Re: LIBATA SCSI command validation changed in 2.6.24

Jeff Garzik
2008-01-11T23:21:54Z

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.

Jeff