Re: [Qemu-devel] [PATCH] iscsi: Refuse to open as writable if the LUN is write protected

[Peter Lieven <pl@kamp.de>]

On 30.10.2014 11:50, Fam Zheng wrote:
> On Thu, 10/30 11:27, Peter Lieven wrote:
>> On 29.10.2014 19:28, Paolo Bonzini wrote:
>>> On 10/29/2014 05:18 PM, Peter Lieven wrote:
>>>> Am 29.10.2014 um 14:31 schrieb Paolo Bonzini:
>>>>> On 10/29/2014 02:13 PM, Fam Zheng wrote:
>>>>>> Before, when a write protected iSCSI target is attached as scsi-disk
>>>>>> with BDRV_O_RDWR, we report it as writable, while in fact all writes
>>>>>> will fail.
>>>>>>
>>>>>> One way to improve this is to report write protect flag as true to
>>>>>> guest, but a even better way is to refuse using a write protected LUN to
>>>>>> guest.
>>>>>>
>>>>>> Target write protect flag is checked with a mode sense query.
>>>>>>
>>>>>> Signed-off-by: Fam Zheng <famz@redhat.com>
>>>>>> ---
>>>>>>   block/iscsi.c | 30 ++++++++++++++++++++++++++++++
>>>>>>   1 file changed, 30 insertions(+)
>>>>>>
>>>>>> diff --git a/block/iscsi.c b/block/iscsi.c
>>>>>> index 233f462..c154928 100644
>>>>>> --- a/block/iscsi.c
>>>>>> +++ b/block/iscsi.c
>>>>>> @@ -1339,6 +1339,36 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
>>>>>>       scsi_free_scsi_task(task);
>>>>>>       task = NULL;
>>>>>> +    /* Check the write protect flag of the LUN if we want to write */
>>>>>> +    if (flags & BDRV_O_RDWR) {
>>>>>> +        struct scsi_mode_sense *ms;
>>>>>> +
>>>>>> +        task = iscsi_modesense6_sync(iscsilun->iscsi, iscsilun->lun,
>>>>>> +                                      1, SCSI_MODESENSE_PC_CURRENT,
>>>>>> +                                      0x3F,
>>>>>> +                                      0, 255);
>>>>>> +
>>>>>> +        if (task == NULL) {
>>>>>> +            error_setg(errp, "Failed to send MODE_SENSE10 command: %s\n",
>>>>> This is MODE SENSE(6).  Fixed and applied.
>>>>>
>>>>> Paolo
>>>>>
>>>>>> +                       iscsi_get_error(iscsilun->iscsi));
>>>>>> +            ret = -EINVAL;
>>>>>> +            goto out;
>>>>>> +        }
>>>>>> +
>>>>>> +        if (task->status != SCSI_STATUS_GOOD) {
>>>>>> +            error_setg(errp, "MODE_SENSE10 failed: %s\n",
>>>>>> +                       iscsi_get_error(iscsi));
>>>>>> +            ret = -EINVAL;
>>>>>> +            goto out;
>>>>>> +        }
>>>>>> +        ms = scsi_datain_unmarshall(task);
>>>> scsi_datain_unmarshall may fail. You need to check for NULL here.
>>> Thanks for the remark, I fixed this too.
>>>
>>> Paolo
>> I am not 100% happy with this patch as it may break support for some targets.
>>
>> It seems that MODESENSE is somewhat tricky with some targets. See function  sd_read_write_protect_flag
>> in <http://lxr.free-electrons.com/ident?i=sd_read_write_protect_flag>drivers/scsi/sd.c of the Linux kernel.
>>
>> I would not fail if this modesense fails, but just assume write enabled. Maybe drop a warning.
> OK.
>
>> In the command itself:
>>   0x3F => SCSI_MODEPAGE_RETURN_ALL_PAGES
> That requires a newer version of libiscsi than we currently check for.
> Seeing drivers/scsi/sd.c used 0x3F, I left this.

Okay, I wasn't ware. It seems it went in for 1.10.0 and we check for 1.9.0, right?


>
>> Can you please post the resulting patch somewhere for review.
> I'll fix this with the error messsage and unmarshal failure and post another
> version.

Thanks,
Peter