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