Re: [PATCH v3 bpf-next 4/5] net: netfilter: add kfunc helper to add a new ct entry

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Wed, May 18, 2022 at 2:09 PM Lorenzo Bianconi
<lorenzo.bianconi@redhat.com> wrote:
>
> > Lorenzo Bianconi <lorenzo@kernel.org> writes:
> >
> > > Introduce bpf_xdp_ct_add and bpf_skb_ct_add kfunc helpers in order to
> > > add a new entry to ct map from an ebpf program.
> > > Introduce bpf_nf_ct_tuple_parse utility routine.
> > >
> > > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > > ---
> > >  net/netfilter/nf_conntrack_bpf.c | 212 +++++++++++++++++++++++++++----
> > >  1 file changed, 189 insertions(+), 23 deletions(-)
> > >
> > > diff --git a/net/netfilter/nf_conntrack_bpf.c b/net/netfilter/nf_conntrack_bpf.c
> > > index a9271418db88..3d31b602fdf1 100644
> > > --- a/net/netfilter/nf_conntrack_bpf.c
> > > +++ b/net/netfilter/nf_conntrack_bpf.c
> > > @@ -55,41 +55,114 @@ enum {
> > >     NF_BPF_CT_OPTS_SZ = 12,
> > >  };
> > >
> > > -static struct nf_conn *__bpf_nf_ct_lookup(struct net *net,
> > > -                                     struct bpf_sock_tuple *bpf_tuple,
> > > -                                     u32 tuple_len, u8 protonum,
> > > -                                     s32 netns_id, u8 *dir)
> > > +static int bpf_nf_ct_tuple_parse(struct bpf_sock_tuple *bpf_tuple,
> > > +                            u32 tuple_len, u8 protonum, u8 dir,
> > > +                            struct nf_conntrack_tuple *tuple)
> > >  {
> > > -   struct nf_conntrack_tuple_hash *hash;
> > > -   struct nf_conntrack_tuple tuple;
> > > -   struct nf_conn *ct;
> > > +   union nf_inet_addr *src = dir ? &tuple->dst.u3 : &tuple->src.u3;
> > > +   union nf_inet_addr *dst = dir ? &tuple->src.u3 : &tuple->dst.u3;
> > > +   union nf_conntrack_man_proto *sport = dir ? (void *)&tuple->dst.u
> > > +                                             : &tuple->src.u;
> > > +   union nf_conntrack_man_proto *dport = dir ? &tuple->src.u
> > > +                                             : (void *)&tuple->dst.u;
> > >
> > >     if (unlikely(protonum != IPPROTO_TCP && protonum != IPPROTO_UDP))
> > > -           return ERR_PTR(-EPROTO);
> > > -   if (unlikely(netns_id < BPF_F_CURRENT_NETNS))
> > > -           return ERR_PTR(-EINVAL);
> > > +           return -EPROTO;
> > > +
> > > +   memset(tuple, 0, sizeof(*tuple));
> > >
> > > -   memset(&tuple, 0, sizeof(tuple));
> > >     switch (tuple_len) {
> > >     case sizeof(bpf_tuple->ipv4):
> > > -           tuple.src.l3num = AF_INET;
> > > -           tuple.src.u3.ip = bpf_tuple->ipv4.saddr;
> > > -           tuple.src.u.tcp.port = bpf_tuple->ipv4.sport;
> > > -           tuple.dst.u3.ip = bpf_tuple->ipv4.daddr;
> > > -           tuple.dst.u.tcp.port = bpf_tuple->ipv4.dport;
> > > +           tuple->src.l3num = AF_INET;
> > > +           src->ip = bpf_tuple->ipv4.saddr;
> > > +           sport->tcp.port = bpf_tuple->ipv4.sport;
> > > +           dst->ip = bpf_tuple->ipv4.daddr;
> > > +           dport->tcp.port = bpf_tuple->ipv4.dport;
> > >             break;
> > >     case sizeof(bpf_tuple->ipv6):
> > > -           tuple.src.l3num = AF_INET6;
> > > -           memcpy(tuple.src.u3.ip6, bpf_tuple->ipv6.saddr, sizeof(bpf_tuple->ipv6.saddr));
> > > -           tuple.src.u.tcp.port = bpf_tuple->ipv6.sport;
> > > -           memcpy(tuple.dst.u3.ip6, bpf_tuple->ipv6.daddr, sizeof(bpf_tuple->ipv6.daddr));
> > > -           tuple.dst.u.tcp.port = bpf_tuple->ipv6.dport;
> > > +           tuple->src.l3num = AF_INET6;
> > > +           memcpy(src->ip6, bpf_tuple->ipv6.saddr, sizeof(bpf_tuple->ipv6.saddr));
> > > +           sport->tcp.port = bpf_tuple->ipv6.sport;
> > > +           memcpy(dst->ip6, bpf_tuple->ipv6.daddr, sizeof(bpf_tuple->ipv6.daddr));
> > > +           dport->tcp.port = bpf_tuple->ipv6.dport;
> > >             break;
> > >     default:
> > > -           return ERR_PTR(-EAFNOSUPPORT);
> > > +           return -EAFNOSUPPORT;
> > >     }
> > > +   tuple->dst.protonum = protonum;
> > > +   tuple->dst.dir = dir;
> > > +
> > > +   return 0;
> > > +}
> > >
> > > -   tuple.dst.protonum = protonum;
> > > +struct nf_conn *
> > > +__bpf_nf_ct_alloc_entry(struct net *net, struct bpf_sock_tuple *bpf_tuple,
> > > +                   u32 tuple_len, u8 protonum, s32 netns_id, u32 timeout)
> > > +{
> > > +   struct nf_conntrack_tuple otuple, rtuple;
> > > +   struct nf_conn *ct;
> > > +   int err;
> > > +
> > > +   if (unlikely(netns_id < BPF_F_CURRENT_NETNS))
> > > +           return ERR_PTR(-EINVAL);
> > > +
> > > +   err = bpf_nf_ct_tuple_parse(bpf_tuple, tuple_len, protonum,
> > > +                               IP_CT_DIR_ORIGINAL, &otuple);
> > > +   if (err < 0)
> > > +           return ERR_PTR(err);
> > > +
> > > +   err = bpf_nf_ct_tuple_parse(bpf_tuple, tuple_len, protonum,
> > > +                               IP_CT_DIR_REPLY, &rtuple);
> > > +   if (err < 0)
> > > +           return ERR_PTR(err);
> > > +
> > > +   if (netns_id >= 0) {
> > > +           net = get_net_ns_by_id(net, netns_id);
> > > +           if (unlikely(!net))
> > > +                   return ERR_PTR(-ENONET);
> > > +   }
> > > +
> > > +   ct = nf_conntrack_alloc(net, &nf_ct_zone_dflt, &otuple, &rtuple,
> > > +                           GFP_ATOMIC);
> > > +   if (IS_ERR(ct))
> > > +           goto out;
> > > +
> > > +   ct->timeout = timeout * HZ + jiffies;
> > > +   ct->status |= IPS_CONFIRMED;
> > > +
> > > +   memset(&ct->proto, 0, sizeof(ct->proto));
> > > +   if (protonum == IPPROTO_TCP)
> > > +           ct->proto.tcp.state = TCP_CONNTRACK_ESTABLISHED;
> >
> > Hmm, isn't it a bit limiting to hard-code this to ESTABLISHED
> > connections? Presumably for TCP you'd want to use this when you see a
> > SYN and then rely on conntrack to help with the subsequent state
> > tracking for when the SYN-ACK comes back? What's the usecase for
> > creating an entry in ESTABLISHED state, exactly?
>
> I guess we can even add a parameter and pass the state from the caller.
> I was not sure if it is mandatory.

It's probably cleaner and more flexible to split
_alloc and _insert into two kfuncs and let bpf
prog populate ct directly.