net: wan: fsl_ucc_hdlc: free tx_skbuff in uhdlc_memclean

When the device is removed all allocated resources should be freed.
In uhdlc_memclean the netdev transmit queue was already stopped. But at
this point we may have pending skb in the transmit queue which must be
freed. Therefore iterate over the tx_skbuff pointers and free all
pending skb. The issue was discovered by sashiko.
Tested on a ls1043a board running HDLC in bus mode on kernel 6.12.

https: //sashiko.dev/#/patchset/20260429114208.941011-1-holger.brunck%40hitachienergy.com
Fixes: c19b6d246a ("drivers/net: support hdlc function for QE-UCC")
Signed-off-by: Holger Brunck <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

drivers/net/wan/fsl_ucc_hdlc.c

@@ -740,6 +740,8 @@ static int uhdlc_open(struct net_device *dev)
 
 static void uhdlc_memclean(struct ucc_hdlc_private *priv)
 {
+	int i;
+
 	qe_muram_free(ioread16be(&priv->ucc_pram->riptr));
 	qe_muram_free(ioread16be(&priv->ucc_pram->tiptr));
 
@@ -770,6 +772,11 @@ static void uhdlc_memclean(struct ucc_hdlc_private *priv)
 	kfree(priv->rx_skbuff);
 	priv->rx_skbuff = NULL;
 
+	for (i = 0; i < TX_BD_RING_LEN; i++) {
+		dev_kfree_skb(priv->tx_skbuff[i]);
+		priv->tx_skbuff[i] = NULL;
+	}
+
 	kfree(priv->tx_skbuff);
 	priv->tx_skbuff = NULL;