mcast6.plen = 0;
 
     routes_prune = g_ptr_array_new_full(head_entry->len, (GDestroyNotify) nm_dedup_multi_obj_unref);
 
@@ -4404,6 +4406,43 @@ nm_platform_ip_route_get_prune_list(NMPlatform *           self,
                         == 0)
                         continue;
                 }
+
+                /* Kernels < 5.11 add a route like:
+                 *
+                 * unicast ff00::/8 dev $IFACE proto boot scope global metric 256 pref medium
+                 *
+                 * to allow sending and receiving IPv6 multicast traffic. Don't remove it.
+                 * Since kernel 5.11 the route looks like:
+                 *
+                 * multicast ff00::/8 dev $IFACE proto kernel metric 256 pref medium
+                 *
+                 * As NM ignores routes with rtm_type multicast, there is no need for the code
+                 * below on newer kernels.
+                 */
+                if (nm_platform_ip_route_get_effective_table(&rt->rx) == local_table
+                    && rt->rx.plen == 8 && rt->rx.rt_source == NM_IP_CONFIG_SOURCE_RTPROT_BOOT
+                    && rt->rx.metric == 256 && rt->r6.rt_pref == NM_ICMPV6_ROUTER_PREF_MEDIUM
+                    && IN6_IS_ADDR_UNSPECIFIED(&rt->r6.gateway)) {
+                    if (rt_mcast6.plen == 0) {
+                        rt_mcast6 = (NMPlatformIP6Route){
+                            .ifindex       = ifindex,
+                            .type_coerced  = nm_platform_route_type_coerce(RTN_UNICAST),
+                            .plen          = 8,
+                            .rt_source     = NM_IP_CONFIG_SOURCE_RTPROT_BOOT,
+                            .metric        = 256,
+                            .table_coerced = nm_platform_route_table_coerce(local_table),
+                            .rt_pref       = NM_ICMPV6_ROUTER_PREF_MEDIUM,
+                            .gateway       = IN6ADDR_ANY_INIT,
+                            .network = {{{0xff, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}}},
+                        };
+                    }
+
+                    if (nm_platform_ip6_route_cmp(&rt->r6,
+                                                  &rt_mcast6,
+                                                  NM_PLATFORM_IP_ROUTE_CMP_TYPE_SEMANTICALLY)
+                        == 0)
+                        continue;
+                }
             }
             break;