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