net: ethernet: mtk_eth_soc: check max allowed hash in mtk_ppe_check_skb

Even if max hash configured in hw in mtk_ppe_hash_entry is
MTK_PPE_ENTRIES - 1, check theoretical OOB accesses in
mtk_ppe_check_skb routine

Fixes: c4f033d ("net: ethernet: mtk_eth_soc: rework hardware flow table management")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mediatek/mtk_ppe.h

@@ -293,6 +293,9 @@ mtk_ppe_check_skb(struct mtk_ppe *ppe, struct sk_buff *skb, u16 hash)
 	if (!ppe)
 		return;
 
+	if (hash > MTK_PPE_HASH_MASK)
+		return;
+
 	now = (u16)jiffies;
 	diff = now - ppe->foe_check_time[hash];
 	if (diff < HZ / 10)