// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * INET         An implementation of the TCP/IP protocol suite for the LINUX
 *              operating system.  INET is implemented using the  BSD Socket
 *              interface as the means of communication with the user level.
 *
 *              Pseudo-driver for the loopback interface.
 *
 * Version:     @(#)loopback.c  1.0.4b  08/16/93
 *
 * Authors:     Ross Biro
 *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 *              Donald Becker, <becker@scyld.com>
 *
 *              Alan Cox        :       Fixed oddments for NET3.014
 *              Alan Cox        :       Rejig for NET3.029 snap #3
 *              Alan Cox        :       Fixed NET3.029 bugs and sped up
 *              Larry McVoy     :       Tiny tweak to double performance
 *              Alan Cox        :       Backed out LMV's tweak - the linux mm
 *                                      can't take it...
 *              Michael Griffith:       Don't bother computing the checksums
 *                                      on packets received on the loopback
 *                                      interface.
 *              Alexey Kuznetsov:       Potential hang under some extreme
 *                                      cases removed.
 */
#include <linux/kernel.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/errno.h>
#include <linux/fcntl.h>
#include <linux/in.h>

#include <linux/uaccess.h>
#include <linux/io.h>

#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/ethtool.h>
#include <net/sch_generic.h>
#include <net/sock.h>
#include <net/checksum.h>
#include <linux/if_ether.h>     /* For the statistics structure. */
#include <linux/if_arp.h>       /* For ARPHRD_ETHER */
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/percpu.h>
#include <linux/net_tstamp.h>
#include <net/net_namespace.h>
#include <net/netdev_lock.h>
#include <linux/u64_stats_sync.h>

/* blackhole_netdev - a device used for dsts that are marked expired!
 * This is global device (instead of per-net-ns) since it's not needed
 * to be per-ns and gets initialized at boot time.
 */
struct net_device *blackhole_netdev;
EXPORT_SYMBOL(blackhole_netdev);

/* The higher levels take care of making this non-reentrant (it's
 * called with bh's disabled).
 */
static netdev_tx_t loopback_xmit(struct sk_buff *skb,
                                 struct net_device *dev)
{
        int len;

        skb_tx_timestamp(skb);

        /* do not fool net_timestamp_check() with various clock bases */
        skb_clear_tstamp(skb);

        skb_orphan(skb);

        /* Before queueing this packet to __netif_rx(),
         * make sure dst is refcounted.
         */
        skb_dst_force(skb);

        skb->protocol = eth_type_trans(skb, dev);

        len = skb->len;
        if (likely(__netif_rx(skb) == NET_RX_SUCCESS))
                dev_lstats_add(dev, len);

        return NETDEV_TX_OK;
}

void dev_lstats_read(struct net_device *dev, u64 *packets, u64 *bytes)
{
        int i;

        *packets = 0;
        *bytes = 0;

        for_each_possible_cpu(i) {
                const struct pcpu_lstats *lb_stats;
                u64 tbytes, tpackets;
                unsigned int start;

                lb_stats = per_cpu_ptr(dev->lstats, i);
                do {
                        start = u64_stats_fetch_begin(&lb_stats->syncp);
                        tpackets = u64_stats_read(&lb_stats->packets);
                        tbytes = u64_stats_read(&lb_stats->bytes);
                } while (u64_stats_fetch_retry(&lb_stats->syncp, start));
                *bytes   += tbytes;
                *packets += tpackets;
        }
}
EXPORT_SYMBOL(dev_lstats_read);

static void loopback_get_stats64(struct net_device *dev,
                                 struct rtnl_link_stats64 *stats)
{
        u64 packets, bytes;

        dev_lstats_read(dev, &packets, &bytes);

        stats->rx_packets = packets;
        stats->tx_packets = packets;
        stats->rx_bytes   = bytes;
        stats->tx_bytes   = bytes;
}

static u32 always_on(struct net_device *dev)
{
        return 1;
}

static const struct ethtool_ops loopback_ethtool_ops = {
        .get_link               = always_on,
        .get_ts_info            = ethtool_op_get_ts_info,
};

static int loopback_dev_init(struct net_device *dev)
{
        netdev_lockdep_set_classes(dev);
        return 0;
}

static void loopback_dev_free(struct net_device *dev)
{
        dev_net(dev)->loopback_dev = NULL;
}

static const struct net_device_ops loopback_ops = {
        .ndo_init        = loopback_dev_init,
        .ndo_start_xmit  = loopback_xmit,
        .ndo_get_stats64 = loopback_get_stats64,
        .ndo_set_mac_address = eth_mac_addr,
};

static void 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))
{
        dev->mtu                = mtu;
        dev->hard_header_len    = ETH_HLEN;     /* 14   */
        dev->min_header_len     = ETH_HLEN;     /* 14   */
        dev->addr_len           = ETH_ALEN;     /* 6    */
        dev->type               = ARPHRD_LOOPBACK;      /* 0x0001*/
        dev->flags              = IFF_LOOPBACK;
        dev->priv_flags         |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
        dev->lltx               = true;
        dev->netns_immutable    = true;
        netif_keep_dst(dev);
        dev->hw_features        = NETIF_F_GSO_SOFTWARE;
        dev->features           = NETIF_F_SG | NETIF_F_FRAGLIST
                | NETIF_F_GSO_SOFTWARE
                | NETIF_F_HW_CSUM
                | NETIF_F_RXCSUM
                | NETIF_F_SCTP_CRC
                | NETIF_F_HIGHDMA
                | NETIF_F_VLAN_CHALLENGED
                | NETIF_F_LOOPBACK;
        dev->ethtool_ops        = eth_ops;
        dev->header_ops         = hdr_ops;
        dev->netdev_ops         = dev_ops;
        dev->needs_free_netdev  = true;
        dev->pcpu_stat_type     = NETDEV_PCPU_STAT_LSTATS;
        dev->priv_destructor    = dev_destructor;

        netif_set_tso_max_size(dev, GSO_MAX_SIZE);
}

/* The loopback device is special. There is only one instance
 * per network namespace.
 */
static void loopback_setup(struct net_device *dev)
{
        gen_lo_setup(dev, (64 * 1024), &loopback_ethtool_ops, &eth_header_ops,
                     &loopback_ops, loopback_dev_free);
}

/* Setup and register the loopback device. */
static __net_init int loopback_net_init(struct net *net)
{
        struct net_device *dev;
        int err;

        err = -ENOMEM;
        dev = alloc_netdev(0, "lo", NET_NAME_PREDICTABLE, loopback_setup);
        if (!dev)
                goto out;

        dev_net_set(dev, net);
        err = register_netdev(dev);
        if (err)
                goto out_free_netdev;

        BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);
        net->loopback_dev = dev;
        return 0;

out_free_netdev:
        free_netdev(dev);
out:
        if (net_eq(net, &init_net))
                panic("loopback: Failed to register netdevice: %d\n", err);
        return err;
}

/* Registered in net/core/dev.c */
struct pernet_operations __net_initdata loopback_net_ops = {
        .init = loopback_net_init,
};

/* blackhole netdevice */
static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb,
                                         struct net_device *dev)
{
        kfree_skb(skb);
        net_warn_ratelimited("%s(): Dropping skb.\n", __func__);
        return NETDEV_TX_OK;
}

static int blackhole_neigh_output(struct neighbour *n, struct sk_buff *skb)
{
        kfree_skb(skb);
        return 0;
}

static int blackhole_neigh_construct(struct net_device *dev,
                                     struct neighbour *n)
{
        n->output = blackhole_neigh_output;
        return 0;
}

static const struct net_device_ops blackhole_netdev_ops = {
        .ndo_start_xmit = blackhole_netdev_xmit,
        .ndo_neigh_construct = blackhole_neigh_construct,
};

/* This is a dst-dummy device used specifically for invalidated
 * DSTs and unlike loopback, this is not per-ns.
 */
static void blackhole_netdev_setup(struct net_device *dev)
{
        gen_lo_setup(dev, ETH_MIN_MTU, NULL, NULL, &blackhole_netdev_ops, NULL);
}

/* Setup and register the blackhole_netdev. */
static int __init blackhole_netdev_init(void)
{
        blackhole_netdev = alloc_netdev(0, "blackhole_dev", NET_NAME_UNKNOWN,
                                        blackhole_netdev_setup);
        if (!blackhole_netdev)
                return -ENOMEM;

        rtnl_net_lock(&init_net);
        dev_init_scheduler(blackhole_netdev);
        dev_activate(blackhole_netdev);
        rtnl_net_unlock(&init_net);

        blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;

        return 0;
}

device_initcall(blackhole_netdev_init);