// SPDX-License-Identifier: GPL-2.0-or-later/* * INET		An implementation of the TCP/IP protocol suite for the LINUX *		operating system.  INET is implemented using the  BSD Socket *		interface as the means of communication with the user level. * *		Pseudo-driver for the loopback interface. * * Version:	@(#)loopback.c	1.0.4b	08/16/93 * * Authors:	Ross Biro *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> *		Donald Becker, <becker@scyld.com> * *		Alan Cox	:	Fixed oddments for NET3.014 *		Alan Cox	:	Rejig for NET3.029 snap #3 *		Alan Cox	:	Fixed NET3.029 bugs and sped up *		Larry McVoy	:	Tiny tweak to double performance *		Alan Cox	:	Backed out LMV's tweak - the linux mm *					can't take it... *              Michael Griffith:       Don't bother computing the checksums *                                      on packets received on the loopback *                                      interface. *		Alexey Kuznetsov:	Potential hang under some extreme *					cases removed. */#include <linux/kernel.h>#include <linux/jiffies.h>#include <linux/module.h>#include <linux/interrupt.h>#include <linux/fs.h>#include <linux/types.h>#include <linux/string.h>#include <linux/socket.h>#include <linux/errno.h>#include <linux/fcntl.h>#include <linux/in.h> #include <linux/uaccess.h>#include <linux/io.h> #include <linux/inet.h>#include <linux/netdevice.h>#include <linux/etherdevice.h>#include <linux/skbuff.h>#include <linux/ethtool.h>#include <net/sch_generic.h>#include <net/sock.h>#include <net/checksum.h>#include <linux/if_ether.h>	/* For the statistics structure. */#include <linux/if_arp.h>	/* For ARPHRD_ETHER */#include <linux/ip.h>#include <linux/tcp.h>#include <linux/percpu.h>#include <linux/net_tstamp.h>#include <net/net_namespace.h>#include <linux/u64_stats_sync.h> /* blackhole_netdev - a device used for dsts that are marked expired! * This is global device (instead of per-net-ns) since it's not needed * to be per-ns and gets initialized at boot time. */struct net_device *blackhole_netdev;EXPORT_SYMBOL(blackhole_netdev); /* The higher levels take care of making this non-reentrant (it's * called with bh's disabled). */static netdev_tx_t loopback_xmit(struct sk_buff *skb,				 struct net_device *dev){	int len; 	skb_tx_timestamp(skb); 	/* do not fool net_timestamp_check() with various clock bases */	skb_clear_tstamp(skb); 	skb_orphan(skb); 	/* Before queueing this packet to __netif_rx(),	 * make sure dst is refcounted.	 */	skb_dst_force(skb); 	skb->protocol = eth_type_trans(skb, dev); 	len = skb->len;	if (likely(__netif_rx(skb) == NET_RX_SUCCESS))		dev_lstats_add(dev, len); 	return NETDEV_TX_OK;} void dev_lstats_read(struct net_device *dev, u64 *packets, u64 *bytes){	int i; 	*packets = 0;	*bytes = 0; 	for_each_possible_cpu(i) {		const struct pcpu_lstats *lb_stats;		u64 tbytes, tpackets;		unsigned int start; 		lb_stats = per_cpu_ptr(dev->lstats, i);		do {			start = u64_stats_fetch_begin(&lb_stats->syncp);			tpackets = u64_stats_read(&lb_stats->packets);			tbytes = u64_stats_read(&lb_stats->bytes);		} while (u64_stats_fetch_retry(&lb_stats->syncp, start));		*bytes   += tbytes;		*packets += tpackets;	}}EXPORT_SYMBOL(dev_lstats_read); static void loopback_get_stats64(struct net_device *dev,				 struct rtnl_link_stats64 *stats){	u64 packets, bytes; 	dev_lstats_read(dev, &packets, &bytes); 	stats->rx_packets = packets;	stats->tx_packets = packets;	stats->rx_bytes   = bytes;	stats->tx_bytes   = bytes;} static u32 always_on(struct net_device *dev){	return 1;} static const struct ethtool_ops loopback_ethtool_ops = {	.get_link		= always_on,	.get_ts_info		= ethtool_op_get_ts_info,}; static int loopback_dev_init(struct net_device *dev){	netdev_lockdep_set_classes(dev);	return 0;} static void loopback_dev_free(struct net_device *dev){	dev_net(dev)->loopback_dev = NULL;} static const struct net_device_ops loopback_ops = {	.ndo_init        = loopback_dev_init,	.ndo_start_xmit  = loopback_xmit,	.ndo_get_stats64 = loopback_get_stats64,	.ndo_set_mac_address = eth_mac_addr,}; static void gen_lo_setup(struct net_device *dev,			 unsigned int mtu,			 const struct ethtool_ops *eth_ops,			 const struct header_ops *hdr_ops,			 const struct net_device_ops *dev_ops,			 void (*dev_destructor)(struct net_device *dev)){	dev->mtu		= mtu;	dev->hard_header_len	= ETH_HLEN;	/* 14	*/	dev->min_header_len	= ETH_HLEN;	/* 14	*/	dev->addr_len		= ETH_ALEN;	/* 6	*/	dev->type		= ARPHRD_LOOPBACK;	/* 0x0001*/	dev->flags		= IFF_LOOPBACK;	dev->priv_flags		|= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;	netif_keep_dst(dev);	dev->hw_features	= NETIF_F_GSO_SOFTWARE;	dev->features		= NETIF_F_SG | NETIF_F_FRAGLIST		| NETIF_F_GSO_SOFTWARE		| NETIF_F_HW_CSUM		| NETIF_F_RXCSUM		| NETIF_F_SCTP_CRC		| NETIF_F_HIGHDMA		| NETIF_F_LLTX		| NETIF_F_NETNS_LOCAL		| NETIF_F_VLAN_CHALLENGED		| NETIF_F_LOOPBACK;	dev->ethtool_ops	= eth_ops;	dev->header_ops		= hdr_ops;	dev->netdev_ops		= dev_ops;	dev->needs_free_netdev	= true;	dev->pcpu_stat_type	= NETDEV_PCPU_STAT_LSTATS;	dev->priv_destructor	= dev_destructor; 	netif_set_tso_max_size(dev, GSO_MAX_SIZE);} /* The loopback device is special. There is only one instance * per network namespace. */static void loopback_setup(struct net_device *dev){	gen_lo_setup(dev, (64 * 1024), &loopback_ethtool_ops, &eth_header_ops,		     &loopback_ops, loopback_dev_free);} /* Setup and register the loopback device. */static __net_init int loopback_net_init(struct net *net){	struct net_device *dev;	int err; 	err = -ENOMEM;	dev = alloc_netdev(0, "lo", NET_NAME_PREDICTABLE, loopback_setup);	if (!dev)		goto out; 	dev_net_set(dev, net);	err = register_netdev(dev);	if (err)		goto out_free_netdev; 	BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);	net->loopback_dev = dev;	return 0; out_free_netdev:	free_netdev(dev);out:	if (net_eq(net, &init_net))		panic("loopback: Failed to register netdevice: %d\n", err);	return err;} /* Registered in net/core/dev.c */struct pernet_operations __net_initdata loopback_net_ops = {	.init = loopback_net_init,}; /* blackhole netdevice */static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb,					 struct net_device *dev){	kfree_skb(skb);	net_warn_ratelimited("%s(): Dropping skb.\n", __func__);	return NETDEV_TX_OK;} static const struct net_device_ops blackhole_netdev_ops = {	.ndo_start_xmit = blackhole_netdev_xmit,}; /* This is a dst-dummy device used specifically for invalidated * DSTs and unlike loopback, this is not per-ns. */static void blackhole_netdev_setup(struct net_device *dev){	gen_lo_setup(dev, ETH_MIN_MTU, NULL, NULL, &blackhole_netdev_ops, NULL);} /* Setup and register the blackhole_netdev. */static int __init blackhole_netdev_init(void){	blackhole_netdev = alloc_netdev(0, "blackhole_dev", NET_NAME_UNKNOWN,					blackhole_netdev_setup);	if (!blackhole_netdev)		return -ENOMEM; 	rtnl_lock();	dev_init_scheduler(blackhole_netdev);	dev_activate(blackhole_netdev);	rtnl_unlock(); 	blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;	dev_net_set(blackhole_netdev, &init_net); 	return 0;} device_initcall(blackhole_netdev_init);