nf_conntrack_extend.c

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/* Structure dynamic extension infrastructure
 * Copyright (C) 2004 Rusty Russell IBM Corporation
 * Copyright (C) 2007 Netfilter Core Team <[email protected]>
 * Copyright (C) 2007 USAGI/WIDE Project <http://www.linux-ipv6.org>
 *
 *      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.
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/rcupdate.h>
#include <linux/slab.h>
#include <linux/skbuff.h>
#include <net/netfilter/nf_conntrack_extend.h>

static struct nf_ct_ext_type __rcu *nf_ct_ext_types[NF_CT_EXT_NUM];
static DEFINE_MUTEX(nf_ct_ext_type_mutex);

void __nf_ct_ext_destroy(struct nf_conn *ct)
{
    unsigned int i;
    struct nf_ct_ext_type *t;
    struct nf_ct_ext *ext = ct->ext;

    for (i = 0; i < NF_CT_EXT_NUM; i++) {
        if (!__nf_ct_ext_exist(ext, i))
            continue;

        rcu_read_lock();
        t = rcu_dereference(nf_ct_ext_types[i]);

        /* Here the nf_ct_ext_type might have been unregisterd.
         * I.e., it has responsible to cleanup private
         * area in all conntracks when it is unregisterd.
         */
        if (t && t->destroy)
            t->destroy(ct);
        rcu_read_unlock();
    }
}
EXPORT_SYMBOL(__nf_ct_ext_destroy);

static void *
nf_ct_ext_create(struct nf_ct_ext **ext, enum nf_ct_ext_id id,
         size_t var_alloc_len, gfp_t gfp)
{
    unsigned int off, len;
    struct nf_ct_ext_type *t;
    size_t alloc_size;

    rcu_read_lock();
    t = rcu_dereference(nf_ct_ext_types[id]);
    BUG_ON(t == NULL);
    off = ALIGN(sizeof(struct nf_ct_ext), t->align);
    len = off + t->len + var_alloc_len;
    alloc_size = t->alloc_size + var_alloc_len;
    rcu_read_unlock();

    *ext = kzalloc(alloc_size, gfp);
    if (!*ext)
        return NULL;

    (*ext)->offset[id] = off;
    (*ext)->len = len;

    return (void *)(*ext) + off;
}

void *__nf_ct_ext_add_length(struct nf_conn *ct, enum nf_ct_ext_id id,
                 size_t var_alloc_len, gfp_t gfp)
{
    struct nf_ct_ext *old, *new;
    int i, newlen, newoff;
    struct nf_ct_ext_type *t;

    /* Conntrack must not be confirmed to avoid races on reallocation. */
    NF_CT_ASSERT(!nf_ct_is_confirmed(ct));

    old = ct->ext;
    if (!old)
        return nf_ct_ext_create(&ct->ext, id, var_alloc_len, gfp);

    if (__nf_ct_ext_exist(old, id))
        return NULL;

    rcu_read_lock();
    t = rcu_dereference(nf_ct_ext_types[id]);
    BUG_ON(t == NULL);

    newoff = ALIGN(old->len, t->align);
    newlen = newoff + t->len + var_alloc_len;
    rcu_read_unlock();

    new = __krealloc(old, newlen, gfp);
    if (!new)
        return NULL;

    if (new != old) {
        for (i = 0; i < NF_CT_EXT_NUM; i++) {
            if (!__nf_ct_ext_exist(old, i))
                continue;

            rcu_read_lock();
            t = rcu_dereference(nf_ct_ext_types[i]);
            if (t && t->move)
                t->move((void *)new + new->offset[i],
                    (void *)old + old->offset[i]);
            rcu_read_unlock();
        }
        kfree_rcu(old, rcu);
        ct->ext = new;
    }

    new->offset[id] = newoff;
    new->len = newlen;
    memset((void *)new + newoff, 0, newlen - newoff);
    return (void *)new + newoff;
}
EXPORT_SYMBOL(__nf_ct_ext_add_length);

static void update_alloc_size(struct nf_ct_ext_type *type)
{
    int i, j;
    struct nf_ct_ext_type *t1, *t2;
    enum nf_ct_ext_id min = 0, max = NF_CT_EXT_NUM - 1;

    /* unnecessary to update all types */
    if ((type->flags & NF_CT_EXT_F_PREALLOC) == 0) {
        min = type->id;
        max = type->id;
    }

    /* This assumes that extended areas in conntrack for the types
       whose NF_CT_EXT_F_PREALLOC bit set are allocated in order */
    for (i = min; i <= max; i++) {
        t1 = rcu_dereference_protected(nf_ct_ext_types[i],
                lockdep_is_held(&nf_ct_ext_type_mutex));
        if (!t1)
            continue;

        t1->alloc_size = ALIGN(sizeof(struct nf_ct_ext), t1->align) +
                 t1->len;
        for (j = 0; j < NF_CT_EXT_NUM; j++) {
            t2 = rcu_dereference_protected(nf_ct_ext_types[j],
                lockdep_is_held(&nf_ct_ext_type_mutex));
            if (t2 == NULL || t2 == t1 ||
                (t2->flags & NF_CT_EXT_F_PREALLOC) == 0)
                continue;

            t1->alloc_size = ALIGN(t1->alloc_size, t2->align)
                     + t2->len;
        }
    }
}

/* This MUST be called in process context. */
int nf_ct_extend_register(struct nf_ct_ext_type *type)
{
    int ret = 0;

    mutex_lock(&nf_ct_ext_type_mutex);
    if (nf_ct_ext_types[type->id]) {
        ret = -EBUSY;
        goto out;
    }

    /* This ensures that nf_ct_ext_create() can allocate enough area
       before updating alloc_size */
    type->alloc_size = ALIGN(sizeof(struct nf_ct_ext), type->align)
               + type->len;
    rcu_assign_pointer(nf_ct_ext_types[type->id], type);
    update_alloc_size(type);
out:
    mutex_unlock(&nf_ct_ext_type_mutex);
    return ret;
}
EXPORT_SYMBOL_GPL(nf_ct_extend_register);

/* This MUST be called in process context. */
void nf_ct_extend_unregister(struct nf_ct_ext_type *type)
{
    mutex_lock(&nf_ct_ext_type_mutex);
    RCU_INIT_POINTER(nf_ct_ext_types[type->id], NULL);
    update_alloc_size(type);
    mutex_unlock(&nf_ct_ext_type_mutex);
    rcu_barrier(); /* Wait for completion of call_rcu()'s */
}
EXPORT_SYMBOL_GPL(nf_ct_extend_unregister);