1 /* (C) 1999-2001 Paul `Rusty' Russell 2 * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org> 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License version 2 as 6 * published by the Free Software Foundation. 7 */ 8 9 #include <linux/module.h> 10 #include <net/ipv6.h> 11 #include <net/ip6_route.h> 12 #include <net/ip6_fib.h> 13 #include <net/ip6_checksum.h> 14 #include <net/netfilter/ipv6/nf_reject.h> 15 #include <linux/netfilter_ipv6.h> 16 #include <linux/netfilter_bridge.h> 17 18 const struct tcphdr *nf_reject_ip6_tcphdr_get(struct sk_buff *oldskb, 19 struct tcphdr *otcph, 20 unsigned int *otcplen, int hook) 21 { 22 const struct ipv6hdr *oip6h = ipv6_hdr(oldskb); 23 u8 proto; 24 __be16 frag_off; 25 int tcphoff; 26 27 proto = oip6h->nexthdr; 28 tcphoff = ipv6_skip_exthdr(oldskb, ((u8 *)(oip6h + 1) - oldskb->data), 29 &proto, &frag_off); 30 31 if ((tcphoff < 0) || (tcphoff > oldskb->len)) { 32 pr_debug("Cannot get TCP header.\n"); 33 return NULL; 34 } 35 36 *otcplen = oldskb->len - tcphoff; 37 38 /* IP header checks: fragment, too short. */ 39 if (proto != IPPROTO_TCP || *otcplen < sizeof(struct tcphdr)) { 40 pr_debug("proto(%d) != IPPROTO_TCP or too short (len = %d)\n", 41 proto, *otcplen); 42 return NULL; 43 } 44 45 otcph = skb_header_pointer(oldskb, tcphoff, sizeof(struct tcphdr), 46 otcph); 47 if (otcph == NULL) 48 return NULL; 49 50 /* No RST for RST. */ 51 if (otcph->rst) { 52 pr_debug("RST is set\n"); 53 return NULL; 54 } 55 56 /* Check checksum. */ 57 if (nf_ip6_checksum(oldskb, hook, tcphoff, IPPROTO_TCP)) { 58 pr_debug("TCP checksum is invalid\n"); 59 return NULL; 60 } 61 62 return otcph; 63 } 64 EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_get); 65 66 struct ipv6hdr *nf_reject_ip6hdr_put(struct sk_buff *nskb, 67 const struct sk_buff *oldskb, 68 __u8 protocol, int hoplimit) 69 { 70 struct ipv6hdr *ip6h; 71 const struct ipv6hdr *oip6h = ipv6_hdr(oldskb); 72 #define DEFAULT_TOS_VALUE 0x0U 73 const __u8 tclass = DEFAULT_TOS_VALUE; 74 75 skb_put(nskb, sizeof(struct ipv6hdr)); 76 skb_reset_network_header(nskb); 77 ip6h = ipv6_hdr(nskb); 78 ip6_flow_hdr(ip6h, tclass, 0); 79 ip6h->hop_limit = hoplimit; 80 ip6h->nexthdr = protocol; 81 ip6h->saddr = oip6h->daddr; 82 ip6h->daddr = oip6h->saddr; 83 84 nskb->protocol = htons(ETH_P_IPV6); 85 86 return ip6h; 87 } 88 EXPORT_SYMBOL_GPL(nf_reject_ip6hdr_put); 89 90 void nf_reject_ip6_tcphdr_put(struct sk_buff *nskb, 91 const struct sk_buff *oldskb, 92 const struct tcphdr *oth, unsigned int otcplen) 93 { 94 struct tcphdr *tcph; 95 int needs_ack; 96 97 skb_reset_transport_header(nskb); 98 tcph = skb_put(nskb, sizeof(struct tcphdr)); 99 /* Truncate to length (no data) */ 100 tcph->doff = sizeof(struct tcphdr)/4; 101 tcph->source = oth->dest; 102 tcph->dest = oth->source; 103 104 if (oth->ack) { 105 needs_ack = 0; 106 tcph->seq = oth->ack_seq; 107 tcph->ack_seq = 0; 108 } else { 109 needs_ack = 1; 110 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin + 111 otcplen - (oth->doff<<2)); 112 tcph->seq = 0; 113 } 114 115 /* Reset flags */ 116 ((u_int8_t *)tcph)[13] = 0; 117 tcph->rst = 1; 118 tcph->ack = needs_ack; 119 tcph->window = 0; 120 tcph->urg_ptr = 0; 121 tcph->check = 0; 122 123 /* Adjust TCP checksum */ 124 tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr, 125 &ipv6_hdr(nskb)->daddr, 126 sizeof(struct tcphdr), IPPROTO_TCP, 127 csum_partial(tcph, 128 sizeof(struct tcphdr), 0)); 129 } 130 EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_put); 131 132 void nf_send_reset6(struct net *net, struct sk_buff *oldskb, int hook) 133 { 134 struct net_device *br_indev __maybe_unused; 135 struct sk_buff *nskb; 136 struct tcphdr _otcph; 137 const struct tcphdr *otcph; 138 unsigned int otcplen, hh_len; 139 const struct ipv6hdr *oip6h = ipv6_hdr(oldskb); 140 struct ipv6hdr *ip6h; 141 struct dst_entry *dst = NULL; 142 struct flowi6 fl6; 143 144 if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) || 145 (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) { 146 pr_debug("addr is not unicast.\n"); 147 return; 148 } 149 150 otcph = nf_reject_ip6_tcphdr_get(oldskb, &_otcph, &otcplen, hook); 151 if (!otcph) 152 return; 153 154 memset(&fl6, 0, sizeof(fl6)); 155 fl6.flowi6_proto = IPPROTO_TCP; 156 fl6.saddr = oip6h->daddr; 157 fl6.daddr = oip6h->saddr; 158 fl6.fl6_sport = otcph->dest; 159 fl6.fl6_dport = otcph->source; 160 fl6.flowi6_oif = l3mdev_master_ifindex(skb_dst(oldskb)->dev); 161 fl6.flowi6_mark = IP6_REPLY_MARK(net, oldskb->mark); 162 security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6)); 163 dst = ip6_route_output(net, NULL, &fl6); 164 if (dst->error) { 165 dst_release(dst); 166 return; 167 } 168 dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0); 169 if (IS_ERR(dst)) 170 return; 171 172 hh_len = (dst->dev->hard_header_len + 15)&~15; 173 nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr) 174 + sizeof(struct tcphdr) + dst->trailer_len, 175 GFP_ATOMIC); 176 177 if (!nskb) { 178 net_dbg_ratelimited("cannot alloc skb\n"); 179 dst_release(dst); 180 return; 181 } 182 183 skb_dst_set(nskb, dst); 184 185 nskb->mark = fl6.flowi6_mark; 186 187 skb_reserve(nskb, hh_len + dst->header_len); 188 ip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP, 189 ip6_dst_hoplimit(dst)); 190 nf_reject_ip6_tcphdr_put(nskb, oldskb, otcph, otcplen); 191 192 nf_ct_attach(nskb, oldskb); 193 194 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER) 195 /* If we use ip6_local_out for bridged traffic, the MAC source on 196 * the RST will be ours, instead of the destination's. This confuses 197 * some routers/firewalls, and they drop the packet. So we need to 198 * build the eth header using the original destination's MAC as the 199 * source, and send the RST packet directly. 200 */ 201 br_indev = nf_bridge_get_physindev(oldskb); 202 if (br_indev) { 203 struct ethhdr *oeth = eth_hdr(oldskb); 204 205 nskb->dev = br_indev; 206 nskb->protocol = htons(ETH_P_IPV6); 207 ip6h->payload_len = htons(sizeof(struct tcphdr)); 208 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol), 209 oeth->h_source, oeth->h_dest, nskb->len) < 0) { 210 kfree_skb(nskb); 211 return; 212 } 213 dev_queue_xmit(nskb); 214 } else 215 #endif 216 ip6_local_out(net, nskb->sk, nskb); 217 } 218 EXPORT_SYMBOL_GPL(nf_send_reset6); 219 220 static bool reject6_csum_ok(struct sk_buff *skb, int hook) 221 { 222 const struct ipv6hdr *ip6h = ipv6_hdr(skb); 223 int thoff; 224 __be16 fo; 225 u8 proto; 226 227 if (skb_csum_unnecessary(skb)) 228 return true; 229 230 proto = ip6h->nexthdr; 231 thoff = ipv6_skip_exthdr(skb, ((u8 *)(ip6h + 1) - skb->data), &proto, &fo); 232 233 if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0) 234 return false; 235 236 if (!nf_reject_verify_csum(proto)) 237 return true; 238 239 return nf_ip6_checksum(skb, hook, thoff, proto) == 0; 240 } 241 242 void nf_send_unreach6(struct net *net, struct sk_buff *skb_in, 243 unsigned char code, unsigned int hooknum) 244 { 245 if (!reject6_csum_ok(skb_in, hooknum)) 246 return; 247 248 if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL) 249 skb_in->dev = net->loopback_dev; 250 251 icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0); 252 } 253 EXPORT_SYMBOL_GPL(nf_send_unreach6); 254 255 MODULE_LICENSE("GPL"); 256