linux/net/ipv6/netfilter/nf_reject_ipv6.c
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   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
  18const 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}
  64EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_get);
  65
  66struct 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}
  88EXPORT_SYMBOL_GPL(nf_reject_ip6hdr_put);
  89
  90void 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}
 130EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_put);
 131
 132void nf_send_reset6(struct net *net, struct sk_buff *oldskb, int hook)
 133{
 134        struct sk_buff *nskb;
 135        struct tcphdr _otcph;
 136        const struct tcphdr *otcph;
 137        unsigned int otcplen, hh_len;
 138        const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
 139        struct ipv6hdr *ip6h;
 140        struct dst_entry *dst = NULL;
 141        struct flowi6 fl6;
 142
 143        if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
 144            (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
 145                pr_debug("addr is not unicast.\n");
 146                return;
 147        }
 148
 149        otcph = nf_reject_ip6_tcphdr_get(oldskb, &_otcph, &otcplen, hook);
 150        if (!otcph)
 151                return;
 152
 153        memset(&fl6, 0, sizeof(fl6));
 154        fl6.flowi6_proto = IPPROTO_TCP;
 155        fl6.saddr = oip6h->daddr;
 156        fl6.daddr = oip6h->saddr;
 157        fl6.fl6_sport = otcph->dest;
 158        fl6.fl6_dport = otcph->source;
 159        fl6.flowi6_oif = l3mdev_master_ifindex(skb_dst(oldskb)->dev);
 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->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}
 214EXPORT_SYMBOL_GPL(nf_send_reset6);
 215
 216static 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_unnecessary(skb))
 224                return true;
 225
 226        proto = ip6h->nexthdr;
 227        thoff = ipv6_skip_exthdr(skb, ((u8 *)(ip6h + 1) - skb->data), &proto, &fo);
 228
 229        if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
 230                return false;
 231
 232        return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
 233}
 234
 235void nf_send_unreach6(struct net *net, struct sk_buff *skb_in,
 236                      unsigned char code, unsigned int hooknum)
 237{
 238        if (!reject6_csum_ok(skb_in, hooknum))
 239                return;
 240
 241        if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 242                skb_in->dev = net->loopback_dev;
 243
 244        icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
 245}
 246EXPORT_SYMBOL_GPL(nf_send_unreach6);
 247
 248MODULE_LICENSE("GPL");
 249
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