[PATCH v2] scsi: sg: fix SG_DXFER_FROM_DEV transfers

[Johannes Thumshirn]

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>
---
Changes to v1:
* Fix breakage of the sg_io v3 interface, verified using sg_inq

 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..1e82d4128a84 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->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;
-- 
2.12.3