SA Usage Leakage
Kevin D Butt
kdbutt at us.ibm.com
Fri Nov 7 13:50:36 PST 2008
Formatted message: <a href="r0811070_f.htm">HTML-formatted message</a>
Ralph,
As I understand it, the SA state is not tied to one initiator or another.
Once it is created it uses the SAI to determine which SA to use. There is
no way to determine if it was another initiator that caused the info to be
cleared. This is a whole new concept where the item in question (the SA)
is not tied to any I_T nexus. Creating a UA for removing SA state
information is not a good idea. In fact it could lead to all applications
out there checking to see if the SA they are using is still available.
This does not make sense to me. In fact, SPC-4 already states that if the
SA Timer expires the state information is discarded and there is no
mention of creating a UA - thankfully. This situation is only slightly
different.
We still believe that:
A) the DS needs to be able to clear space for a new SA
B) no notification of lost SA should be reported to AC until the AC
attempts to use an SA
C) the expected behaviors of the DS and the AC should be explicitly stated
in SPC-4 and be general (i.e., not tied to each usage defined (e.g.,
ESP-SCSI))
D) There should be a unique additional sense code for when an attempt to
use an unknown SAI is made (not just 5/2600 pointing to the SA field)
Thanks,
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-2869 / 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
http://www-03.ibm.com/servers/storage/
From:
Ralph Weber <roweber at IEEE.org>
To:
t10 at t10.org
Date:
10/31/2008 06:55 PM
Subject:
Re: SA Usage Leakage
Kevin,
Why is it better to have to define, establish, etc. a UA for
SA CLEARED BY ANOTHER USER than to simply refuse to do that
which cannot be done?
Do not for a minute think that SCSI is going to allow
SAs to be discarded without establishing a UA. That is
simply not done.
Either way there is a messy Denial of Service problem: UAs
out the ying-yang or full frontal request rejection.
Think about it!
All the best,
.Ralph
Kevin D Butt wrote:
I sent out a note on SA Usage Leakage a while back and then lost track of
this item. David Black responded with "I don't see a problem with this in
principle. The original IKEv2 allows state to be discarded at will."
The original note is:
===========
We have concerns related to SA usage leakage. That is, it is possible for
application clients to create enough SA's in a device server - with the
timeout values long enough - that the device server is out of resources to
create another. While the answer seems obvious - allow the device server
to implicitly abandon an SA for vendor-specific reasons, there is no
explicit mention of this in SPC-4 that we can find. If the DS is not
allowed to implicitly abandon an SA, the opens up the avenue for Denial of
Service attacks - an attacker could use up all the SA resources with
maximum timeout values.
Key points being:
A) the DS needs to be able to clear space for a new SA
B) no notification of lost SA should be reported to AC until the AC
attempts to use an SA
C) the expected behaviors of the DS and the AC should be explicitly stated
in SPC-4 and be general (i.e., not tied to each usage defined (e.g.,
ESP-SCSI))
D) There should be a unique additional sense code for when an attempt to
use an unknown SAI is made
===========
Also there should be a high-level statement/behavior in the usage model
about attempts to use an unknown SA (not just 5/2600 pointing to the SA
field).
Does anybody disagree with this or agree that this would be a good thing
to do?
Thanks,
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-2869 / 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
http://www-03.ibm.com/servers/storage/
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