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Linux/net/netfilter/xt_cluster.c

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  1 /*
  2  * (C) 2008-2009 Pablo Neira Ayuso <pablo@netfilter.org>
  3  *
  4  * This program is free software; you can redistribute it and/or modify
  5  * it under the terms of the GNU General Public License version 2 as
  6  * published by the Free Software Foundation.
  7  */
  8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  9 #include <linux/module.h>
 10 #include <linux/skbuff.h>
 11 #include <linux/jhash.h>
 12 #include <linux/ip.h>
 13 #include <net/ipv6.h>
 14 
 15 #include <linux/netfilter/x_tables.h>
 16 #include <net/netfilter/nf_conntrack.h>
 17 #include <linux/netfilter/xt_cluster.h>
 18 
 19 static inline u32 nf_ct_orig_ipv4_src(const struct nf_conn *ct)
 20 {
 21         return (__force u32)ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip;
 22 }
 23 
 24 static inline const u32 *nf_ct_orig_ipv6_src(const struct nf_conn *ct)
 25 {
 26         return (__force u32 *)ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip6;
 27 }
 28 
 29 static inline u_int32_t
 30 xt_cluster_hash_ipv4(u_int32_t ip, const struct xt_cluster_match_info *info)
 31 {
 32         return jhash_1word(ip, info->hash_seed);
 33 }
 34 
 35 static inline u_int32_t
 36 xt_cluster_hash_ipv6(const void *ip, const struct xt_cluster_match_info *info)
 37 {
 38         return jhash2(ip, NF_CT_TUPLE_L3SIZE / sizeof(__u32), info->hash_seed);
 39 }
 40 
 41 static inline u_int32_t
 42 xt_cluster_hash(const struct nf_conn *ct,
 43                 const struct xt_cluster_match_info *info)
 44 {
 45         u_int32_t hash = 0;
 46 
 47         switch(nf_ct_l3num(ct)) {
 48         case AF_INET:
 49                 hash = xt_cluster_hash_ipv4(nf_ct_orig_ipv4_src(ct), info);
 50                 break;
 51         case AF_INET6:
 52                 hash = xt_cluster_hash_ipv6(nf_ct_orig_ipv6_src(ct), info);
 53                 break;
 54         default:
 55                 WARN_ON(1);
 56                 break;
 57         }
 58 
 59         return reciprocal_scale(hash, info->total_nodes);
 60 }
 61 
 62 static inline bool
 63 xt_cluster_ipv6_is_multicast(const struct in6_addr *addr)
 64 {
 65         __be32 st = addr->s6_addr32[0];
 66         return ((st & htonl(0xFF000000)) == htonl(0xFF000000));
 67 }
 68 
 69 static inline bool
 70 xt_cluster_is_multicast_addr(const struct sk_buff *skb, u_int8_t family)
 71 {
 72         bool is_multicast = false;
 73 
 74         switch(family) {
 75         case NFPROTO_IPV4:
 76                 is_multicast = ipv4_is_multicast(ip_hdr(skb)->daddr);
 77                 break;
 78         case NFPROTO_IPV6:
 79                 is_multicast =
 80                         xt_cluster_ipv6_is_multicast(&ipv6_hdr(skb)->daddr);
 81                 break;
 82         default:
 83                 WARN_ON(1);
 84                 break;
 85         }
 86         return is_multicast;
 87 }
 88 
 89 static bool
 90 xt_cluster_mt(const struct sk_buff *skb, struct xt_action_param *par)
 91 {
 92         struct sk_buff *pskb = (struct sk_buff *)skb;
 93         const struct xt_cluster_match_info *info = par->matchinfo;
 94         const struct nf_conn *ct;
 95         enum ip_conntrack_info ctinfo;
 96         unsigned long hash;
 97 
 98         /* This match assumes that all nodes see the same packets. This can be
 99          * achieved if the switch that connects the cluster nodes support some
100          * sort of 'port mirroring'. However, if your switch does not support
101          * this, your cluster nodes can reply ARP request using a multicast MAC
102          * address. Thus, your switch will flood the same packets to the
103          * cluster nodes with the same multicast MAC address. Using a multicast
104          * link address is a RFC 1812 (section 3.3.2) violation, but this works
105          * fine in practise.
106          *
107          * Unfortunately, if you use the multicast MAC address, the link layer
108          * sets skbuff's pkt_type to PACKET_MULTICAST, which is not accepted
109          * by TCP and others for packets coming to this node. For that reason,
110          * this match mangles skbuff's pkt_type if it detects a packet
111          * addressed to a unicast address but using PACKET_MULTICAST. Yes, I
112          * know, matches should not alter packets, but we are doing this here
113          * because we would need to add a PKTTYPE target for this sole purpose.
114          */
115         if (!xt_cluster_is_multicast_addr(skb, par->family) &&
116             skb->pkt_type == PACKET_MULTICAST) {
117                 pskb->pkt_type = PACKET_HOST;
118         }
119 
120         ct = nf_ct_get(skb, &ctinfo);
121         if (ct == NULL)
122                 return false;
123 
124         if (nf_ct_is_untracked(ct))
125                 return false;
126 
127         if (ct->master)
128                 hash = xt_cluster_hash(ct->master, info);
129         else
130                 hash = xt_cluster_hash(ct, info);
131 
132         return !!((1 << hash) & info->node_mask) ^
133                !!(info->flags & XT_CLUSTER_F_INV);
134 }
135 
136 static int xt_cluster_mt_checkentry(const struct xt_mtchk_param *par)
137 {
138         struct xt_cluster_match_info *info = par->matchinfo;
139 
140         if (info->total_nodes > XT_CLUSTER_NODES_MAX) {
141                 pr_info("you have exceeded the maximum "
142                         "number of cluster nodes (%u > %u)\n",
143                         info->total_nodes, XT_CLUSTER_NODES_MAX);
144                 return -EINVAL;
145         }
146         if (info->node_mask >= (1ULL << info->total_nodes)) {
147                 pr_info("this node mask cannot be "
148                         "higher than the total number of nodes\n");
149                 return -EDOM;
150         }
151         return 0;
152 }
153 
154 static struct xt_match xt_cluster_match __read_mostly = {
155         .name           = "cluster",
156         .family         = NFPROTO_UNSPEC,
157         .match          = xt_cluster_mt,
158         .checkentry     = xt_cluster_mt_checkentry,
159         .matchsize      = sizeof(struct xt_cluster_match_info),
160         .me             = THIS_MODULE,
161 };
162 
163 static int __init xt_cluster_mt_init(void)
164 {
165         return xt_register_match(&xt_cluster_match);
166 }
167 
168 static void __exit xt_cluster_mt_fini(void)
169 {
170         xt_unregister_match(&xt_cluster_match);
171 }
172 
173 MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
174 MODULE_LICENSE("GPL");
175 MODULE_DESCRIPTION("Xtables: hash-based cluster match");
176 MODULE_ALIAS("ipt_cluster");
177 MODULE_ALIAS("ip6t_cluster");
178 module_init(xt_cluster_mt_init);
179 module_exit(xt_cluster_mt_fini);
180 

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