Re: [PATCH] scsi: sg: fix SG_DXFER_FROM_DEV transfers

Douglas Gilbert
2017-07-06T18:55:36Z

On 2017-07-05 09:49 AM, Johannes Thumshirn wrote:
> SG_DXFER_FROM_DEV transfers do not have a dxferp as we set it to NULL,
> but must have a length bigger than 0. This fixes a regression introduced
> by commit 28676d869bbb ("scsi: sg: check for valid direction before
> starting the request")

It is not clear to me that dxferp is set to NULL for the newer sg_v3
interface. In the sg.c source of lk 4.12.0 around line 654 (in the
sg_write(...) function) only the older interface passes through; the
newer interface bypasses that section with a 'return sg_new_write(...)'
on line 606.

Can you check your patch with one of the utilities from sg3_utils
such as sg_inq which will use SG_DXFER_FROM_DEV with the newer
interface?

BTW I'm not sure why dxferp is set to NULL for SG_DXFER_FROM_DEV
transfers; perhaps some magic done by the block layer. Maybe a
comment in the code (e.g. on line 654) would help.

Also sg_is_valid_dxfer() is only called once and is more complex
than it looks; so perhaps it could be inlined back in
sg_common_write().

Doug Gilbert

> Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
> Fixes: 28676d869bbb ("scsi: sg: check for valid direction before starting the request")
> Reported-by: Chris Clayton <chris2553@googlemail.com>
> Tested-by: Chris Clayton <chris2553@googlemail.com>
> Cc: Doug Gilbert <dgilbert@interlog.com>
> ---
> drivers/scsi/sg.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index 21225d62b0c1..3c91593260aa 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -758,8 +758,11 @@ static bool sg_is_valid_dxfer(sg_io_hdr_t *hp)
> if (hp->dxferp || hp->dxfer_len > 0)
> return false;
> return true;
> - case SG_DXFER_TO_DEV:
> case SG_DXFER_FROM_DEV:
> + if (hp->dxferp || hp->dxfer_len < 0)
> + return false;
> + return true;
> + case SG_DXFER_TO_DEV:
> case SG_DXFER_TO_FROM_DEV:
> if (!hp->dxferp || hp->dxfer_len == 0)
> return false;
>