Why network stack not reply RST

Why network stack not reply RST

[zrpeng]

Hi:
    Why network stack not reply RST?
    I am doing test recently based on kernel 2.6.32. In my case:
    1) The server application closed the established socket, the network stack 
sent FIN to client. The socket status in kernel's network stack was 
TCP_FIN_WAIT1.
    2) The client sent out a tcp packet with ACK bit set for the server's FIN, 
the packet also took new data.
    3) When the server received the packet, network stack entered "step 5" in 
function "tcp_rcv_state_process".
    4) Then came to 'case TCP_FIN_WAIT1:'
    5) Then came to judgement
if (tp->linger2 < 0 ||
					    (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
					     after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
.....
}
    6) Because the previous packet took data and ACK (for the FIN), it entered 
the judgement. So, the socket is deleted in function 'tcp_done(sk)'.
    7) No TCP message was sent back to client side from then on, and client 
was left in LAST_ACK status.

    My questions are:
    1) Is this process correct? I think the server should sent RST to client, 
is this correct?
    2) What's the using of judgement 
 (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
					     after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)

       The code exists from kernel 2.3.41 and 2.3.42. 

    Thank you very much!
    Best Regards.

    Peng Zhaoran from Linx-Info Tech.
    
    www.linx-info.com

Re: Why network stack not reply RST

[Zhen-Hua Li]

Hi,
    Are you sure your client did not called fork() ?  If it has
subprocess, there may be such problems.


On Tue, Dec 27, 2011 at 4:31 PM, zrpeng <zrpeng@linx-info.com> wrote:
> Hi:
>    Why network stack not reply RST?
>    I am doing test recently based on kernel 2.6.32. In my case:
>    1) The server application closed the established socket, the network stack
> sent FIN to client. The socket status in kernel's network stack was
> TCP_FIN_WAIT1.
>    2) The client sent out a tcp packet with ACK bit set for the server's FIN,
> the packet also took new data.
>    3) When the server received the packet, network stack entered "step 5" in
> function "tcp_rcv_state_process".
>    4) Then came to 'case TCP_FIN_WAIT1:'
>    5) Then came to judgement
> if (tp->linger2 < 0 ||
>                                            (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
>                                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
> .....
> }
>    6) Because the previous packet took data and ACK (for the FIN), it entered
> the judgement. So, the socket is deleted in function 'tcp_done(sk)'.
>    7) No TCP message was sent back to client side from then on, and client
> was left in LAST_ACK status.
>
>    My questions are:
>    1) Is this process correct? I think the server should sent RST to client,
> is this correct?
>    2) What's the using of judgement
>  (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
>                                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)
>
>       The code exists from kernel 2.3.41 and 2.3.42.
>
>    Thank you very much!
>    Best Regards.
>
>    Peng Zhaoran from Linx-Info Tech.
>
>    www.linx-info.com
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Why network stack not reply RST

[zrpeng]

Hi:
   It is my error. After returned from the judgement, the network stack will 
send RST according to return value.

   Thank you very much! And Happy New Year!
   Best Regards.

   Peng Zhaoran from Linx-Info Tech.

www.linx-info.com

在 Thursday 29 December 2011 11:04:10，Zhen-Hua Li 写道：
> Hi,
>     Are you sure your client did not called fork() ?  If it has
> subprocess, there may be such problems.
>
> On Tue, Dec 27, 2011 at 4:31 PM, zrpeng <zrpeng@linx-info.com> wrote:
> > Hi:
> >    Why network stack not reply RST?
> >    I am doing test recently based on kernel 2.6.32. In my case:
> >    1) The server application closed the established socket, the network
> > stack sent FIN to client. The socket status in kernel's network stack was
> > TCP_FIN_WAIT1.
> >    2) The client sent out a tcp packet with ACK bit set for the server's
> > FIN, the packet also took new data.
> >    3) When the server received the packet, network stack entered "step 5"
> > in function "tcp_rcv_state_process".
> >    4) Then came to 'case TCP_FIN_WAIT1:'
> >    5) Then came to judgement
> > if (tp->linger2 < 0 ||
> >                                            (TCP_SKB_CB(skb)->end_seq !=
> > TCP_SKB_CB(skb)->seq && after(TCP_SKB_CB(skb)->end_seq - th->fin,
> > tp->rcv_nxt))) { .....
> > }
> >    6) Because the previous packet took data and ACK (for the FIN), it
> > entered the judgement. So, the socket is deleted in function
> > 'tcp_done(sk)'. 7) No TCP message was sent back to client side from then
> > on, and client was left in LAST_ACK status.
> >
> >    My questions are:
> >    1) Is this process correct? I think the server should sent RST to
> > client, is this correct?
> >    2) What's the using of judgement
> >  (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
> >                                            
> > after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)
> >
> >       The code exists from kernel 2.3.41 and 2.3.42.
> >
> >    Thank you very much!
> >    Best Regards.
> >
> >    Peng Zhaoran from Linx-Info Tech.
> >
> >    www.linx-info.com
> > --
> > To unsubscribe from this list: send the line "unsubscribe netdev" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html