net: wan: fsl_qmc_hdlc: Discard received CRC

Received frame from QMC contains the CRC.
Upper layers don't need this CRC and tcpdump mentioned trailing junk
data due to this CRC presence.

As some other HDLC driver, simply discard this CRC.

Fixes: d0f2258 ("net: wan: Add support for QMC HDLC")
Cc: stable@vger.kernel.org
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240730063133.179598-1-herve.codina@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: hcodina

drivers/net/wan/fsl_qmc_hdlc.c

@@ -250,6 +250,7 @@ static void qmc_hcld_recv_complete(void *context, size_t length, unsigned int fl
 	struct qmc_hdlc_desc *desc = context;
 	struct net_device *netdev;
 	struct qmc_hdlc *qmc_hdlc;
+	size_t crc_size;
 	int ret;
 
 	netdev = desc->netdev;
@@ -268,15 +269,26 @@ static void qmc_hcld_recv_complete(void *context, size_t length, unsigned int fl
 		if (flags & QMC_RX_FLAG_HDLC_CRC) /* CRC error */
 			netdev->stats.rx_crc_errors++;
 		kfree_skb(desc->skb);
-	} else {
-		netdev->stats.rx_packets++;
-		netdev->stats.rx_bytes += length;
+		goto re_queue;
+	}
 
-		skb_put(desc->skb, length);
-		desc->skb->protocol = hdlc_type_trans(desc->skb, netdev);
-		netif_rx(desc->skb);
+	/* Discard the CRC */
+	crc_size = qmc_hdlc->is_crc32 ? 4 : 2;
+	if (length < crc_size) {
+		netdev->stats.rx_length_errors++;
+		kfree_skb(desc->skb);
+		goto re_queue;
 	}
+	length -= crc_size;
+
+	netdev->stats.rx_packets++;
+	netdev->stats.rx_bytes += length;
+
+	skb_put(desc->skb, length);
+	desc->skb->protocol = hdlc_type_trans(desc->skb, netdev);
+	netif_rx(desc->skb);
 
+re_queue:
 	/* Re-queue a transfer using the same descriptor */
 	ret = qmc_hdlc_recv_queue(qmc_hdlc, desc, desc->dma_size);
 	if (ret) {