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 <linux/u64_stats_sync.h>
58 
59 /* blackhole_netdev - a device used for dsts that are marked expired!
60  * This is global device (instead of per-net-ns) since it's not needed
61  * to be per-ns and gets initialized at boot time.
62  */
63 struct net_device *blackhole_netdev;
64 EXPORT_SYMBOL(blackhole_netdev);
65 
66 /* The higher levels take care of making this non-reentrant (it's
67  * called with bh's disabled).
68  */
loopback_xmit(struct sk_buff * skb,struct net_device * dev)69 static netdev_tx_t loopback_xmit(struct sk_buff *skb,
70 				 struct net_device *dev)
71 {
72 	int len;
73 
74 	skb_tx_timestamp(skb);
75 
76 	/* do not fool net_timestamp_check() with various clock bases */
77 	skb_clear_tstamp(skb);
78 
79 	skb_orphan(skb);
80 
81 	/* Before queueing this packet to __netif_rx(),
82 	 * make sure dst is refcounted.
83 	 */
84 	skb_dst_force(skb);
85 
86 	skb->protocol = eth_type_trans(skb, dev);
87 
88 	len = skb->len;
89 	if (likely(__netif_rx(skb) == NET_RX_SUCCESS))
90 		dev_lstats_add(dev, len);
91 
92 	return NETDEV_TX_OK;
93 }
94 
dev_lstats_read(struct net_device * dev,u64 * packets,u64 * bytes)95 void dev_lstats_read(struct net_device *dev, u64 *packets, u64 *bytes)
96 {
97 	int i;
98 
99 	*packets = 0;
100 	*bytes = 0;
101 
102 	for_each_possible_cpu(i) {
103 		const struct pcpu_lstats *lb_stats;
104 		u64 tbytes, tpackets;
105 		unsigned int start;
106 
107 		lb_stats = per_cpu_ptr(dev->lstats, i);
108 		do {
109 			start = u64_stats_fetch_begin(&lb_stats->syncp);
110 			tpackets = u64_stats_read(&lb_stats->packets);
111 			tbytes = u64_stats_read(&lb_stats->bytes);
112 		} while (u64_stats_fetch_retry(&lb_stats->syncp, start));
113 		*bytes   += tbytes;
114 		*packets += tpackets;
115 	}
116 }
117 EXPORT_SYMBOL(dev_lstats_read);
118 
loopback_get_stats64(struct net_device * dev,struct rtnl_link_stats64 * stats)119 static void loopback_get_stats64(struct net_device *dev,
120 				 struct rtnl_link_stats64 *stats)
121 {
122 	u64 packets, bytes;
123 
124 	dev_lstats_read(dev, &packets, &bytes);
125 
126 	stats->rx_packets = packets;
127 	stats->tx_packets = packets;
128 	stats->rx_bytes   = bytes;
129 	stats->tx_bytes   = bytes;
130 }
131 
always_on(struct net_device * dev)132 static u32 always_on(struct net_device *dev)
133 {
134 	return 1;
135 }
136 
137 static const struct ethtool_ops loopback_ethtool_ops = {
138 	.get_link		= always_on,
139 	.get_ts_info		= ethtool_op_get_ts_info,
140 };
141 
loopback_dev_init(struct net_device * dev)142 static int loopback_dev_init(struct net_device *dev)
143 {
144 	dev->lstats = netdev_alloc_pcpu_stats(struct pcpu_lstats);
145 	if (!dev->lstats)
146 		return -ENOMEM;
147 	return 0;
148 }
149 
loopback_dev_free(struct net_device * dev)150 static void loopback_dev_free(struct net_device *dev)
151 {
152 	dev_net(dev)->loopback_dev = NULL;
153 	free_percpu(dev->lstats);
154 }
155 
156 static const struct net_device_ops loopback_ops = {
157 	.ndo_init        = loopback_dev_init,
158 	.ndo_start_xmit  = loopback_xmit,
159 	.ndo_get_stats64 = loopback_get_stats64,
160 	.ndo_set_mac_address = eth_mac_addr,
161 };
162 
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))163 static void gen_lo_setup(struct net_device *dev,
164 			 unsigned int mtu,
165 			 const struct ethtool_ops *eth_ops,
166 			 const struct header_ops *hdr_ops,
167 			 const struct net_device_ops *dev_ops,
168 			 void (*dev_destructor)(struct net_device *dev))
169 {
170 	dev->mtu		= mtu;
171 	dev->hard_header_len	= ETH_HLEN;	/* 14	*/
172 	dev->min_header_len	= ETH_HLEN;	/* 14	*/
173 	dev->addr_len		= ETH_ALEN;	/* 6	*/
174 	dev->type		= ARPHRD_LOOPBACK;	/* 0x0001*/
175 	dev->flags		= IFF_LOOPBACK;
176 	dev->priv_flags		|= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
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_LLTX
186 		| NETIF_F_NETNS_LOCAL
187 		| NETIF_F_VLAN_CHALLENGED
188 		| NETIF_F_LOOPBACK;
189 	dev->ethtool_ops	= eth_ops;
190 	dev->header_ops		= hdr_ops;
191 	dev->netdev_ops		= dev_ops;
192 	dev->needs_free_netdev	= true;
193 	dev->priv_destructor	= dev_destructor;
194 
195 	netif_set_tso_max_size(dev, GSO_MAX_SIZE);
196 }
197 
198 /* The loopback device is special. There is only one instance
199  * per network namespace.
200  */
loopback_setup(struct net_device * dev)201 static void loopback_setup(struct net_device *dev)
202 {
203 	gen_lo_setup(dev, (64 * 1024), &loopback_ethtool_ops, &eth_header_ops,
204 		     &loopback_ops, loopback_dev_free);
205 }
206 
207 /* Setup and register the loopback device. */
loopback_net_init(struct net * net)208 static __net_init int loopback_net_init(struct net *net)
209 {
210 	struct net_device *dev;
211 	int err;
212 
213 	err = -ENOMEM;
214 	dev = alloc_netdev(0, "lo", NET_NAME_PREDICTABLE, loopback_setup);
215 	if (!dev)
216 		goto out;
217 
218 	dev_net_set(dev, net);
219 	err = register_netdev(dev);
220 	if (err)
221 		goto out_free_netdev;
222 
223 	BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);
224 	net->loopback_dev = dev;
225 	return 0;
226 
227 out_free_netdev:
228 	free_netdev(dev);
229 out:
230 	if (net_eq(net, &init_net))
231 		panic("loopback: Failed to register netdevice: %d\n", err);
232 	return err;
233 }
234 
235 /* Registered in net/core/dev.c */
236 struct pernet_operations __net_initdata loopback_net_ops = {
237 	.init = loopback_net_init,
238 };
239 
240 /* blackhole netdevice */
blackhole_netdev_xmit(struct sk_buff * skb,struct net_device * dev)241 static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb,
242 					 struct net_device *dev)
243 {
244 	kfree_skb(skb);
245 	net_warn_ratelimited("%s(): Dropping skb.\n", __func__);
246 	return NETDEV_TX_OK;
247 }
248 
249 static const struct net_device_ops blackhole_netdev_ops = {
250 	.ndo_start_xmit = blackhole_netdev_xmit,
251 };
252 
253 /* This is a dst-dummy device used specifically for invalidated
254  * DSTs and unlike loopback, this is not per-ns.
255  */
blackhole_netdev_setup(struct net_device * dev)256 static void blackhole_netdev_setup(struct net_device *dev)
257 {
258 	gen_lo_setup(dev, ETH_MIN_MTU, NULL, NULL, &blackhole_netdev_ops, NULL);
259 }
260 
261 /* Setup and register the blackhole_netdev. */
blackhole_netdev_init(void)262 static int __init blackhole_netdev_init(void)
263 {
264 	blackhole_netdev = alloc_netdev(0, "blackhole_dev", NET_NAME_UNKNOWN,
265 					blackhole_netdev_setup);
266 	if (!blackhole_netdev)
267 		return -ENOMEM;
268 
269 	rtnl_lock();
270 	dev_init_scheduler(blackhole_netdev);
271 	dev_activate(blackhole_netdev);
272 	rtnl_unlock();
273 
274 	blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;
275 	dev_net_set(blackhole_netdev, &init_net);
276 
277 	return 0;
278 }
279 
280 device_initcall(blackhole_netdev_init);
281