nf_queue.c

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#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/proc_fs.h>
#include <linux/skbuff.h>
#include <linux/netfilter.h>
#include <linux/seq_file.h>
#include <linux/rcupdate.h>
#include <net/protocol.h>
#include <net/netfilter/nf_queue.h>
#include <net/dst.h>

#include "nf_internals.h"

/*
 * A queue handler may be registered for each protocol.  Each is protected by
 * long term mutex.  The handler must provide an an outfn() to accept packets
 * for queueing and must reinject all packets it receives, no matter what.
 */
static const struct nf_queue_handler __rcu *queue_handler[NFPROTO_NUMPROTO] __read_mostly;

static DEFINE_MUTEX(queue_handler_mutex);

/* return EBUSY when somebody else is registered, return EEXIST if the
 * same handler is registered, return 0 in case of success. */
int nf_register_queue_handler(u_int8_t pf, const struct nf_queue_handler *qh)
{
    int ret;
    const struct nf_queue_handler *old;

    if (pf >= ARRAY_SIZE(queue_handler))
        return -EINVAL;

    mutex_lock(&queue_handler_mutex);
    old = rcu_dereference_protected(queue_handler[pf],
                    lockdep_is_held(&queue_handler_mutex));
    if (old == qh)
        ret = -EEXIST;
    else if (old)
        ret = -EBUSY;
    else {
        rcu_assign_pointer(queue_handler[pf], qh);
        ret = 0;
    }
    mutex_unlock(&queue_handler_mutex);

    return ret;
}
EXPORT_SYMBOL(nf_register_queue_handler);

/* The caller must flush their queue before this */
int nf_unregister_queue_handler(u_int8_t pf, const struct nf_queue_handler *qh)
{
    const struct nf_queue_handler *old;

    if (pf >= ARRAY_SIZE(queue_handler))
        return -EINVAL;

    mutex_lock(&queue_handler_mutex);
    old = rcu_dereference_protected(queue_handler[pf],
                    lockdep_is_held(&queue_handler_mutex));
    if (old && old != qh) {
        mutex_unlock(&queue_handler_mutex);
        return -EINVAL;
    }

    RCU_INIT_POINTER(queue_handler[pf], NULL);
    mutex_unlock(&queue_handler_mutex);

    synchronize_rcu();

    return 0;
}
EXPORT_SYMBOL(nf_unregister_queue_handler);

void nf_unregister_queue_handlers(const struct nf_queue_handler *qh)
{
    u_int8_t pf;

    mutex_lock(&queue_handler_mutex);
    for (pf = 0; pf < ARRAY_SIZE(queue_handler); pf++)  {
        if (rcu_dereference_protected(
                queue_handler[pf],
                lockdep_is_held(&queue_handler_mutex)
                ) == qh)
            RCU_INIT_POINTER(queue_handler[pf], NULL);
    }
    mutex_unlock(&queue_handler_mutex);

    synchronize_rcu();
}
EXPORT_SYMBOL_GPL(nf_unregister_queue_handlers);

static void nf_queue_entry_release_refs(struct nf_queue_entry *entry)
{
    /* Release those devices we held, or Alexey will kill me. */
    if (entry->indev)
        dev_put(entry->indev);
    if (entry->outdev)
        dev_put(entry->outdev);
#ifdef CONFIG_BRIDGE_NETFILTER
    if (entry->skb->nf_bridge) {
        struct nf_bridge_info *nf_bridge = entry->skb->nf_bridge;

        if (nf_bridge->physindev)
            dev_put(nf_bridge->physindev);
        if (nf_bridge->physoutdev)
            dev_put(nf_bridge->physoutdev);
    }
#endif
    /* Drop reference to owner of hook which queued us. */
    module_put(entry->elem->owner);
}

/*
 * Any packet that leaves via this function must come back
 * through nf_reinject().
 */
static int __nf_queue(struct sk_buff *skb,
              struct nf_hook_ops *elem,
              u_int8_t pf, unsigned int hook,
              struct net_device *indev,
              struct net_device *outdev,
              int (*okfn)(struct sk_buff *),
              unsigned int queuenum)
{
    int status = -ENOENT;
    struct nf_queue_entry *entry = NULL;
#ifdef CONFIG_BRIDGE_NETFILTER
    struct net_device *physindev;
    struct net_device *physoutdev;
#endif
    const struct nf_afinfo *afinfo;
    const struct nf_queue_handler *qh;

    /* QUEUE == DROP if no one is waiting, to be safe. */
    rcu_read_lock();

    qh = rcu_dereference(queue_handler[pf]);
    if (!qh) {
        status = -ESRCH;
        goto err_unlock;
    }

    afinfo = nf_get_afinfo(pf);
    if (!afinfo)
        goto err_unlock;

    entry = kmalloc(sizeof(*entry) + afinfo->route_key_size, GFP_ATOMIC);
    if (!entry) {
        status = -ENOMEM;
        goto err_unlock;
    }

    *entry = (struct nf_queue_entry) {
        .skb    = skb,
        .elem   = elem,
        .pf = pf,
        .hook   = hook,
        .indev  = indev,
        .outdev = outdev,
        .okfn   = okfn,
    };

    /* If it's going away, ignore hook. */
    if (!try_module_get(entry->elem->owner)) {
        status = -ECANCELED;
        goto err_unlock;
    }
    /* Bump dev refs so they don't vanish while packet is out */
    if (indev)
        dev_hold(indev);
    if (outdev)
        dev_hold(outdev);
#ifdef CONFIG_BRIDGE_NETFILTER
    if (skb->nf_bridge) {
        physindev = skb->nf_bridge->physindev;
        if (physindev)
            dev_hold(physindev);
        physoutdev = skb->nf_bridge->physoutdev;
        if (physoutdev)
            dev_hold(physoutdev);
    }
#endif
    skb_dst_force(skb);
    afinfo->saveroute(skb, entry);
    status = qh->outfn(entry, queuenum);

    rcu_read_unlock();

    if (status < 0) {
        nf_queue_entry_release_refs(entry);
        goto err;
    }

    return 0;

err_unlock:
    rcu_read_unlock();
err:
    kfree(entry);
    return status;
}

#ifdef CONFIG_BRIDGE_NETFILTER
/* When called from bridge netfilter, skb->data must point to MAC header
 * before calling skb_gso_segment(). Else, original MAC header is lost
 * and segmented skbs will be sent to wrong destination.
 */
static void nf_bridge_adjust_skb_data(struct sk_buff *skb)
{
    if (skb->nf_bridge)
        __skb_push(skb, skb->network_header - skb->mac_header);
}

static void nf_bridge_adjust_segmented_data(struct sk_buff *skb)
{
    if (skb->nf_bridge)
        __skb_pull(skb, skb->network_header - skb->mac_header);
}
#else
#define nf_bridge_adjust_skb_data(s) do {} while (0)
#define nf_bridge_adjust_segmented_data(s) do {} while (0)
#endif

int nf_queue(struct sk_buff *skb,
         struct nf_hook_ops *elem,
         u_int8_t pf, unsigned int hook,
         struct net_device *indev,
         struct net_device *outdev,
         int (*okfn)(struct sk_buff *),
         unsigned int queuenum)
{
    struct sk_buff *segs;
    int err = -EINVAL;
    unsigned int queued;

    if (!skb_is_gso(skb))
        return __nf_queue(skb, elem, pf, hook, indev, outdev, okfn,
                  queuenum);

    switch (pf) {
    case NFPROTO_IPV4:
        skb->protocol = htons(ETH_P_IP);
        break;
    case NFPROTO_IPV6:
        skb->protocol = htons(ETH_P_IPV6);
        break;
    }

    nf_bridge_adjust_skb_data(skb);
    segs = skb_gso_segment(skb, 0);
    /* Does not use PTR_ERR to limit the number of error codes that can be
     * returned by nf_queue.  For instance, callers rely on -ECANCELED to mean
     * 'ignore this hook'.
     */
    if (IS_ERR(segs))
        goto out_err;
    queued = 0;
    err = 0;
    do {
        struct sk_buff *nskb = segs->next;

        segs->next = NULL;
        if (err == 0) {
            nf_bridge_adjust_segmented_data(segs);
            err = __nf_queue(segs, elem, pf, hook, indev,
                       outdev, okfn, queuenum);
        }
        if (err == 0)
            queued++;
        else
            kfree_skb(segs);
        segs = nskb;
    } while (segs);

    if (queued) {
        kfree_skb(skb);
        return 0;
    }
  out_err:
    nf_bridge_adjust_segmented_data(skb);
    return err;
}

void nf_reinject(struct nf_queue_entry *entry, unsigned int verdict)
{
    struct sk_buff *skb = entry->skb;
    struct nf_hook_ops *elem = entry->elem;
    const struct nf_afinfo *afinfo;
    int err;

    rcu_read_lock();

    nf_queue_entry_release_refs(entry);

    /* Continue traversal iff userspace said ok... */
    if (verdict == NF_REPEAT) {
        elem = list_entry(elem->list.prev, struct nf_hook_ops, list);
        verdict = NF_ACCEPT;
    }

    if (verdict == NF_ACCEPT) {
        afinfo = nf_get_afinfo(entry->pf);
        if (!afinfo || afinfo->reroute(skb, entry) < 0)
            verdict = NF_DROP;
    }

    if (verdict == NF_ACCEPT) {
    next_hook:
        verdict = nf_iterate(&nf_hooks[entry->pf][entry->hook],
                     skb, entry->hook,
                     entry->indev, entry->outdev, &elem,
                     entry->okfn, INT_MIN);
    }

    switch (verdict & NF_VERDICT_MASK) {
    case NF_ACCEPT:
    case NF_STOP:
        local_bh_disable();
        entry->okfn(skb);
        local_bh_enable();
        break;
    case NF_QUEUE:
        err = __nf_queue(skb, elem, entry->pf, entry->hook,
                 entry->indev, entry->outdev, entry->okfn,
                 verdict >> NF_VERDICT_QBITS);
        if (err < 0) {
            if (err == -ECANCELED)
                goto next_hook;
            if (err == -ESRCH &&
               (verdict & NF_VERDICT_FLAG_QUEUE_BYPASS))
                goto next_hook;
            kfree_skb(skb);
        }
        break;
    case NF_STOLEN:
        break;
    default:
        kfree_skb(skb);
    }
    rcu_read_unlock();
    kfree(entry);
}
EXPORT_SYMBOL(nf_reinject);

#ifdef CONFIG_PROC_FS
static void *seq_start(struct seq_file *seq, loff_t *pos)
{
    if (*pos >= ARRAY_SIZE(queue_handler))
        return NULL;

    return pos;
}

static void *seq_next(struct seq_file *s, void *v, loff_t *pos)
{
    (*pos)++;

    if (*pos >= ARRAY_SIZE(queue_handler))
        return NULL;

    return pos;
}

static void seq_stop(struct seq_file *s, void *v)
{

}

static int seq_show(struct seq_file *s, void *v)
{
    int ret;
    loff_t *pos = v;
    const struct nf_queue_handler *qh;

    rcu_read_lock();
    qh = rcu_dereference(queue_handler[*pos]);
    if (!qh)
        ret = seq_printf(s, "%2lld NONE\n", *pos);
    else
        ret = seq_printf(s, "%2lld %s\n", *pos, qh->name);
    rcu_read_unlock();

    return ret;
}

static const struct seq_operations nfqueue_seq_ops = {
    .start  = seq_start,
    .next   = seq_next,
    .stop   = seq_stop,
    .show   = seq_show,
};

static int nfqueue_open(struct inode *inode, struct file *file)
{
    return seq_open(file, &nfqueue_seq_ops);
}

static const struct file_operations nfqueue_file_ops = {
    .owner   = THIS_MODULE,
    .open    = nfqueue_open,
    .read    = seq_read,
    .llseek  = seq_lseek,
    .release = seq_release,
};
#endif /* PROC_FS */


int __init netfilter_queue_init(void)
{
#ifdef CONFIG_PROC_FS
    if (!proc_create("nf_queue", S_IRUGO,
             proc_net_netfilter, &nfqueue_file_ops))
        return -1;
#endif
    return 0;
}