// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      G8BPQ compatible "AX.25 via ethernet" driver release 004
 *
 *      This code REQUIRES 2.0.0 or higher/ NET3.029
 *
 *      This is a "pseudo" network driver to allow AX.25 over Ethernet
 *      using G8BPQ encapsulation. It has been extracted from the protocol
 *      implementation because
 *
 *              - things got unreadable within the protocol stack
 *              - to cure the protocol stack from "feature-ism"
 *              - a protocol implementation shouldn't need to know on
 *                which hardware it is running
 *              - user-level programs like the AX.25 utilities shouldn't
 *                need to know about the hardware.
 *              - IP over ethernet encapsulated AX.25 was impossible
 *              - rxecho.c did not work
 *              - to have room for extensions
 *              - it just deserves to "live" as an own driver
 *
 *      This driver can use any ethernet destination address, and can be
 *      limited to accept frames from one dedicated ethernet card only.
 *
 *      Note that the driver sets up the BPQ devices automagically on
 *      startup or (if started before the "insmod" of an ethernet device)
 *      on "ifconfig up". It hopefully will remove the BPQ on "rmmod"ing
 *      the ethernet device (in fact: as soon as another ethernet or bpq
 *      device gets "ifconfig"ured).
 *
 *      I have heard that several people are thinking of experiments
 *      with highspeed packet radio using existing ethernet cards.
 *      Well, this driver is prepared for this purpose, just add
 *      your tx key control and a txdelay / tailtime algorithm,
 *      probably some buffering, and /voila/...
 *
 *      History
 *      BPQ   001       Joerg(DL1BKE)           Extracted BPQ code from AX.25
 *                                              protocol stack and added my own
 *                                              yet existing patches
 *      BPQ   002       Joerg(DL1BKE)           Scan network device list on
 *                                              startup.
 *      BPQ   003       Joerg(DL1BKE)           Ethernet destination address
 *                                              and accepted source address
 *                                              can be configured by an ioctl()
 *                                              call.
 *                                              Fixed to match Linux networking
 *                                              changes - 2.1.15.
 *      BPQ   004       Joerg(DL1BKE)           Fixed to not lock up on ifconfig.
 */

#include <linux/errno.h>
#include <linux/types.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/net.h>
#include <linux/slab.h>
#include <net/ax25.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/if_arp.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <linux/uaccess.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/rtnetlink.h>

#include <net/ip.h>
#include <net/arp.h>
#include <net/netdev_lock.h>
#include <net/net_namespace.h>

#include <linux/bpqether.h>

static const char banner[] __initconst = KERN_INFO \
        "AX.25: bpqether driver version 004\n";

static int bpq_rcv(struct sk_buff *, struct net_device *, struct packet_type *, struct net_device *);
static int bpq_device_event(struct notifier_block *, unsigned long, void *);

static struct packet_type bpq_packet_type __read_mostly = {
        .type   = cpu_to_be16(ETH_P_BPQ),
        .func   = bpq_rcv,
};

static struct notifier_block bpq_dev_notifier = {
        .notifier_call = bpq_device_event,
};


struct bpqdev {
        struct list_head bpq_list;      /* list of bpq devices chain */
        struct net_device *ethdev;      /* link to ethernet device */
        struct net_device *axdev;       /* bpq device (bpq#) */
        char   dest_addr[6];            /* ether destination address */
        char   acpt_addr[6];            /* accept ether frames from this address only */
};

static LIST_HEAD(bpq_devices);

/* ------------------------------------------------------------------------ */


/*
 *      Get the ethernet device for a BPQ device
 */
static inline struct net_device *bpq_get_ether_dev(struct net_device *dev)
{
        struct bpqdev *bpq = netdev_priv(dev);

        return bpq ? bpq->ethdev : NULL;
}

/*
 *      Get the BPQ device for the ethernet device
 */
static inline struct net_device *bpq_get_ax25_dev(struct net_device *dev)
{
        struct bpqdev *bpq;

        list_for_each_entry_rcu(bpq, &bpq_devices, bpq_list,
                                lockdep_rtnl_is_held()) {
                if (bpq->ethdev == dev)
                        return bpq->axdev;
        }
        return NULL;
}

static inline int dev_is_ethdev(struct net_device *dev)
{
        return dev->type == ARPHRD_ETHER && !netdev_need_ops_lock(dev);
}

/* ------------------------------------------------------------------------ */


/*
 *      Receive an AX.25 frame via an ethernet interface.
 */
static int bpq_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *ptype, struct net_device *orig_dev)
{
        int len;
        char * ptr;
        struct ethhdr *eth;
        struct bpqdev *bpq;

        if (!net_eq(dev_net(dev), &init_net))
                goto drop;

        if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL)
                return NET_RX_DROP;

        if (!pskb_may_pull(skb, sizeof(struct ethhdr)))
                goto drop;

        rcu_read_lock();
        dev = bpq_get_ax25_dev(dev);

        if (dev == NULL || !netif_running(dev)) 
                goto drop_unlock;

        /*
         * if we want to accept frames from just one ethernet device
         * we check the source address of the sender.
         */

        bpq = netdev_priv(dev);

        eth = eth_hdr(skb);

        if (!(bpq->acpt_addr[0] & 0x01) &&
            !ether_addr_equal(eth->h_source, bpq->acpt_addr))
                goto drop_unlock;

        if (skb_cow(skb, sizeof(struct ethhdr)))
                goto drop_unlock;

        len = skb->data[0] + skb->data[1] * 256 - 5;

        skb_pull(skb, 2);       /* Remove the length bytes */
        skb_trim(skb, len);     /* Set the length of the data */

        dev->stats.rx_packets++;
        dev->stats.rx_bytes += len;

        ptr = skb_push(skb, 1);
        *ptr = 0;

        skb->protocol = ax25_type_trans(skb, dev);
        netif_rx(skb);
unlock:

        rcu_read_unlock();

        return 0;
drop_unlock:
        kfree_skb(skb);
        goto unlock;

drop:
        kfree_skb(skb);
        return 0;
}

/*
 *      Send an AX.25 frame via an ethernet interface
 */
static netdev_tx_t bpq_xmit(struct sk_buff *skb, struct net_device *dev)
{
        unsigned char *ptr;
        struct bpqdev *bpq;
        struct net_device *orig_dev;
        int size;

        if (skb->protocol == htons(ETH_P_IP))
                return ax25_ip_xmit(skb);

        /*
         * Just to be *really* sure not to send anything if the interface
         * is down, the ethernet device may have gone.
         */
        if (!netif_running(dev)) {
                kfree_skb(skb);
                return NETDEV_TX_OK;
        }

        skb_pull(skb, 1);                       /* Drop KISS byte */
        size = skb->len;

        /*
         * We're about to mess with the skb which may still shared with the
         * generic networking code so unshare and ensure it's got enough
         * space for the BPQ headers.
         */
        if (skb_cow(skb, AX25_BPQ_HEADER_LEN)) {
                if (net_ratelimit())
                        pr_err("bpqether: out of memory\n");
                kfree_skb(skb);

                return NETDEV_TX_OK;
        }

        ptr = skb_push(skb, 2);                 /* Make space for length */

        *ptr++ = (size + 5) % 256;
        *ptr++ = (size + 5) / 256;

        bpq = netdev_priv(dev);

        orig_dev = dev;
        if ((dev = bpq_get_ether_dev(dev)) == NULL) {
                orig_dev->stats.tx_dropped++;
                kfree_skb(skb);
                return NETDEV_TX_OK;
        }

        skb->protocol = ax25_type_trans(skb, dev);
        skb_reset_network_header(skb);
        dev_hard_header(skb, dev, ETH_P_BPQ, bpq->dest_addr, NULL, 0);
        dev->stats.tx_packets++;
        dev->stats.tx_bytes+=skb->len;
  
        dev_queue_xmit(skb);
        netif_wake_queue(dev);
        return NETDEV_TX_OK;
}

/*
 *      Set AX.25 callsign
 */
static int bpq_set_mac_address(struct net_device *dev, void *addr)
{
    struct sockaddr *sa = (struct sockaddr *)addr;

    dev_addr_set(dev, sa->sa_data);

    return 0;
}

/*      Ioctl commands
 *
 *              SIOCSBPQETHOPT          reserved for enhancements
 *              SIOCSBPQETHADDR         set the destination and accepted
 *                                      source ethernet address (broadcast
 *                                      or multicast: accept all)
 */
static int bpq_siocdevprivate(struct net_device *dev, struct ifreq *ifr,
                              void __user *data, int cmd)
{
        struct bpq_ethaddr __user *ethaddr = data;
        struct bpqdev *bpq = netdev_priv(dev);
        struct bpq_req req;

        if (!capable(CAP_NET_ADMIN))
                return -EPERM;

        switch (cmd) {
                case SIOCSBPQETHOPT:
                        if (copy_from_user(&req, data, sizeof(struct bpq_req)))
                                return -EFAULT;
                        switch (req.cmd) {
                                case SIOCGBPQETHPARAM:
                                case SIOCSBPQETHPARAM:
                                default:
                                        return -EINVAL;
                        }

                        break;

                case SIOCSBPQETHADDR:
                        if (copy_from_user(bpq->dest_addr, ethaddr->destination, ETH_ALEN))
                                return -EFAULT;
                        if (copy_from_user(bpq->acpt_addr, ethaddr->accept, ETH_ALEN))
                                return -EFAULT;
                        break;

                default:
                        return -EINVAL;
        }

        return 0;
}

/*
 * open/close a device
 */
static int bpq_open(struct net_device *dev)
{
        netif_start_queue(dev);
        return 0;
}

static int bpq_close(struct net_device *dev)
{
        netif_stop_queue(dev);
        return 0;
}


/* ------------------------------------------------------------------------ */

#ifdef CONFIG_PROC_FS
/*
 *      Proc filesystem
 */
static void *bpq_seq_start(struct seq_file *seq, loff_t *pos)
        __acquires(RCU)
{
        int i = 1;
        struct bpqdev *bpqdev;

        rcu_read_lock();

        if (*pos == 0)
                return SEQ_START_TOKEN;
        
        list_for_each_entry_rcu(bpqdev, &bpq_devices, bpq_list) {
                if (i == *pos)
                        return bpqdev;
        }
        return NULL;
}

static void *bpq_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct list_head *p;
        struct bpqdev *bpqdev = v;

        ++*pos;

        if (v == SEQ_START_TOKEN)
                p = rcu_dereference(list_next_rcu(&bpq_devices));
        else
                p = rcu_dereference(list_next_rcu(&bpqdev->bpq_list));

        return (p == &bpq_devices) ? NULL 
                : list_entry(p, struct bpqdev, bpq_list);
}

static void bpq_seq_stop(struct seq_file *seq, void *v)
        __releases(RCU)
{
        rcu_read_unlock();
}


static int bpq_seq_show(struct seq_file *seq, void *v)
{
        if (v == SEQ_START_TOKEN)
                seq_puts(seq, 
                         "dev   ether      destination        accept from\n");
        else {
                const struct bpqdev *bpqdev = v;

                seq_printf(seq, "%-5s %-10s %pM  ",
                        bpqdev->axdev->name, bpqdev->ethdev->name,
                        bpqdev->dest_addr);

                if (is_multicast_ether_addr(bpqdev->acpt_addr))
                        seq_printf(seq, "*\n");
                else
                        seq_printf(seq, "%pM\n", bpqdev->acpt_addr);

        }
        return 0;
}

static const struct seq_operations bpq_seqops = {
        .start = bpq_seq_start,
        .next = bpq_seq_next,
        .stop = bpq_seq_stop,
        .show = bpq_seq_show,
};
#endif
/* ------------------------------------------------------------------------ */

static const struct net_device_ops bpq_netdev_ops = {
        .ndo_open            = bpq_open,
        .ndo_stop            = bpq_close,
        .ndo_start_xmit      = bpq_xmit,
        .ndo_set_mac_address = bpq_set_mac_address,
        .ndo_siocdevprivate  = bpq_siocdevprivate,
};

static void bpq_setup(struct net_device *dev)
{
        netdev_lockdep_set_classes(dev);

        dev->netdev_ops      = &bpq_netdev_ops;
        dev->needs_free_netdev = true;

        dev->flags      = 0;
        dev->lltx = true;       /* Allow recursion */

#if IS_ENABLED(CONFIG_AX25)
        dev->header_ops      = &ax25_header_ops;
#endif

        dev->type            = ARPHRD_AX25;
        dev->hard_header_len = AX25_MAX_HEADER_LEN + AX25_BPQ_HEADER_LEN;
        dev->mtu             = AX25_DEF_PACLEN;
        dev->addr_len        = AX25_ADDR_LEN;

        memcpy(dev->broadcast, &ax25_bcast, AX25_ADDR_LEN);
        dev_addr_set(dev, (u8 *)&ax25_defaddr);
}

/*
 *      Setup a new device.
 */
static int bpq_new_device(struct net_device *edev)
{
        int err;
        struct net_device *ndev;
        struct bpqdev *bpq;

        ndev = alloc_netdev(sizeof(struct bpqdev), "bpq%d", NET_NAME_UNKNOWN,
                            bpq_setup);
        if (!ndev)
                return -ENOMEM;

                
        bpq = netdev_priv(ndev);
        dev_hold(edev);
        bpq->ethdev = edev;
        bpq->axdev = ndev;

        eth_broadcast_addr(bpq->dest_addr);
        eth_broadcast_addr(bpq->acpt_addr);

        err = register_netdevice(ndev);
        if (err)
                goto error;

        /* List protected by RTNL */
        list_add_rcu(&bpq->bpq_list, &bpq_devices);
        return 0;

 error:
        dev_put(edev);
        free_netdev(ndev);
        return err;
        
}

static void bpq_free_device(struct net_device *ndev)
{
        struct bpqdev *bpq = netdev_priv(ndev);

        dev_put(bpq->ethdev);
        list_del_rcu(&bpq->bpq_list);

        unregister_netdevice(ndev);
}

/*
 *      Handle device status changes.
 */
static int bpq_device_event(struct notifier_block *this,
                            unsigned long event, void *ptr)
{
        struct net_device *dev = netdev_notifier_info_to_dev(ptr);

        if (!net_eq(dev_net(dev), &init_net))
                return NOTIFY_DONE;

        if (!dev_is_ethdev(dev) && !bpq_get_ax25_dev(dev))
                return NOTIFY_DONE;

        switch (event) {
        case NETDEV_UP:         /* new ethernet device -> new BPQ interface */
                if (bpq_get_ax25_dev(dev) == NULL)
                        bpq_new_device(dev);
                break;

        case NETDEV_DOWN:       /* ethernet device closed -> close BPQ interface */
                if ((dev = bpq_get_ax25_dev(dev)) != NULL)
                        dev_close(dev);
                break;

        case NETDEV_UNREGISTER: /* ethernet device removed -> free BPQ interface */
                if ((dev = bpq_get_ax25_dev(dev)) != NULL)
                        bpq_free_device(dev);
                break;
        default:
                break;
        }

        return NOTIFY_DONE;
}


/* ------------------------------------------------------------------------ */

/*
 * Initialize driver. To be called from af_ax25 if not compiled as a
 * module
 */
static int __init bpq_init_driver(void)
{
#ifdef CONFIG_PROC_FS
        if (!proc_create_seq("bpqether", 0444, init_net.proc_net, &bpq_seqops)) {
                printk(KERN_ERR
                        "bpq: cannot create /proc/net/bpqether entry.\n");
                return -ENOENT;
        }
#endif  /* CONFIG_PROC_FS */

        dev_add_pack(&bpq_packet_type);

        register_netdevice_notifier(&bpq_dev_notifier);

        printk(banner);

        return 0;
}

static void __exit bpq_cleanup_driver(void)
{
        struct bpqdev *bpq;

        dev_remove_pack(&bpq_packet_type);

        unregister_netdevice_notifier(&bpq_dev_notifier);

        remove_proc_entry("bpqether", init_net.proc_net);

        rtnl_lock();
        while (!list_empty(&bpq_devices)) {
                bpq = list_entry(bpq_devices.next, struct bpqdev, bpq_list);
                bpq_free_device(bpq->axdev);
        }
        rtnl_unlock();
}

MODULE_AUTHOR("Joerg Reuter DL1BKE <jreuter@yaina.de>");
MODULE_DESCRIPTION("Transmit and receive AX.25 packets over Ethernet");
MODULE_LICENSE("GPL");
module_init(bpq_init_driver);
module_exit(bpq_cleanup_driver);