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 /* blackhole_netdev - a device used for dsts that are marked expired!
  59  * This is global device (instead of per-net-ns) since it's not needed
  60  * to be per-ns and gets initialized at boot time.
  61  */
  62 struct net_device *blackhole_netdev;
  63 EXPORT_SYMBOL(blackhole_netdev);
  64
  65 /* The higher levels take care of making this non-reentrant (it's
  66  * called with bh's disabled).
  67  */
  68 static netdev_tx_t loopback_xmit(struct sk_buff *skb,
  69                                  struct net_device *dev)
  70 {
  71         struct pcpu_lstats *lb_stats;
  72         int len;
  73
  74         skb_tx_timestamp(skb);
  75
  76         /* do not fool net_timestamp_check() with various clock bases */
  77         skb->tstamp = 0;
  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         /* it's OK to use per_cpu_ptr() because BHs are off */
  89         lb_stats = this_cpu_ptr(dev->lstats);
  90
  91         len = skb->len;
  92         if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {
  93                 u64_stats_update_begin(&lb_stats->syncp);
  94                 lb_stats->bytes += len;
  95                 lb_stats->packets++;
  96                 u64_stats_update_end(&lb_stats->syncp);
  97         }
  98
  99         return NETDEV_TX_OK;
 100 }
 101
 102 static void loopback_get_stats64(struct net_device *dev,
 103                                  struct rtnl_link_stats64 *stats)
 104 {
 105         u64 bytes = 0;
 106         u64 packets = 0;
 107         int i;
 108
 109         for_each_possible_cpu(i) {
 110                 const struct pcpu_lstats *lb_stats;
 111                 u64 tbytes, tpackets;
 112                 unsigned int start;
 113
 114                 lb_stats = per_cpu_ptr(dev->lstats, i);
 115                 do {
 116                         start = u64_stats_fetch_begin_irq(&lb_stats->syncp);
 117                         tbytes = lb_stats->bytes;
 118                         tpackets = lb_stats->packets;
 119                 } while (u64_stats_fetch_retry_irq(&lb_stats->syncp, start));
 120                 bytes   += tbytes;
 121                 packets += tpackets;
 122         }
 123         stats->rx_packets = packets;
 124         stats->tx_packets = packets;
 125         stats->rx_bytes   = bytes;
 126         stats->tx_bytes   = bytes;
 127 }
 128
 129 static u32 always_on(struct net_device *dev)
 130 {
 131         return 1;
 132 }
 133
 134 static const struct ethtool_ops loopback_ethtool_ops = {
 135         .get_link               = always_on,
 136         .get_ts_info            = ethtool_op_get_ts_info,
 137 };
 138
 139 static int loopback_dev_init(struct net_device *dev)
 140 {
 141         dev->lstats = netdev_alloc_pcpu_stats(struct pcpu_lstats);
 142         if (!dev->lstats)
 143                 return -ENOMEM;
 144         return 0;
 145 }
 146
 147 static void loopback_dev_free(struct net_device *dev)
 148 {
 149         dev_net(dev)->loopback_dev = NULL;
 150         free_percpu(dev->lstats);
 151 }
 152
 153 static const struct net_device_ops loopback_ops = {
 154         .ndo_init        = loopback_dev_init,
 155         .ndo_start_xmit  = loopback_xmit,
 156         .ndo_get_stats64 = loopback_get_stats64,
 157         .ndo_set_mac_address = eth_mac_addr,
 158 };
 159
 160 static void gen_lo_setup(struct net_device *dev,
 161                          unsigned int mtu,
 162                          const struct ethtool_ops *eth_ops,
 163                          const struct header_ops *hdr_ops,
 164                          const struct net_device_ops *dev_ops,
 165                          void (*dev_destructor)(struct net_device *dev))
 166 {
 167         dev->mtu                = mtu;
 168         dev->hard_header_len    = ETH_HLEN;     /* 14   */
 169         dev->min_header_len     = ETH_HLEN;     /* 14   */
 170         dev->addr_len           = ETH_ALEN;     /* 6    */
 171         dev->type               = ARPHRD_LOOPBACK;      /* 0x0001*/
 172         dev->flags              = IFF_LOOPBACK;
 173         dev->priv_flags         |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
 174         netif_keep_dst(dev);
 175         dev->hw_features        = NETIF_F_GSO_SOFTWARE;
 176         dev->features           = NETIF_F_SG | NETIF_F_FRAGLIST
 177                 | NETIF_F_GSO_SOFTWARE
 178                 | NETIF_F_HW_CSUM
 179                 | NETIF_F_RXCSUM
 180                 | NETIF_F_SCTP_CRC
 181                 | NETIF_F_HIGHDMA
 182                 | NETIF_F_LLTX
 183                 | NETIF_F_NETNS_LOCAL
 184                 | NETIF_F_VLAN_CHALLENGED
 185                 | NETIF_F_LOOPBACK;
 186         dev->ethtool_ops        = eth_ops;
 187         dev->header_ops         = hdr_ops;
 188         dev->netdev_ops         = dev_ops;
 189         dev->needs_free_netdev  = true;
 190         dev->priv_destructor    = dev_destructor;
 191 }
 192
 193 /* The loopback device is special. There is only one instance
 194  * per network namespace.
 195  */
 196 static void loopback_setup(struct net_device *dev)
 197 {
 198         gen_lo_setup(dev, (64 * 1024), &loopback_ethtool_ops, &eth_header_ops,
 199                      &loopback_ops, loopback_dev_free);
 200 }
 201
 202 /* Setup and register the loopback device. */
 203 static __net_init int loopback_net_init(struct net *net)
 204 {
 205         struct net_device *dev;
 206         int err;
 207
 208         err = -ENOMEM;
 209         dev = alloc_netdev(0, "lo", NET_NAME_UNKNOWN, loopback_setup);
 210         if (!dev)
 211                 goto out;
 212
 213         dev_net_set(dev, net);
 214         err = register_netdev(dev);
 215         if (err)
 216                 goto out_free_netdev;
 217
 218         BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);
 219         net->loopback_dev = dev;
 220         return 0;
 221
 222 out_free_netdev:
 223         free_netdev(dev);
 224 out:
 225         if (net_eq(net, &init_net))
 226                 panic("loopback: Failed to register netdevice: %d\n", err);
 227         return err;
 228 }
 229
 230 /* Registered in net/core/dev.c */
 231 struct pernet_operations __net_initdata loopback_net_ops = {
 232         .init = loopback_net_init,
 233 };
 234
 235 /* blackhole netdevice */
 236 static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb,
 237                                          struct net_device *dev)
 238 {
 239         kfree_skb(skb);
 240         net_warn_ratelimited("%s(): Dropping skb.\n", __func__);
 241         return NETDEV_TX_OK;
 242 }
 243
 244 static const struct net_device_ops blackhole_netdev_ops = {
 245         .ndo_start_xmit = blackhole_netdev_xmit,
 246 };
 247
 248 /* This is a dst-dummy device used specifically for invalidated
 249  * DSTs and unlike loopback, this is not per-ns.
 250  */
 251 static void blackhole_netdev_setup(struct net_device *dev)
 252 {
 253         gen_lo_setup(dev, ETH_MIN_MTU, NULL, NULL, &blackhole_netdev_ops, NULL);
 254 }
 255
 256 /* Setup and register the blackhole_netdev. */
 257 static int __init blackhole_netdev_init(void)
 258 {
 259         blackhole_netdev = alloc_netdev(0, "blackhole_dev", NET_NAME_UNKNOWN,
 260                                         blackhole_netdev_setup);
 261         if (!blackhole_netdev)
 262                 return -ENOMEM;
 263
 264         rtnl_lock();
 265         dev_init_scheduler(blackhole_netdev);
 266         dev_activate(blackhole_netdev);
 267         rtnl_unlock();
 268
 269         blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;
 270         dev_net_set(blackhole_netdev, &init_net);
 271
 272         return 0;
 273 }
 274
 275 device_initcall(blackhole_netdev_init);