Subject: RE: ISCSI: CmdSN in non-leading login

From: "THALER,PAT (A-Roseville,ex1)" <[email-masked]>
Date: Mon, 13 May 2002 13:05:53 -0600

John,

I don't understand your point. An outstanding immediate command doesn't affect the progress of ExpCmdSN or MaxCmdSN. In the situation you describe, the target would act on the non-immediate commands 1000 and 1001 when it got them. It would then increase MaxCmdSN as it empties those non-immediate commands from its queue. 

The login immediate command with CmdSN would be processed when it arrives regardless of the current non-immediate command's CmdSN. Any immediate command can arrive with a CmdSN lower than ExpCmdSN or higher than MaxCmdSN. The use of CmdSN in immediate commands is to allow the immediate command to have a relationship to the non-immediate commands - e.g. CLEAR TASK SET.

Pat

-----Original Message-----
From: Bill Studenmund [mailto:[email-masked]]
Sent: Monday, May 13, 2002 10:57 AM
To: Julian Satran
Cc: John Hufferd; [email-masked]; Mark S. Edwards;
[email-masked]
Subject: Re: ISCSI: CmdSN in non-leading login

On Sun, 12 May 2002, Julian Satran wrote:

> John,
>
> My only point was that there is enough information in the section to
> describe correct behavior.

> And immediate commands do not create any blockage regardless of their
> CmdSN.

Don't they though? Say I have a queue depth of 2, and I start a secondary
login with a CmdSN of 1000. I can then send other immediate commands at
1000, and a non-immediate command at 1000. I can then also send a
non-immeidate command at 1001. But can I send a command at 1002 before the
login has finished? If we increase the queue depth, there will still be
some other command number that would overflow it.

Say the login takes a while. Won't the login pin the queue at 1002 until
it's done? Now let the login take a while, it requires talking to say a
low kerberos server or doing a DH computation. If we really pay attention
to CmdSN, then the slow login process can effectively take the device
off-line while it completes, since we can't enqueue new commands.

Worse yet, say the secondary connection is NOT from our initiator, but
from an imposter. All the rogue has to do is get the TSIH right & guess a
CmdSN, and stall at trying to add another connection. Say do leading
negotiation, but just never send any security negotiations. The queue will
eventually become pinned until the target times out. Nice little DOS
attack; all you have to do is get the TSIH right & guess a CmdSN. You
don't have to do any security negotiation.  :-)

I'd like to suggest that we just ignore CmdSN on non-leading sessions,
beyond the fact that a well-behaved initiator should pick a CmdSN in its
current command window. We certainly shouldn't pay attention to it before
security negotiations have completed. :-) Oh also no commands should be
sent over the new connection with a CmdSN lower than the one used in the
new connection.

Take care,

Bill

---

From: Bill Studenmund <[email-masked]>
Date: Mon, 13 May 2002 13:40:33 -0700 (PDT)

> John,

I think that was supposed to be me, not John. :-)

> I don't understand your point. An outstanding immediate command
> doesn't affect the progress of ExpCmdSN or MaxCmdSN. In the situation
> you describe, the target would act on the non-immediate commands 1000
> and 1001 when it got them. It would then increase MaxCmdSN as it
> empties those non-immediate commands from its queue.
>
> The login immediate command with CmdSN would be processed when it
> arrives regardless of the current non-immediate command's CmdSN. Any
> immediate command can arrive with a CmdSN lower than ExpCmdSN or
> higher than MaxCmdSN. The use of CmdSN in immediate commands is to
> allow the immediate command to have a relationship to the
> non-immediate commands - e.g. CLEAR TASK SET.

I thought that immediate commands weren't supposed to be processed (or
weren't supposed to be seen to be processed) until their CmdSN came up in
the stream.  From that I also assumed (evidently incorrectly :-) that they
counted against the outstanding command window.

Take care,

Bill