netdev - Re: [PATCH] netfilter: nft_paylaod: add base type NFT_PAYLOAD_LL_HEADER_NO

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Date:   Tue, 18 Jun 2019 00:30:04 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Florian Westphal <fw@...len.de>
Cc:     wenxu@...oud.cn, netfilter-devel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH] netfilter: nft_paylaod: add base type
 NFT_PAYLOAD_LL_HEADER_NO_TAG

Hi Florian,

On Mon, Jun 10, 2019 at 11:44:33AM +0200, Florian Westphal wrote:
> wenxu@...oud.cn <wenxu@...oud.cn> wrote:
> > From: wenxu <wenxu@...oud.cn>
> > 
> > nft add rule bridge firewall rule-100-ingress ip protocol icmp drop
> 
> nft --debug=netlink add rule bridge firewall rule-100-ingress ip protocol icmp drop
> bridge firewall rule-100-ingress
>   [ payload load 2b @ link header + 12 => reg 1 ]
>   [ cmp eq reg 1 0x00000008 ]
>   [ payload load 1b @ network header + 9 => reg 1 ]
>   [ cmp eq reg 1 0x00000001 ]
>   [ immediate reg 0 drop ]
> 
> so problem is that nft inserts a dependency on the ethernet protocol
> type (0x800).
> 
> But when vlan is involved, that will fail to compare.
> 
> It would also fail for qinq etc.
> 
> Because of vlan tag offload, the rule about will probably already work
> just fine when nft userspace is patched to insert the dependency based
> on 'meta protocol'.  Can you see if this patch works?
> 
> Subject: Change bridge l3 dependency to meta protocol
> 
> This examines skb->protocol instead of ethernet header type, which
> might be different when vlan is involved.
> 
> nft payload expression will re-insert the vlan tag so ether type
> will not be ETH_P_IP.
> 
> ---
>  src/meta.c    |  6 +++++-
>  src/payload.c | 20 ++++++++++++++++++++
>  2 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/src/meta.c b/src/meta.c
> index 583e790ff47d..1e8964eb48c4 100644
> --- a/src/meta.c
> +++ b/src/meta.c
> @@ -539,7 +539,11 @@ static void meta_expr_pctx_update(struct proto_ctx *ctx,
>  		proto_ctx_update(ctx, PROTO_BASE_TRANSPORT_HDR, &expr->location, desc);
>  		break;
>  	case NFT_META_PROTOCOL:
> -		if (h->base < PROTO_BASE_NETWORK_HDR && ctx->family != NFPROTO_NETDEV)
> +		if (h->base != PROTO_BASE_LL_HDR)
> +			return;
> +
> +		if (ctx->family != NFPROTO_NETDEV &&
> +		    ctx->family != NFPROTO_BRIDGE)
>  			return;
>  
>  		desc = proto_find_upper(h->desc, ntohs(mpz_get_uint16(right->value)));
> diff --git a/src/payload.c b/src/payload.c
> index 6a8118ece890..c99bb2f69977 100644
> --- a/src/payload.c
> +++ b/src/payload.c
> @@ -18,6 +18,7 @@
>  #include <net/if_arp.h>
>  #include <arpa/inet.h>
>  #include <linux/netfilter.h>
> +#include <linux/if_ether.h>
>  
>  #include <rule.h>
>  #include <expression.h>
> @@ -307,6 +308,19 @@ payload_gen_special_dependency(struct eval_ctx *ctx, const struct expr *expr)
>  	return NULL;
>  }
>  
> +static const struct proto_desc proto_metaeth = {
> +	.name		= "ethmeta",
> +	.base		= PROTO_BASE_LL_HDR,
> +	.protocols	= {
> +		PROTO_LINK(__constant_htons(ETH_P_IP),	 &proto_ip),
> +		PROTO_LINK(__constant_htons(ETH_P_ARP),	 &proto_arp),
> +		PROTO_LINK(__constant_htons(ETH_P_IPV6), &proto_ip6),
> +	},
> +	.templates	= {
> +		[0]	= PROTO_META_TEMPLATE("protocol", &ethertype_type, NFT_META_PROTOCOL, 16),
> +	},
> +};
> +
>  /**
>   * payload_gen_dependency - generate match expression on payload dependency
>   *
> @@ -369,6 +383,12 @@ int payload_gen_dependency(struct eval_ctx *ctx, const struct expr *expr,
>  				  "no %s protocol specified",
>  				  proto_base_names[expr->payload.base - 1]);
>  
> +	if (ctx->pctx.family == NFPROTO_BRIDGE && desc == &proto_eth) {
> +		if (expr->payload.desc == &proto_ip ||
> +		    expr->payload.desc == &proto_ip6)
> +			desc = &proto_metaeth;
> +	}i

Is this sufficient to restrict the matching? Is this still buggy from
ingress?

I wonder if an explicit NFT_PAYLOAD_CHECK_VLAN flag would be useful in
the kernel, if so we could rename NFTA_PAYLOAD_CSUM_FLAGS to
NFTA_PAYLOAD_FLAGS and place it there. Just an idea.

Thanks!