ipt_ULOG.c

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/*
 * netfilter module for userspace packet logging daemons
 *
 * (C) 2000-2004 by Harald Welte <[email protected]>
 * (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2004 Netfilter Core Team <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * 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.
 *
 * Actually you should use nlbufsiz a bit smaller than PAGE_SIZE, since
 * nlbufsiz is used with alloc_skb, which adds another
 * sizeof(struct skb_shared_info).  Use NLMSG_GOODSIZE instead.
 *
 * 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/spinlock.h>
#include <linux/socket.h>
#include <linux/slab.h>
#include <linux/skbuff.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/netlink.h>
#include <linux/netdevice.h>
#include <linux/mm.h>
#include <linux/moduleparam.h>
#include <linux/netfilter.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv4/ipt_ULOG.h>
#include <net/netfilter/nf_log.h>
#include <net/sock.h>
#include <linux/bitops.h>
#include <asm/unaligned.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <[email protected]>");
MODULE_DESCRIPTION("Xtables: packet logging to netlink using ULOG");
MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NFLOG);

#define ULOG_NL_EVENT       111     /* Harald's favorite number */
#define ULOG_MAXNLGROUPS    32      /* numer of nlgroups */

static unsigned int nlbufsiz = NLMSG_GOODSIZE;
module_param(nlbufsiz, uint, 0400);
MODULE_PARM_DESC(nlbufsiz, "netlink buffer size");

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

static bool nflog = true;
module_param(nflog, bool, 0400);
MODULE_PARM_DESC(nflog, "register as internal netfilter logging module");

/* global data structures */

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 */
} ulog_buff_t;

static ulog_buff_t ulog_buffers[ULOG_MAXNLGROUPS];  /* array of buffers */

static struct sock *nflognl;        /* our socket */
static DEFINE_SPINLOCK(ulog_lock);  /* spinlock */

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

    if (timer_pending(&ub->timer)) {
        pr_debug("ulog_send: timer was pending, deleting\n");
        del_timer(&ub->timer);
    }

    if (!ub->skb) {
        pr_debug("ulog_send: nothing to send\n");
        return;
    }

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

    NETLINK_CB(ub->skb).dst_group = nlgroupnum + 1;
    pr_debug("throwing %d packets to netlink group %u\n",
         ub->qlen, nlgroupnum + 1);
    netlink_broadcast(nflognl, ub->skb, 0, nlgroupnum + 1, GFP_ATOMIC);

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


/* timer function to flush queue in flushtimeout time */
static void ulog_timer(unsigned long data)
{
    pr_debug("timer function called, calling ulog_send\n");

    /* lock to protect against somebody modifying our structure
     * from ipt_ulog_target at the same time */
    spin_lock_bh(&ulog_lock);
    ulog_send(data);
    spin_unlock_bh(&ulog_lock);
}

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

    /* alloc skb which should be big enough for a whole
     * multipart message. WARNING: has to be <= 131000
     * due to slab allocator restrictions */

    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 %ub\n", size);
        }
    }

    return skb;
}

static void ipt_ulog_packet(unsigned int hooknum,
                const struct sk_buff *skb,
                const struct net_device *in,
                const struct net_device *out,
                const struct ipt_ulog_info *loginfo,
                const char *prefix)
{
    ulog_buff_t *ub;
    ulog_packet_msg_t *pm;
    size_t size, copy_len;
    struct nlmsghdr *nlh;
    struct timeval tv;

    /* ffs == find first bit set, necessary because userspace
     * is already shifting groupnumber, but we need unshifted.
     * ffs() returns [1..32], we need [0..31] */
    unsigned int groupnum = ffs(loginfo->nl_group) - 1;

    /* calculate the size of the skb needed */
    if (loginfo->copy_range == 0 || loginfo->copy_range > skb->len)
        copy_len = skb->len;
    else
        copy_len = loginfo->copy_range;

    size = NLMSG_SPACE(sizeof(*pm) + copy_len);

    ub = &ulog_buffers[groupnum];

    spin_lock_bh(&ulog_lock);

    if (!ub->skb) {
        if (!(ub->skb = ulog_alloc_skb(size)))
            goto alloc_failure;
    } else if (ub->qlen >= loginfo->qthreshold ||
           size > skb_tailroom(ub->skb)) {
        /* either the queue len is too high or we don't have
         * enough room in nlskb left. send it to userspace. */

        ulog_send(groupnum);

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

    pr_debug("qlen %d, qthreshold %Zu\n", ub->qlen, loginfo->qthreshold);

    nlh = nlmsg_put(ub->skb, 0, ub->qlen, ULOG_NL_EVENT,
            sizeof(*pm)+copy_len, 0);
    if (!nlh) {
        pr_debug("error during nlmsg_put\n");
        goto out_unlock;
    }
    ub->qlen++;

    pm = nlmsg_data(nlh);

    /* We might not have a timestamp, get one */
    if (skb->tstamp.tv64 == 0)
        __net_timestamp((struct sk_buff *)skb);

    /* copy hook, prefix, timestamp, payload, etc. */
    pm->data_len = copy_len;
    tv = ktime_to_timeval(skb->tstamp);
    put_unaligned(tv.tv_sec, &pm->timestamp_sec);
    put_unaligned(tv.tv_usec, &pm->timestamp_usec);
    put_unaligned(skb->mark, &pm->mark);
    pm->hook = hooknum;
    if (prefix != NULL)
        strncpy(pm->prefix, prefix, sizeof(pm->prefix));
    else if (loginfo->prefix[0] != '\0')
        strncpy(pm->prefix, loginfo->prefix, sizeof(pm->prefix));
    else
        *(pm->prefix) = '\0';

    if (in && in->hard_header_len > 0 &&
        skb->mac_header != skb->network_header &&
        in->hard_header_len <= ULOG_MAC_LEN) {
        memcpy(pm->mac, skb_mac_header(skb), in->hard_header_len);
        pm->mac_len = in->hard_header_len;
    } else
        pm->mac_len = 0;

    if (in)
        strncpy(pm->indev_name, in->name, sizeof(pm->indev_name));
    else
        pm->indev_name[0] = '\0';

    if (out)
        strncpy(pm->outdev_name, out->name, sizeof(pm->outdev_name));
    else
        pm->outdev_name[0] = '\0';

    /* copy_len <= skb->len, so can't fail. */
    if (skb_copy_bits(skb, 0, pm->payload, copy_len) < 0)
        BUG();

    /* check if we are building multi-part messages */
    if (ub->qlen > 1)
        ub->lastnlh->nlmsg_flags |= NLM_F_MULTI;

    ub->lastnlh = nlh;

    /* if timer isn't already running, start it */
    if (!timer_pending(&ub->timer)) {
        ub->timer.expires = jiffies + flushtimeout * HZ / 100;
        add_timer(&ub->timer);
    }

    /* if threshold is reached, send message to userspace */
    if (ub->qlen >= loginfo->qthreshold) {
        if (loginfo->qthreshold > 1)
            nlh->nlmsg_type = NLMSG_DONE;
        ulog_send(groupnum);
    }
out_unlock:
    spin_unlock_bh(&ulog_lock);

    return;

alloc_failure:
    pr_debug("Error building netlink message\n");
    spin_unlock_bh(&ulog_lock);
}

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

static void ipt_logfn(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 ipt_ulog_info loginfo;

    if (!li || li->type != NF_LOG_TYPE_ULOG) {
        loginfo.nl_group = ULOG_DEFAULT_NLGROUP;
        loginfo.copy_range = 0;
        loginfo.qthreshold = ULOG_DEFAULT_QTHRESHOLD;
        loginfo.prefix[0] = '\0';
    } else {
        loginfo.nl_group = li->u.ulog.group;
        loginfo.copy_range = li->u.ulog.copy_len;
        loginfo.qthreshold = li->u.ulog.qthreshold;
        strlcpy(loginfo.prefix, prefix, sizeof(loginfo.prefix));
    }

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

static int ulog_tg_check(const struct xt_tgchk_param *par)
{
    const struct ipt_ulog_info *loginfo = par->targinfo;

    if (loginfo->prefix[sizeof(loginfo->prefix) - 1] != '\0') {
        pr_debug("prefix not null-terminated\n");
        return -EINVAL;
    }
    if (loginfo->qthreshold > ULOG_MAX_QLEN) {
        pr_debug("queue threshold %Zu > MAX_QLEN\n",
             loginfo->qthreshold);
        return -EINVAL;
    }
    return 0;
}

#ifdef CONFIG_COMPAT
struct compat_ipt_ulog_info {
    compat_uint_t   nl_group;
    compat_size_t   copy_range;
    compat_size_t   qthreshold;
    char        prefix[ULOG_PREFIX_LEN];
};

static void ulog_tg_compat_from_user(void *dst, const void *src)
{
    const struct compat_ipt_ulog_info *cl = src;
    struct ipt_ulog_info l = {
        .nl_group   = cl->nl_group,
        .copy_range = cl->copy_range,
        .qthreshold = cl->qthreshold,
    };

    memcpy(l.prefix, cl->prefix, sizeof(l.prefix));
    memcpy(dst, &l, sizeof(l));
}

static int ulog_tg_compat_to_user(void __user *dst, const void *src)
{
    const struct ipt_ulog_info *l = src;
    struct compat_ipt_ulog_info cl = {
        .nl_group   = l->nl_group,
        .copy_range = l->copy_range,
        .qthreshold = l->qthreshold,
    };

    memcpy(cl.prefix, l->prefix, sizeof(cl.prefix));
    return copy_to_user(dst, &cl, sizeof(cl)) ? -EFAULT : 0;
}
#endif /* CONFIG_COMPAT */

static struct xt_target ulog_tg_reg __read_mostly = {
    .name       = "ULOG",
    .family     = NFPROTO_IPV4,
    .target     = ulog_tg,
    .targetsize = sizeof(struct ipt_ulog_info),
    .checkentry = ulog_tg_check,
#ifdef CONFIG_COMPAT
    .compatsize = sizeof(struct compat_ipt_ulog_info),
    .compat_from_user = ulog_tg_compat_from_user,
    .compat_to_user = ulog_tg_compat_to_user,
#endif
    .me     = THIS_MODULE,
};

static struct nf_logger ipt_ulog_logger __read_mostly = {
    .name       = "ipt_ULOG",
    .logfn      = ipt_logfn,
    .me     = THIS_MODULE,
};

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

    pr_debug("init module\n");

    if (nlbufsiz > 128*1024) {
        pr_warning("Netlink buffer has to be <= 128kB\n");
        return -EINVAL;
    }

    /* initialize ulog_buffers */
    for (i = 0; i < ULOG_MAXNLGROUPS; i++)
        setup_timer(&ulog_buffers[i].timer, ulog_timer, i);

    nflognl = netlink_kernel_create(&init_net, NETLINK_NFLOG, &cfg);
    if (!nflognl)
        return -ENOMEM;

    ret = xt_register_target(&ulog_tg_reg);
    if (ret < 0) {
        netlink_kernel_release(nflognl);
        return ret;
    }
    if (nflog)
        nf_log_register(NFPROTO_IPV4, &ipt_ulog_logger);

    return 0;
}

static void __exit ulog_tg_exit(void)
{
    ulog_buff_t *ub;
    int i;

    pr_debug("cleanup_module\n");

    if (nflog)
        nf_log_unregister(&ipt_ulog_logger);
    xt_unregister_target(&ulog_tg_reg);
    netlink_kernel_release(nflognl);

    /* remove pending timers and free allocated skb's */
    for (i = 0; i < ULOG_MAXNLGROUPS; i++) {
        ub = &ulog_buffers[i];
        if (timer_pending(&ub->timer)) {
            pr_debug("timer was pending, deleting\n");
            del_timer(&ub->timer);
        }

        if (ub->skb) {
            kfree_skb(ub->skb);
            ub->skb = NULL;
        }
    }
}

module_init(ulog_tg_init);
module_exit(ulog_tg_exit);