Wireshark · Ethereal-dev: [Ethereal-dev] Re: (possible) patch for SCTP

[Jeff Morriss <jeff.morriss@xxxxxxxxxxx>]

Hello list,

Any thoughts on the below patch (or how it can be improved)?

Regards,
-Jeff

Jeff Morriss wrote:
> 
> Hello list,
> 
> Here's a (potential) patch for the SCTP dissector. It still has one
> problem, but I think it's the best that can be done (more below).
> 
> Two things are fixed:
> 
> 1.  When calling a sub-dissector on a DATA chunk, dissect the padding on
> that chunk as part of the DATA chunk (since it's not part of the
> payload;  this avoids confusing sub-dissectors).
> 
> The problem with this fix is that the padding on the SCTP DATA chunk is
> at the end of the chunk.  The data that goes to the sub-dissector is
> fine and the padding shows up where one *might* expect it (that is,
> attached to the DATA chunk tree), BUT it is NOT highlighted as part of
> the SCTP protocol tree when you select that tree in the GUI.  :(
> 
> I can find no better way of doing this, though...  (I really don't think
> sub-dissectors should have to think about SCTP's padding.)  Any
> thoughts/suggestions?
> 
> 2.  Change the text name of the 'hf_sctp_data_chunk_payload_proto_id'
> field to be "sctp.ppi" instead of "sctp.payload_proto_id"--to be
> consistent with how SCTP is advertised to sub-dissectors.
> 
> Another option would be to change SCTP, M3UA, IUA, and SUAL (and the
> M2PA dissector I will submit shortly) to use "sctp.payload_proto_id"
> instead of "sctp.ppi".  I'm willing to go that way (will re-submit
> patch) if you think it's better.
> 
> Regards,
> -Jeff
> 
>   ------------------------------------------------------------------------
> Index: packet-sctp.c
> ===================================================================
> RCS file: /cvsroot/ethereal/packet-sctp.c,v
> retrieving revision 1.17
> diff -u -r1.17 packet-sctp.c
> --- packet-sctp.c       2001/06/18 02:17:52     1.17
> +++ packet-sctp.c       2001/06/21 20:53:21
> @@ -985,24 +985,34 @@
>  dissect_payload(tvbuff_t *payload_tvb, packet_info *pinfo, proto_tree *tree,
>                 proto_tree *chunk_tree, guint32 ppi, guint16 payload_length, guint16 padding_length)
>  {
> +  gboolean ret = FALSE;
> +  tvbuff_t *user_tvb;
> +
> +  if (padding_length > 0)
> +    /* create a tvb without padding (to pass to sub-dissector) */
> +    user_tvb = tvb_new_subset(payload_tvb, 0, payload_length, payload_length);
> +  else
> +    user_tvb = payload_tvb;
> +
>    /* do lookup with the subdissector table */
> -  if (dissector_try_port (sctp_ppi_dissector_table, ppi,  payload_tvb, pinfo, tree) ||
> -      dissector_try_port(sctp_port_dissector_table, pi.srcport,  payload_tvb, pinfo, tree) ||
> -      dissector_try_port(sctp_port_dissector_table, pi.destport, payload_tvb, pinfo, tree)){
> -    return TRUE;
> +  if (dissector_try_port (sctp_ppi_dissector_table, ppi,  user_tvb, pinfo, tree) ||
> +      dissector_try_port(sctp_port_dissector_table, pi.srcport,  user_tvb, pinfo, tree) ||
> +      dissector_try_port(sctp_port_dissector_table, pi.destport, user_tvb, pinfo, tree)){
> +    ret = TRUE;
>    }
>    else {
>      if (check_col(pinfo->fd, COL_INFO))
>        col_append_str(pinfo->fd, COL_INFO, "DATA ");
>      proto_tree_add_text(chunk_tree, payload_tvb, 0, payload_length,
>                         "Payload (%u byte%s)",
> -                       payload_length, plurality(payload_length, "", "s"));
> -    if (padding_length > 0)
> -      proto_tree_add_text(chunk_tree, payload_tvb, payload_length, padding_length,
> -                         "Padding: %u byte%s",
> -                         padding_length, plurality(padding_length, "", "s"));
> -    return FALSE;
> +                       payload_length, plurality(payload_length, "", "s"));
> +    ret = FALSE;
>    }
> +  if (padding_length > 0)
> +    proto_tree_add_text(chunk_tree, payload_tvb, payload_length, padding_length,
> +                       "Padding: %u byte%s",
> +                       padding_length, plurality(padding_length, "", "s"));
> +  return ret;
>  }
> 
>  static gboolean
> @@ -1768,7 +1778,7 @@
>         "", HFILL }
>      },
>      {&hf_sctp_data_chunk_payload_proto_id,
> -     { "Payload Protocol identifier", "sctp.payload_proto_id",
> +     { "Payload Protocol identifier", "sctp.ppi",
>         FT_UINT32, BASE_HEX, NULL, 0x0,
>         "", HFILL }
>      },

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