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/sock.h> 48 #include <net/checksum.h> 49 #include <linux/if_ether.h> /* For the statistics structure. */ 50 #include <linux/if_arp.h> /* For ARPHRD_ETHER */ 51 #include <linux/ip.h> 52 #include <linux/tcp.h> 53 #include <linux/percpu.h> 54 #include <linux/net_tstamp.h> 55 #include <net/net_namespace.h> 56 #include <linux/u64_stats_sync.h> 57 58 /* The higher levels take care of making this non-reentrant (it's 59 * called with bh's disabled). 60 */ 61 static netdev_tx_t loopback_xmit(struct sk_buff *skb, 62 struct net_device *dev) 63 { 64 struct pcpu_lstats *lb_stats; 65 int len; 66 67 skb_tx_timestamp(skb); 68 69 /* do not fool net_timestamp_check() with various clock bases */ 70 skb->tstamp = 0; 71 72 skb_orphan(skb); 73 74 /* Before queueing this packet to netif_rx(), 75 * make sure dst is refcounted. 76 */ 77 skb_dst_force(skb); 78 79 skb->protocol = eth_type_trans(skb, dev); 80 81 /* it's OK to use per_cpu_ptr() because BHs are off */ 82 lb_stats = this_cpu_ptr(dev->lstats); 83 84 len = skb->len; 85 if (likely(netif_rx(skb) == NET_RX_SUCCESS)) { 86 u64_stats_update_begin(&lb_stats->syncp); 87 lb_stats->bytes += len; 88 lb_stats->packets++; 89 u64_stats_update_end(&lb_stats->syncp); 90 } 91 92 return NETDEV_TX_OK; 93 } 94 95 static void loopback_get_stats64(struct net_device *dev, 96 struct rtnl_link_stats64 *stats) 97 { 98 u64 bytes = 0; 99 u64 packets = 0; 100 int i; 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_irq(&lb_stats->syncp); 110 tbytes = lb_stats->bytes; 111 tpackets = lb_stats->packets; 112 } while (u64_stats_fetch_retry_irq(&lb_stats->syncp, start)); 113 bytes += tbytes; 114 packets += tpackets; 115 } 116 stats->rx_packets = packets; 117 stats->tx_packets = packets; 118 stats->rx_bytes = bytes; 119 stats->tx_bytes = bytes; 120 } 121 122 static u32 always_on(struct net_device *dev) 123 { 124 return 1; 125 } 126 127 static const struct ethtool_ops loopback_ethtool_ops = { 128 .get_link = always_on, 129 .get_ts_info = ethtool_op_get_ts_info, 130 }; 131 132 static int loopback_dev_init(struct net_device *dev) 133 { 134 dev->lstats = netdev_alloc_pcpu_stats(struct pcpu_lstats); 135 if (!dev->lstats) 136 return -ENOMEM; 137 return 0; 138 } 139 140 static void loopback_dev_free(struct net_device *dev) 141 { 142 dev_net(dev)->loopback_dev = NULL; 143 free_percpu(dev->lstats); 144 } 145 146 static const struct net_device_ops loopback_ops = { 147 .ndo_init = loopback_dev_init, 148 .ndo_start_xmit = loopback_xmit, 149 .ndo_get_stats64 = loopback_get_stats64, 150 .ndo_set_mac_address = eth_mac_addr, 151 }; 152 153 /* The loopback device is special. There is only one instance 154 * per network namespace. 155 */ 156 static void loopback_setup(struct net_device *dev) 157 { 158 dev->mtu = 64 * 1024; 159 dev->hard_header_len = ETH_HLEN; /* 14 */ 160 dev->min_header_len = ETH_HLEN; /* 14 */ 161 dev->addr_len = ETH_ALEN; /* 6 */ 162 dev->type = ARPHRD_LOOPBACK; /* 0x0001*/ 163 dev->flags = IFF_LOOPBACK; 164 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE; 165 netif_keep_dst(dev); 166 dev->hw_features = NETIF_F_GSO_SOFTWARE; 167 dev->features = NETIF_F_SG | NETIF_F_FRAGLIST 168 | NETIF_F_GSO_SOFTWARE 169 | NETIF_F_HW_CSUM 170 | NETIF_F_RXCSUM 171 | NETIF_F_SCTP_CRC 172 | NETIF_F_HIGHDMA 173 | NETIF_F_LLTX 174 | NETIF_F_NETNS_LOCAL 175 | NETIF_F_VLAN_CHALLENGED 176 | NETIF_F_LOOPBACK; 177 dev->ethtool_ops = &loopback_ethtool_ops; 178 dev->header_ops = ð_header_ops; 179 dev->netdev_ops = &loopback_ops; 180 dev->needs_free_netdev = true; 181 dev->priv_destructor = loopback_dev_free; 182 } 183 184 /* Setup and register the loopback device. */ 185 static __net_init int loopback_net_init(struct net *net) 186 { 187 struct net_device *dev; 188 int err; 189 190 err = -ENOMEM; 191 dev = alloc_netdev(0, "lo", NET_NAME_UNKNOWN, loopback_setup); 192 if (!dev) 193 goto out; 194 195 dev_net_set(dev, net); 196 err = register_netdev(dev); 197 if (err) 198 goto out_free_netdev; 199 200 BUG_ON(dev->ifindex != LOOPBACK_IFINDEX); 201 net->loopback_dev = dev; 202 return 0; 203 204 out_free_netdev: 205 free_netdev(dev); 206 out: 207 if (net_eq(net, &init_net)) 208 panic("loopback: Failed to register netdevice: %d\n", err); 209 return err; 210 } 211 212 /* Registered in net/core/dev.c */ 213 struct pernet_operations __net_initdata loopback_net_ops = { 214 .init = loopback_net_init, 215 }; 216