linux-kernel - [PATCH 5.2 167/215] xhci: Fix crash if scatter gather is used with Immediate Data Transfer (IDT).

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Date:   Mon, 29 Jul 2019 21:22:43 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Maik Stohn <maik.stohn@...l-one.com>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>
Subject: [PATCH 5.2 167/215] xhci: Fix crash if scatter gather is used with Immediate Data Transfer (IDT).

From: Mathias Nyman <mathias.nyman@...ux.intel.com>

commit d39b5bad8658d6d94cb2d98a44a7e159db4f5030 upstream.

A second regression was found in the immediate data transfer (IDT)
support which was added to 5.2 kernel

IDT is used to transfer small amounts of data (up to 8 bytes) in the
field normally used for data dma address, thus avoiding dma mapping.

If the data was not already dma mapped, then IDT support assumed data was
in urb->transfer_buffer, and did not take into accound that even
small amounts of data (8 bytes) can be in a scatterlist instead.

This caused a NULL pointer dereference when sg_dma_len() was used
with non-dma mapped data.

Solve this by not using IDT if scatter gather buffer list is used.

Fixes: 33e39350ebd2 ("usb: xhci: add Immediate Data Transfer support")
Cc: <stable@...r.kernel.org> # v5.2
Reported-by: Maik Stohn <maik.stohn@...l-one.com>
Tested-by: Maik Stohn <maik.stohn@...l-one.com>
CC: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Signed-off-by: Mathias Nyman <mathias.nyman@...ux.intel.com>
Link: https://lore.kernel.org/r/1564044861-1445-1-git-send-email-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/host/xhci.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -2170,7 +2170,8 @@ static inline bool xhci_urb_suitable_for
 	if (!usb_endpoint_xfer_isoc(&urb->ep->desc) && usb_urb_dir_out(urb) &&
 	    usb_endpoint_maxp(&urb->ep->desc) >= TRB_IDT_MAX_SIZE &&
 	    urb->transfer_buffer_length <= TRB_IDT_MAX_SIZE &&
-	    !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP))
+	    !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP) &&
+	    !urb->num_sgs)
 		return true;
 
 	return false;