Wireshark · Ethereal-dev: RE: [Ethereal-dev] Should the BER dissector throw an exception onatagmismatch?

["Tim" <tim@xxxxxxxxxxxxxxx>]

Only fixed in sequence and not set, if it finds a tag mis-match it skips
the tag and rewinds back to the last known good tag match.

Mainly checked with a packet with an undefined tag length value then
continues with defined ones.

Please test and check in for the next release.

Tim

-----Original Message-----
From: ethereal-dev-bounces@xxxxxxxxxxxx
[mailto:ethereal-dev-bounces@xxxxxxxxxxxx] On Behalf Of Tim
Sent: 26 September 2005 07:51
To: 'Ethereal development'
Subject: RE: [Ethereal-dev] Should the BER dissector throw an exception
onatagmismatch?


I had a play and saw that it is not reported at all, if I have time I
will fix this at the weekend.

Tim

-----Original Message-----
From: ethereal-dev-bounces@xxxxxxxxxxxx
[mailto:ethereal-dev-bounces@xxxxxxxxxxxx] On Behalf Of Tomas Kukosa
Sent: 22 September 2005 08:04
To: tim@xxxxxxxxxxxxxxx; Ethereal development
Subject: Re: [Ethereal-dev] Should the BER dissector throw an exception
onatag mismatch?


It is supported in asn2eth and PER decoder but as I remember it is not
supported in BER 
decoder.
But we should still discern between extension and invalid packet.

Tim wrote:

> I am not sure about this, the history of ASN.1 has definitions that
> include the "..." clause, which basically means add anything required 
> for future expansions in here.
> 
> I not sure if the asn.1 compiler supports this, I need to have a look,

> but the practice of companies extending asn.1 definitions is common
> place. In the case where an unexpected Octet string is found we should

> report the problem then skip the item, and continue dissecting.
> 
> 
> Tim
> 
> -----Original Message-----
> From: ethereal-dev-bounces@xxxxxxxxxxxx
> [mailto:ethereal-dev-bounces@xxxxxxxxxxxx] On Behalf Of Tomas Kukosa
> Sent: 22 September 2005 06:46
> To: ronnie sahlberg; Ethereal development
> Subject: Re: [Ethereal-dev] Should the BER dissector throw an 
> exception ona tag mismatch?
> 
> 
> I agree.
> 
> And the wrong packet will be more visible.
> BTW do we have any any exception like "Invalid packet"?
> 
> ronnie sahlberg wrote:
> 
> 
>>i think it would be valid to throw an exception right there when the 
>>tag is wrong.
>>
>>even it the length is correct  it is more than likely something is
>>pretty broken anyway so it is unlikely in my opinion that any attempts
> 
> 
>>to try to skip to the next token and continue would work.
>>
>>
>>
>>
>>On 9/22/05, Guy Harris <gharris@xxxxxxxxx <mailto:gharris@xxxxxxxxx>>
>>wrote:
>>
>>    Currently, the BER dissector will put a "BER Error" item into the
>>    protocol
>>    tree if it is attempting to dissect an item of a particular type
> 
> but the
> 
>>    tag on the item says it has another type.  It returns an offset
> 
> that
> 
>>    runs
>>    past the end of the item after that.
>>
>>    This means that, for example, callers to
> 
> dissect_ber_octet_string() who
> 
>>    pass it a tvbuff_t ** have to check whether the tvbuff_t *
> 
> returned is
> 
>>    null, which it will be if the item didn't have a tag  appropriate
> 
> to an
> 
>>    octet string.  I've checked in a bunch of changes to add checks
> 
> for
> 
>>    that.
>>
>>    Should we, for any or all of the cases where a "BER Error" item is
>>    currently put into the protocol tree, be throwing an exception and
>>    giving
>>    up on dissection?  One could argue that, if the tag is wrong but
> 
> the
> 
>>    length is correct, *not* throwing an exception lets us try
>>    dissecting more
>>    of the packet.
>>

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