staging: et131x: zero allocation of fbr to prevent random address access

If et131x_rx_dma_memory_alloc() allocates rx_ring->fbr[0] but fails to
allocate rx_ring->fbr[1], this leaves fbr[0]->ring_virtaddr with the
possibility of being accessed in et131x_rx_dma_memory_free() as it
contains a random value, potentially causing an oops.

Fix this by zeroing the fbr memory on allocation. Subsequent frees of
this fbr memory explicitly zeros the ring_virtaddr value.
Reported-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/et131x/et131x.c

@@ -2003,10 +2003,10 @@ static int et131x_rx_dma_memory_alloc(struct et131x_adapter *adapter)
 	struct fbr_lookup *fbr;
 
 	/* Alloc memory for the lookup table */
-	rx_ring->fbr[0] = kmalloc(sizeof(*fbr), GFP_KERNEL);
+	rx_ring->fbr[0] = kzalloc(sizeof(*fbr), GFP_KERNEL);
 	if (rx_ring->fbr[0] == NULL)
 		return -ENOMEM;
-	rx_ring->fbr[1] = kmalloc(sizeof(*fbr), GFP_KERNEL);
+	rx_ring->fbr[1] = kzalloc(sizeof(*fbr), GFP_KERNEL);
 	if (rx_ring->fbr[1] == NULL)
 		return -ENOMEM;