ebt_ulog.c

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/*
 * netfilter module for userspace bridged Ethernet frames logging daemons
 *
 *  Authors:
 *  Bart De Schuymer <[email protected]>
 *  Harald Welte <[email protected]>
 *
 *  November, 2004
 *
 * Based on ipt_ULOG.c, which is
 * (C) 2000-2002 by Harald Welte <[email protected]>
 *
 * This module accepts two parameters:
 *
 * nlbufsiz:
 *   The parameter specifies how big the buffer for each netlink multicast
 * group is. e.g. If you say nlbufsiz=8192, up to eight kb of packets will
 * get accumulated in the kernel until they are sent to userspace. It is
 * NOT possible to allocate more than 128kB, and it is strongly discouraged,
 * because atomically allocating 128kB inside the network rx softirq is not
 * reliable. Please also keep in mind that this buffer size is allocated for
 * each nlgroup you are using, so the total kernel memory usage increases
 * by that factor.
 *
 * flushtimeout:
 *   Specify, after how many hundredths of a second the queue should be
 *   flushed even if it is not full yet.
 *
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/socket.h>
#include <linux/skbuff.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/netlink.h>
#include <linux/netdevice.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_bridge/ebt_ulog.h>
#include <net/netfilter/nf_log.h>
#include <net/sock.h>
#include "../br_private.h"

static unsigned int nlbufsiz = NLMSG_GOODSIZE;
module_param(nlbufsiz, uint, 0600);
MODULE_PARM_DESC(nlbufsiz, "netlink buffer size (number of bytes) "
               "(defaults to 4096)");

static unsigned int flushtimeout = 10;
module_param(flushtimeout, uint, 0600);
MODULE_PARM_DESC(flushtimeout, "buffer flush timeout (hundredths ofa second) "
                   "(defaults to 10)");

typedef struct {
    unsigned int qlen;      /* number of nlmsgs' in the skb */
    struct nlmsghdr *lastnlh;   /* netlink header of last msg in skb */
    struct sk_buff *skb;        /* the pre-allocated skb */
    struct timer_list timer;    /* the timer function */
    spinlock_t lock;        /* the per-queue lock */
} ebt_ulog_buff_t;

static ebt_ulog_buff_t ulog_buffers[EBT_ULOG_MAXNLGROUPS];
static struct sock *ebtulognl;

/* send one ulog_buff_t to userspace */
static void ulog_send(unsigned int nlgroup)
{
    ebt_ulog_buff_t *ub = &ulog_buffers[nlgroup];

    if (timer_pending(&ub->timer))
        del_timer(&ub->timer);

    if (!ub->skb)
        return;

    /* last nlmsg needs NLMSG_DONE */
    if (ub->qlen > 1)
        ub->lastnlh->nlmsg_type = NLMSG_DONE;

    NETLINK_CB(ub->skb).dst_group = nlgroup + 1;
    netlink_broadcast(ebtulognl, ub->skb, 0, nlgroup + 1, GFP_ATOMIC);

    ub->qlen = 0;
    ub->skb = NULL;
}

/* timer function to flush queue in flushtimeout time */
static void ulog_timer(unsigned long data)
{
    spin_lock_bh(&ulog_buffers[data].lock);
    if (ulog_buffers[data].skb)
        ulog_send(data);
    spin_unlock_bh(&ulog_buffers[data].lock);
}

static struct sk_buff *ulog_alloc_skb(unsigned int size)
{
    struct sk_buff *skb;
    unsigned int n;

    n = max(size, nlbufsiz);
    skb = alloc_skb(n, GFP_ATOMIC | __GFP_NOWARN);
    if (!skb) {
        if (n > size) {
            /* try to allocate only as much as we need for
             * current packet */
            skb = alloc_skb(size, GFP_ATOMIC);
            if (!skb)
                pr_debug("cannot even allocate buffer of size %ub\n",
                     size);
        }
    }

    return skb;
}

static void ebt_ulog_packet(unsigned int hooknr, const struct sk_buff *skb,
   const struct net_device *in, const struct net_device *out,
   const struct ebt_ulog_info *uloginfo, const char *prefix)
{
    ebt_ulog_packet_msg_t *pm;
    size_t size, copy_len;
    struct nlmsghdr *nlh;
    unsigned int group = uloginfo->nlgroup;
    ebt_ulog_buff_t *ub = &ulog_buffers[group];
    spinlock_t *lock = &ub->lock;
    ktime_t kt;

    if ((uloginfo->cprange == 0) ||
        (uloginfo->cprange > skb->len + ETH_HLEN))
        copy_len = skb->len + ETH_HLEN;
    else
        copy_len = uloginfo->cprange;

    size = NLMSG_SPACE(sizeof(*pm) + copy_len);
    if (size > nlbufsiz) {
        pr_debug("Size %Zd needed, but nlbufsiz=%d\n", size, nlbufsiz);
        return;
    }

    spin_lock_bh(lock);

    if (!ub->skb) {
        if (!(ub->skb = ulog_alloc_skb(size)))
            goto unlock;
    } else if (size > skb_tailroom(ub->skb)) {
        ulog_send(group);

        if (!(ub->skb = ulog_alloc_skb(size)))
            goto unlock;
    }

    nlh = nlmsg_put(ub->skb, 0, ub->qlen, 0,
            size - NLMSG_ALIGN(sizeof(*nlh)), 0);
    if (!nlh) {
        kfree_skb(ub->skb);
        ub->skb = NULL;
        goto unlock;
    }
    ub->qlen++;

    pm = nlmsg_data(nlh);

    /* Fill in the ulog data */
    pm->version = EBT_ULOG_VERSION;
    kt = ktime_get_real();
    pm->stamp = ktime_to_timeval(kt);
    if (ub->qlen == 1)
        ub->skb->tstamp = kt;
    pm->data_len = copy_len;
    pm->mark = skb->mark;
    pm->hook = hooknr;
    if (uloginfo->prefix != NULL)
        strcpy(pm->prefix, uloginfo->prefix);
    else
        *(pm->prefix) = '\0';

    if (in) {
        strcpy(pm->physindev, in->name);
        /* If in isn't a bridge, then physindev==indev */
        if (br_port_exists(in))
            /* rcu_read_lock()ed by nf_hook_slow */
            strcpy(pm->indev, br_port_get_rcu(in)->br->dev->name);
        else
            strcpy(pm->indev, in->name);
    } else
        pm->indev[0] = pm->physindev[0] = '\0';

    if (out) {
        /* If out exists, then out is a bridge port */
        strcpy(pm->physoutdev, out->name);
        /* rcu_read_lock()ed by nf_hook_slow */
        strcpy(pm->outdev, br_port_get_rcu(out)->br->dev->name);
    } else
        pm->outdev[0] = pm->physoutdev[0] = '\0';

    if (skb_copy_bits(skb, -ETH_HLEN, pm->data, copy_len) < 0)
        BUG();

    if (ub->qlen > 1)
        ub->lastnlh->nlmsg_flags |= NLM_F_MULTI;

    ub->lastnlh = nlh;

    if (ub->qlen >= uloginfo->qthreshold)
        ulog_send(group);
    else if (!timer_pending(&ub->timer)) {
        ub->timer.expires = jiffies + flushtimeout * HZ / 100;
        add_timer(&ub->timer);
    }

unlock:
    spin_unlock_bh(lock);
}

/* this function is registered with the netfilter core */
static void ebt_log_packet(u_int8_t pf, unsigned int hooknum,
   const struct sk_buff *skb, const struct net_device *in,
   const struct net_device *out, const struct nf_loginfo *li,
   const char *prefix)
{
    struct ebt_ulog_info loginfo;

    if (!li || li->type != NF_LOG_TYPE_ULOG) {
        loginfo.nlgroup = EBT_ULOG_DEFAULT_NLGROUP;
        loginfo.cprange = 0;
        loginfo.qthreshold = EBT_ULOG_DEFAULT_QTHRESHOLD;
        loginfo.prefix[0] = '\0';
    } else {
        loginfo.nlgroup = li->u.ulog.group;
        loginfo.cprange = li->u.ulog.copy_len;
        loginfo.qthreshold = li->u.ulog.qthreshold;
        strlcpy(loginfo.prefix, prefix, sizeof(loginfo.prefix));
    }

    ebt_ulog_packet(hooknum, skb, in, out, &loginfo, prefix);
}

static unsigned int
ebt_ulog_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
    ebt_ulog_packet(par->hooknum, skb, par->in, par->out,
                    par->targinfo, NULL);
    return EBT_CONTINUE;
}

static int ebt_ulog_tg_check(const struct xt_tgchk_param *par)
{
    struct ebt_ulog_info *uloginfo = par->targinfo;

    if (uloginfo->nlgroup > 31)
        return -EINVAL;

    uloginfo->prefix[EBT_ULOG_PREFIX_LEN - 1] = '\0';

    if (uloginfo->qthreshold > EBT_ULOG_MAX_QLEN)
        uloginfo->qthreshold = EBT_ULOG_MAX_QLEN;

    return 0;
}

static struct xt_target ebt_ulog_tg_reg __read_mostly = {
    .name       = "ulog",
    .revision   = 0,
    .family     = NFPROTO_BRIDGE,
    .target     = ebt_ulog_tg,
    .checkentry = ebt_ulog_tg_check,
    .targetsize = sizeof(struct ebt_ulog_info),
    .me     = THIS_MODULE,
};

static struct nf_logger ebt_ulog_logger __read_mostly = {
    .name       = "ebt_ulog",
    .logfn      = &ebt_log_packet,
    .me     = THIS_MODULE,
};

static int __init ebt_ulog_init(void)
{
    int ret;
    int i;
    struct netlink_kernel_cfg cfg = {
        .groups = EBT_ULOG_MAXNLGROUPS,
    };

    if (nlbufsiz >= 128*1024) {
        pr_warning("Netlink buffer has to be <= 128kB,"
               " please try a smaller nlbufsiz parameter.\n");
        return -EINVAL;
    }

    /* initialize ulog_buffers */
    for (i = 0; i < EBT_ULOG_MAXNLGROUPS; i++) {
        setup_timer(&ulog_buffers[i].timer, ulog_timer, i);
        spin_lock_init(&ulog_buffers[i].lock);
    }

    ebtulognl = netlink_kernel_create(&init_net, NETLINK_NFLOG, &cfg);
    if (!ebtulognl)
        ret = -ENOMEM;
    else if ((ret = xt_register_target(&ebt_ulog_tg_reg)) != 0)
        netlink_kernel_release(ebtulognl);

    if (ret == 0)
        nf_log_register(NFPROTO_BRIDGE, &ebt_ulog_logger);

    return ret;
}

static void __exit ebt_ulog_fini(void)
{
    ebt_ulog_buff_t *ub;
    int i;

    nf_log_unregister(&ebt_ulog_logger);
    xt_unregister_target(&ebt_ulog_tg_reg);
    for (i = 0; i < EBT_ULOG_MAXNLGROUPS; i++) {
        ub = &ulog_buffers[i];
        if (timer_pending(&ub->timer))
            del_timer(&ub->timer);
        spin_lock_bh(&ub->lock);
        if (ub->skb) {
            kfree_skb(ub->skb);
            ub->skb = NULL;
        }
        spin_unlock_bh(&ub->lock);
    }
    netlink_kernel_release(ebtulognl);
}

module_init(ebt_ulog_init);
module_exit(ebt_ulog_fini);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Bart De Schuymer <[email protected]>");
MODULE_DESCRIPTION("Ebtables: Packet logging to netlink using ULOG");