linux/net/netfilter/nf_conntrack_helper.c
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   1/* Helper handling for netfilter. */
   2
   3/* (C) 1999-2001 Paul `Rusty' Russell
   4 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
   5 * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
   6 *
   7 * This program is free software; you can redistribute it and/or modify
   8 * it under the terms of the GNU General Public License version 2 as
   9 * published by the Free Software Foundation.
  10 */
  11
  12#include <linux/types.h>
  13#include <linux/netfilter.h>
  14#include <linux/module.h>
  15#include <linux/skbuff.h>
  16#include <linux/vmalloc.h>
  17#include <linux/stddef.h>
  18#include <linux/random.h>
  19#include <linux/err.h>
  20#include <linux/kernel.h>
  21#include <linux/netdevice.h>
  22#include <linux/rculist.h>
  23#include <linux/rtnetlink.h>
  24
  25#include <net/netfilter/nf_conntrack.h>
  26#include <net/netfilter/nf_conntrack_l3proto.h>
  27#include <net/netfilter/nf_conntrack_l4proto.h>
  28#include <net/netfilter/nf_conntrack_helper.h>
  29#include <net/netfilter/nf_conntrack_core.h>
  30#include <net/netfilter/nf_conntrack_extend.h>
  31
  32static DEFINE_MUTEX(nf_ct_helper_mutex);
  33static struct hlist_head *nf_ct_helper_hash __read_mostly;
  34static unsigned int nf_ct_helper_hsize __read_mostly;
  35static unsigned int nf_ct_helper_count __read_mostly;
  36
  37
  38/* Stupid hash, but collision free for the default registrations of the
  39 * helpers currently in the kernel. */
  40static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
  41{
  42        return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
  43                (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
  44}
  45
  46static struct nf_conntrack_helper *
  47__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
  48{
  49        struct nf_conntrack_helper *helper;
  50        struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
  51        struct hlist_node *n;
  52        unsigned int h;
  53
  54        if (!nf_ct_helper_count)
  55                return NULL;
  56
  57        h = helper_hash(tuple);
  58        hlist_for_each_entry_rcu(helper, n, &nf_ct_helper_hash[h], hnode) {
  59                if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
  60                        return helper;
  61        }
  62        return NULL;
  63}
  64
  65struct nf_conntrack_helper *
  66__nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
  67{
  68        struct nf_conntrack_helper *h;
  69        struct hlist_node *n;
  70        unsigned int i;
  71
  72        for (i = 0; i < nf_ct_helper_hsize; i++) {
  73                hlist_for_each_entry_rcu(h, n, &nf_ct_helper_hash[i], hnode) {
  74                        if (!strcmp(h->name, name) &&
  75                            h->tuple.src.l3num == l3num &&
  76                            h->tuple.dst.protonum == protonum)
  77                                return h;
  78                }
  79        }
  80        return NULL;
  81}
  82EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
  83
  84struct nf_conntrack_helper *
  85nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
  86{
  87        struct nf_conntrack_helper *h;
  88
  89        h = __nf_conntrack_helper_find(name, l3num, protonum);
  90#ifdef CONFIG_MODULES
  91        if (h == NULL) {
  92                if (request_module("nfct-helper-%s", name) == 0)
  93                        h = __nf_conntrack_helper_find(name, l3num, protonum);
  94        }
  95#endif
  96        if (h != NULL && !try_module_get(h->me))
  97                h = NULL;
  98
  99        return h;
 100}
 101EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 102
 103struct nf_conn_help *nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
 104{
 105        struct nf_conn_help *help;
 106
 107        help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
 108        if (help)
 109                INIT_HLIST_HEAD(&help->expectations);
 110        else
 111                pr_debug("failed to add helper extension area");
 112        return help;
 113}
 114EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 115
 116int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 117                              gfp_t flags)
 118{
 119        struct nf_conntrack_helper *helper = NULL;
 120        struct nf_conn_help *help;
 121        int ret = 0;
 122
 123        if (tmpl != NULL) {
 124                help = nfct_help(tmpl);
 125                if (help != NULL)
 126                        helper = help->helper;
 127        }
 128
 129        help = nfct_help(ct);
 130        if (helper == NULL)
 131                helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 132        if (helper == NULL) {
 133                if (help)
 134                        RCU_INIT_POINTER(help->helper, NULL);
 135                goto out;
 136        }
 137
 138        if (help == NULL) {
 139                help = nf_ct_helper_ext_add(ct, flags);
 140                if (help == NULL) {
 141                        ret = -ENOMEM;
 142                        goto out;
 143                }
 144        } else {
 145                memset(&help->help, 0, sizeof(help->help));
 146        }
 147
 148        rcu_assign_pointer(help->helper, helper);
 149out:
 150        return ret;
 151}
 152EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 153
 154static inline int unhelp(struct nf_conntrack_tuple_hash *i,
 155                         const struct nf_conntrack_helper *me)
 156{
 157        struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
 158        struct nf_conn_help *help = nfct_help(ct);
 159
 160        if (help && rcu_dereference_protected(
 161                        help->helper,
 162                        lockdep_is_held(&nf_conntrack_lock)
 163                        ) == me) {
 164                nf_conntrack_event(IPCT_HELPER, ct);
 165                RCU_INIT_POINTER(help->helper, NULL);
 166        }
 167        return 0;
 168}
 169
 170void nf_ct_helper_destroy(struct nf_conn *ct)
 171{
 172        struct nf_conn_help *help = nfct_help(ct);
 173        struct nf_conntrack_helper *helper;
 174
 175        if (help) {
 176                rcu_read_lock();
 177                helper = rcu_dereference(help->helper);
 178                if (helper && helper->destroy)
 179                        helper->destroy(ct);
 180                rcu_read_unlock();
 181        }
 182}
 183
 184int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 185{
 186        unsigned int h = helper_hash(&me->tuple);
 187
 188        BUG_ON(me->expect_policy == NULL);
 189        BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 190        BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 191
 192        mutex_lock(&nf_ct_helper_mutex);
 193        hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 194        nf_ct_helper_count++;
 195        mutex_unlock(&nf_ct_helper_mutex);
 196
 197        return 0;
 198}
 199EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 200
 201static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
 202                                             struct net *net)
 203{
 204        struct nf_conntrack_tuple_hash *h;
 205        struct nf_conntrack_expect *exp;
 206        const struct hlist_node *n, *next;
 207        const struct hlist_nulls_node *nn;
 208        unsigned int i;
 209
 210        /* Get rid of expectations */
 211        for (i = 0; i < nf_ct_expect_hsize; i++) {
 212                hlist_for_each_entry_safe(exp, n, next,
 213                                          &net->ct.expect_hash[i], hnode) {
 214                        struct nf_conn_help *help = nfct_help(exp->master);
 215                        if ((rcu_dereference_protected(
 216                                        help->helper,
 217                                        lockdep_is_held(&nf_conntrack_lock)
 218                                        ) == me || exp->helper == me) &&
 219                            del_timer(&exp->timeout)) {
 220                                nf_ct_unlink_expect(exp);
 221                                nf_ct_expect_put(exp);
 222                        }
 223                }
 224        }
 225
 226        /* Get rid of expecteds, set helpers to NULL. */
 227        hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
 228                unhelp(h, me);
 229        for (i = 0; i < net->ct.htable_size; i++) {
 230                hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
 231                        unhelp(h, me);
 232        }
 233}
 234
 235void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 236{
 237        struct net *net;
 238
 239        mutex_lock(&nf_ct_helper_mutex);
 240        hlist_del_rcu(&me->hnode);
 241        nf_ct_helper_count--;
 242        mutex_unlock(&nf_ct_helper_mutex);
 243
 244        /* Make sure every nothing is still using the helper unless its a
 245         * connection in the hash.
 246         */
 247        synchronize_rcu();
 248
 249        rtnl_lock();
 250        spin_lock_bh(&nf_conntrack_lock);
 251        for_each_net(net)
 252                __nf_conntrack_helper_unregister(me, net);
 253        spin_unlock_bh(&nf_conntrack_lock);
 254        rtnl_unlock();
 255}
 256EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 257
 258static struct nf_ct_ext_type helper_extend __read_mostly = {
 259        .len    = sizeof(struct nf_conn_help),
 260        .align  = __alignof__(struct nf_conn_help),
 261        .id     = NF_CT_EXT_HELPER,
 262};
 263
 264int nf_conntrack_helper_init(void)
 265{
 266        int err;
 267
 268        nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 269        nf_ct_helper_hash = nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 270        if (!nf_ct_helper_hash)
 271                return -ENOMEM;
 272
 273        err = nf_ct_extend_register(&helper_extend);
 274        if (err < 0)
 275                goto err1;
 276
 277        return 0;
 278
 279err1:
 280        nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 281        return err;
 282}
 283
 284void nf_conntrack_helper_fini(void)
 285{
 286        nf_ct_extend_unregister(&helper_extend);
 287        nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 288}
 289
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