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