linux-kernel - Re: [PATCH bpf-next 2/3] bpf: Add support for writing to nf

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Date:   Tue, 16 Aug 2022 00:40:11 +0200
From:   Florian Westphal <fw@...len.de>
To:     Toke Høiland-Jørgensen <toke@...nel.org>
Cc:     Daniel Xu <dxu@...uu.xyz>, bpf@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, memxor@...il.com,
        pablo@...filter.org, fw@...len.de, netfilter-devel@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 2/3] bpf: Add support for writing to nf_conn:mark

Toke Høiland-Jørgensen <toke@...nel.org> wrote:
> > Support direct writes to nf_conn:mark from TC and XDP prog types. This
> > is useful when applications want to store per-connection metadata. This
> > is also particularly useful for applications that run both bpf and
> > iptables/nftables because the latter can trivially access this metadata.
> >
> > One example use case would be if a bpf prog is responsible for advanced
> > packet classification and iptables/nftables is later used for routing
> > due to pre-existing/legacy code.
> >
> > Signed-off-by: Daniel Xu <dxu@...uu.xyz>
> 
> Didn't we agree the last time around that all field access should be
> using helper kfuncs instead of allowing direct writes to struct nf_conn?

I don't see why ct->mark needs special handling.

It might be possible we need to change accesses on nf/tc side to use
READ/WRITE_ONCE though.