gre.c

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/*
 *  GRE over IPv4 demultiplexer driver
 *
 *  Authors: Dmitry Kozlov ([email protected])
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/kmod.h>
#include <linux/skbuff.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/netdevice.h>
#include <linux/spinlock.h>
#include <net/protocol.h>
#include <net/gre.h>


static const struct gre_protocol __rcu *gre_proto[GREPROTO_MAX] __read_mostly;
static DEFINE_SPINLOCK(gre_proto_lock);

int gre_add_protocol(const struct gre_protocol *proto, u8 version)
{
    if (version >= GREPROTO_MAX)
        goto err_out;

    spin_lock(&gre_proto_lock);
    if (gre_proto[version])
        goto err_out_unlock;

    RCU_INIT_POINTER(gre_proto[version], proto);
    spin_unlock(&gre_proto_lock);
    return 0;

err_out_unlock:
    spin_unlock(&gre_proto_lock);
err_out:
    return -1;
}
EXPORT_SYMBOL_GPL(gre_add_protocol);

int gre_del_protocol(const struct gre_protocol *proto, u8 version)
{
    if (version >= GREPROTO_MAX)
        goto err_out;

    spin_lock(&gre_proto_lock);
    if (rcu_dereference_protected(gre_proto[version],
            lockdep_is_held(&gre_proto_lock)) != proto)
        goto err_out_unlock;
    RCU_INIT_POINTER(gre_proto[version], NULL);
    spin_unlock(&gre_proto_lock);
    synchronize_rcu();
    return 0;

err_out_unlock:
    spin_unlock(&gre_proto_lock);
err_out:
    return -1;
}
EXPORT_SYMBOL_GPL(gre_del_protocol);

static int gre_rcv(struct sk_buff *skb)
{
    const struct gre_protocol *proto;
    u8 ver;
    int ret;

    if (!pskb_may_pull(skb, 12))
        goto drop;

    ver = skb->data[1]&0x7f;
    if (ver >= GREPROTO_MAX)
        goto drop;

    rcu_read_lock();
    proto = rcu_dereference(gre_proto[ver]);
    if (!proto || !proto->handler)
        goto drop_unlock;
    ret = proto->handler(skb);
    rcu_read_unlock();
    return ret;

drop_unlock:
    rcu_read_unlock();
drop:
    kfree_skb(skb);
    return NET_RX_DROP;
}

static void gre_err(struct sk_buff *skb, u32 info)
{
    const struct gre_protocol *proto;
    const struct iphdr *iph = (const struct iphdr *)skb->data;
    u8 ver = skb->data[(iph->ihl<<2) + 1]&0x7f;

    if (ver >= GREPROTO_MAX)
        return;

    rcu_read_lock();
    proto = rcu_dereference(gre_proto[ver]);
    if (proto && proto->err_handler)
        proto->err_handler(skb, info);
    rcu_read_unlock();
}

static const struct net_protocol net_gre_protocol = {
    .handler     = gre_rcv,
    .err_handler = gre_err,
    .netns_ok    = 1,
};

static int __init gre_init(void)
{
    pr_info("GRE over IPv4 demultiplexor driver\n");

    if (inet_add_protocol(&net_gre_protocol, IPPROTO_GRE) < 0) {
        pr_err("can't add protocol\n");
        return -EAGAIN;
    }

    return 0;
}

static void __exit gre_exit(void)
{
    inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
}

module_init(gre_init);
module_exit(gre_exit);

MODULE_DESCRIPTION("GRE over IPv4 demultiplexer driver");
MODULE_AUTHOR("D. Kozlov ([email protected])");
MODULE_LICENSE("GPL");