Subject: Re: [PATCH 09/11 net-next v5] bpf: remove ipv6_bpf_stub completely and use direct function calls

From: Martin KaFai Lau <[email-masked]>
Date: Wed, 25 Mar 2026 12:11:17 -0700

On 3/25/26 5:08 AM, Fernando Fernandez Mancera wrote:
> As IPv6 is built-in only, the ipv6_bpf_stub can be removed completely.
> 
> Convert all ipv6_bpf_stub usage to direct function calls instead. The
> fallback functions introduced previously will prevent linkage errors
> when CONFIG_IPV6 is disabled.

Thanks for working on this.

> @@ -6221,8 +6215,8 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
>   	if (likely(nhc->nhc_gw_family != AF_INET6))
>   		neigh = __ipv4_neigh_lookup_noref(dev,
>   						  (__force u32)params->ipv4_dst);
> -	else
> -		neigh = __ipv6_neigh_lookup_noref_stub(dev, params->ipv6_dst);
> +	else if (IS_ENABLED(CONFIG_IPV6))
> +		neigh = __ipv6_neigh_lookup_noref(dev, params->ipv6_dst);

Should it be ipv6_mod_enabled() instead of IS_ENABLED(CONFIG_IPV6)?
Is nd_tbl always initialized?

>   
>   	if (!neigh || !(READ_ONCE(neigh->nud_state) & NUD_VALID))
>   		return BPF_FIB_LKUP_RET_NO_NEIGH;
> @@ -6290,12 +6284,11 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
>   			params->tbid = 0;
>   		}
>   
> -		tb = ipv6_stub->fib6_get_table(net, tbid);
> +		tb = fib6_get_table(net, tbid);
>   		if (unlikely(!tb))
>   			return BPF_FIB_LKUP_RET_NOT_FWDED;
>   
> -		err = ipv6_stub->fib6_table_lookup(net, tb, oif, &fl6, &res,
> -						   strict);
> +		err = fib6_table_lookup(net, tb, oif, &fl6, &res, strict);

A similar question here and other changes in the patch.

I think bpf_ipv6_fib_lookup() is fine because the earlier
"!idev" check should fail when ipv6 is disabled at boot time?

>   	} else {
>   		if (flags & BPF_FIB_LOOKUP_MARK)
>   			fl6.flowi6_mark = params->mark;
> @@ -6305,7 +6298,7 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
>   		fl6.flowi6_tun_key.tun_id = 0;
>   		fl6.flowi6_uid = sock_net_uid(net, NULL);
>   
> -		err = ipv6_stub->fib6_lookup(net, oif, &fl6, &res, strict);
> +		err = fib6_lookup(net, oif, &fl6, &res, strict);
>   	}
>   
>   	if (unlikely(err || IS_ERR_OR_NULL(res.f6i) ||
> @@ -6326,11 +6319,11 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
>   		return BPF_FIB_LKUP_RET_NOT_FWDED;
>   	}
>   
> -	ipv6_stub->fib6_select_path(net, &res, &fl6, fl6.flowi6_oif,
> -				    fl6.flowi6_oif != 0, NULL, strict);
> +	fib6_select_path(net, &res, &fl6, fl6.flowi6_oif,
> +			 fl6.flowi6_oif != 0, NULL, strict);
>   
>   	if (check_mtu) {
> -		mtu = ipv6_stub->ip6_mtu_from_fib6(&res, dst, src);
> +		mtu = ip6_mtu_from_fib6(&res, dst, src);
>   		if (params->tot_len > mtu) {
>   			params->mtu_result = mtu; /* union with tot_len */
>   			return BPF_FIB_LKUP_RET_FRAG_NEEDED;
> @@ -6351,9 +6344,7 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
>   		if (res.f6i->fib6_prefsrc.plen) {
>   			*src = res.f6i->fib6_prefsrc.addr;
>   		} else {
> -			err = ipv6_bpf_stub->ipv6_dev_get_saddr(net, dev,
> -								&fl6.daddr, 0,
> -								src);
> +			err = ipv6_dev_get_saddr(net, dev, &fl6.daddr, 0, src);
>   			if (err)
>   				return BPF_FIB_LKUP_RET_NO_SRC_ADDR;
>   		}
> @@ -6365,7 +6356,7 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
>   	/* xdp and cls_bpf programs are run in RCU-bh so rcu_read_lock_bh is
>   	 * not needed here.
>   	 */
> -	neigh = __ipv6_neigh_lookup_noref_stub(dev, dst);
> +	neigh = __ipv6_neigh_lookup_noref(dev, dst);
>   	if (!neigh || !(READ_ONCE(neigh->nud_state) & NUD_VALID))
>   		return BPF_FIB_LKUP_RET_NO_NEIGH;
>   	memcpy(params->dmac, neigh->ha, ETH_ALEN);
> @@ -6900,11 +6891,10 @@ static struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
>   					    src6, tuple->ipv6.sport,
>   					    dst6, ntohs(tuple->ipv6.dport),
>   					    dif, sdif, &refcounted);
> -		else if (likely(ipv6_bpf_stub))
> -			sk = ipv6_bpf_stub->udp6_lib_lookup(net,
> -							    src6, tuple->ipv6.sport,
> -							    dst6, tuple->ipv6.dport,
> -							    dif, sdif, NULL);
> +		else if (likely(ipv6_mod_enabled()))
> +			sk = __udp6_lib_lookup(net, src6, tuple->ipv6.sport,
> +					       dst6, tuple->ipv6.dport,
> +					       dif, sdif, NULL);
>   #endif
>   	}
>   
> diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c
> index 9f40be0c3e71..f71ef82a5f3d 100644
> --- a/net/core/lwt_bpf.c
> +++ b/net/core/lwt_bpf.c
> @@ -13,7 +13,6 @@
>   #include <net/gre.h>
>   #include <net/ip.h>
>   #include <net/ip6_route.h>
> -#include <net/ipv6_stubs.h>
>   
>   struct bpf_lwt_prog {
>   	struct bpf_prog *prog;
> @@ -103,7 +102,12 @@ static int bpf_lwt_input_reroute(struct sk_buff *skb)
>   		dev_put(dev);
>   	} else if (skb->protocol == htons(ETH_P_IPV6)) {
>   		skb_dst_drop(skb);
> -		err = ipv6_stub->ipv6_route_input(skb);
> +		if (IS_ENABLED(CONFIG_IPV6)) {
> +			ip6_route_input(skb);
> +			err = skb_dst(skb)->error;
> +		} else {
> +			err = -EAFNOSUPPORT;
> +		}
>   	} else {
>   		err = -EAFNOSUPPORT;
>   	}
> @@ -233,7 +237,7 @@ static int bpf_lwt_xmit_reroute(struct sk_buff *skb)
>   		fl6.daddr = iph6->daddr;
>   		fl6.saddr = iph6->saddr;
>   
> -		dst = ipv6_stub->ipv6_dst_lookup_flow(net, skb->sk, &fl6, NULL);
> +		dst = ip6_dst_lookup_flow(net, skb->sk, &fl6, NULL);
>   		if (IS_ERR(dst)) {
>   			err = PTR_ERR(dst);
>   			goto err;
> diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
> index bb29b29fdcfb..07ae6ea7743a 100644
> --- a/net/ipv6/af_inet6.c
> +++ b/net/ipv6/af_inet6.c
> @@ -264,8 +264,8 @@ static int inet6_create(struct net *net, struct socket *sock, int protocol,
>   	goto out;
>   }
>   
> -static int __inet6_bind(struct sock *sk, struct sockaddr_unsized *uaddr, int addr_len,
> -			u32 flags)
> +int __inet6_bind(struct sock *sk, struct sockaddr_unsized *uaddr, int addr_len,
> +		 u32 flags)
>   {
>   	struct sockaddr_in6 *addr = (struct sockaddr_in6 *)uaddr;
>   	struct inet_sock *inet = inet_sk(sk);
> @@ -1032,14 +1032,6 @@ static const struct ipv6_stub ipv6_stub_impl = {
>   	.ip6_xmit = ip6_xmit,
>   };
>   
> -static const struct ipv6_bpf_stub ipv6_bpf_stub_impl = {
> -	.inet6_bind = __inet6_bind,
> -	.udp6_lib_lookup = __udp6_lib_lookup,
> -	.ipv6_setsockopt = do_ipv6_setsockopt,
> -	.ipv6_getsockopt = do_ipv6_getsockopt,
> -	.ipv6_dev_get_saddr = ipv6_dev_get_saddr,
> -};
> -
>   static int __init inet6_init(void)
>   {
>   	struct list_head *r;
> @@ -1199,7 +1191,6 @@ static int __init inet6_init(void)
>   	/* ensure that ipv6 stubs are visible only after ipv6 is ready */
>   	wmb();
>   	ipv6_stub = &ipv6_stub_impl;
> -	ipv6_bpf_stub = &ipv6_bpf_stub_impl;
>   out:
>   	return err;
>