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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: ISCSI: CmdSN in non-leading loginJohn, 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:wrstuden@wasabisystems.com] Sent: Monday, May 13, 2002 10:57 AM To: Julian Satran Cc: John Hufferd; ips@ece.cmu.edu; Mark S. Edwards; owner-ips@ece.cmu.edu 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
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