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")

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: Doug Gilbert <dgilb...@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;
-- 
2.12.3

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