linux-kernel - Re: LIBATA SCSI command validation changed in 2.6.24

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Date:	Fri, 11 Jan 2008 18:28:04 -0500
From:	Chuck Ebbert <cebbert@...hat.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	linux-kernel <linux-kernel@...r.kernel.org>,
	IDE/ATA development list <linux-ide@...r.kernel.org>
Subject: Re: LIBATA SCSI command validation changed in 2.6.24

On 01/11/2008 06:21 PM, Jeff Garzik wrote:
> Chuck Ebbert wrote:
>> On 01/11/2008 04:35 PM, Jeff Garzik wrote:
>>> Chuck Ebbert wrote:
>>>> commit 607126c2a21cd6e9bb807fdd415c1a992f7b9009 changed command
>>>> validation
>>>> to allow short commands in 16-byte CDBs, but it also made checking more
>>>> strict. Before the change, a 10-byte SG_IO command could have its
>>>> length set
>>>> to 9 and still work. Now it fails. Not sure if this is a bug, but it
>>>> has
>>>> caused at least one application to fail that used to work (qpxtool.)
>>>>
>>>> [https://bugzilla.redhat.com/show_bug.cgi?id=428281]
>>> Can you get us an example CDB?  Its unclear if the hexdump in the bug
>>> report is a returned mode page or the CDB or what...?
>>>
>>
>> Not easily, but the maintainer of that program forced the length of
>> the MODE_SENSE(10) command to 10 and that command started working.
>>
>> By looking at the source I could tell that it was setting the command
>> length to (1 + the index of the last byte written to the CDB) and
>> only wrote up to offset 8 when building the command, so it must have
>> been sending the command with a length of 9. (It zeroed the whole CDB
>> first and only wrote what it needed to.)
>>
>> (And it used the C++ operator [] to build the command, that was fun
>> to trace...)
> 
> Even if allocation length is present in the CDB, the CDB may be missing
> important information that is required to process the command.  So it
> may have caught a bug in the program... depending on the CDB.
> 

Yeah, the change is probably good. We should have been validating that
the length was at least as long the expected length all along. But some
programs are going to break because of this...
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