Re: [PATCH 2/5]: Fix Reset/Sync-Flood Bug

[Arnaldo Carvalho de Melo <acme@ghostprotocols.net>]

Em Wed, Jun 20, 2007 at 10:55:39AM +0100, Gerrit Renker escreveu:
> [DCCP]: Fix Reset/Sync-Flood Bug
> 
> This updates sequence number checking with regard to RFC 4340, 7.5.4.
> Missing in the code was an exception for sequence-invalid Reset packets, 
> which get a Sync acknowledging GSR, instead of (as usual) P.seqno.
> 
> This can lead to an oscillating ping-pong flood of Reset packets. 
> 
> In fact, it has been observed on the wire as follows:
> 
>  1. client establishes connection to server;
>  2. before server can write to client, client crashes without notifying
>     the server (NB: now no longer possible due to ABORT function);
>  3. server sends DCCP-Data packet (has no ackno);
>  4. client generates Reset "No Connection", seqno=0, increments seqno;
>  5. server replies with Sync, using ackno = P.seqno;
>  6. client generates Reset "No Connection" with seqno = ackno + 1;
>  7. goto (5).
> 
> The difference is that now in (5) the server uses GSR.  This causes the
> Reset sent by the client in (6) to become sequence-valid, so that in (7)
> the vicious circle is broken; the Reset is then enqueued and causes the
> socket to enter TIMEWAIT state.

Well spotted! I wonder if Step 6 in the RFC pseudocode changed from what
was in the draft I used... 8)

- Arnaldo