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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 net *net, struct sk_buff *skb, unsigned int addr_type)
 21 {
 22         const struct iphdr *iph = ip_hdr(skb);
 23         struct rtable *rt;
 24         struct flowi4 fl4 = {};
 25         __be32 saddr = iph->saddr;
 26         const struct sock *sk = skb_to_full_sk(skb);
 27         __u8 flags = sk ? inet_sk_flowi_flags(sk) : 0;
 28         struct net_device *dev = skb_dst(skb)->dev;
 29         unsigned int hh_len;
 30 
 31         if (addr_type == RTN_UNSPEC)
 32                 addr_type = inet_addr_type_dev_table(net, dev, saddr);
 33         if (addr_type == RTN_LOCAL || addr_type == RTN_UNICAST)
 34                 flags |= FLOWI_FLAG_ANYSRC;
 35         else
 36                 saddr = 0;
 37 
 38         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
 39          * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
 40          */
 41         fl4.daddr = iph->daddr;
 42         fl4.saddr = saddr;
 43         fl4.flowi4_tos = RT_TOS(iph->tos);
 44         fl4.flowi4_oif = sk ? sk->sk_bound_dev_if : 0;
 45         if (!fl4.flowi4_oif)
 46                 fl4.flowi4_oif = l3mdev_master_ifindex(dev);
 47         fl4.flowi4_mark = skb->mark;
 48         fl4.flowi4_flags = flags;
 49         rt = ip_route_output_key(net, &fl4);
 50         if (IS_ERR(rt))
 51                 return PTR_ERR(rt);
 52 
 53         /* Drop old route. */
 54         skb_dst_drop(skb);
 55         skb_dst_set(skb, &rt->dst);
 56 
 57         if (skb_dst(skb)->error)
 58                 return skb_dst(skb)->error;
 59 
 60 #ifdef CONFIG_XFRM
 61         if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
 62             xfrm_decode_session(skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
 63                 struct dst_entry *dst = skb_dst(skb);
 64                 skb_dst_set(skb, NULL);
 65                 dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), sk, 0);
 66                 if (IS_ERR(dst))
 67                         return PTR_ERR(dst);
 68                 skb_dst_set(skb, dst);
 69         }
 70 #endif
 71 
 72         /* Change in oif may mean change in hh_len. */
 73         hh_len = skb_dst(skb)->dev->hard_header_len;
 74         if (skb_headroom(skb) < hh_len &&
 75             pskb_expand_head(skb, HH_DATA_ALIGN(hh_len - skb_headroom(skb)),
 76                                 0, GFP_ATOMIC))
 77                 return -ENOMEM;
 78 
 79         return 0;
 80 }
 81 EXPORT_SYMBOL(ip_route_me_harder);
 82 
 83 /*
 84  * Extra routing may needed on local out, as the QUEUE target never
 85  * returns control to the table.
 86  */
 87 
 88 struct ip_rt_info {
 89         __be32 daddr;
 90         __be32 saddr;
 91         u_int8_t tos;
 92         u_int32_t mark;
 93 };
 94 
 95 static void nf_ip_saveroute(const struct sk_buff *skb,
 96                             struct nf_queue_entry *entry)
 97 {
 98         struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 99 
100         if (entry->state.hook == NF_INET_LOCAL_OUT) {
101                 const struct iphdr *iph = ip_hdr(skb);
102 
103                 rt_info->tos = iph->tos;
104                 rt_info->daddr = iph->daddr;
105                 rt_info->saddr = iph->saddr;
106                 rt_info->mark = skb->mark;
107         }
108 }
109 
110 static int nf_ip_reroute(struct net *net, struct sk_buff *skb,
111                          const struct nf_queue_entry *entry)
112 {
113         const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
114 
115         if (entry->state.hook == NF_INET_LOCAL_OUT) {
116                 const struct iphdr *iph = ip_hdr(skb);
117 
118                 if (!(iph->tos == rt_info->tos &&
119                       skb->mark == rt_info->mark &&
120                       iph->daddr == rt_info->daddr &&
121                       iph->saddr == rt_info->saddr))
122                         return ip_route_me_harder(net, skb, RTN_UNSPEC);
123         }
124         return 0;
125 }
126 
127 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
128                             unsigned int dataoff, u_int8_t protocol)
129 {
130         const struct iphdr *iph = ip_hdr(skb);
131         __sum16 csum = 0;
132 
133         switch (skb->ip_summed) {
134         case CHECKSUM_COMPLETE:
135                 if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
136                         break;
137                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
138                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
139                                        skb->len - dataoff, protocol,
140                                        skb->csum)) {
141                         skb->ip_summed = CHECKSUM_UNNECESSARY;
142                         break;
143                 }
144                 /* fall through */
145         case CHECKSUM_NONE:
146                 if (protocol == 0)
147                         skb->csum = 0;
148                 else
149                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
150                                                        skb->len - dataoff,
151                                                        protocol, 0);
152                 csum = __skb_checksum_complete(skb);
153         }
154         return csum;
155 }
156 EXPORT_SYMBOL(nf_ip_checksum);
157 
158 static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
159                                       unsigned int dataoff, unsigned int len,
160                                       u_int8_t protocol)
161 {
162         const struct iphdr *iph = ip_hdr(skb);
163         __sum16 csum = 0;
164 
165         switch (skb->ip_summed) {
166         case CHECKSUM_COMPLETE:
167                 if (len == skb->len - dataoff)
168                         return nf_ip_checksum(skb, hook, dataoff, protocol);
169                 /* fall through */
170         case CHECKSUM_NONE:
171                 skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
172                                                skb->len - dataoff, 0);
173                 skb->ip_summed = CHECKSUM_NONE;
174                 return __skb_checksum_complete_head(skb, dataoff + len);
175         }
176         return csum;
177 }
178 
179 static int nf_ip_route(struct net *net, struct dst_entry **dst,
180                        struct flowi *fl, bool strict __always_unused)
181 {
182         struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
183         if (IS_ERR(rt))
184                 return PTR_ERR(rt);
185         *dst = &rt->dst;
186         return 0;
187 }
188 
189 static const struct nf_afinfo nf_ip_afinfo = {
190         .family                 = AF_INET,
191         .checksum               = nf_ip_checksum,
192         .checksum_partial       = nf_ip_checksum_partial,
193         .route                  = nf_ip_route,
194         .saveroute              = nf_ip_saveroute,
195         .reroute                = nf_ip_reroute,
196         .route_key_size         = sizeof(struct ip_rt_info),
197 };
198 
199 static int __init ipv4_netfilter_init(void)
200 {
201         return nf_register_afinfo(&nf_ip_afinfo);
202 }
203 subsys_initcall(ipv4_netfilter_init);
204 

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