netdev - Re: [Patch bpf-next v2 8/9] sock_map: update sock type checks for UDP

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Message-ID: <33a6d38b-28dd-0c38-05a0-6fa09290fbea@fb.com>
Date:   Wed, 3 Mar 2021 10:50:38 -0800
From:   Yonghong Song <yhs@...com>
To:     Cong Wang <xiyou.wangcong@...il.com>
CC:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, <duanxiongchun@...edance.com>,
        Dongdong Wang <wangdongdong.6@...edance.com>,
        Jiang Wang <jiang.wang@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [Patch bpf-next v2 8/9] sock_map: update sock type checks for UDP



On 3/3/21 10:02 AM, Cong Wang wrote:
> On Tue, Mar 2, 2021 at 10:37 PM Yonghong Song <yhs@...com> wrote:
>>
>>
>>
>> On 3/1/21 6:37 PM, Cong Wang wrote:
>>> From: Cong Wang <cong.wang@...edance.com>
>>>
>>> Now UDP supports sockmap and redirection, we can safely update
>>> the sock type checks for it accordingly.
>>>
>>> Cc: John Fastabend <john.fastabend@...il.com>
>>> Cc: Daniel Borkmann <daniel@...earbox.net>
>>> Cc: Jakub Sitnicki <jakub@...udflare.com>
>>> Cc: Lorenz Bauer <lmb@...udflare.com>
>>> Signed-off-by: Cong Wang <cong.wang@...edance.com>
>>> ---
>>>    net/core/sock_map.c | 5 ++++-
>>>    1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
>>> index 13d2af5bb81c..f7eee4b7b994 100644
>>> --- a/net/core/sock_map.c
>>> +++ b/net/core/sock_map.c
>>> @@ -549,7 +549,10 @@ static bool sk_is_udp(const struct sock *sk)
>>>
>>>    static bool sock_map_redirect_allowed(const struct sock *sk)
>>>    {
>>> -     return sk_is_tcp(sk) && sk->sk_state != TCP_LISTEN;
>>> +     if (sk_is_tcp(sk))
>>> +             return sk->sk_state != TCP_LISTEN;
>>> +     else
>>> +             return sk->sk_state == TCP_ESTABLISHED;
>>
>> Not a networking expert, a dump question. Here we tested
>> whether sk_is_tcp(sk) or not, if not we compare
>> sk->sk_state == TCP_ESTABLISHED, could this be
>> always false? Mostly I missed something, some comments
>> here will be good.
> 
> No, dgram sockets also use TCP_ESTABLISHED as a valid
> state. I know its name looks confusing, but it is already widely
> used in networking:
> 
> net/appletalk/ddp.c:    sk->sk_state = TCP_ESTABLISHED;
> net/appletalk/ddp.c:            if (sk->sk_state != TCP_ESTABLISHED)
> net/appletalk/ddp.c:            if (sk->sk_state != TCP_ESTABLISHED)
> net/ax25/af_ax25.c:     sk->sk_state    = TCP_ESTABLISHED;
> net/ax25/af_ax25.c:             case TCP_ESTABLISHED: /* connection
> established */
> net/ax25/af_ax25.c:     if (sk->sk_state == TCP_ESTABLISHED &&
> sk->sk_type == SOCK_SEQPACKET) {
> net/ax25/af_ax25.c:             sk->sk_state   = TCP_ESTABLISHED;
> net/ax25/af_ax25.c:     if (sk->sk_state != TCP_ESTABLISHED && (flags
> & O_NONBLOCK)) {
> net/ax25/af_ax25.c:     if (sk->sk_state != TCP_ESTABLISHED) {
> net/ax25/af_ax25.c:             if (sk->sk_state != TCP_ESTABLISHED) {
> net/ax25/af_ax25.c:             if (sk->sk_state != TCP_ESTABLISHED) {
> net/ax25/af_ax25.c:             if (sk->sk_state != TCP_ESTABLISHED) {
> net/ax25/af_ax25.c:     if (sk->sk_type == SOCK_SEQPACKET &&
> sk->sk_state != TCP_ESTABLISHED) {
> net/ax25/ax25_ds_in.c:                  ax25->sk->sk_state = TCP_ESTABLISHED;
> net/ax25/ax25_in.c:             make->sk_state = TCP_ESTABLISHED;
> net/ax25/ax25_std_in.c:                         ax25->sk->sk_state =
> TCP_ESTABLISHED;
> net/caif/caif_socket.c: CAIF_CONNECTED          = TCP_ESTABLISHED,
> net/ceph/messenger.c:   case TCP_ESTABLISHED:
> net/ceph/messenger.c:           dout("%s TCP_ESTABLISHED\n", __func__);
> net/core/datagram.c:        !(sk->sk_state == TCP_ESTABLISHED ||
> sk->sk_state == TCP_LISTEN))
> ...
> 
> Hence, I believe it is okay to use it as it is, otherwise we would need
> to comment on every use of it. ;)

That is okay. Thanks for explanation!

> 
> Thanks.
>