net: qualcomm: rmnet: Skip processing loopback packets

RMNET RX handler was processing invalid packets that were
originally sent on the real device and were looped back via
dev_loopback_xmit(). This was detected using syzkaller.

Fixes: ceed73a2 ("drivers: net: ethernet: qualcomm: rmnet: Initial implementation")
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c

@@ -189,6 +189,9 @@ rx_handler_result_t rmnet_rx_handler(struct sk_buff **pskb)
 	if (!skb)
 		goto done;
 
+	if (skb->pkt_type == PACKET_LOOPBACK)
+		return RX_HANDLER_PASS;
+
 	dev = skb->dev;
 	port = rmnet_get_port(dev);