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         int len;
  72
  73         skb_tx_timestamp(skb);
  74
  75         /* do not fool net_timestamp_check() with various clock bases */
  76         skb->tstamp = 0;
  77
  78         skb_orphan(skb);
  79
  80         /* Before queueing this packet to netif_rx(),
  81          * make sure dst is refcounted.
  82          */
  83         skb_dst_force(skb);
  84
  85         skb->protocol = eth_type_trans(skb, dev);
  86
  87         len = skb->len;
  88         if (likely(netif_rx(skb) == NET_RX_SUCCESS))
  89                 dev_lstats_add(dev, len);
  90
  91         return NETDEV_TX_OK;
  92 }
  93
  94 void dev_lstats_read(struct net_device *dev, u64 *packets, u64 *bytes)
  95 {
  96         int i;
  97
  98         *packets = 0;
  99         *bytes = 0;
 100
 101         for_each_possible_cpu(i) {
 102                 const struct pcpu_lstats *lb_stats;
 103                 u64 tbytes, tpackets;
 104                 unsigned int start;
 105
 106                 lb_stats = per_cpu_ptr(dev->lstats, i);
 107                 do {
 108                         start = u64_stats_fetch_begin_irq(&lb_stats->syncp);
 109                         tpackets = u64_stats_read(&lb_stats->packets);
 110                         tbytes = u64_stats_read(&lb_stats->bytes);
 111                 } while (u64_stats_fetch_retry_irq(&lb_stats->syncp, start));
 112                 *bytes   += tbytes;
 113                 *packets += tpackets;
 114         }
 115 }
 116 EXPORT_SYMBOL(dev_lstats_read);
 117
 118 static void loopback_get_stats64(struct net_device *dev,
 119                                  struct rtnl_link_stats64 *stats)
 120 {
 121         u64 packets, bytes;
 122
 123         dev_lstats_read(dev, &packets, &bytes);
 124
 125         stats->rx_packets = packets;
 126         stats->tx_packets = packets;
 127         stats->rx_bytes   = bytes;
 128         stats->tx_bytes   = bytes;
 129 }
 130
 131 static u32 always_on(struct net_device *dev)
 132 {
 133         return 1;
 134 }
 135
 136 static const struct ethtool_ops loopback_ethtool_ops = {
 137         .get_link               = always_on,
 138         .get_ts_info            = ethtool_op_get_ts_info,
 139 };
 140
 141 static int loopback_dev_init(struct net_device *dev)
 142 {
 143         dev->lstats = netdev_alloc_pcpu_stats(struct pcpu_lstats);
 144         if (!dev->lstats)
 145                 return -ENOMEM;
 146         return 0;
 147 }
 148
 149 static void loopback_dev_free(struct net_device *dev)
 150 {
 151         dev_net(dev)->loopback_dev = NULL;
 152         free_percpu(dev->lstats);
 153 }
 154
 155 static const struct net_device_ops loopback_ops = {
 156         .ndo_init        = loopback_dev_init,
 157         .ndo_start_xmit  = loopback_xmit,
 158         .ndo_get_stats64 = loopback_get_stats64,
 159         .ndo_set_mac_address = eth_mac_addr,
 160 };
 161
 162 static void gen_lo_setup(struct net_device *dev,
 163                          unsigned int mtu,
 164                          const struct ethtool_ops *eth_ops,
 165                          const struct header_ops *hdr_ops,
 166                          const struct net_device_ops *dev_ops,
 167                          void (*dev_destructor)(struct net_device *dev))
 168 {
 169         dev->mtu                = mtu;
 170         dev->hard_header_len    = ETH_HLEN;     /* 14   */
 171         dev->min_header_len     = ETH_HLEN;     /* 14   */
 172         dev->addr_len           = ETH_ALEN;     /* 6    */
 173         dev->type               = ARPHRD_LOOPBACK;      /* 0x0001*/
 174         dev->flags              = IFF_LOOPBACK;
 175         dev->priv_flags         |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
 176         netif_keep_dst(dev);
 177         dev->hw_features        = NETIF_F_GSO_SOFTWARE;
 178         dev->features           = NETIF_F_SG | NETIF_F_FRAGLIST
 179                 | NETIF_F_GSO_SOFTWARE
 180                 | NETIF_F_HW_CSUM
 181                 | NETIF_F_RXCSUM
 182                 | NETIF_F_SCTP_CRC
 183                 | NETIF_F_HIGHDMA
 184                 | NETIF_F_LLTX
 185                 | NETIF_F_NETNS_LOCAL
 186                 | NETIF_F_VLAN_CHALLENGED
 187                 | NETIF_F_LOOPBACK;
 188         dev->ethtool_ops        = eth_ops;
 189         dev->header_ops         = hdr_ops;
 190         dev->netdev_ops         = dev_ops;
 191         dev->needs_free_netdev  = true;
 192         dev->priv_destructor    = dev_destructor;
 193 }
 194
 195 /* The loopback device is special. There is only one instance
 196  * per network namespace.
 197  */
 198 static void loopback_setup(struct net_device *dev)
 199 {
 200         gen_lo_setup(dev, (64 * 1024), &loopback_ethtool_ops, &eth_header_ops,
 201                      &loopback_ops, loopback_dev_free);
 202 }
 203
 204 /* Setup and register the loopback device. */
 205 static __net_init int loopback_net_init(struct net *net)
 206 {
 207         struct net_device *dev;
 208         int err;
 209
 210         err = -ENOMEM;
 211         dev = alloc_netdev(0, "lo", NET_NAME_UNKNOWN, loopback_setup);
 212         if (!dev)
 213                 goto out;
 214
 215         dev_net_set(dev, net);
 216         err = register_netdev(dev);
 217         if (err)
 218                 goto out_free_netdev;
 219
 220         BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);
 221         net->loopback_dev = dev;
 222         return 0;
 223
 224 out_free_netdev:
 225         free_netdev(dev);
 226 out:
 227         if (net_eq(net, &init_net))
 228                 panic("loopback: Failed to register netdevice: %d\n", err);
 229         return err;
 230 }
 231
 232 /* Registered in net/core/dev.c */
 233 struct pernet_operations __net_initdata loopback_net_ops = {
 234         .init = loopback_net_init,
 235 };
 236
 237 /* blackhole netdevice */
 238 static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb,
 239                                          struct net_device *dev)
 240 {
 241         kfree_skb(skb);
 242         net_warn_ratelimited("%s(): Dropping skb.\n", __func__);
 243         return NETDEV_TX_OK;
 244 }
 245
 246 static const struct net_device_ops blackhole_netdev_ops = {
 247         .ndo_start_xmit = blackhole_netdev_xmit,
 248 };
 249
 250 /* This is a dst-dummy device used specifically for invalidated
 251  * DSTs and unlike loopback, this is not per-ns.
 252  */
 253 static void blackhole_netdev_setup(struct net_device *dev)
 254 {
 255         gen_lo_setup(dev, ETH_MIN_MTU, NULL, NULL, &blackhole_netdev_ops, NULL);
 256 }
 257
 258 /* Setup and register the blackhole_netdev. */
 259 static int __init blackhole_netdev_init(void)
 260 {
 261         blackhole_netdev = alloc_netdev(0, "blackhole_dev", NET_NAME_UNKNOWN,
 262                                         blackhole_netdev_setup);
 263         if (!blackhole_netdev)
 264                 return -ENOMEM;
 265
 266         rtnl_lock();
 267         dev_init_scheduler(blackhole_netdev);
 268         dev_activate(blackhole_netdev);
 269         rtnl_unlock();
 270
 271         blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;
 272         dev_net_set(blackhole_netdev, &init_net);
 273
 274         return 0;
 275 }
 276
 277 device_initcall(blackhole_netdev_init);