netfilter: nft_meta_bridge: introduce NFT_META_BRI_IIFHWADDR support

Expose the input bridge interface ethernet address so it can be used to
redirect the packet to the receiving physical device for processing.

Tested with nft command line tool.

table bridge nat {
chain PREROUTING {
type filter hook prerouting priority 0; policy accept;
ether daddr de:ad:00:00:be:ef meta pkttype set host ether daddr set meta ibrhwdr accept
}
}

Joint work with Pablo Neira.

Signed-off-by: Fernando Fernandez Mancera <[e-mail]>
Signed-off-by: Florian Westphal <[e-mail]>

include/uapi/linux/netfilter/nf_tables.h

···
  * @NFT_META_SDIF: slave device interface index
  * @NFT_META_SDIFNAME: slave device interface name
  * @NFT_META_BRI_BROUTE: packet br_netfilter_broute bit
+ * @NFT_META_BRI_IIFHWADDR: packet input bridge interface ethernet address
  */
 enum nft_meta_keys {
 	NFT_META_LEN,
···
 	NFT_META_SDIFNAME,
 	NFT_META_BRI_BROUTE,
 	__NFT_META_IIFTYPE,
+	NFT_META_BRI_IIFHWADDR,
 };
 
 /**

net/bridge/netfilter/nft_meta_bridge.c

···
 		nft_reg_store_be16(dest, htons(p_proto));
 		return;
 	}
+	case NFT_META_BRI_IIFHWADDR:
+		br_dev = nft_meta_get_bridge(in);
+		if (!br_dev)
+			goto err;
+
+		memcpy(dest, br_dev->dev_addr, ETH_ALEN);
+		return;
 	default:
 		return nft_meta_get_eval(expr, regs, pkt);
 	}
···
 	case NFT_META_BRI_IIFPVID:
 	case NFT_META_BRI_IIFVPROTO:
 		len = sizeof(u16);
+		break;
+	case NFT_META_BRI_IIFHWADDR:
+		len = ETH_ALEN;
 		break;
 	default:
 		return nft_meta_get_init(ctx, expr, tb);
···
 
 	switch (priv->key) {
 	case NFT_META_BRI_BROUTE:
+	case NFT_META_BRI_IIFHWADDR:
 		hooks = 1 << NF_BR_PRE_ROUTING;
 		break;
 	default: