Re: [RFC ebtables-nft] unify ether type and meta protocol decoding

[Phil Sutter <phil@nwl.cc>]

On Wed, Nov 30, 2022 at 12:37:18PM +0100, Florian Westphal wrote:
> Handle "ether protocol" and "meta protcol" the same.
> 
> Problem is that this breaks the test case *again*:
> 
> I: [EXECUTING]   iptables/tests/shell/testcases/ebtables/0006-flush_0
> --A FORWARD --among-dst fe:ed:ba:be:13:37=10.0.0.1 -j ACCEPT
> --A OUTPUT --among-src c0:ff:ee:90:0:0=192.168.0.1 -j DROP
> +-A FORWARD -p IPv4 --among-dst fe:ed:ba:be:13:37=10.0.0.1 -j ACCEPT
> +-A OUTPUT -p IPv4 --among-src c0:ff:ee:90:0:0=192.168.0.1 -j DROP
> 
> ... because ebtables-nft will now render meta protocol as "-p IPv4".
> 
> ebtables-legacy does not have any special handling for this.
> 
> Solving this would need more internal annotations during decode, so
> we can suppress/ignore "meta protocol" once a "among-type" set is
> encountered.
> 
> Any (other) suggestions?

Since ebtables among does not support IPv6, match elimination should be
pretty simple, no? Entirely untested:

diff --git a/iptables/nft-bridge.c b/iptables/nft-bridge.c
index 08c93feeba2c9..0daebfd983127 100644
--- a/iptables/nft-bridge.c
+++ b/iptables/nft-bridge.c
@@ -520,6 +520,10 @@ static void nft_bridge_parse_lookup(struct nft_xt_ctx *ctx,
        if (set_elems_to_among_pairs(among_data->pairs + poff, s, cnt))
                xtables_error(OTHER_PROBLEM,
                              "ebtables among pair parsing failed");
+
+       if (!(ctx->cs.eb.bitmask & EBT_NOPROTO) &&
+           ctx->cs.eb.ethproto == htons(0x0800))
+               ctx->cs.eb.bitmask |= EBT_NOPROTO;
 }
 
 static void parse_watcher(void *object, struct ebt_match **match_list,

Cheers, Phil