4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johannes Thumshirn <jthumsh...@suse.de>

commit 68c59fcea1f2c6a54c62aa896cc623c1b5bc9b47 upstream.

SG_DXFER_FROM_DEV transfers do not necessarily have a dxferp as we set
it to NULL for the old sg_io read/write interface, 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")

Signed-off-by: Johannes Thumshirn <jthumsh...@suse.de>
Fixes: 28676d869bbb ("scsi: sg: check for valid direction before starting the 
request")
Reported-by: Chris Clayton <chris2...@googlemail.com>
Tested-by: Chris Clayton <chris2...@googlemail.com>
Cc: Douglas Gilbert <dgilb...@interlog.com>
Reviewed-by: Hannes Reinecke <h...@suse.com>
Tested-by: Chris Clayton <chris2...@googlemail.com>
Acked-by: Douglas Gilbert <dgilb...@interlog.com>
Signed-off-by: Martin K. Petersen <martin.peter...@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/scsi/sg.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -758,8 +758,11 @@ static bool sg_is_valid_dxfer(sg_io_hdr_
                if (hp->dxferp || hp->dxfer_len > 0)
                        return false;
                return true;
-       case SG_DXFER_TO_DEV:
        case SG_DXFER_FROM_DEV:
+               if (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;


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