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 #include <net/ipv6.h>
   9 #include <net/ip6_route.h>
  10 #include <net/ip6_fib.h>
  11 #include <net/ip6_checksum.h>
  12 #include <linux/netfilter_ipv6.h>
  13
  14 void nf_send_reset6(struct net *net, struct sk_buff *oldskb, int hook)
  15 {
  16         struct sk_buff *nskb;
  17         struct tcphdr otcph, *tcph;
  18         unsigned int otcplen, hh_len;
  19         int tcphoff, needs_ack;
  20         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
  21         struct ipv6hdr *ip6h;
  22 #define DEFAULT_TOS_VALUE       0x0U
  23         const __u8 tclass = DEFAULT_TOS_VALUE;
  24         struct dst_entry *dst = NULL;
  25         u8 proto;
  26         __be16 frag_off;
  27         struct flowi6 fl6;
  28
  29         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
  30             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
  31                 pr_debug("addr is not unicast.\n");
  32                 return;
  33         }
  34
  35         proto = oip6h->nexthdr;
  36         tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto, &frag_off);
  37
  38         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
  39                 pr_debug("Cannot get TCP header.\n");
  40                 return;
  41         }
  42
  43         otcplen = oldskb->len - tcphoff;
  44
  45         /* IP header checks: fragment, too short. */
  46         if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
  47                 pr_debug("proto(%d) != IPPROTO_TCP, "
  48                          "or too short. otcplen = %d\n",
  49                          proto, otcplen);
  50                 return;
  51         }
  52
  53         if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
  54                 BUG();
  55
  56         /* No RST for RST. */
  57         if (otcph.rst) {
  58                 pr_debug("RST is set\n");
  59                 return;
  60         }
  61
  62         /* Check checksum. */
  63         if (nf_ip6_checksum(oldskb, hook, tcphoff, IPPROTO_TCP)) {
  64                 pr_debug("TCP checksum is invalid\n");
  65                 return;
  66         }
  67
  68         memset(&fl6, 0, sizeof(fl6));
  69         fl6.flowi6_proto = IPPROTO_TCP;
  70         fl6.saddr = oip6h->daddr;
  71         fl6.daddr = oip6h->saddr;
  72         fl6.fl6_sport = otcph.dest;
  73         fl6.fl6_dport = otcph.source;
  74         security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
  75         dst = ip6_route_output(net, NULL, &fl6);
  76         if (dst == NULL || dst->error) {
  77                 dst_release(dst);
  78                 return;
  79         }
  80         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
  81         if (IS_ERR(dst))
  82                 return;
  83
  84         hh_len = (dst->dev->hard_header_len + 15)&~15;
  85         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
  86                          + sizeof(struct tcphdr) + dst->trailer_len,
  87                          GFP_ATOMIC);
  88
  89         if (!nskb) {
  90                 net_dbg_ratelimited("cannot alloc skb\n");
  91                 dst_release(dst);
  92                 return;
  93         }
  94
  95         skb_dst_set(nskb, dst);
  96
  97         skb_reserve(nskb, hh_len + dst->header_len);
  98
  99         skb_put(nskb, sizeof(struct ipv6hdr));
 100         skb_reset_network_header(nskb);
 101         ip6h = ipv6_hdr(nskb);
 102         ip6_flow_hdr(ip6h, tclass, 0);
 103         ip6h->hop_limit = ip6_dst_hoplimit(dst);
 104         ip6h->nexthdr = IPPROTO_TCP;
 105         ip6h->saddr = oip6h->daddr;
 106         ip6h->daddr = oip6h->saddr;
 107
 108         skb_reset_transport_header(nskb);
 109         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
 110         /* Truncate to length (no data) */
 111         tcph->doff = sizeof(struct tcphdr)/4;
 112         tcph->source = otcph.dest;
 113         tcph->dest = otcph.source;
 114
 115         if (otcph.ack) {
 116                 needs_ack = 0;
 117                 tcph->seq = otcph.ack_seq;
 118                 tcph->ack_seq = 0;
 119         } else {
 120                 needs_ack = 1;
 121                 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
 122                                       + otcplen - (otcph.doff<<2));
 123                 tcph->seq = 0;
 124         }
 125
 126         /* Reset flags */
 127         ((u_int8_t *)tcph)[13] = 0;
 128         tcph->rst = 1;
 129         tcph->ack = needs_ack;
 130         tcph->window = 0;
 131         tcph->urg_ptr = 0;
 132         tcph->check = 0;
 133
 134         /* Adjust TCP checksum */
 135         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 136                                       &ipv6_hdr(nskb)->daddr,
 137                                       sizeof(struct tcphdr), IPPROTO_TCP,
 138                                       csum_partial(tcph,
 139                                                    sizeof(struct tcphdr), 0));
 140
 141         nf_ct_attach(nskb, oldskb);
 142
 143 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 144         /* If we use ip6_local_out for bridged traffic, the MAC source on
 145          * the RST will be ours, instead of the destination's.  This confuses
 146          * some routers/firewalls, and they drop the packet.  So we need to
 147          * build the eth header using the original destination's MAC as the
 148          * source, and send the RST packet directly.
 149          */
 150         if (oldskb->nf_bridge) {
 151                 struct ethhdr *oeth = eth_hdr(oldskb);
 152                 nskb->dev = oldskb->nf_bridge->physindev;
 153                 nskb->protocol = htons(ETH_P_IPV6);
 154                 ip6h->payload_len = htons(sizeof(struct tcphdr));
 155                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 156                                     oeth->h_source, oeth->h_dest, nskb->len) < 0)
 157                         return;
 158                 dev_queue_xmit(nskb);
 159         } else
 160 #endif
 161                 ip6_local_out(nskb);
 162 }
 163 EXPORT_SYMBOL_GPL(nf_send_reset6);