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Date:   Sun, 5 Nov 2023 18:41:39 +0100
From:   Florian Westphal <fw@strlen.de>
To:     Pablo Neira Ayuso <pablo@netfilter.org>
Cc:     Florian Westphal <fw@strlen.de>,
        Brian Davidson <davidson.brian@gmail.com>,
        netfilter@vger.kernel.org
Subject: Re: ip6 dscp fails map lookup
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Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > >  	if (shift) {
> > > -		if (ctx->stmt_len > 0 && div_round_up(masklen, BITS_PER_BYTE) > 1) {
> > > +		if (masklen > BITS_PER_BYTE) {
> > 
> > I think this is right but binop xfer
> > won't remove the inserted byteorder conversion
> > in case the shift is to be removed by adjusting
> > a constant right hand side value.
> 
> ctx->stmt_len > 0 is also set from stmt_evaluate_{ct,meta}() so this
> transformation is restricted to statements.
> 
> I was conservative edecd58755a8 with ("evaluate: support shifts larger than
> the width of the left operand") to restrict this transformation to
> statements only.
> 
> Do you think think this applies to other cases too?
> 
> BTW, whatever the final fix is, Fixes: tag for this should be:
> 
> Fixes: 668c18f67203 ("evaluate: place byteorder conversion before rshift in payload statement")

I don't think this is a regression, I do not think it has worked before.

table ip6 t {
	map mapv6 {
		typeof ip6 dscp : meta mark
		elements = { cs1 : 0x0000002a }
	}

	chain output {
		type filter hook output priority filter; policy accept;
		meta mark set ip6 dscp map @mapv6
		meta mark 0x0000002a counter
		ip6 dscp @mapv6 counter
		ip6 dscp cs1 counter
	}
}

A "ping6 -q -Q 0x20 ::1 -c1" should cause all counters
in above ruleset to increment, but that is not the case.

Even before above commit.