Re: [Qemu-devel] [PATCH v2 2/3] filter-rewriter: fix memory leak for connection in connection_track_table

[Hailiang Zhang]

On 2017/2/27 17:05, Jason Wang wrote:
> On 2017年02月27日 14:53, Hailiang Zhang wrote:
> > > I think the issue is that your code can not differ A from B.
> >
> > We have a parameter 'fin_ack_seq' recording the sequence of
> > 'FIN=1,ACK=1,seq=w,ack=u+1' and if the ack value from the opposite
> > side is is 'w+1', we can consider this connection is closed, no ?

Hi Jason,

Thanks very much for your patience.

> Let's see what happens, consider VM is doing active close (reuse the
> figure above):

(We didn't support tracking the connection start
by the VM in current rewriter codes.
I mean the Client side is VM).

Your figure is not quite correct, the process should be:
                                          (VM)
Client:                                    Server:

ESTABLISHED|                               |
           | -> FIN=1,seq=u   ->           |
FIN_WAIT_1 |                               |
           | <- ACK=1,seq=v,ack=u+1 <-     |
FINA_WAIT_2|                               |CLOSE_WAIT
           | <- FIN=1,ACK=1,seq=w,ack=u+1<-|
handle_secondary():
fin_ack_seq = w
tcp_state = TCPS_LAST_ACK

           |                               |LAST+ACK
           |   -> ACK=1,seq=u+1,ack=w+1    |
TIME_WAIT  |                               |CLOSED
CLOSED     |                               |

handle_primary():
if (ack = fin_ack_seq + 1)
   g_hash_table_remove()

> (VM)
> Client:                                    Server:
>
> ESTABLISHED|                               |
>              | -> FIN=1,seq=u   ->           |
>
> handle_secondary():
> fin_ack_seq = u
> tcp_state = TCPS_LAST_ACK
>
> FIN_WAIT_1 |                               |
>              | <- ACK=1,seq=v,ack=u+1 <-     |
>
> handle_primary():
> fin_ack_seq = ack + 1
> g_hash_table_remove()
>
> But we probably want it to be removed in TIME_WAIT_CLOSED.

Yes, we should removed it after 2MSL, because the last
the sever side may not get the 'ACK=1,seq=v,ack=u+1' packet,
and it will resend the 'FIN=1,ACK=1,seq=w,ack=u+1'.

Thanks.


> Thanks
>
> .