Re: [PATCH 1/1] netfilter: nft_fib: Fix for rpath check with VRF devices

[Guillaume Nault <gnault@redhat.com>]

On Wed, Sep 28, 2022 at 01:39:08PM +0200, Florian Westphal wrote:
> From: Phil Sutter <phil@nwl.cc>
> 
> Analogous to commit b575b24b8eee3 ("netfilter: Fix rpfilter
> dropping vrf packets by mistake") but for nftables fib expression:
> Add special treatment of VRF devices so that typical reverse path
> filtering via 'fib saddr . iif oif' expression works as expected.
> 
> Fixes: f6d0cbcf09c50 ("netfilter: nf_tables: add fib expression")
> Signed-off-by: Phil Sutter <phil@nwl.cc>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
>  net/ipv4/netfilter/nft_fib_ipv4.c | 3 +++
>  net/ipv6/netfilter/nft_fib_ipv6.c | 6 +++++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/netfilter/nft_fib_ipv4.c b/net/ipv4/netfilter/nft_fib_ipv4.c
> index b75cac69bd7e..7ade04ff972d 100644
> --- a/net/ipv4/netfilter/nft_fib_ipv4.c
> +++ b/net/ipv4/netfilter/nft_fib_ipv4.c
> @@ -83,6 +83,9 @@ void nft_fib4_eval(const struct nft_expr *expr, struct nft_regs *regs,
>  	else
>  		oif = NULL;
>  
> +	if (priv->flags & NFTA_FIB_F_IIF)
> +		fl4.flowi4_oif = l3mdev_master_ifindex_rcu(oif);
> +

Shouldn't we set .flowi4_l3mdev instead of .flowi4_oif?

>  	if (nft_hook(pkt) == NF_INET_PRE_ROUTING &&
>  	    nft_fib_is_loopback(pkt->skb, nft_in(pkt))) {
>  		nft_fib_store_result(dest, priv, nft_in(pkt));
> diff --git a/net/ipv6/netfilter/nft_fib_ipv6.c b/net/ipv6/netfilter/nft_fib_ipv6.c
> index 8970d0b4faeb..1d7e520d9966 100644
> --- a/net/ipv6/netfilter/nft_fib_ipv6.c
> +++ b/net/ipv6/netfilter/nft_fib_ipv6.c
> @@ -41,6 +41,9 @@ static int nft_fib6_flowi_init(struct flowi6 *fl6, const struct nft_fib *priv,
>  	if (ipv6_addr_type(&fl6->daddr) & IPV6_ADDR_LINKLOCAL) {
>  		lookup_flags |= RT6_LOOKUP_F_IFACE;
>  		fl6->flowi6_oif = get_ifindex(dev ? dev : pkt->skb->dev);
> +	} else if ((priv->flags & NFTA_FIB_F_IIF) &&
> +		   (netif_is_l3_master(dev) || netif_is_l3_slave(dev))) {
> +		fl6->flowi6_oif = dev->ifindex;
>  	}
>  
>  	if (ipv6_addr_type(&fl6->saddr) & IPV6_ADDR_UNICAST)
> @@ -197,7 +200,8 @@ void nft_fib6_eval(const struct nft_expr *expr, struct nft_regs *regs,
>  	if (rt->rt6i_flags & (RTF_REJECT | RTF_ANYCAST | RTF_LOCAL))
>  		goto put_rt_err;
>  
> -	if (oif && oif != rt->rt6i_idev->dev)
> +	if (oif && oif != rt->rt6i_idev->dev &&
> +	    l3mdev_master_ifindex_rcu(rt->rt6i_idev->dev) != oif->ifindex)
>  		goto put_rt_err;
>  
>  	nft_fib_store_result(dest, priv, rt->rt6i_idev->dev);
> -- 
> 2.35.1
>