nf_conntrack_helper.c

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/* Helper handling for netfilter. */

/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2006 Netfilter Core Team <[email protected]>
 * (C) 2003,2004 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 version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/types.h>
#include <linux/netfilter.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/vmalloc.h>
#include <linux/stddef.h>
#include <linux/random.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/netdevice.h>
#include <linux/rculist.h>
#include <linux/rtnetlink.h>

#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_l3proto.h>
#include <net/netfilter/nf_conntrack_l4proto.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_core.h>
#include <net/netfilter/nf_conntrack_extend.h>

static DEFINE_MUTEX(nf_ct_helper_mutex);
struct hlist_head *nf_ct_helper_hash __read_mostly;
EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
unsigned int nf_ct_helper_hsize __read_mostly;
EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
static unsigned int nf_ct_helper_count __read_mostly;

static bool nf_ct_auto_assign_helper __read_mostly = true;
module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
MODULE_PARM_DESC(nf_conntrack_helper,
         "Enable automatic conntrack helper assignment (default 1)");

#ifdef CONFIG_SYSCTL
static struct ctl_table helper_sysctl_table[] = {
    {
        .procname   = "nf_conntrack_helper",
        .data       = &init_net.ct.sysctl_auto_assign_helper,
        .maxlen     = sizeof(unsigned int),
        .mode       = 0644,
        .proc_handler   = proc_dointvec,
    },
    {}
};

static int nf_conntrack_helper_init_sysctl(struct net *net)
{
    struct ctl_table *table;

    table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
            GFP_KERNEL);
    if (!table)
        goto out;

    table[0].data = &net->ct.sysctl_auto_assign_helper;

    net->ct.helper_sysctl_header =
        register_net_sysctl(net, "net/netfilter", table);

    if (!net->ct.helper_sysctl_header) {
        pr_err("nf_conntrack_helper: can't register to sysctl.\n");
        goto out_register;
    }
    return 0;

out_register:
    kfree(table);
out:
    return -ENOMEM;
}

static void nf_conntrack_helper_fini_sysctl(struct net *net)
{
    struct ctl_table *table;

    table = net->ct.helper_sysctl_header->ctl_table_arg;
    unregister_net_sysctl_table(net->ct.helper_sysctl_header);
    kfree(table);
}
#else
static int nf_conntrack_helper_init_sysctl(struct net *net)
{
    return 0;
}

static void nf_conntrack_helper_fini_sysctl(struct net *net)
{
}
#endif /* CONFIG_SYSCTL */

/* Stupid hash, but collision free for the default registrations of the
 * helpers currently in the kernel. */
static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
{
    return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
        (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
}

static struct nf_conntrack_helper *
__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
{
    struct nf_conntrack_helper *helper;
    struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
    struct hlist_node *n;
    unsigned int h;

    if (!nf_ct_helper_count)
        return NULL;

    h = helper_hash(tuple);
    hlist_for_each_entry_rcu(helper, n, &nf_ct_helper_hash[h], hnode) {
        if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
            return helper;
    }
    return NULL;
}

struct nf_conntrack_helper *
__nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
{
    struct nf_conntrack_helper *h;
    struct hlist_node *n;
    unsigned int i;

    for (i = 0; i < nf_ct_helper_hsize; i++) {
        hlist_for_each_entry_rcu(h, n, &nf_ct_helper_hash[i], hnode) {
            if (!strcmp(h->name, name) &&
                h->tuple.src.l3num == l3num &&
                h->tuple.dst.protonum == protonum)
                return h;
        }
    }
    return NULL;
}
EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);

struct nf_conntrack_helper *
nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
{
    struct nf_conntrack_helper *h;

    h = __nf_conntrack_helper_find(name, l3num, protonum);
#ifdef CONFIG_MODULES
    if (h == NULL) {
        if (request_module("nfct-helper-%s", name) == 0)
            h = __nf_conntrack_helper_find(name, l3num, protonum);
    }
#endif
    if (h != NULL && !try_module_get(h->me))
        h = NULL;

    return h;
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);

struct nf_conn_help *
nf_ct_helper_ext_add(struct nf_conn *ct,
             struct nf_conntrack_helper *helper, gfp_t gfp)
{
    struct nf_conn_help *help;

    help = nf_ct_ext_add_length(ct, NF_CT_EXT_HELPER,
                    helper->data_len, gfp);
    if (help)
        INIT_HLIST_HEAD(&help->expectations);
    else
        pr_debug("failed to add helper extension area");
    return help;
}
EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);

int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
                  gfp_t flags)
{
    struct nf_conntrack_helper *helper = NULL;
    struct nf_conn_help *help;
    struct net *net = nf_ct_net(ct);
    int ret = 0;

    /* We already got a helper explicitly attached. The function
     * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
     * the helper up again. Since now the user is in full control of
     * making consistent helper configurations, skip this automatic
     * re-lookup, otherwise we'll lose the helper.
     */
    if (test_bit(IPS_HELPER_BIT, &ct->status))
        return 0;

    if (tmpl != NULL) {
        help = nfct_help(tmpl);
        if (help != NULL) {
            helper = help->helper;
            set_bit(IPS_HELPER_BIT, &ct->status);
        }
    }

    help = nfct_help(ct);
    if (net->ct.sysctl_auto_assign_helper && helper == NULL) {
        helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
        if (unlikely(!net->ct.auto_assign_helper_warned && helper)) {
            pr_info("nf_conntrack: automatic helper "
                "assignment is deprecated and it will "
                "be removed soon. Use the iptables CT target "
                "to attach helpers instead.\n");
            net->ct.auto_assign_helper_warned = true;
        }
    }

    if (helper == NULL) {
        if (help)
            RCU_INIT_POINTER(help->helper, NULL);
        goto out;
    }

    if (help == NULL) {
        help = nf_ct_helper_ext_add(ct, helper, flags);
        if (help == NULL) {
            ret = -ENOMEM;
            goto out;
        }
    } else {
        /* We only allow helper re-assignment of the same sort since
         * we cannot reallocate the helper extension area.
         */
        if (help->helper != helper) {
            RCU_INIT_POINTER(help->helper, NULL);
            goto out;
        }
    }

    rcu_assign_pointer(help->helper, helper);
out:
    return ret;
}
EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);

static inline int unhelp(struct nf_conntrack_tuple_hash *i,
             const struct nf_conntrack_helper *me)
{
    struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
    struct nf_conn_help *help = nfct_help(ct);

    if (help && rcu_dereference_protected(
            help->helper,
            lockdep_is_held(&nf_conntrack_lock)
            ) == me) {
        nf_conntrack_event(IPCT_HELPER, ct);
        RCU_INIT_POINTER(help->helper, NULL);
    }
    return 0;
}

void nf_ct_helper_destroy(struct nf_conn *ct)
{
    struct nf_conn_help *help = nfct_help(ct);
    struct nf_conntrack_helper *helper;

    if (help) {
        rcu_read_lock();
        helper = rcu_dereference(help->helper);
        if (helper && helper->destroy)
            helper->destroy(ct);
        rcu_read_unlock();
    }
}

static LIST_HEAD(nf_ct_helper_expectfn_list);

void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
{
    spin_lock_bh(&nf_conntrack_lock);
    list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
    spin_unlock_bh(&nf_conntrack_lock);
}
EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);

void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
{
    spin_lock_bh(&nf_conntrack_lock);
    list_del_rcu(&n->head);
    spin_unlock_bh(&nf_conntrack_lock);
}
EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);

struct nf_ct_helper_expectfn *
nf_ct_helper_expectfn_find_by_name(const char *name)
{
    struct nf_ct_helper_expectfn *cur;
    bool found = false;

    rcu_read_lock();
    list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
        if (!strcmp(cur->name, name)) {
            found = true;
            break;
        }
    }
    rcu_read_unlock();
    return found ? cur : NULL;
}
EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);

struct nf_ct_helper_expectfn *
nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
{
    struct nf_ct_helper_expectfn *cur;
    bool found = false;

    rcu_read_lock();
    list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
        if (cur->expectfn == symbol) {
            found = true;
            break;
        }
    }
    rcu_read_unlock();
    return found ? cur : NULL;
}
EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);

int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
{
    int ret = 0;
    struct nf_conntrack_helper *cur;
    struct hlist_node *n;
    unsigned int h = helper_hash(&me->tuple);

    BUG_ON(me->expect_policy == NULL);
    BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
    BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);

    mutex_lock(&nf_ct_helper_mutex);
    hlist_for_each_entry(cur, n, &nf_ct_helper_hash[h], hnode) {
        if (strncmp(cur->name, me->name, NF_CT_HELPER_NAME_LEN) == 0 &&
            cur->tuple.src.l3num == me->tuple.src.l3num &&
            cur->tuple.dst.protonum == me->tuple.dst.protonum) {
            ret = -EEXIST;
            goto out;
        }
    }
    hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
    nf_ct_helper_count++;
out:
    mutex_unlock(&nf_ct_helper_mutex);
    return ret;
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);

static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
                         struct net *net)
{
    struct nf_conntrack_tuple_hash *h;
    struct nf_conntrack_expect *exp;
    const struct hlist_node *n, *next;
    const struct hlist_nulls_node *nn;
    unsigned int i;

    /* Get rid of expectations */
    for (i = 0; i < nf_ct_expect_hsize; i++) {
        hlist_for_each_entry_safe(exp, n, next,
                      &net->ct.expect_hash[i], hnode) {
            struct nf_conn_help *help = nfct_help(exp->master);
            if ((rcu_dereference_protected(
                    help->helper,
                    lockdep_is_held(&nf_conntrack_lock)
                    ) == me || exp->helper == me) &&
                del_timer(&exp->timeout)) {
                nf_ct_unlink_expect(exp);
                nf_ct_expect_put(exp);
            }
        }
    }

    /* Get rid of expecteds, set helpers to NULL. */
    hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
        unhelp(h, me);
    for (i = 0; i < net->ct.htable_size; i++) {
        hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
            unhelp(h, me);
    }
}

void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
{
    struct net *net;

    mutex_lock(&nf_ct_helper_mutex);
    hlist_del_rcu(&me->hnode);
    nf_ct_helper_count--;
    mutex_unlock(&nf_ct_helper_mutex);

    /* Make sure every nothing is still using the helper unless its a
     * connection in the hash.
     */
    synchronize_rcu();

    rtnl_lock();
    spin_lock_bh(&nf_conntrack_lock);
    for_each_net(net)
        __nf_conntrack_helper_unregister(me, net);
    spin_unlock_bh(&nf_conntrack_lock);
    rtnl_unlock();
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);

static struct nf_ct_ext_type helper_extend __read_mostly = {
    .len    = sizeof(struct nf_conn_help),
    .align  = __alignof__(struct nf_conn_help),
    .id = NF_CT_EXT_HELPER,
};

int nf_conntrack_helper_init(struct net *net)
{
    int err;

    net->ct.auto_assign_helper_warned = false;
    net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;

    if (net_eq(net, &init_net)) {
        nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
        nf_ct_helper_hash =
            nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
        if (!nf_ct_helper_hash)
            return -ENOMEM;

        err = nf_ct_extend_register(&helper_extend);
        if (err < 0)
            goto err1;
    }

    err = nf_conntrack_helper_init_sysctl(net);
    if (err < 0)
        goto out_sysctl;

    return 0;

out_sysctl:
    if (net_eq(net, &init_net))
        nf_ct_extend_unregister(&helper_extend);
err1:
    nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
    return err;
}

void nf_conntrack_helper_fini(struct net *net)
{
    nf_conntrack_helper_fini_sysctl(net);
    if (net_eq(net, &init_net)) {
        nf_ct_extend_unregister(&helper_extend);
        nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
    }
}