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Date: Thu, 19 May 2022 10:00:45 -0700
From: Yonghong Song <yhs@...com>
To: Kumar Kartikeya Dwivedi <memxor@...il.com>,
Toke Høiland-Jørgensen <toke@...hat.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,
Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
Lorenzo Bianconi <lorenzo@...nel.org>,
bpf <bpf@...r.kernel.org>,
Network Development <netdev@...r.kernel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Eric Dumazet <edumazet@...gle.com>,
Paolo Abeni <pabeni@...hat.com>,
Pablo Neira Ayuso <pablo@...filter.org>,
Florian Westphal <fw@...len.de>,
netfilter-devel <netfilter-devel@...r.kernel.org>,
Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH v3 bpf-next 4/5] net: netfilter: add kfunc helper to add a
new ct entry
On 5/19/22 4:23 AM, Kumar Kartikeya Dwivedi wrote:
> On Thu, May 19, 2022 at 04:15:51PM IST, Toke Høiland-Jørgensen wrote:
>> Kumar Kartikeya Dwivedi <memxor@...il.com> writes:
>>
>>> On Thu, May 19, 2022 at 03:44:58AM IST, Alexei Starovoitov wrote:
>>>> On Wed, May 18, 2022 at 2:09 PM Lorenzo Bianconi
>>>> <lorenzo.bianconi@...hat.com> wrote:
>>>>>
>>>>>> Lorenzo Bianconi <lorenzo@...nel.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@...nel.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.
>>>
>>> Right, so we can just whitelist a few fields and allow assignments into those.
>>> One small problem is that we should probably only permit this for nf_conn
>>> PTR_TO_BTF_ID obtained from _alloc, and make it rdonly on _insert.
>>>
>>> We can do the rw->ro conversion by taking in ref from alloc, and releasing on
>>> _insert, then returning ref from _insert.
>>
>> Sounds reasonable enough; I guess _insert would also need to
>> sanity-check some of the values to prevent injecting invalid state into
>> the conntrack table.
>>
>>> For the other part, either return a different shadow PTR_TO_BTF_ID
>>> with only the fields that can be set, convert insns for it, and then
>>> on insert return the rdonly PTR_TO_BTF_ID of struct nf_conn, or
>>> otherwise store the source func in the per-register state and use that
>>> to deny BPF_WRITE for normal nf_conn. Thoughts?
>>
>> Hmm, if they're different BTF IDs wouldn't the BPF program have to be
>> aware of this and use two different structs for the pointer storage?
>> That seems a bit awkward from an API PoV?
>>
>
> You only need to use a different pointer after _alloc and pass it into _insert.
>
> Like:
> struct nf_conn_alloc *nfa = nf_alloc(...);
> if (!nfa) { ... }
> nfa->status = ...; // gets converted to nf_conn access
> nfa->tcp_status = ...; // ditto
> struct nf_conn *nf = nf_insert(nfa, ...); // nfa released, nf acquired
>
> The problem is that if I whitelist it for nf_conn as a whole so that we can
> assign after _alloc, there is no way to prevent BPF_WRITE for nf_conn obtained
> from other functions. We can fix it though by remembering which function a
> pointer came from, then you wouldn't need a different struct. I was just
> soliciting opinions for different options. I am leaning towards not having to
> use a separate struct as well.
Is it possible that we define the signature of nf_insert() as
const struct nf_conn *nf_insert(...)
so for
const struct nf_conn *nf = nf_insert(nfa, ...);
if there are any nf->status = ..., the compiler will emit a warning.
Also verifier can know the return value of nf_insert() is read-only
and can prevent value overwrite.
Maybe I missed some context, but the above is based on what
I understood so far.
>
>> Also, what about updating? For this to be useful with TCP, you'd really
>> want to be able to update the CT state as the connection is going
>> through the handshake state transitions...
>>
>
> I think updates should be done using dedicated functions, like the timeout
> helper. Whatever synchronization is needed to update the CT can go into that
> function, instead of allowing direct writes after _insert.
>
>> -Toke
>>
>
> --
> Kartikeya
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