netdev - Re: [nf-next PATCH] net: netfilter: Support iif matches in POSTROUTING

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Date:   Thu, 14 Nov 2019 00:08:42 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Phil Sutter <phil@....cc>
Cc:     netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
        Eric Garver <eric@...ver.life>
Subject: Re: [nf-next PATCH] net: netfilter: Support iif matches in
 POSTROUTING

On Tue, Nov 12, 2019 at 05:14:37PM +0100, Phil Sutter wrote:
> Instead of generally passing NULL to NF_HOOK_COND() for input device,
> pass skb->dev which contains input device for routed skbs.
> 
> Note that iptables (both legacy and nft) reject rules with input
> interface match from being added to POSTROUTING chains, but nftables
> allows this.

Yes, it allows this but it will not ever match, right? So even if the
rule is loaded, it will be useless.

Do you have a usecase in mind that would benefit from this specifically?

> Cc: Eric Garver <eric@...ver.life>
> Signed-off-by: Phil Sutter <phil@....cc>
> ---
>  net/ipv4/ip_output.c    | 4 ++--
>  net/ipv4/xfrm4_output.c | 2 +-
>  net/ipv6/ip6_output.c   | 4 ++--
>  net/ipv6/xfrm6_output.c | 2 +-
>  4 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index 3d8baaaf7086d..9d83cb320dcb7 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -422,7 +422,7 @@ int ip_mc_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  
>  int ip_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  {
> -	struct net_device *dev = skb_dst(skb)->dev;
> +	struct net_device *dev = skb_dst(skb)->dev, *indev = skb->dev;
>  
>  	IP_UPD_PO_STATS(net, IPSTATS_MIB_OUT, skb->len);
>  
> @@ -430,7 +430,7 @@ int ip_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  	skb->protocol = htons(ETH_P_IP);
>  
>  	return NF_HOOK_COND(NFPROTO_IPV4, NF_INET_POST_ROUTING,
> -			    net, sk, skb, NULL, dev,
> +			    net, sk, skb, indev, dev,
>  			    ip_finish_output,
>  			    !(IPCB(skb)->flags & IPSKB_REROUTED));
>  }
> diff --git a/net/ipv4/xfrm4_output.c b/net/ipv4/xfrm4_output.c
> index ecff3fce98073..89ba7c87de5df 100644
> --- a/net/ipv4/xfrm4_output.c
> +++ b/net/ipv4/xfrm4_output.c
> @@ -92,7 +92,7 @@ static int __xfrm4_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  int xfrm4_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  {
>  	return NF_HOOK_COND(NFPROTO_IPV4, NF_INET_POST_ROUTING,
> -			    net, sk, skb, NULL, skb_dst(skb)->dev,
> +			    net, sk, skb, skb->dev, skb_dst(skb)->dev,
>  			    __xfrm4_output,
>  			    !(IPCB(skb)->flags & IPSKB_REROUTED));
>  }
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 71827b56c0063..945508a7cb0f1 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -160,7 +160,7 @@ static int ip6_finish_output(struct net *net, struct sock *sk, struct sk_buff *s
>  
>  int ip6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  {
> -	struct net_device *dev = skb_dst(skb)->dev;
> +	struct net_device *dev = skb_dst(skb)->dev, *indev = skb->dev;
>  	struct inet6_dev *idev = ip6_dst_idev(skb_dst(skb));
>  
>  	skb->protocol = htons(ETH_P_IPV6);
> @@ -173,7 +173,7 @@ int ip6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  	}
>  
>  	return NF_HOOK_COND(NFPROTO_IPV6, NF_INET_POST_ROUTING,
> -			    net, sk, skb, NULL, dev,
> +			    net, sk, skb, indev, dev,
>  			    ip6_finish_output,
>  			    !(IP6CB(skb)->flags & IP6SKB_REROUTED));
>  }
> diff --git a/net/ipv6/xfrm6_output.c b/net/ipv6/xfrm6_output.c
> index eecac1b7148e5..fbe51d40bd7e9 100644
> --- a/net/ipv6/xfrm6_output.c
> +++ b/net/ipv6/xfrm6_output.c
> @@ -187,7 +187,7 @@ static int __xfrm6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  int xfrm6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  {
>  	return NF_HOOK_COND(NFPROTO_IPV6, NF_INET_POST_ROUTING,
> -			    net, sk, skb,  NULL, skb_dst(skb)->dev,
> +			    net, sk, skb,  skb->dev, skb_dst(skb)->dev,
>  			    __xfrm6_output,
>  			    !(IP6CB(skb)->flags & IP6SKB_REROUTED));
>  }
> -- 
> 2.24.0
>