net/netfilter/nf_conntrack_helper.c

   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/slab.h>
  19 #include <linux/random.h>
  20 #include <linux/err.h>
  21 #include <linux/kernel.h>
  22 #include <linux/netdevice.h>
  23
  24 #define ASSERT_READ_LOCK(x)
  25 #define ASSERT_WRITE_LOCK(x)
  26
  27 #include <net/netfilter/nf_conntrack.h>
  28 #include <net/netfilter/nf_conntrack_l3proto.h>
  29 #include <net/netfilter/nf_conntrack_l4proto.h>
  30 #include <net/netfilter/nf_conntrack_helper.h>
  31 #include <net/netfilter/nf_conntrack_core.h>
  32
  33 static __read_mostly LIST_HEAD(helpers);
  34
  35 struct nf_conntrack_helper *
  36 __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
  37 {
  38         struct nf_conntrack_helper *h;
  39
  40         list_for_each_entry(h, &helpers, list) {
  41                 if (nf_ct_tuple_mask_cmp(tuple, &h->tuple, &h->mask))
  42                         return h;
  43         }
  44         return NULL;
  45 }
  46
  47 struct nf_conntrack_helper *
  48 nf_ct_helper_find_get( const struct nf_conntrack_tuple *tuple)
  49 {
  50         struct nf_conntrack_helper *helper;
  51
  52         /* need nf_conntrack_lock to assure that helper exists until
  53          * try_module_get() is called */
  54         read_lock_bh(&nf_conntrack_lock);
  55
  56         helper = __nf_ct_helper_find(tuple);
  57         if (helper) {
  58                 /* need to increase module usage count to assure helper will
  59                  * not go away while the caller is e.g. busy putting a
  60                  * conntrack in the hash that uses the helper */
  61                 if (!try_module_get(helper->me))
  62                         helper = NULL;
  63         }
  64
  65         read_unlock_bh(&nf_conntrack_lock);
  66
  67         return helper;
  68 }
  69
  70 void nf_ct_helper_put(struct nf_conntrack_helper *helper)
  71 {
  72         module_put(helper->me);
  73 }
  74
  75 struct nf_conntrack_helper *
  76 __nf_conntrack_helper_find_byname(const char *name)
  77 {
  78         struct nf_conntrack_helper *h;
  79
  80         list_for_each_entry(h, &helpers, list) {
  81                 if (!strcmp(h->name, name))
  82                         return h;
  83         }
  84
  85         return NULL;
  86 }
  87
  88 static inline int unhelp(struct nf_conntrack_tuple_hash *i,
  89                          const struct nf_conntrack_helper *me)
  90 {
  91         struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
  92         struct nf_conn_help *help = nfct_help(ct);
  93
  94         if (help && help->helper == me) {
  95                 nf_conntrack_event(IPCT_HELPER, ct);
  96                 help->helper = NULL;
  97         }
  98         return 0;
  99 }
 100
 101 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 102 {
 103         int ret;
 104         BUG_ON(me->timeout == 0);
 105
 106         ret = nf_conntrack_register_cache(NF_CT_F_HELP, "nf_conntrack:help",
 107                                           sizeof(struct nf_conn)
 108                                           + sizeof(struct nf_conn_help)
 109                                           + __alignof__(struct nf_conn_help));
 110         if (ret < 0) {
 111                 printk(KERN_ERR "nf_conntrack_helper_register: Unable to create slab cache for conntracks\n");
 112                 return ret;
 113         }
 114         write_lock_bh(&nf_conntrack_lock);
 115         list_add(&me->list, &helpers);
 116         write_unlock_bh(&nf_conntrack_lock);
 117
 118         return 0;
 119 }
 120
 121 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 122 {
 123         unsigned int i;
 124         struct nf_conntrack_tuple_hash *h;
 125         struct nf_conntrack_expect *exp, *tmp;
 126
 127         /* Need write lock here, to delete helper. */
 128         write_lock_bh(&nf_conntrack_lock);
 129         list_del(&me->list);
 130
 131         /* Get rid of expectations */
 132         list_for_each_entry_safe(exp, tmp, &nf_conntrack_expect_list, list) {
 133                 struct nf_conn_help *help = nfct_help(exp->master);
 134                 if (help->helper == me && del_timer(&exp->timeout)) {
 135                         nf_ct_unlink_expect(exp);
 136                         nf_conntrack_expect_put(exp);
 137                 }
 138         }
 139
 140         /* Get rid of expecteds, set helpers to NULL. */
 141         list_for_each_entry(h, &unconfirmed, list)
 142                 unhelp(h, me);
 143         for (i = 0; i < nf_conntrack_htable_size; i++) {
 144                 list_for_each_entry(h, &nf_conntrack_hash[i], list)
 145                         unhelp(h, me);
 146         }
 147         write_unlock_bh(&nf_conntrack_lock);
 148
 149         /* Someone could be still looking at the helper in a bh. */
 150         synchronize_net();
 151 }