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Linux/net/ipv4/netfilter.c

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  1 /*
  2  * IPv4 specific functions of netfilter core
  3  *
  4  * Rusty Russell (C) 2000 -- This code is GPL.
  5  * Patrick McHardy (C) 2006-2012
  6  */
  7 #include <linux/kernel.h>
  8 #include <linux/netfilter.h>
  9 #include <linux/netfilter_ipv4.h>
 10 #include <linux/ip.h>
 11 #include <linux/skbuff.h>
 12 #include <linux/gfp.h>
 13 #include <linux/export.h>
 14 #include <net/route.h>
 15 #include <net/xfrm.h>
 16 #include <net/ip.h>
 17 #include <net/netfilter/nf_queue.h>
 18 
 19 /* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
 20 int ip_route_me_harder(struct sk_buff *skb, unsigned int addr_type)
 21 {
 22         struct net *net = dev_net(skb_dst(skb)->dev);
 23         const struct iphdr *iph = ip_hdr(skb);
 24         struct rtable *rt;
 25         struct flowi4 fl4 = {};
 26         __be32 saddr = iph->saddr;
 27         __u8 flags = skb->sk ? inet_sk_flowi_flags(skb->sk) : 0;
 28         unsigned int hh_len;
 29 
 30         if (addr_type == RTN_UNSPEC)
 31                 addr_type = inet_addr_type(net, saddr);
 32         if (addr_type == RTN_LOCAL || addr_type == RTN_UNICAST)
 33                 flags |= FLOWI_FLAG_ANYSRC;
 34         else
 35                 saddr = 0;
 36 
 37         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
 38          * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
 39          */
 40         fl4.daddr = iph->daddr;
 41         fl4.saddr = saddr;
 42         fl4.flowi4_tos = RT_TOS(iph->tos);
 43         fl4.flowi4_oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
 44         fl4.flowi4_mark = skb->mark;
 45         fl4.flowi4_flags = flags;
 46         rt = ip_route_output_key(net, &fl4);
 47         if (IS_ERR(rt))
 48                 return PTR_ERR(rt);
 49 
 50         /* Drop old route. */
 51         skb_dst_drop(skb);
 52         skb_dst_set(skb, &rt->dst);
 53 
 54         if (skb_dst(skb)->error)
 55                 return skb_dst(skb)->error;
 56 
 57 #ifdef CONFIG_XFRM
 58         if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
 59             xfrm_decode_session(skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
 60                 struct dst_entry *dst = skb_dst(skb);
 61                 skb_dst_set(skb, NULL);
 62                 dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), skb->sk, 0);
 63                 if (IS_ERR(dst))
 64                         return PTR_ERR(dst);
 65                 skb_dst_set(skb, dst);
 66         }
 67 #endif
 68 
 69         /* Change in oif may mean change in hh_len. */
 70         hh_len = skb_dst(skb)->dev->hard_header_len;
 71         if (skb_headroom(skb) < hh_len &&
 72             pskb_expand_head(skb, HH_DATA_ALIGN(hh_len - skb_headroom(skb)),
 73                                 0, GFP_ATOMIC))
 74                 return -ENOMEM;
 75 
 76         return 0;
 77 }
 78 EXPORT_SYMBOL(ip_route_me_harder);
 79 
 80 /*
 81  * Extra routing may needed on local out, as the QUEUE target never
 82  * returns control to the table.
 83  */
 84 
 85 struct ip_rt_info {
 86         __be32 daddr;
 87         __be32 saddr;
 88         u_int8_t tos;
 89         u_int32_t mark;
 90 };
 91 
 92 static void nf_ip_saveroute(const struct sk_buff *skb,
 93                             struct nf_queue_entry *entry)
 94 {
 95         struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 96 
 97         if (entry->state.hook == NF_INET_LOCAL_OUT) {
 98                 const struct iphdr *iph = ip_hdr(skb);
 99 
100                 rt_info->tos = iph->tos;
101                 rt_info->daddr = iph->daddr;
102                 rt_info->saddr = iph->saddr;
103                 rt_info->mark = skb->mark;
104         }
105 }
106 
107 static int nf_ip_reroute(struct sk_buff *skb,
108                          const struct nf_queue_entry *entry)
109 {
110         const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
111 
112         if (entry->state.hook == NF_INET_LOCAL_OUT) {
113                 const struct iphdr *iph = ip_hdr(skb);
114 
115                 if (!(iph->tos == rt_info->tos &&
116                       skb->mark == rt_info->mark &&
117                       iph->daddr == rt_info->daddr &&
118                       iph->saddr == rt_info->saddr))
119                         return ip_route_me_harder(skb, RTN_UNSPEC);
120         }
121         return 0;
122 }
123 
124 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
125                             unsigned int dataoff, u_int8_t protocol)
126 {
127         const struct iphdr *iph = ip_hdr(skb);
128         __sum16 csum = 0;
129 
130         switch (skb->ip_summed) {
131         case CHECKSUM_COMPLETE:
132                 if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
133                         break;
134                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
135                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
136                                        skb->len - dataoff, protocol,
137                                        skb->csum)) {
138                         skb->ip_summed = CHECKSUM_UNNECESSARY;
139                         break;
140                 }
141                 /* fall through */
142         case CHECKSUM_NONE:
143                 if (protocol == 0)
144                         skb->csum = 0;
145                 else
146                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
147                                                        skb->len - dataoff,
148                                                        protocol, 0);
149                 csum = __skb_checksum_complete(skb);
150         }
151         return csum;
152 }
153 EXPORT_SYMBOL(nf_ip_checksum);
154 
155 static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
156                                       unsigned int dataoff, unsigned int len,
157                                       u_int8_t protocol)
158 {
159         const struct iphdr *iph = ip_hdr(skb);
160         __sum16 csum = 0;
161 
162         switch (skb->ip_summed) {
163         case CHECKSUM_COMPLETE:
164                 if (len == skb->len - dataoff)
165                         return nf_ip_checksum(skb, hook, dataoff, protocol);
166                 /* fall through */
167         case CHECKSUM_NONE:
168                 skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
169                                                skb->len - dataoff, 0);
170                 skb->ip_summed = CHECKSUM_NONE;
171                 return __skb_checksum_complete_head(skb, dataoff + len);
172         }
173         return csum;
174 }
175 
176 static int nf_ip_route(struct net *net, struct dst_entry **dst,
177                        struct flowi *fl, bool strict __always_unused)
178 {
179         struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
180         if (IS_ERR(rt))
181                 return PTR_ERR(rt);
182         *dst = &rt->dst;
183         return 0;
184 }
185 
186 static const struct nf_afinfo nf_ip_afinfo = {
187         .family                 = AF_INET,
188         .checksum               = nf_ip_checksum,
189         .checksum_partial       = nf_ip_checksum_partial,
190         .route                  = nf_ip_route,
191         .saveroute              = nf_ip_saveroute,
192         .reroute                = nf_ip_reroute,
193         .route_key_size         = sizeof(struct ip_rt_info),
194 };
195 
196 static int __init ipv4_netfilter_init(void)
197 {
198         return nf_register_afinfo(&nf_ip_afinfo);
199 }
200 subsys_initcall(ipv4_netfilter_init);
201 

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