[PATCH 1/1] xhci: fix bounce buffer usage for non-sg list case

[Mathias Nyman <mathias.nyman@linux.intel.com>]

xhci driver may in some special cases need to copy small amounts
of payload data to a bounce buffer in order to meet the boundary
and alignment restrictions set by the xHCI specification.

In the majority of these cases the data is in a sg list, and
driver incorrectly assumed data is always in urb->sg when using
the bounce buffer.

If data instead is contiguous, and in urb->transfer_buffer, we may still
need to bounce buffer a small part if data starts very close (less than
packet size) to a 64k boundary.

Check if sg list is used before copying data to/from it.

Fixes: f9c589e142d0 ("xhci: TD-fragment, align the unsplittable case with a bounce buffer")
Cc: stable@vger.kernel.org
Reported-by: Andreas Hartmann <andihartmann@01019freenet.de>
Tested-by: Andreas Hartmann <andihartmann@01019freenet.de>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
---
 drivers/usb/host/xhci-ring.c | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index cf0c93a90200..89c3be9917f6 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -699,11 +699,16 @@ static void xhci_unmap_td_bounce_buffer(struct xhci_hcd *xhci,
 	dma_unmap_single(dev, seg->bounce_dma, ring->bounce_buf_len,
 			 DMA_FROM_DEVICE);
 	/* for in tranfers we need to copy the data from bounce to sg */
-	len = sg_pcopy_from_buffer(urb->sg, urb->num_sgs, seg->bounce_buf,
-			     seg->bounce_len, seg->bounce_offs);
-	if (len != seg->bounce_len)
-		xhci_warn(xhci, "WARN Wrong bounce buffer read length: %zu != %d\n",
-				len, seg->bounce_len);
+	if (urb->num_sgs) {
+		len = sg_pcopy_from_buffer(urb->sg, urb->num_sgs, seg->bounce_buf,
+					   seg->bounce_len, seg->bounce_offs);
+		if (len != seg->bounce_len)
+			xhci_warn(xhci, "WARN Wrong bounce buffer read length: %zu != %d\n",
+				  len, seg->bounce_len);
+	} else {
+		memcpy(urb->transfer_buffer + seg->bounce_offs, seg->bounce_buf,
+		       seg->bounce_len);
+	}
 	seg->bounce_len = 0;
 	seg->bounce_offs = 0;
 }
@@ -3277,12 +3282,16 @@ static int xhci_align_td(struct xhci_hcd *xhci, struct urb *urb, u32 enqd_len,
 
 	/* create a max max_pkt sized bounce buffer pointed to by last trb */
 	if (usb_urb_dir_out(urb)) {
-		len = sg_pcopy_to_buffer(urb->sg, urb->num_sgs,
-				   seg->bounce_buf, new_buff_len, enqd_len);
-		if (len != new_buff_len)
-			xhci_warn(xhci,
-				"WARN Wrong bounce buffer write length: %zu != %d\n",
-				len, new_buff_len);
+		if (urb->num_sgs) {
+			len = sg_pcopy_to_buffer(urb->sg, urb->num_sgs,
+						 seg->bounce_buf, new_buff_len, enqd_len);
+			if (len != new_buff_len)
+				xhci_warn(xhci, "WARN Wrong bounce buffer write length: %zu != %d\n",
+					  len, new_buff_len);
+		} else {
+			memcpy(seg->bounce_buf, urb->transfer_buffer + enqd_len, new_buff_len);
+		}
+
 		seg->bounce_dma = dma_map_single(dev, seg->bounce_buf,
 						 max_pkt, DMA_TO_DEVICE);
 	} else {
-- 
2.25.1