Re: [PATCH bpf-next v2 1/2] net: netfilter: Make ct zone opts configurable for bpf ct helpers

[Martin KaFai Lau <martin.lau@xxxxxxxxx>]

On 4/30/24 9:59 PM, Brad Cowie wrote:
> On Fri, 26 Apr 2024 at 11:27, Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote:
> > On 4/23/24 8:00 PM, Brad Cowie wrote:
> > >    };
> > >
> > >    static int bpf_nf_ct_tuple_parse(struct bpf_sock_tuple *bpf_tuple,
> > > @@ -104,11 +107,13 @@ __bpf_nf_ct_alloc_entry(struct net *net, struct bpf_sock_tuple *bpf_tuple,
> > >    			u32 timeout)
> > >    {
> > >    	struct nf_conntrack_tuple otuple, rtuple;
> > > +	struct nf_conntrack_zone ct_zone;
> > >    	struct nf_conn *ct;
> > >    	int err;
> > >
> > > -	if (!opts || !bpf_tuple || opts->reserved[0] || opts->reserved[1] ||
> > > -	    opts_len != NF_BPF_CT_OPTS_SZ)
> > > +	if (!opts || !bpf_tuple)
> > > +		return ERR_PTR(-EINVAL);
> > > +	if (!(opts_len == NF_BPF_CT_OPTS_SZ || opts_len == NF_BPF_CT_OPTS_OLD_SZ))
> > >    		return ERR_PTR(-EINVAL);
> > >
> > >    	if (unlikely(opts->netns_id < BPF_F_CURRENT_NETNS))
> > > @@ -130,7 +135,16 @@ __bpf_nf_ct_alloc_entry(struct net *net, struct bpf_sock_tuple *bpf_tuple,
> > >    			return ERR_PTR(-ENONET);
> > >    	}
> > >
> > > -	ct = nf_conntrack_alloc(net, &nf_ct_zone_dflt, &otuple, &rtuple,
> > > +	if (opts_len == NF_BPF_CT_OPTS_SZ) {
> > > +		if (opts->ct_zone_dir == 0)
> >
> > I don't know the details about the dir in ct_zone, so a question: a 0
> > ct_zone_dir is invalid and can be reused to mean NF_CT_DEFAULT_ZONE_DIR?
>
> ct_zone_dir is a bitmask that can have two different bits set,
> NF_CT_ZONE_DIR_ORIG (1) and NF_CT_ZONE_DIR_REPL (2).
>
> The comparison function nf_ct_zone_matches_dir() in nf_conntrack_zones.h
> checks if ct_zone_dir & (1 << ip_conntrack_dir dir). ip_conntrack_dir
> has two possible values IP_CT_DIR_ORIGINAL (0) and IP_CT_DIR_REPLY (1).
>
> If ct_zone_dir has a value of 0, this makes nf_ct_zone_matches_dir()
> always return false which makes nf_ct_zone_id() always return
> NF_CT_DEFAULT_ZONE_ID instead of the specified ct zone id.
>
> I chose to override ct_zone_dir here and set NF_CT_DEFAULT_ZONE_DIR (3),
> to make the behaviour more obvious when a user calls the bpf ct helper
> kfuncs while only setting ct_zone_id but not ct_zone_dir.

Ok. make sense.

> > > +			opts->ct_zone_dir = NF_CT_DEFAULT_ZONE_DIR;
> > > +		nf_ct_zone_init(&ct_zone,
> > > +				opts->ct_zone_id, opts->ct_zone_dir, opts->ct_zone_flags);
> > > +	} else {
> >
> > Better enforce "ct_zone_id == 0" also instead of ignoring it.
>
> Could I ask for clarification here, do you mean changing this
> else statement to:
>
> +	} else if (opts->ct_zone_id == 0) {
>
> Or should I be setting opts->ct_zone_id = 0 inside the else block?

Testing non zero inside the else and return error instead of silently ignoring 
it and then use nf_ct_zone_dflt:

	} else {
		if (opts->ct_zone_id)
			/* don't ignore the opts->ct_zone_id */
			return ERR_PTR(-EINVAL);
		
		ct_zone = nf_ct_zone_dflt;
	}