Wireshark · Wireshark-dev: Re: [Wireshark-dev] Fwd: And again BER errors while decoding H248packets

["Anders Broman" <a.broman@xxxxxxxxx>]

Hi,
I think part of the problem is that we are uncertain if this isn't a
protocol error in the stack you are using - zero length items??

Brg
Anders 

-----Ursprungligt meddelande-----
Från: wireshark-dev-bounces@xxxxxxxxxxxxx
[mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] För Oleg Kostenko
Skickat: den 19 september 2006 20:03
Till: wireshark-dev@xxxxxxxxxxxxx
Ämne: [Wireshark-dev] Fwd: And again BER errors while decoding H248packets

Hello,

Is there any progress on this issue (see below)?

-- 
Best regards,
 Oleg                            mailto:oleg.kostenko@xxxxxxxxxxxx


This is a forwarded message
From: Oleg Kostenko <oleg.kostenko@xxxxxxxxxxxx>
To: wireshark-dev@xxxxxxxxxxxxx
Date: Tuesday, August 22, 2006, 5:14:59 PM
Subject: And again BER errors while decoding H248 packets

===8<==============Original message text===============
Hello,

  Some time ago Eugene Tarlovskij posted the message about BER errors
  while decoding H248 packets. Here are the links to his posts:

  http://www.wireshark.org/lists/ethereal-dev/200605/msg01641.html
  http://www.wireshark.org/lists/ethereal-dev/200605/msg01723.html

  The solution he proposed was to change packet-ber.cpp:

      if((len!=0)&&(count==0)&&(seq->flags&BER_FLAGS_OPTIONAL)){

      change to:

 
if((len!=0)&&(count==0)&&(count!=length_remaining)&&(seq->flags&BER_FLAGS_OP
TIONAL)){

  (This is currently line number 1222).

  However, Eugene's patch was rejected and another patch was proposed
  by Tim Endean.
  http://www.wireshark.org/lists/ethereal-dev/200606/msg01532.html

  Lines 1076-1080:

       if(ind_field && (len == 2)){
           /* disgusting indefinite length zero length field, what are these
people doing */
         offset = eoffset;
         continue;
       }

  This patch is currently checked in, but doesn't work well enough.
  Please, take a look at this packet that I've captured (in attach).
  Here's a fragment of its decoding:
  
    Item: mediaDescriptor (1)
      mediaDescriptor
        termStateDescr
          BER Error: Wrong field in SEQUENCE  expected class:2 (CONTEXT)
tag:0 but found class:2 tag:2
        streams: oneStream (0)
          oneStream
            localControlDescriptor
              reserveValue: False
              reserveGroup: False

  With Eugene's patch this looks like this:
  
    Item: mediaDescriptor (1)
      mediaDescriptor
        termStateDescr
          propertyParms: 0 items
          serviceState: inSvc (2)
        streams: oneStream (0)
          oneStream
            localControlDescriptor
              reserveValue: False
              reserveGroup: False

  Would you please review both patches again, to see what's wrong with
  them. As for me, the Eugene's patch works just fine, but I don't
  actually understand the code well enough to make any conclusions.
  Probably, you would be able to make another patch, which would be
  better than these two.

  Thanks.

  Attached is the hex dump of the problematic packet.
              
-- 
Best regards,
 Oleg                          mailto:oleg.kostenko@xxxxxxxxxxxx

===8<===========End of original message text===========