Generate RTM_NEWROUTE netlink notification when the route preference
 changes on an existing kernel generated default route in response to
 RA messages. Currently netlink notifications are generated only when
 this route is added or deleted but not when the route preference
 changes, which can cause userspace routing application state to go
 out of sync with kernel.

Signed-off-by: Kalash Nainwal <kalash@arista.com>
---
 net/ipv6/ndisc.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index f03b597e4121..fd14f5b1c767 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1337,8 +1337,12 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 			return;
 		}
 		neigh->flags |= NTF_ROUTER;
-	} else if (rt) {
+	} else if (rt && IPV6_EXTRACT_PREF(rt->fib6_flags) != pref) {
+		struct nl_info nlinfo = {
+			.nl_net = net,
+		};
 		rt->fib6_flags = (rt->fib6_flags & ~RTF_PREF_MASK) | RTF_PREF(pref);
+		inet6_rt_notify(RTM_NEWROUTE, rt, &nlinfo, NLM_F_CREATE);
 	}
 
 	if (rt)
-- 
2.30.1 (Apple Git-130)

On 2/9/22 12:38 PM, Kalash Nainwal wrote:
> diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
> index f03b597e4121..fd14f5b1c767 100644
> --- a/net/ipv6/ndisc.c
> +++ b/net/ipv6/ndisc.c
> @@ -1337,8 +1337,12 @@ static void ndisc_router_discovery(struct sk_buff *skb)
>  			return;
>  		}
>  		neigh->flags |= NTF_ROUTER;
> -	} else if (rt) {
> +	} else if (rt && IPV6_EXTRACT_PREF(rt->fib6_flags) != pref) {
> +		struct nl_info nlinfo = {
> +			.nl_net = net,
> +		};
>  		rt->fib6_flags = (rt->fib6_flags & ~RTF_PREF_MASK) | RTF_PREF(pref);
> +		inet6_rt_notify(RTM_NEWROUTE, rt, &nlinfo, NLM_F_CREATE);
>  	}
>  
>  	if (rt)

route exists, but the flags are updated so that should be NLM_F_REPLACE.