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->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->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 } 200 201 static void __exit ipv4_netfilter_fini(void) 202 { 203 nf_unregister_afinfo(&nf_ip_afinfo); 204 } 205 206 module_init(ipv4_netfilter_init); 207 module_exit(ipv4_netfilter_fini); 208