drivers/net/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/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         = &eth_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 };