net: stmmac: fix maxmtu assignment to be within valid range

There is no checking valid value of maxmtu when getting it from
device tree. This resolution added the checking condition to
ensure the assignment is made within a valid range.
Signed-off-by: Kweh, Hock Leong <hock.leong.kweh@intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -3319,8 +3319,16 @@ int stmmac_dvr_probe(struct device *device,
 		ndev->max_mtu = JUMBO_LEN;
 	else
 		ndev->max_mtu = SKB_MAX_HEAD(NET_SKB_PAD + NET_IP_ALIGN);
-	if (priv->plat->maxmtu < ndev->max_mtu)
+	/* Will not overwrite ndev->max_mtu if plat->maxmtu > ndev->max_mtu
+	 * as well as plat->maxmtu < ndev->min_mtu which is a invalid range.
+	 */
+	if ((priv->plat->maxmtu < ndev->max_mtu) &&
+	    (priv->plat->maxmtu >= ndev->min_mtu))
 		ndev->max_mtu = priv->plat->maxmtu;
+	else if (priv->plat->maxmtu < ndev->min_mtu)
+		netdev_warn(priv->dev,
+			    "%s: warning: maxmtu having invalid value (%d)\n",
+			    __func__, priv->plat->maxmtu);
 
 	if (flow_ctrl)
 		priv->flow_ctrl = FLOW_AUTO;	/* RX/TX pause on */

drivers/net/ethernet/stmicro/stmmac/stmmac_pci.c

@@ -89,6 +89,9 @@ static void stmmac_default_data(struct plat_stmmacenet_data *plat)
 
 	/* Set default value for unicast filter entries */
 	plat->unicast_filter_entries = 1;
+
+	/* Set the maxmtu to a default of JUMBO_LEN */
+	plat->maxmtu = JUMBO_LEN;
 }
 
 static int quark_default_data(struct plat_stmmacenet_data *plat,
@@ -126,6 +129,9 @@ static int quark_default_data(struct plat_stmmacenet_data *plat,
 	/* Set default value for unicast filter entries */
 	plat->unicast_filter_entries = 1;
 
+	/* Set the maxmtu to a default of JUMBO_LEN */
+	plat->maxmtu = JUMBO_LEN;
+
 	return 0;
 }