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Linux/net/ipv4/netfilter.c

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  1 /* IPv4 specific functions of netfilter core */
  2 #include <linux/kernel.h>
  3 #include <linux/netfilter.h>
  4 #include <linux/netfilter_ipv4.h>
  5 #include <linux/ip.h>
  6 #include <linux/skbuff.h>
  7 #include <linux/gfp.h>
  8 #include <linux/export.h>
  9 #include <net/route.h>
 10 #include <net/xfrm.h>
 11 #include <net/ip.h>
 12 #include <net/netfilter/nf_queue.h>
 13 
 14 /* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
 15 int ip_route_me_harder(struct sk_buff *skb, unsigned int addr_type)
 16 {
 17         struct net *net = dev_net(skb_dst(skb)->dev);
 18         const struct iphdr *iph = ip_hdr(skb);
 19         struct rtable *rt;
 20         struct flowi4 fl4 = {};
 21         __be32 saddr = iph->saddr;
 22         __u8 flags = skb->sk ? inet_sk_flowi_flags(skb->sk) : 0;
 23         unsigned int hh_len;
 24 
 25         if (addr_type == RTN_UNSPEC)
 26                 addr_type = inet_addr_type(net, saddr);
 27         if (addr_type == RTN_LOCAL || addr_type == RTN_UNICAST)
 28                 flags |= FLOWI_FLAG_ANYSRC;
 29         else
 30                 saddr = 0;
 31 
 32         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
 33          * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
 34          */
 35         fl4.daddr = iph->daddr;
 36         fl4.saddr = saddr;
 37         fl4.flowi4_tos = RT_TOS(iph->tos);
 38         fl4.flowi4_oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
 39         fl4.flowi4_mark = skb->mark;
 40         fl4.flowi4_flags = flags;
 41         rt = ip_route_output_key(net, &fl4);
 42         if (IS_ERR(rt))
 43                 return -1;
 44 
 45         /* Drop old route. */
 46         skb_dst_drop(skb);
 47         skb_dst_set(skb, &rt->dst);
 48 
 49         if (skb_dst(skb)->error)
 50                 return -1;
 51 
 52 #ifdef CONFIG_XFRM
 53         if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
 54             xfrm_decode_session(skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
 55                 struct dst_entry *dst = skb_dst(skb);
 56                 skb_dst_set(skb, NULL);
 57                 dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), skb->sk, 0);
 58                 if (IS_ERR(dst))
 59                         return -1;
 60                 skb_dst_set(skb, dst);
 61         }
 62 #endif
 63 
 64         /* Change in oif may mean change in hh_len. */
 65         hh_len = skb_dst(skb)->dev->hard_header_len;
 66         if (skb_headroom(skb) < hh_len &&
 67             pskb_expand_head(skb, HH_DATA_ALIGN(hh_len - skb_headroom(skb)),
 68                                 0, GFP_ATOMIC))
 69                 return -1;
 70 
 71         return 0;
 72 }
 73 EXPORT_SYMBOL(ip_route_me_harder);
 74 
 75 /*
 76  * Extra routing may needed on local out, as the QUEUE target never
 77  * returns control to the table.
 78  */
 79 
 80 struct ip_rt_info {
 81         __be32 daddr;
 82         __be32 saddr;
 83         u_int8_t tos;
 84         u_int32_t mark;
 85 };
 86 
 87 static void nf_ip_saveroute(const struct sk_buff *skb,
 88                             struct nf_queue_entry *entry)
 89 {
 90         struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 91 
 92         if (entry->hook == NF_INET_LOCAL_OUT) {
 93                 const struct iphdr *iph = ip_hdr(skb);
 94 
 95                 rt_info->tos = iph->tos;
 96                 rt_info->daddr = iph->daddr;
 97                 rt_info->saddr = iph->saddr;
 98                 rt_info->mark = skb->mark;
 99         }
100 }
101 
102 static int nf_ip_reroute(struct sk_buff *skb,
103                          const struct nf_queue_entry *entry)
104 {
105         const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
106 
107         if (entry->hook == NF_INET_LOCAL_OUT) {
108                 const struct iphdr *iph = ip_hdr(skb);
109 
110                 if (!(iph->tos == rt_info->tos &&
111                       skb->mark == rt_info->mark &&
112                       iph->daddr == rt_info->daddr &&
113                       iph->saddr == rt_info->saddr))
114                         return ip_route_me_harder(skb, RTN_UNSPEC);
115         }
116         return 0;
117 }
118 
119 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
120                             unsigned int dataoff, u_int8_t protocol)
121 {
122         const struct iphdr *iph = ip_hdr(skb);
123         __sum16 csum = 0;
124 
125         switch (skb->ip_summed) {
126         case CHECKSUM_COMPLETE:
127                 if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
128                         break;
129                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
130                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
131                                        skb->len - dataoff, protocol,
132                                        skb->csum)) {
133                         skb->ip_summed = CHECKSUM_UNNECESSARY;
134                         break;
135                 }
136                 /* fall through */
137         case CHECKSUM_NONE:
138                 if (protocol == 0)
139                         skb->csum = 0;
140                 else
141                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
142                                                        skb->len - dataoff,
143                                                        protocol, 0);
144                 csum = __skb_checksum_complete(skb);
145         }
146         return csum;
147 }
148 EXPORT_SYMBOL(nf_ip_checksum);
149 
150 static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
151                                       unsigned int dataoff, unsigned int len,
152                                       u_int8_t protocol)
153 {
154         const struct iphdr *iph = ip_hdr(skb);
155         __sum16 csum = 0;
156 
157         switch (skb->ip_summed) {
158         case CHECKSUM_COMPLETE:
159                 if (len == skb->len - dataoff)
160                         return nf_ip_checksum(skb, hook, dataoff, protocol);
161                 /* fall through */
162         case CHECKSUM_NONE:
163                 skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
164                                                skb->len - dataoff, 0);
165                 skb->ip_summed = CHECKSUM_NONE;
166                 return __skb_checksum_complete_head(skb, dataoff + len);
167         }
168         return csum;
169 }
170 
171 static int nf_ip_route(struct net *net, struct dst_entry **dst,
172                        struct flowi *fl, bool strict __always_unused)
173 {
174         struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
175         if (IS_ERR(rt))
176                 return PTR_ERR(rt);
177         *dst = &rt->dst;
178         return 0;
179 }
180 
181 static const struct nf_afinfo nf_ip_afinfo = {
182         .family                 = AF_INET,
183         .checksum               = nf_ip_checksum,
184         .checksum_partial       = nf_ip_checksum_partial,
185         .route                  = nf_ip_route,
186         .saveroute              = nf_ip_saveroute,
187         .reroute                = nf_ip_reroute,
188         .route_key_size         = sizeof(struct ip_rt_info),
189 };
190 
191 static int __init ipv4_netfilter_init(void)
192 {
193         return nf_register_afinfo(&nf_ip_afinfo);
194 }
195 
196 static void __exit ipv4_netfilter_fini(void)
197 {
198         nf_unregister_afinfo(&nf_ip_afinfo);
199 }
200 
201 module_init(ipv4_netfilter_init);
202 module_exit(ipv4_netfilter_fini);
203 

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