loopback.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * INET		An implementation of the TCP/IP protocol suite for the LINUX
  4 *		operating system.  INET is implemented using the  BSD Socket
  5 *		interface as the means of communication with the user level.
  6 *
  7 *		Pseudo-driver for the loopback interface.
  8 *
  9 * Version:	@(#)loopback.c	1.0.4b	08/16/93
 10 *
 11 * Authors:	Ross Biro
 12 *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 13 *		Donald Becker, <becker@scyld.com>
 14 *
 15 *		Alan Cox	:	Fixed oddments for NET3.014
 16 *		Alan Cox	:	Rejig for NET3.029 snap #3
 17 *		Alan Cox	:	Fixed NET3.029 bugs and sped up
 18 *		Larry McVoy	:	Tiny tweak to double performance
 19 *		Alan Cox	:	Backed out LMV's tweak - the linux mm
 20 *					can't take it...
 21 *              Michael Griffith:       Don't bother computing the checksums
 22 *                                      on packets received on the loopback
 23 *                                      interface.
 24 *		Alexey Kuznetsov:	Potential hang under some extreme
 25 *					cases removed.
 26 */
 27#include <linux/kernel.h>
 28#include <linux/jiffies.h>
 29#include <linux/module.h>
 30#include <linux/interrupt.h>
 31#include <linux/fs.h>
 32#include <linux/types.h>
 33#include <linux/string.h>
 34#include <linux/socket.h>
 35#include <linux/errno.h>
 36#include <linux/fcntl.h>
 37#include <linux/in.h>
 38
 39#include <linux/uaccess.h>
 40#include <linux/io.h>
 41
 42#include <linux/inet.h>
 43#include <linux/netdevice.h>
 44#include <linux/etherdevice.h>
 45#include <linux/skbuff.h>
 46#include <linux/ethtool.h>
 47#include <net/sch_generic.h>
 48#include <net/sock.h>
 49#include <net/checksum.h>
 50#include <linux/if_ether.h>	/* For the statistics structure. */
 51#include <linux/if_arp.h>	/* For ARPHRD_ETHER */
 52#include <linux/ip.h>
 53#include <linux/tcp.h>
 54#include <linux/percpu.h>
 55#include <linux/net_tstamp.h>
 56#include <net/net_namespace.h>
 57#include <net/netdev_lock.h>
 58#include <linux/u64_stats_sync.h>
 59
 60/* blackhole_netdev - a device used for dsts that are marked expired!
 61 * This is global device (instead of per-net-ns) since it's not needed
 62 * to be per-ns and gets initialized at boot time.
 63 */
 64struct net_device *blackhole_netdev;
 65EXPORT_SYMBOL(blackhole_netdev);
 66
 67/* The higher levels take care of making this non-reentrant (it's
 68 * called with bh's disabled).
 69 */
 70static netdev_tx_t loopback_xmit(struct sk_buff *skb,
 71				 struct net_device *dev)
 72{
 73	int len;
 74
 75	skb_tx_timestamp(skb);
 76
 77	/* do not fool net_timestamp_check() with various clock bases */
 78	skb_clear_tstamp(skb);
 79
 80	skb_orphan(skb);
 81
 82	/* Before queueing this packet to __netif_rx(),
 83	 * make sure dst is refcounted.
 84	 */
 85	skb_dst_force(skb);
 86
 87	skb->protocol = eth_type_trans(skb, dev);
 88
 89	len = skb->len;
 90	if (likely(__netif_rx(skb) == NET_RX_SUCCESS))
 91		dev_lstats_add(dev, len);
 92
 93	return NETDEV_TX_OK;
 94}
 95
 96void dev_lstats_read(struct net_device *dev, u64 *packets, u64 *bytes)
 97{
 98	int i;
 99
100	*packets = 0;
101	*bytes = 0;
102
103	for_each_possible_cpu(i) {
104		const struct pcpu_lstats *lb_stats;
105		u64 tbytes, tpackets;
106		unsigned int start;
107
108		lb_stats = per_cpu_ptr(dev->lstats, i);
109		do {
110			start = u64_stats_fetch_begin(&lb_stats->syncp);
111			tpackets = u64_stats_read(&lb_stats->packets);
112			tbytes = u64_stats_read(&lb_stats->bytes);
113		} while (u64_stats_fetch_retry(&lb_stats->syncp, start));
114		*bytes   += tbytes;
115		*packets += tpackets;
116	}
117}
118EXPORT_SYMBOL(dev_lstats_read);
119
120static void loopback_get_stats64(struct net_device *dev,
121				 struct rtnl_link_stats64 *stats)
122{
123	u64 packets, bytes;
124
125	dev_lstats_read(dev, &packets, &bytes);
126
127	stats->rx_packets = packets;
128	stats->tx_packets = packets;
129	stats->rx_bytes   = bytes;
130	stats->tx_bytes   = bytes;
131}
132
133static u32 always_on(struct net_device *dev)
134{
135	return 1;
136}
137
138static const struct ethtool_ops loopback_ethtool_ops = {
139	.get_link		= always_on,
140	.get_ts_info		= ethtool_op_get_ts_info,
141};
142
143static int loopback_dev_init(struct net_device *dev)
144{
145	netdev_lockdep_set_classes(dev);
146	return 0;
147}
148
149static void loopback_dev_free(struct net_device *dev)
150{
151	dev_net(dev)->loopback_dev = NULL;
152}
153
154static const struct net_device_ops loopback_ops = {
155	.ndo_init        = loopback_dev_init,
156	.ndo_start_xmit  = loopback_xmit,
157	.ndo_get_stats64 = loopback_get_stats64,
158	.ndo_set_mac_address = eth_mac_addr,
159};
160
161static void gen_lo_setup(struct net_device *dev,
162			 unsigned int mtu,
163			 const struct ethtool_ops *eth_ops,
164			 const struct header_ops *hdr_ops,
165			 const struct net_device_ops *dev_ops,
166			 void (*dev_destructor)(struct net_device *dev))
167{
168	dev->mtu		= mtu;
169	dev->hard_header_len	= ETH_HLEN;	/* 14	*/
170	dev->min_header_len	= ETH_HLEN;	/* 14	*/
171	dev->addr_len		= ETH_ALEN;	/* 6	*/
172	dev->type		= ARPHRD_LOOPBACK;	/* 0x0001*/
173	dev->flags		= IFF_LOOPBACK;
174	dev->priv_flags		|= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
175	dev->lltx		= true;
176	dev->netns_immutable	= true;
177	netif_keep_dst(dev);
178	dev->hw_features	= NETIF_F_GSO_SOFTWARE;
179	dev->features		= NETIF_F_SG | NETIF_F_FRAGLIST
180		| NETIF_F_GSO_SOFTWARE
181		| NETIF_F_HW_CSUM
182		| NETIF_F_RXCSUM
183		| NETIF_F_SCTP_CRC
184		| NETIF_F_HIGHDMA
185		| NETIF_F_VLAN_CHALLENGED
186		| NETIF_F_LOOPBACK;
187	dev->ethtool_ops	= eth_ops;
188	dev->header_ops		= hdr_ops;
189	dev->netdev_ops		= dev_ops;
190	dev->needs_free_netdev	= true;
191	dev->pcpu_stat_type	= NETDEV_PCPU_STAT_LSTATS;
192	dev->priv_destructor	= dev_destructor;
193
194	netif_set_tso_max_size(dev, GSO_MAX_SIZE);
195}
196
197/* The loopback device is special. There is only one instance
198 * per network namespace.
199 */
200static void loopback_setup(struct net_device *dev)
201{
202	gen_lo_setup(dev, (64 * 1024), &loopback_ethtool_ops, &eth_header_ops,
203		     &loopback_ops, loopback_dev_free);
204}
205
206/* Setup and register the loopback device. */
207static __net_init int loopback_net_init(struct net *net)
208{
209	struct net_device *dev;
210	int err;
211
212	err = -ENOMEM;
213	dev = alloc_netdev(0, "lo", NET_NAME_PREDICTABLE, loopback_setup);
214	if (!dev)
215		goto out;
216
217	dev_net_set(dev, net);
218	err = register_netdev(dev);
219	if (err)
220		goto out_free_netdev;
221
222	BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);
223	net->loopback_dev = dev;
224	return 0;
225
226out_free_netdev:
227	free_netdev(dev);
228out:
229	if (net_eq(net, &init_net))
230		panic("loopback: Failed to register netdevice: %d\n", err);
231	return err;
232}
233
234/* Registered in net/core/dev.c */
235struct pernet_operations __net_initdata loopback_net_ops = {
236	.init = loopback_net_init,
237};
238
239/* blackhole netdevice */
240static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb,
241					 struct net_device *dev)
242{
243	kfree_skb(skb);
244	net_warn_ratelimited("%s(): Dropping skb.\n", __func__);
245	return NETDEV_TX_OK;
246}
247
248static int blackhole_neigh_output(struct neighbour *n, struct sk_buff *skb)
249{
250	kfree_skb(skb);
251	return 0;
252}
253
254static int blackhole_neigh_construct(struct net_device *dev,
255				     struct neighbour *n)
256{
257	n->output = blackhole_neigh_output;
258	return 0;
259}
260
261static const struct net_device_ops blackhole_netdev_ops = {
262	.ndo_start_xmit = blackhole_netdev_xmit,
263	.ndo_neigh_construct = blackhole_neigh_construct,
264};
265
266/* This is a dst-dummy device used specifically for invalidated
267 * DSTs and unlike loopback, this is not per-ns.
268 */
269static void blackhole_netdev_setup(struct net_device *dev)
270{
271	gen_lo_setup(dev, ETH_MIN_MTU, NULL, NULL, &blackhole_netdev_ops, NULL);
272}
273
274/* Setup and register the blackhole_netdev. */
275static int __init blackhole_netdev_init(void)
276{
277	blackhole_netdev = alloc_netdev(0, "blackhole_dev", NET_NAME_UNKNOWN,
278					blackhole_netdev_setup);
279	if (!blackhole_netdev)
280		return -ENOMEM;
281
282	rtnl_net_lock(&init_net);
283	dev_init_scheduler(blackhole_netdev);
284	dev_activate(blackhole_netdev);
285	rtnl_net_unlock(&init_net);
286
287	blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;
288
289	return 0;
290}
291
292device_initcall(blackhole_netdev_init);