nfnetlink.c

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/* Netfilter messages via netlink socket. Allows for user space
 * protocol helpers and general trouble making from userspace.
 *
 * (C) 2001 by Jay Schulist <[email protected]>,
 * (C) 2002-2005 by Harald Welte <[email protected]>
 * (C) 2005,2007 by Pablo Neira Ayuso <[email protected]>
 *
 * Initial netfilter messages via netlink development funded and
 * generally made possible by Network Robots, Inc. (www.networkrobots.com)
 *
 * Further development of this code funded by Astaro AG (http://www.astaro.com)
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/socket.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/sockios.h>
#include <linux/net.h>
#include <linux/skbuff.h>
#include <asm/uaccess.h>
#include <net/sock.h>
#include <net/netlink.h>
#include <linux/init.h>

#include <linux/netlink.h>
#include <linux/netfilter/nfnetlink.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <[email protected]>");
MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NETFILTER);

static char __initdata nfversion[] = "0.30";

static const struct nfnetlink_subsystem __rcu *subsys_table[NFNL_SUBSYS_COUNT];
static DEFINE_MUTEX(nfnl_mutex);

static const int nfnl_group2type[NFNLGRP_MAX+1] = {
    [NFNLGRP_CONNTRACK_NEW]     = NFNL_SUBSYS_CTNETLINK,
    [NFNLGRP_CONNTRACK_UPDATE]  = NFNL_SUBSYS_CTNETLINK,
    [NFNLGRP_CONNTRACK_DESTROY] = NFNL_SUBSYS_CTNETLINK,
    [NFNLGRP_CONNTRACK_EXP_NEW] = NFNL_SUBSYS_CTNETLINK_EXP,
    [NFNLGRP_CONNTRACK_EXP_UPDATE]  = NFNL_SUBSYS_CTNETLINK_EXP,
    [NFNLGRP_CONNTRACK_EXP_DESTROY] = NFNL_SUBSYS_CTNETLINK_EXP,
};

void nfnl_lock(void)
{
    mutex_lock(&nfnl_mutex);
}
EXPORT_SYMBOL_GPL(nfnl_lock);

void nfnl_unlock(void)
{
    mutex_unlock(&nfnl_mutex);
}
EXPORT_SYMBOL_GPL(nfnl_unlock);

int nfnetlink_subsys_register(const struct nfnetlink_subsystem *n)
{
    nfnl_lock();
    if (subsys_table[n->subsys_id]) {
        nfnl_unlock();
        return -EBUSY;
    }
    rcu_assign_pointer(subsys_table[n->subsys_id], n);
    nfnl_unlock();

    return 0;
}
EXPORT_SYMBOL_GPL(nfnetlink_subsys_register);

int nfnetlink_subsys_unregister(const struct nfnetlink_subsystem *n)
{
    nfnl_lock();
    subsys_table[n->subsys_id] = NULL;
    nfnl_unlock();
    synchronize_rcu();
    return 0;
}
EXPORT_SYMBOL_GPL(nfnetlink_subsys_unregister);

static inline const struct nfnetlink_subsystem *nfnetlink_get_subsys(u_int16_t type)
{
    u_int8_t subsys_id = NFNL_SUBSYS_ID(type);

    if (subsys_id >= NFNL_SUBSYS_COUNT)
        return NULL;

    return rcu_dereference(subsys_table[subsys_id]);
}

static inline const struct nfnl_callback *
nfnetlink_find_client(u_int16_t type, const struct nfnetlink_subsystem *ss)
{
    u_int8_t cb_id = NFNL_MSG_TYPE(type);

    if (cb_id >= ss->cb_count)
        return NULL;

    return &ss->cb[cb_id];
}

int nfnetlink_has_listeners(struct net *net, unsigned int group)
{
    return netlink_has_listeners(net->nfnl, group);
}
EXPORT_SYMBOL_GPL(nfnetlink_has_listeners);

int nfnetlink_send(struct sk_buff *skb, struct net *net, u32 pid,
           unsigned int group, int echo, gfp_t flags)
{
    return nlmsg_notify(net->nfnl, skb, pid, group, echo, flags);
}
EXPORT_SYMBOL_GPL(nfnetlink_send);

int nfnetlink_set_err(struct net *net, u32 pid, u32 group, int error)
{
    return netlink_set_err(net->nfnl, pid, group, error);
}
EXPORT_SYMBOL_GPL(nfnetlink_set_err);

int nfnetlink_unicast(struct sk_buff *skb, struct net *net, u_int32_t pid, int flags)
{
    return netlink_unicast(net->nfnl, skb, pid, flags);
}
EXPORT_SYMBOL_GPL(nfnetlink_unicast);

/* Process one complete nfnetlink message. */
static int nfnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
{
    struct net *net = sock_net(skb->sk);
    const struct nfnl_callback *nc;
    const struct nfnetlink_subsystem *ss;
    int type, err;

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

    /* All the messages must at least contain nfgenmsg */
    if (nlh->nlmsg_len < NLMSG_LENGTH(sizeof(struct nfgenmsg)))
        return 0;

    type = nlh->nlmsg_type;
replay:
    rcu_read_lock();
    ss = nfnetlink_get_subsys(type);
    if (!ss) {
#ifdef CONFIG_MODULES
        rcu_read_unlock();
        request_module("nfnetlink-subsys-%d", NFNL_SUBSYS_ID(type));
        rcu_read_lock();
        ss = nfnetlink_get_subsys(type);
        if (!ss)
#endif
        {
            rcu_read_unlock();
            return -EINVAL;
        }
    }

    nc = nfnetlink_find_client(type, ss);
    if (!nc) {
        rcu_read_unlock();
        return -EINVAL;
    }

    {
        int min_len = NLMSG_SPACE(sizeof(struct nfgenmsg));
        u_int8_t cb_id = NFNL_MSG_TYPE(nlh->nlmsg_type);
        struct nlattr *cda[ss->cb[cb_id].attr_count + 1];
        struct nlattr *attr = (void *)nlh + min_len;
        int attrlen = nlh->nlmsg_len - min_len;

        err = nla_parse(cda, ss->cb[cb_id].attr_count,
                attr, attrlen, ss->cb[cb_id].policy);
        if (err < 0) {
            rcu_read_unlock();
            return err;
        }

        if (nc->call_rcu) {
            err = nc->call_rcu(net->nfnl, skb, nlh,
                       (const struct nlattr **)cda);
            rcu_read_unlock();
        } else {
            rcu_read_unlock();
            nfnl_lock();
            if (rcu_dereference_protected(
                    subsys_table[NFNL_SUBSYS_ID(type)],
                    lockdep_is_held(&nfnl_mutex)) != ss ||
                nfnetlink_find_client(type, ss) != nc)
                err = -EAGAIN;
            else if (nc->call)
                err = nc->call(net->nfnl, skb, nlh,
                           (const struct nlattr **)cda);
            else
                err = -EINVAL;
            nfnl_unlock();
        }
        if (err == -EAGAIN)
            goto replay;
        return err;
    }
}

static void nfnetlink_rcv(struct sk_buff *skb)
{
    netlink_rcv_skb(skb, &nfnetlink_rcv_msg);
}

#ifdef CONFIG_MODULES
static void nfnetlink_bind(int group)
{
    const struct nfnetlink_subsystem *ss;
    int type = nfnl_group2type[group];

    rcu_read_lock();
    ss = nfnetlink_get_subsys(type);
    if (!ss) {
        rcu_read_unlock();
        request_module("nfnetlink-subsys-%d", type);
        return;
    }
    rcu_read_unlock();
}
#endif

static int __net_init nfnetlink_net_init(struct net *net)
{
    struct sock *nfnl;
    struct netlink_kernel_cfg cfg = {
        .groups = NFNLGRP_MAX,
        .input  = nfnetlink_rcv,
#ifdef CONFIG_MODULES
        .bind   = nfnetlink_bind,
#endif
    };

    nfnl = netlink_kernel_create(net, NETLINK_NETFILTER, &cfg);
    if (!nfnl)
        return -ENOMEM;
    net->nfnl_stash = nfnl;
    rcu_assign_pointer(net->nfnl, nfnl);
    return 0;
}

static void __net_exit nfnetlink_net_exit_batch(struct list_head *net_exit_list)
{
    struct net *net;

    list_for_each_entry(net, net_exit_list, exit_list)
        RCU_INIT_POINTER(net->nfnl, NULL);
    synchronize_net();
    list_for_each_entry(net, net_exit_list, exit_list)
        netlink_kernel_release(net->nfnl_stash);
}

static struct pernet_operations nfnetlink_net_ops = {
    .init       = nfnetlink_net_init,
    .exit_batch = nfnetlink_net_exit_batch,
};

static int __init nfnetlink_init(void)
{
    pr_info("Netfilter messages via NETLINK v%s.\n", nfversion);
    return register_pernet_subsys(&nfnetlink_net_ops);
}

static void __exit nfnetlink_exit(void)
{
    pr_info("Removing netfilter NETLINK layer.\n");
    unregister_pernet_subsys(&nfnetlink_net_ops);
}
module_init(nfnetlink_init);
module_exit(nfnetlink_exit);