netdev - Re: [PATCH bpf v2 1/3] bpf_redirect_neigh: Support supplying the nexthop as a helper parameter

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Date:   Tue, 20 Oct 2020 17:08:42 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH bpf v2 1/3] bpf_redirect_neigh: Support supplying the
 nexthop as a helper parameter

On 10/20/20 12:51 PM, Toke Høiland-Jørgensen wrote:
> From: Toke Høiland-Jørgensen <toke@...hat.com>
[...]
>   BPF_CALL_3(bpf_clone_redirect, struct sk_buff *, skb, u32, ifindex, u64, flags)
> @@ -2455,8 +2487,8 @@ int skb_do_redirect(struct sk_buff *skb)
>   		return -EAGAIN;
>   	}
>   	return flags & BPF_F_NEIGH ?
> -	       __bpf_redirect_neigh(skb, dev) :
> -	       __bpf_redirect(skb, dev, flags);
> +		__bpf_redirect_neigh(skb, dev, flags & BPF_F_NEXTHOP ? &ri->nh : NULL) :
> +		__bpf_redirect(skb, dev, flags);
>   out_drop:
>   	kfree_skb(skb);
>   	return -EINVAL;
> @@ -2504,16 +2536,25 @@ static const struct bpf_func_proto bpf_redirect_peer_proto = {
>   	.arg2_type      = ARG_ANYTHING,
>   };
>   
> -BPF_CALL_2(bpf_redirect_neigh, u32, ifindex, u64, flags)
> +BPF_CALL_4(bpf_redirect_neigh, u32, ifindex, struct bpf_redir_neigh *, params,
> +	   int, plen, u64, flags)
>   {
>   	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
>   
> -	if (unlikely(flags))
> +	if (unlikely((plen && plen < sizeof(*params)) || flags))
> +		return TC_ACT_SHOT;
> +
> +	if (unlikely(plen && (params->unused[0] || params->unused[1] ||
> +			      params->unused[2])))

small nit: maybe fold this into the prior check that already tests non-zero plen

if (unlikely((plen && (plen < sizeof(*params) ||
                        (params->unused[0] | params->unused[1] |
                         params->unused[2]))) || flags))
         return TC_ACT_SHOT;

>   		return TC_ACT_SHOT;
>   
> -	ri->flags = BPF_F_NEIGH;
> +	ri->flags = BPF_F_NEIGH | (plen ? BPF_F_NEXTHOP : 0);
>   	ri->tgt_index = ifindex;
>   
> +	BUILD_BUG_ON(sizeof(struct bpf_redir_neigh) != sizeof(struct bpf_nh_params));
> +	if (plen)
> +		memcpy(&ri->nh, params, sizeof(ri->nh));
> +
>   	return TC_ACT_REDIRECT;
>   }
>