bgmac: add check for oversized packets

In very rare cases, the MAC can catch an internal buffer that is bigger
than it's supposed to be. Instead of crashing the kernel, simply pass
the buffer back to the hardware
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bgmac.c

@@ -445,6 +445,13 @@ static int bgmac_dma_rx_read(struct bgmac *bgmac, struct bgmac_dma_ring *ring,
 				break;
 			}
 
+			if (len > BGMAC_RX_ALLOC_SIZE) {
+				bgmac_err(bgmac, "Found oversized packet at slot %d, DMA issue!\n",
+					  ring->start);
+				put_page(virt_to_head_page(buf));
+				break;
+			}
+
 			/* Omit CRC. */
 			len -= ETH_FCS_LEN;