net: calxedaxgmac: throw away overrun frames

The xgmac driver assumes 1 frame per descriptor. If a frame larger than
the descriptor's buffer size is received, the frame will spill over into
the next descriptor. So check for received frames that span more than one
descriptor and discard them. This prevents a crash if we receive erroneous
large packets.
Signed-off-by: NRob Herring <rob.herring@calxeda.com>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/calxeda/xgmac.c

@@ -548,6 +548,10 @@ static int desc_get_rx_status(struct xgmac_priv *priv, struct xgmac_dma_desc *p)
 		return -1;
 	}
 
+	/* All frames should fit into a single buffer */
+	if (!(status & RXDESC_FIRST_SEG) || !(status & RXDESC_LAST_SEG))
+		return -1;
+
 	/* Check if packet has checksum already */
 	if ((status & RXDESC_FRAME_TYPE) && (status & RXDESC_EXT_STATUS) &&
 		!(ext_status & RXDESC_IP_PAYLOAD_MASK))