net: dpaa: Pad packets to ETH_ZLEN

When sending packets under 60 bytes, up to three bytes of the buffer
following the data may be leaked. Avoid this by extending all packets to
ETH_ZLEN, ensuring nothing is leaked in the padding. This bug can be
reproduced by running

	$ ping -s 11 destination

Fixes: 9ad1a37 ("dpaa_eth: add support for DPAA Ethernet")
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20240910143144.1439910-1-sean.anderson@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/freescale/dpaa/dpaa_eth.c

@@ -2272,12 +2272,12 @@ static netdev_tx_t
 dpaa_start_xmit(struct sk_buff *skb, struct net_device *net_dev)
 {
 	const int queue_mapping = skb_get_queue_mapping(skb);
-	bool nonlinear = skb_is_nonlinear(skb);
 	struct rtnl_link_stats64 *percpu_stats;
 	struct dpaa_percpu_priv *percpu_priv;
 	struct netdev_queue *txq;
 	struct dpaa_priv *priv;
 	struct qm_fd fd;
+	bool nonlinear;
 	int offset = 0;
 	int err = 0;
 
@@ -2287,6 +2287,13 @@ dpaa_start_xmit(struct sk_buff *skb, struct net_device *net_dev)
 
 	qm_fd_clear_fd(&fd);
 
+	/* Packet data is always read as 32-bit words, so zero out any part of
+	 * the skb which might be sent if we have to pad the packet
+	 */
+	if (__skb_put_padto(skb, ETH_ZLEN, false))
+		goto enomem;
+
+	nonlinear = skb_is_nonlinear(skb);
 	if (!nonlinear) {
 		/* We're going to store the skb backpointer at the beginning
 		 * of the data buffer, so we need a privately owned skb