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