net/ipv6/netfilter/nf_reject_ipv6.c

   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 <linux/netfilter_ipv6.h>
  15 #include <net/netfilter/ipv6/nf_reject.h>
  16
  17 const struct tcphdr *nf_reject_ip6_tcphdr_get(struct sk_buff *oldskb,
  18                                               struct tcphdr *otcph,
  19                                               unsigned int *otcplen, int hook)
  20 {
  21         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
  22         u8 proto;
  23         __be16 frag_off;
  24         int tcphoff;
  25
  26         proto = oip6h->nexthdr;
  27         tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data),
  28                                    &proto, &frag_off);
  29
  30         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
  31                 pr_debug("Cannot get TCP header.\n");
  32                 return NULL;
  33         }
  34
  35         *otcplen = oldskb->len - tcphoff;
  36
  37         /* IP header checks: fragment, too short. */
  38         if (proto != IPPROTO_TCP || *otcplen < sizeof(struct tcphdr)) {
  39                 pr_debug("proto(%d) != IPPROTO_TCP or too short (len = %d)\n",
  40                          proto, *otcplen);
  41                 return NULL;
  42         }
  43
  44         otcph = skb_header_pointer(oldskb, tcphoff, sizeof(struct tcphdr),
  45                                    otcph);
  46         if (otcph == NULL)
  47                 return NULL;
  48
  49         /* No RST for RST. */
  50         if (otcph->rst) {
  51                 pr_debug("RST is set\n");
  52                 return NULL;
  53         }
  54
  55         /* Check checksum. */
  56         if (nf_ip6_checksum(oldskb, hook, tcphoff, IPPROTO_TCP)) {
  57                 pr_debug("TCP checksum is invalid\n");
  58                 return NULL;
  59         }
  60
  61         return otcph;
  62 }
  63 EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_get);
  64
  65 struct ipv6hdr *nf_reject_ip6hdr_put(struct sk_buff *nskb,
  66                                      const struct sk_buff *oldskb,
  67                                      __be16 protocol, int hoplimit)
  68 {
  69         struct ipv6hdr *ip6h;
  70         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
  71 #define DEFAULT_TOS_VALUE       0x0U
  72         const __u8 tclass = DEFAULT_TOS_VALUE;
  73
  74         skb_put(nskb, sizeof(struct ipv6hdr));
  75         skb_reset_network_header(nskb);
  76         ip6h = ipv6_hdr(nskb);
  77         ip6_flow_hdr(ip6h, tclass, 0);
  78         ip6h->hop_limit = hoplimit;
  79         ip6h->nexthdr = protocol;
  80         ip6h->saddr = oip6h->daddr;
  81         ip6h->daddr = oip6h->saddr;
  82
  83         nskb->protocol = htons(ETH_P_IPV6);
  84
  85         return ip6h;
  86 }
  87 EXPORT_SYMBOL_GPL(nf_reject_ip6hdr_put);
  88
  89 void nf_reject_ip6_tcphdr_put(struct sk_buff *nskb,
  90                               const struct sk_buff *oldskb,
  91                               const struct tcphdr *oth, unsigned int otcplen)
  92 {
  93         struct tcphdr *tcph;
  94         int needs_ack;
  95
  96         skb_reset_transport_header(nskb);
  97         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
  98         /* Truncate to length (no data) */
  99         tcph->doff = sizeof(struct tcphdr)/4;
 100         tcph->source = oth->dest;
 101         tcph->dest = oth->source;
 102
 103         if (oth->ack) {
 104                 needs_ack = 0;
 105                 tcph->seq = oth->ack_seq;
 106                 tcph->ack_seq = 0;
 107         } else {
 108                 needs_ack = 1;
 109                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
 110                                       otcplen - (oth->doff<<2));
 111                 tcph->seq = 0;
 112         }
 113
 114         /* Reset flags */
 115         ((u_int8_t *)tcph)[13] = 0;
 116         tcph->rst = 1;
 117         tcph->ack = needs_ack;
 118         tcph->window = 0;
 119         tcph->urg_ptr = 0;
 120         tcph->check = 0;
 121
 122         /* Adjust TCP checksum */
 123         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 124                                       &ipv6_hdr(nskb)->daddr,
 125                                       sizeof(struct tcphdr), IPPROTO_TCP,
 126                                       csum_partial(tcph,
 127                                                    sizeof(struct tcphdr), 0));
 128 }
 129 EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_put);
 130
 131 void nf_send_reset6(struct net *net, struct sk_buff *oldskb, int hook)
 132 {
 133         struct sk_buff *nskb;
 134         struct tcphdr _otcph;
 135         const struct tcphdr *otcph;
 136         unsigned int otcplen, hh_len;
 137         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
 138         struct ipv6hdr *ip6h;
 139         struct dst_entry *dst = NULL;
 140         struct flowi6 fl6;
 141
 142         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
 143             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
 144                 pr_debug("addr is not unicast.\n");
 145                 return;
 146         }
 147
 148         otcph = nf_reject_ip6_tcphdr_get(oldskb, &_otcph, &otcplen, hook);
 149         if (!otcph)
 150                 return;
 151
 152         memset(&fl6, 0, sizeof(fl6));
 153         fl6.flowi6_proto = IPPROTO_TCP;
 154         fl6.saddr = oip6h->daddr;
 155         fl6.daddr = oip6h->saddr;
 156         fl6.fl6_sport = otcph->dest;
 157         fl6.fl6_dport = otcph->source;
 158         security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
 159         dst = ip6_route_output(net, NULL, &fl6);
 160         if (dst == NULL || dst->error) {
 161                 dst_release(dst);
 162                 return;
 163         }
 164         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
 165         if (IS_ERR(dst))
 166                 return;
 167
 168         hh_len = (dst->dev->hard_header_len + 15)&~15;
 169         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 170                          + sizeof(struct tcphdr) + dst->trailer_len,
 171                          GFP_ATOMIC);
 172
 173         if (!nskb) {
 174                 net_dbg_ratelimited("cannot alloc skb\n");
 175                 dst_release(dst);
 176                 return;
 177         }
 178
 179         skb_dst_set(nskb, dst);
 180
 181         skb_reserve(nskb, hh_len + dst->header_len);
 182         ip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
 183                                     ip6_dst_hoplimit(dst));
 184         nf_reject_ip6_tcphdr_put(nskb, oldskb, otcph, otcplen);
 185
 186         nf_ct_attach(nskb, oldskb);
 187
 188 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 189         /* If we use ip6_local_out for bridged traffic, the MAC source on
 190          * the RST will be ours, instead of the destination's.  This confuses
 191          * some routers/firewalls, and they drop the packet.  So we need to
 192          * build the eth header using the original destination's MAC as the
 193          * source, and send the RST packet directly.
 194          */
 195         if (oldskb->nf_bridge) {
 196                 struct ethhdr *oeth = eth_hdr(oldskb);
 197                 nskb->dev = oldskb->nf_bridge->physindev;
 198                 nskb->protocol = htons(ETH_P_IPV6);
 199                 ip6h->payload_len = htons(sizeof(struct tcphdr));
 200                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 201                                     oeth->h_source, oeth->h_dest, nskb->len) < 0)
 202                         return;
 203                 dev_queue_xmit(nskb);
 204         } else
 205 #endif
 206                 ip6_local_out(nskb);
 207 }
 208 EXPORT_SYMBOL_GPL(nf_send_reset6);
 209
 210 MODULE_LICENSE("GPL");