[PATCH 4.12 004/106] scsi: sg: fix SG_DXFER_FROM_DEV transfers

[Greg Kroah-Hartman]

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

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

From: Johannes Thumshirn <jthumshirn@xxxxxxx>

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 <jthumshirn@xxxxxxx>
Fixes: 28676d869bbb ("scsi: sg: check for valid direction before starting the request")
Reported-by: Chris Clayton <chris2553@xxxxxxxxxxxxxx>
Tested-by: Chris Clayton <chris2553@xxxxxxxxxxxxxx>
Cc: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>
Tested-by: Chris Clayton <chris2553@xxxxxxxxxxxxxx>
Acked-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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;