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Linux/net/netfilter/xt_cluster.c

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  1 // SPDX-License-Identifier: GPL-2.0-only
  2 /*
  3  * (C) 2008-2009 Pablo Neira Ayuso <pablo@netfilter.org>
  4  */
  5 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  6 #include <linux/module.h>
  7 #include <linux/skbuff.h>
  8 #include <linux/jhash.h>
  9 #include <linux/ip.h>
 10 #include <net/ipv6.h>
 11 
 12 #include <linux/netfilter/x_tables.h>
 13 #include <net/netfilter/nf_conntrack.h>
 14 #include <linux/netfilter/xt_cluster.h>
 15 
 16 static inline u32 nf_ct_orig_ipv4_src(const struct nf_conn *ct)
 17 {
 18         return (__force u32)ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip;
 19 }
 20 
 21 static inline const u32 *nf_ct_orig_ipv6_src(const struct nf_conn *ct)
 22 {
 23         return (__force u32 *)ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip6;
 24 }
 25 
 26 static inline u_int32_t
 27 xt_cluster_hash_ipv4(u_int32_t ip, const struct xt_cluster_match_info *info)
 28 {
 29         return jhash_1word(ip, info->hash_seed);
 30 }
 31 
 32 static inline u_int32_t
 33 xt_cluster_hash_ipv6(const void *ip, const struct xt_cluster_match_info *info)
 34 {
 35         return jhash2(ip, NF_CT_TUPLE_L3SIZE / sizeof(__u32), info->hash_seed);
 36 }
 37 
 38 static inline u_int32_t
 39 xt_cluster_hash(const struct nf_conn *ct,
 40                 const struct xt_cluster_match_info *info)
 41 {
 42         u_int32_t hash = 0;
 43 
 44         switch(nf_ct_l3num(ct)) {
 45         case AF_INET:
 46                 hash = xt_cluster_hash_ipv4(nf_ct_orig_ipv4_src(ct), info);
 47                 break;
 48         case AF_INET6:
 49                 hash = xt_cluster_hash_ipv6(nf_ct_orig_ipv6_src(ct), info);
 50                 break;
 51         default:
 52                 WARN_ON(1);
 53                 break;
 54         }
 55 
 56         return reciprocal_scale(hash, info->total_nodes);
 57 }
 58 
 59 static inline bool
 60 xt_cluster_is_multicast_addr(const struct sk_buff *skb, u_int8_t family)
 61 {
 62         bool is_multicast = false;
 63 
 64         switch(family) {
 65         case NFPROTO_IPV4:
 66                 is_multicast = ipv4_is_multicast(ip_hdr(skb)->daddr);
 67                 break;
 68         case NFPROTO_IPV6:
 69                 is_multicast = ipv6_addr_is_multicast(&ipv6_hdr(skb)->daddr);
 70                 break;
 71         default:
 72                 WARN_ON(1);
 73                 break;
 74         }
 75         return is_multicast;
 76 }
 77 
 78 static bool
 79 xt_cluster_mt(const struct sk_buff *skb, struct xt_action_param *par)
 80 {
 81         struct sk_buff *pskb = (struct sk_buff *)skb;
 82         const struct xt_cluster_match_info *info = par->matchinfo;
 83         const struct nf_conn *ct;
 84         enum ip_conntrack_info ctinfo;
 85         unsigned long hash;
 86 
 87         /* This match assumes that all nodes see the same packets. This can be
 88          * achieved if the switch that connects the cluster nodes support some
 89          * sort of 'port mirroring'. However, if your switch does not support
 90          * this, your cluster nodes can reply ARP request using a multicast MAC
 91          * address. Thus, your switch will flood the same packets to the
 92          * cluster nodes with the same multicast MAC address. Using a multicast
 93          * link address is a RFC 1812 (section 3.3.2) violation, but this works
 94          * fine in practise.
 95          *
 96          * Unfortunately, if you use the multicast MAC address, the link layer
 97          * sets skbuff's pkt_type to PACKET_MULTICAST, which is not accepted
 98          * by TCP and others for packets coming to this node. For that reason,
 99          * this match mangles skbuff's pkt_type if it detects a packet
100          * addressed to a unicast address but using PACKET_MULTICAST. Yes, I
101          * know, matches should not alter packets, but we are doing this here
102          * because we would need to add a PKTTYPE target for this sole purpose.
103          */
104         if (!xt_cluster_is_multicast_addr(skb, xt_family(par)) &&
105             skb->pkt_type == PACKET_MULTICAST) {
106                 pskb->pkt_type = PACKET_HOST;
107         }
108 
109         ct = nf_ct_get(skb, &ctinfo);
110         if (ct == NULL)
111                 return false;
112 
113         if (ct->master)
114                 hash = xt_cluster_hash(ct->master, info);
115         else
116                 hash = xt_cluster_hash(ct, info);
117 
118         return !!((1 << hash) & info->node_mask) ^
119                !!(info->flags & XT_CLUSTER_F_INV);
120 }
121 
122 static int xt_cluster_mt_checkentry(const struct xt_mtchk_param *par)
123 {
124         struct xt_cluster_match_info *info = par->matchinfo;
125         int ret;
126 
127         if (info->total_nodes > XT_CLUSTER_NODES_MAX) {
128                 pr_info_ratelimited("you have exceeded the maximum number of cluster nodes (%u > %u)\n",
129                                     info->total_nodes, XT_CLUSTER_NODES_MAX);
130                 return -EINVAL;
131         }
132         if (info->node_mask >= (1ULL << info->total_nodes)) {
133                 pr_info_ratelimited("node mask cannot exceed total number of nodes\n");
134                 return -EDOM;
135         }
136 
137         ret = nf_ct_netns_get(par->net, par->family);
138         if (ret < 0)
139                 pr_info_ratelimited("cannot load conntrack support for proto=%u\n",
140                                     par->family);
141         return ret;
142 }
143 
144 static void xt_cluster_mt_destroy(const struct xt_mtdtor_param *par)
145 {
146         nf_ct_netns_put(par->net, par->family);
147 }
148 
149 static struct xt_match xt_cluster_match __read_mostly = {
150         .name           = "cluster",
151         .family         = NFPROTO_UNSPEC,
152         .match          = xt_cluster_mt,
153         .checkentry     = xt_cluster_mt_checkentry,
154         .matchsize      = sizeof(struct xt_cluster_match_info),
155         .destroy        = xt_cluster_mt_destroy,
156         .me             = THIS_MODULE,
157 };
158 
159 static int __init xt_cluster_mt_init(void)
160 {
161         return xt_register_match(&xt_cluster_match);
162 }
163 
164 static void __exit xt_cluster_mt_fini(void)
165 {
166         xt_unregister_match(&xt_cluster_match);
167 }
168 
169 MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
170 MODULE_LICENSE("GPL");
171 MODULE_DESCRIPTION("Xtables: hash-based cluster match");
172 MODULE_ALIAS("ipt_cluster");
173 MODULE_ALIAS("ip6t_cluster");
174 module_init(xt_cluster_mt_init);
175 module_exit(xt_cluster_mt_fini);
176 

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