[PATCH net v2 3/8] net: stmmac: Do not accept invalid MTU values

[Jose Abreu <Jose.Abreu@synopsys.com>]

The maximum MTU value is determined by the maximum size of TX FIFO so
that a full packet can fit in the FIFO. Add a check for this in the MTU
change callback.

Also check if provided and rounded MTU does not passes the maximum limit
of 16K.

Fixes: 7ac6653a085b ("stmmac: Move the STMicroelectronics driver")
Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>

---
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Jose Abreu <joabreu@synopsys.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: netdev@vger.kernel.org
Cc: linux-stm32@st-md-mailman.stormreply.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index dfecced43f29..2ebac89049ed 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -3827,12 +3827,22 @@ static void stmmac_set_rx_mode(struct net_device *dev)
 static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
 {
 	struct stmmac_priv *priv = netdev_priv(dev);
+	int txfifosz = priv->plat->tx_fifo_size;
+
+	if (txfifosz == 0)
+		txfifosz = priv->dma_cap.tx_fifo_size;
+
+	txfifosz /= priv->plat->tx_queues_to_use;
 
 	if (netif_running(dev)) {
 		netdev_err(priv->dev, "must be stopped to change its MTU\n");
 		return -EBUSY;
 	}
 
+	/* If condition true, FIFO is too small or MTU too large */
+	if ((txfifosz < new_mtu) || (new_mtu > STMMAC_ALIGN(BUF_SIZE_16KiB)))
+		return -EINVAL;
+
 	dev->mtu = new_mtu;
 
 	netdev_update_features(dev);
-- 
2.7.4