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 <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");