Re: [Re: Linux 2.6.26-rc2] Write protect on on

Peter Teoh
2008-06-24T04:09:22Z

Sorry, missed this one - in case u need it:

Tested-by: Peter Teoh <htmldeveloper@gmail.com>

Thanks.

On Tue, Jun 24, 2008 at 11:25 AM, Peter Teoh <htmldeveloper@gmail.com> wrote:
> On Mon, Jun 23, 2008 at 11:04 PM, Alan Stern <stern@rowland.harvard.edu> wrote:
>> On Fri, 20 Jun 2008, James Bottomley wrote:
>>
>>> Yes, thanks. It's a bit nasty from a security point of view, since the
>>> leaking data apparently belonged to a different command. Wouldn't a
>>> better fix (and a more secure one) be to clear from the end of the valid
>>> data to the end of the buffer?
>>
>> Here's the promised patch. Maciej and Peter, please try it out.
>>
>> Alan Stern
>>
>>
>> Index: usb-2.6/drivers/scsi/scsi_lib.c
>> ===================================================================
>> --- usb-2.6.orig/drivers/scsi/scsi_lib.c
>> +++ usb-2.6/drivers/scsi/scsi_lib.c
>> @@ -207,6 +207,15 @@ int scsi_execute(struct scsi_device *sde
>> */
>> blk_execute_rq(req->q, NULL, req, 1);
>>
>> + /*
>> + * Some devices (USB mass-storage in particular) may transfer
>> + * garbage data together with a residue indicating that the data
>> + * is invalid. Prevent the garbage from being misinterpreted
>> + * and prevent security leaks by zeroing out the excess data.
>> + */
>> + if (unlikely(req->data_len > 0 && req->data_len <= bufflen))
>> + memset(buffer + (bufflen - req->data_len), 0, req->data_len);
>> +
>> ret = req->errors;
>> out:
>> blk_put_request(req);
>>
>>
>
> Yes, it worked (based on latest linus git tree) the before and after
> patch dmesg are as follows:
>
> [ 387.015562] scsi 3:0:0:0: Direct-Access WD
> 1600BEAExternal 1.02 PQ: 0 ANSI: 0
> [ 387.018563] sd 3:0:0:0: [sde] 312581808 512-byte hardware sectors (160042 MB)
> [ 387.018573] sd 3:0:0:0: [sde] Write Protect is on
> [ 387.018583] sd 3:0:0:0: [sde] Mode Sense: 12 a1 9e af
> [ 387.018589] sd 3:0:0:0: [sde] Assuming drive cache: write through
> [ 387.020182] sd 3:0:0:0: [sde] 312581808 512-byte hardware sectors (160042 MB)
> [ 387.020602] sd 3:0:0:0: [sde] Write Protect is on
> [ 387.020602] sd 3:0:0:0: [sde] Mode Sense: 12 a1 9e af
> [ 387.020602] sd 3:0:0:0: [sde] Assuming drive cache: write through
> [ 387.020602] sde: sde1 sde2 sde3 < sde5 > sde4
> [ 387.094903] sd 3:0:0:0: [sde] Attached SCSI disk
> [ 387.095304] sd 3:0:0:0: Attached scsi generic sg4 type 0
>
> After patching and recompiling and reboot:
>
> [ 230.281708] sd 3:0:0:0: [sdd] 312581808 512-byte hardware sectors (160042 MB)
> [ 230.282708] sd 3:0:0:0: [sdd] Write Protect is off
> [ 230.282708] sd 3:0:0:0: [sdd] Mode Sense: 00 00 00 00
> [ 230.282708] sd 3:0:0:0: [sdd] Assuming drive cache: write through
> [ 230.283708] sd 3:0:0:0: [sdd] 312581808 512-byte hardware sectors (160042 MB)
> [ 230.284709] sd 3:0:0:0: [sdd] Write Protect is off
> [ 230.284709] sd 3:0:0:0: [sdd] Mode Sense: 00 00 00 00
> [ 230.284709] sd 3:0:0:0: [sdd] Assuming drive cache: write through
> [ 230.284709] sdd: sdd1 sdd2 sdd3 < sdd5 > sdd4
> [ 230.364830] sd 3:0:0:0: [sdd] Attached SCSI disk
>
> Thank you very much Alan.
>
> --
> Regards,
> Peter Teoh
>

--
Regards,
Peter Teoh