Re: [PATCH] scsi_debug: fix lba and data length calculation bugs

[Douglas Gilbert <dougg@torque.net>]

FUJITA Tomonori wrote:
> On Wed, 26 Mar 2008 17:21:30 -0400
> Douglas Gilbert <dougg@torque.net> wrote:
> 
>> FUJITA Tomonori wrote:
>>> This fixes lba calculation bugs in scsi_debug (it might happen only
>>> with over 1TB virtual devices).
>>>
>>> This is against scsi-misc. scsi-fixes, 2.6.24, 2.6.23, ... probably
>>> all the versions of scsi_debug have the same bugs too but I guess that
>>> there are few people who play scsi_debug with over virtual 1TB devices
>>> (though this can be cleanly applied to scsi-fixes).
>>>
>>> Several LLDs have the own code to do the same calculation. It might be
>>> nice to sweep up them?
>>>
>>> =
>>> From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
>>>
>>> For example, `modprobe scsi_debug virtual_gb=1100` gives:
>>>
>>> scsi7 : scsi_debug, version 1.81 [20070104], dev_size_mb=8, opts=0x0
>>> scsi 7:0:0:0: Direct-Access     Linux    scsi_debug       0004 PQ: 0 ANSI: 5
>>> sd 7:0:0:0: [sdc] 2306867200 512-byte hardware sectors (1181116 MB)
>>> sd 7:0:0:0: [sdc] Write Protect is off
>>> sd 7:0:0:0: [sdc] Mode Sense: 73 00 10 08
>>> sd 7:0:0:0: [sdc] Write cache: enabled, read cache: enabled, supports DPO and FUA
>>> sd 7:0:0:0: [sdc] 2306867200 512-byte hardware sectors (1181116 MB)
>>> sd 7:0:0:0: [sdc] Write Protect is off
>>> sd 7:0:0:0: [sdc] Mode Sense: 73 00 10 08
>>> sd 7:0:0:0: [sdc] Write cache: enabled, read cache: enabled, supports DPO and FUA
>>>  sdc: unknown partition table
>>> sd 7:0:0:0: [sdc] Attached SCSI disk
>>> sd 7:0:0:0: Attached scsi generic sg6 type 0
>>> end_request: I/O error, dev sdc, sector 2306867072
>>> Buffer I/O error on device sdc, logical block 288358384
>>> end_request: I/O error, dev sdc, sector 2306867072
>>> Buffer I/O error on device sdc, logical block 288358384
>>> end_request: I/O error, dev sdc, sector 2306867192
>>>
>>> (snip)
>>>
>>> Note that this converts all the calculations (including the correct
>>> calculations) for unification.
>>>
>>> Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
>>> Cc: Douglas Gilbert <dougg@torque.net>
>>> Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
>>> ---
>>>  drivers/scsi/scsi_debug.c |   32 ++++++++++++++++++--------------
>>>  1 files changed, 18 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
>>> index 4f4c5b7..46a136a 100644
>>> --- a/drivers/scsi/scsi_debug.c
>>> +++ b/drivers/scsi/scsi_debug.c
>>> @@ -251,33 +251,37 @@ static struct bus_type pseudo_lld_bus;
>>>  static void get_data_transfer_info(unsigned char *cmd,
>>>  				   unsigned long long *lba, unsigned int *num)
>>>  {
>>> -	int i;
>>> -
>>>  	switch (*cmd) {
>>>  	case WRITE_16:
>>>  	case READ_16:
>>> -		for (*lba = 0, i = 0; i < 8; ++i) {
>>> -			if (i > 0)
>>> -				*lba <<= 8;
>>> -			*lba += cmd[2 + i];
>>> -		}
>>> -		*num = cmd[13] + (cmd[12] << 8) +
>>> -			(cmd[11] << 16) + (cmd[10] << 24);
>>> +		*lba = (u64)cmd[9] | (u64)cmd[8] << 8 |
>>> +			(u64)cmd[7] << 16 | (u64)cmd[6] << 24 |
>>> +			(u64)cmd[5] << 32 | (u64)cmd[4] << 40 |
>>> +			(u64)cmd[3] << 48 | (u64)cmd[2] << 56;
>>> +
>>> +		*num = (u32)cmd[13] | (u32)cmd[12] << 8 | (u32)cmd[11] << 16 |
>>> +			(u32)cmd[10] << 24;
>>>  		break;
>>>  	case WRITE_12:
>>>  	case READ_12:
>>> -		*lba = cmd[5] + (cmd[4] << 8) +	(cmd[3] << 16) + (cmd[2] << 24);
>>> -		*num = cmd[9] + (cmd[8] << 8) +	(cmd[7] << 16) + (cmd[6] << 24);
>>> +		*lba = (u32)cmd[5] | (u32)cmd[4] << 8 | (u32)cmd[3] << 16 |
>>> +			(u32)cmd[2] << 24;
>>> +
>>> +		*num = (u32)cmd[9] | (u32)cmd[8] << 8 | (u32)cmd[7] << 16 |
>>> +			(u32)cmd[6] << 24;
>>>  		break;
>>>  	case WRITE_10:
>>>  	case READ_10:
>>>  	case XDWRITEREAD_10:
>>> -		*lba = cmd[5] + (cmd[4] << 8) +	(cmd[3] << 16) + (cmd[2] << 24);
>>> -		*num = cmd[8] + (cmd[7] << 8);
>>> +		*lba = (u32)cmd[5] | (u32)cmd[4] << 8 |	(u32)cmd[3] << 16 |
>>> +			(u32)cmd[2] << 24;
>>> +
>>> +		*num = (u32)cmd[8] | (u32)cmd[7] << 8;
>>>  		break;
>>>  	case WRITE_6:
>>>  	case READ_6:
>>> -		*lba = cmd[3] + (cmd[2] << 8) + ((cmd[1] & 0x1f) << 16);
>>> +		*lba = (u32)cmd[3] | (u32)cmd[2] << 8 |
>>> +			(u32)(cmd[1] & 0x1f) << 16;
>>>  		*num = (0 == cmd[4]) ? 256 : cmd[4];
>>>  		break;
>>>  	default:
>> Signed-off-by: Douglas Gilbert <dougg@torque.net>
>>
>>
>> Can't actually see the "lba calculation bugs" but I'm happy
>> to let Tomo do it his way.
> 
> Let me make things clear though we've already agreed offline.
> 
> Something like the following code doesn't work.
> 
> unsigned char *cmd;
> unsigned long long *lba;
> 
> *lba = cmd[2] << 24;
> 
> 
> So surely there are lba calculation bugs.

It gives a surprising result when cmd[2] >= 0x80 .

And it gets worse. On a 64 bit architecture using the LP64
data model, Tomo's above example will fail in a similar
fashion with a 'unsigned long *lba;' declaration.

I just did a small audit of sg3_utils with respect to this
bug and the 'unsigned long' case is more prevalent.

Doug Gilbert