RE: Problem with use of NotUnderstood in negotiations

[pat_thaler@agilent.com]

Julian,

 

Saying that a violation of a rule is a protocol error is not the same as saying that the receiver must detect and react to the error. I don't think your suggested change to the text changes anything. If we want to say that receiving an offer for any key (even if the key is not understood) with a value of "Reject", "Irrelevant" or "NotUnderstood" MUST be detected and treated as a protocol failure, then a specific statement to that effect should be added.

 

Secondly, there is no requirement that re-negotiation MUST be detected. The specific text on renegotiation is (for login):

If an attempt to re-negotiate/redeclare parameters not specifically allowed is detected by the target the target MUST respond with Login reject (initiator error); if detected by the initiator the initiator MUST drop the connection.

The text for operational negotiation is similar except that the actions taken on detection are different.

 

It says "If an attempt ...is detected" which is entirely different than saying such attempts "MUST be detected".

 

As Bill as pointed out, detecting re-negotiation of unknown parameters is onerous and I am very opposed to adding such a requirement. It adds unnecessary cost for minimal benefit. For the keys that are supported, on just needs a couple of bits per parameter to keep track of whether the state is unnegotiated, received offer, sent offer or negotiation complete and one may need that state even if one wasn't going to detect re-negotiation. Thus, it is pretty trivial to detect re-negotiation of supported keys.

 

If someone wants to maliciously tie up a negotiation, they can do so by continuously offering new unknown keys and no working non-malicious implementation will keep offering the same key. One would have to save all

received unsupported keys and each time an unsupported key was received it would have to be compared to the list. This is time and memory consuming and unnecessary. It isn't required by draft 15 and no such requirement should be added.

 

A simpler solution to concerns about the silent data corruption problem Bill identified is either

 

1) add in text requiring that an offer the value equal to NotUnderstood be detected as a protocol error even if the key is not supported/not understood

 

or

 

2) rely on timing out the negotiation if it doesn't complete after reasonable time or number of exchanges (definition of reasoanble left to the implementation probably).

 

Personally, I prefer number 2 because it will catch anything that hangs up a negotiation with one test. I don't know that we can find every corner case. Even if we could, it is better to have one test that digs us out for all corner case errors than to put in many specific tests.

 

However, number 1 would also be acceptable to me.

 

Regards,

Pat

 

-----Original Message-----
From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
Sent: Saturday, August 10, 2002 9:40 PM
To: Bill Studenmund
Cc: ips@ece.cmu.edu
Subject: RE: Problem with use of NotUnderstood in negotiations

Bill, 

My only intention in the note was to be 
brief.  If you viewed that as rude I am really sorry. 
I have a lot of mail to reply to and a limited 
time. 

As for the crux of the matter 
- if one of the parties receives a key it has not seen before 
with NotUnderstood as value it MUST act on it as a 
protocol error. The text is unambiguous on this. 
However we may want to strengthen the rule in 4 (and add 
another line of text) as follows: 

The constants "None", "Reject", "Irrelevant", and "NotUnderstood" are 
reserved and MUST ONLY be used as described here. Violation of this rule is a 
protocol error (in particular the use of "Reject", "Irrele-vant", and 
"NotUnderstood" as proposed values). 

In the second part of my comment I was just saying that if you 
 failed to implement the above check you still can't enter a loop 
because the double negotiation rule. 

To get you in a loop in which every party 
think it answers - then either both are buggy or somebody is altering the 
messages maliciously. 
The protocol is 
not designed to handle either. 

Julo

Bill Studenmund <wrstuden@wasabisystems.com> 08/11/2002 06:11 AM

To:        Julian Satran/Haifa/IBM@IBMIL         cc:        <ips@ece.cmu.edu>         Subject:        RE: Problem with use of NotUnderstood in negotiations

On 
Sat, 10 Aug 2002, Julian Satran wrote:

> Bill,
>
> Perhaps 
the text is unabiguos but you just ignored the text that forbids
> 
it.

Julian,

I must say that the tone above is very unbecoming of 
the author of a
protocol spec. In the past, I've often gotten snippy comments 
from you,
but written them off to, well, I'm not sure what. But it seems that 
you
really don't listen to what I say. You read a message, make 
an
interpretation, do not question that interpretation, and then you run 
with
it. That's really bad. Besides being quite rude and exceedingly 
arrogant,
you'll miss things. And the iSCSI spec will suffer for it. Do you 
think
whatever is going on between us worth more than a bad iSCSI spec? I 
don't.

Also, if you're going to say that the text is unambiguous, please 
quote
said text. That makes the discussion much clearer.

> The use 
of Notunderstood is limited to responses. Using it as you suggest
> is a 
protocol error.

Julian, I have to ask, what exactly do you think I'm 
suggesting? From
parsing your sentence, I read that you are telling me that 
I'm suggesting
using NotUnderstood outside its limited scope, of 
responses.

As I understand the situation I described, both parties think 
they are
using NotUnderstood as a response. How is using it as a response 
outside
its use as a response?

> A repeated use will also violate 
the "no renegotiation rule".

Please be VERY VERY VERY careful when saying 
that. Have you thought about
what the statement you just made will 
imply?

We are (or at least I started) talking about the case where one 
side
THOUGHT it sent key X, but somehow it was key Y that made it to the 
other
side. Be it a bug in the code on one side or the other, a PCI bus error 
in
transfer, a router glitch, or what. Key Y doesn't exist in the spec, 
and
it's in the negotiation stream. OGMarker or DataPDPInOrder would 
be
examples.

The point is, BOTH SIDES THINK THEY ARE RESPONDING to a 
key they don't
understand. Reading the spec, it succinctly states if you get 
a key you
don't understand, you MUST reply "NotUnderstood".

Getting 
back to the "repeated use is a protocol violation," how is each
side supposed 
to realize that they are seeing "OGMarker=NotUnderstood" for
the second time, 
other than by remembering that it saw OGMarker as a
not-understood key. i.e. 
by in addition to replying, "NotUnderstood", each
side has to remember that 
it responded NotUnderstood to key foo. That
seems unwise. I can think of at 
least one DoS attack if that really is
what implementations 
do.

Getting back to addressing the topic of the thread, what is wrong 
with
this text, slightly modified from the I proposed in the first 
message?

***
Any key not understood by the acceptor may be ignored by 
the acceptor
without affecting the basic function. However, unless the value 
for the
key was "NotUnderstood", the answer for a key not understood MUST 
be
key=NotUnderstood. The value "NotUnderstood" for a key not understood 
MUST
be considered a protocol violation.
***

As I said before, my 
main interest is the spec point out that if for a key
you don't understand 
you get the value "NotUnderstood" (i.e. the other
side is telling you it 
didn't understand a key that it turns out you also
don't understand), you 
don't just answer "NotUnderstood". Either
saying nothing, or considering it a 
protocol violation (since if we both
didn't understand the key it should have 
never gotten into the
negotiations) are both fine options. I now favor 
protocol violation as if
neither side understood the key, it should not be 
there. If it's there, 
something is 
wrong.

Take care,

Bill