[PATCH v4 1/1] can: gs_usb: fix DMA memory leak on close

[Rhett Aultman <rhett.aultman@samsara.com>]

The gs_usb driver allocates DMA memory with usb_alloc_coherent() in
gs_can_open() and then keeps this memory in an URB, with the expectation
that the memory will be freed when the URB is killed in gs_can_close().
Memory allocated with usb_alloc_coherent() cannot be freed in this way
and must be freed using usb_free_coherent() instead.  This means that
repeated cycles of calling gs_can_open() and gs_can_close() will lead to
a memory leak.

Historically, drivers have handled this by keeping an array of pointers
to their DMA rx buffers and explicitly freeing them.  For an example of
this technique used in the esd_usb2 driver, see here:
928150fad41b ("can: esd_usb2: fix memory leak")

While the above method works, the conditions that cause this leak are
not apparent to driver writers and the method for solving it at the
driver level has been piecemeal.  This patch makes use of a new
URB_FREE_COHERENT flag on the URB, reducing the solution of this memory
leak down to a single line of code.

Fixes: d08e973a77d1 ("can: gs_usb: Added support for the GS_USB CAN devices")
Signed-off-by: Rhett Aultman <rhett.aultman@samsara.com>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
 drivers/net/can/usb/gs_usb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c
index b29ba9138866..4e7e6a7b961a 100644
--- a/drivers/net/can/usb/gs_usb.c
+++ b/drivers/net/can/usb/gs_usb.c
@@ -768,7 +768,7 @@ static int gs_can_open(struct net_device *netdev)
 					  buf,
 					  dev->parent->hf_size_rx,
 					  gs_usb_receive_bulk_callback, parent);
-			urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
+			urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP | URB_FREE_COHERENT;
 
 			usb_anchor_urb(urb, &parent->rx_submitted);
 
-- 
2.30.2