net/ipv6/netfilter/nf_reject_ipv6.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* (C) 1999-2001 Paul `Rusty' Russell
   3  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   4  */
   5
   6 #include <linux/module.h>
   7 #include <net/ipv6.h>
   8 #include <net/ip6_route.h>
   9 #include <net/ip6_fib.h>
  10 #include <net/ip6_checksum.h>
  11 #include <net/netfilter/ipv6/nf_reject.h>
  12 #include <linux/netfilter_ipv6.h>
  13 #include <linux/netfilter_bridge.h>
  14
  15 const struct tcphdr *nf_reject_ip6_tcphdr_get(struct sk_buff *oldskb,
  16                                               struct tcphdr *otcph,
  17                                               unsigned int *otcplen, int hook)
  18 {
  19         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
  20         u8 proto;
  21         __be16 frag_off;
  22         int tcphoff;
  23
  24         proto = oip6h->nexthdr;
  25         tcphoff = ipv6_skip_exthdr(oldskb, ((u8 *)(oip6h + 1) - oldskb->data),
  26                                    &proto, &frag_off);
  27
  28         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
  29                 pr_debug("Cannot get TCP header.\n");
  30                 return NULL;
  31         }
  32
  33         *otcplen = oldskb->len - tcphoff;
  34
  35         /* IP header checks: fragment, too short. */
  36         if (proto != IPPROTO_TCP || *otcplen < sizeof(struct tcphdr)) {
  37                 pr_debug("proto(%d) != IPPROTO_TCP or too short (len = %d)\n",
  38                          proto, *otcplen);
  39                 return NULL;
  40         }
  41
  42         otcph = skb_header_pointer(oldskb, tcphoff, sizeof(struct tcphdr),
  43                                    otcph);
  44         if (otcph == NULL)
  45                 return NULL;
  46
  47         /* No RST for RST. */
  48         if (otcph->rst) {
  49                 pr_debug("RST is set\n");
  50                 return NULL;
  51         }
  52
  53         /* Check checksum. */
  54         if (nf_ip6_checksum(oldskb, hook, tcphoff, IPPROTO_TCP)) {
  55                 pr_debug("TCP checksum is invalid\n");
  56                 return NULL;
  57         }
  58
  59         return otcph;
  60 }
  61 EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_get);
  62
  63 struct ipv6hdr *nf_reject_ip6hdr_put(struct sk_buff *nskb,
  64                                      const struct sk_buff *oldskb,
  65                                      __u8 protocol, int hoplimit)
  66 {
  67         struct ipv6hdr *ip6h;
  68         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
  69 #define DEFAULT_TOS_VALUE       0x0U
  70         const __u8 tclass = DEFAULT_TOS_VALUE;
  71
  72         skb_put(nskb, sizeof(struct ipv6hdr));
  73         skb_reset_network_header(nskb);
  74         ip6h = ipv6_hdr(nskb);
  75         ip6_flow_hdr(ip6h, tclass, 0);
  76         ip6h->hop_limit = hoplimit;
  77         ip6h->nexthdr = protocol;
  78         ip6h->saddr = oip6h->daddr;
  79         ip6h->daddr = oip6h->saddr;
  80
  81         nskb->protocol = htons(ETH_P_IPV6);
  82
  83         return ip6h;
  84 }
  85 EXPORT_SYMBOL_GPL(nf_reject_ip6hdr_put);
  86
  87 void nf_reject_ip6_tcphdr_put(struct sk_buff *nskb,
  88                               const struct sk_buff *oldskb,
  89                               const struct tcphdr *oth, unsigned int otcplen)
  90 {
  91         struct tcphdr *tcph;
  92         int needs_ack;
  93
  94         skb_reset_transport_header(nskb);
  95         tcph = skb_put(nskb, sizeof(struct tcphdr));
  96         /* Truncate to length (no data) */
  97         tcph->doff = sizeof(struct tcphdr)/4;
  98         tcph->source = oth->dest;
  99         tcph->dest = oth->source;
 100
 101         if (oth->ack) {
 102                 needs_ack = 0;
 103                 tcph->seq = oth->ack_seq;
 104                 tcph->ack_seq = 0;
 105         } else {
 106                 needs_ack = 1;
 107                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
 108                                       otcplen - (oth->doff<<2));
 109                 tcph->seq = 0;
 110         }
 111
 112         /* Reset flags */
 113         ((u_int8_t *)tcph)[13] = 0;
 114         tcph->rst = 1;
 115         tcph->ack = needs_ack;
 116         tcph->window = 0;
 117         tcph->urg_ptr = 0;
 118         tcph->check = 0;
 119
 120         /* Adjust TCP checksum */
 121         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 122                                       &ipv6_hdr(nskb)->daddr,
 123                                       sizeof(struct tcphdr), IPPROTO_TCP,
 124                                       csum_partial(tcph,
 125                                                    sizeof(struct tcphdr), 0));
 126 }
 127 EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_put);
 128
 129 static int nf_reject6_fill_skb_dst(struct sk_buff *skb_in)
 130 {
 131         struct dst_entry *dst = NULL;
 132         struct flowi fl;
 133
 134         memset(&fl, 0, sizeof(struct flowi));
 135         fl.u.ip6.daddr = ipv6_hdr(skb_in)->saddr;
 136         nf_ip6_route(dev_net(skb_in->dev), &dst, &fl, false);
 137         if (!dst)
 138                 return -1;
 139
 140         skb_dst_set(skb_in, dst);
 141         return 0;
 142 }
 143
 144 void nf_send_reset6(struct net *net, struct sk_buff *oldskb, int hook)
 145 {
 146         struct net_device *br_indev __maybe_unused;
 147         struct sk_buff *nskb;
 148         struct tcphdr _otcph;
 149         const struct tcphdr *otcph;
 150         unsigned int otcplen, hh_len;
 151         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
 152         struct ipv6hdr *ip6h;
 153         struct dst_entry *dst = NULL;
 154         struct flowi6 fl6;
 155
 156         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
 157             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
 158                 pr_debug("addr is not unicast.\n");
 159                 return;
 160         }
 161
 162         otcph = nf_reject_ip6_tcphdr_get(oldskb, &_otcph, &otcplen, hook);
 163         if (!otcph)
 164                 return;
 165
 166         memset(&fl6, 0, sizeof(fl6));
 167         fl6.flowi6_proto = IPPROTO_TCP;
 168         fl6.saddr = oip6h->daddr;
 169         fl6.daddr = oip6h->saddr;
 170         fl6.fl6_sport = otcph->dest;
 171         fl6.fl6_dport = otcph->source;
 172
 173         if (hook == NF_INET_PRE_ROUTING) {
 174                 nf_ip6_route(net, &dst, flowi6_to_flowi(&fl6), false);
 175                 if (!dst)
 176                         return;
 177                 skb_dst_set(oldskb, dst);
 178         }
 179
 180         fl6.flowi6_oif = l3mdev_master_ifindex(skb_dst(oldskb)->dev);
 181         fl6.flowi6_mark = IP6_REPLY_MARK(net, oldskb->mark);
 182         security_skb_classify_flow(oldskb, flowi6_to_flowi_common(&fl6));
 183         dst = ip6_route_output(net, NULL, &fl6);
 184         if (dst->error) {
 185                 dst_release(dst);
 186                 return;
 187         }
 188         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
 189         if (IS_ERR(dst))
 190                 return;
 191
 192         hh_len = (dst->dev->hard_header_len + 15)&~15;
 193         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 194                          + sizeof(struct tcphdr) + dst->trailer_len,
 195                          GFP_ATOMIC);
 196
 197         if (!nskb) {
 198                 net_dbg_ratelimited("cannot alloc skb\n");
 199                 dst_release(dst);
 200                 return;
 201         }
 202
 203         skb_dst_set(nskb, dst);
 204
 205         nskb->mark = fl6.flowi6_mark;
 206
 207         skb_reserve(nskb, hh_len + dst->header_len);
 208         ip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
 209                                     ip6_dst_hoplimit(dst));
 210         nf_reject_ip6_tcphdr_put(nskb, oldskb, otcph, otcplen);
 211
 212         nf_ct_attach(nskb, oldskb);
 213
 214 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 215         /* If we use ip6_local_out for bridged traffic, the MAC source on
 216          * the RST will be ours, instead of the destination's.  This confuses
 217          * some routers/firewalls, and they drop the packet.  So we need to
 218          * build the eth header using the original destination's MAC as the
 219          * source, and send the RST packet directly.
 220          */
 221         br_indev = nf_bridge_get_physindev(oldskb);
 222         if (br_indev) {
 223                 struct ethhdr *oeth = eth_hdr(oldskb);
 224
 225                 nskb->dev = br_indev;
 226                 nskb->protocol = htons(ETH_P_IPV6);
 227                 ip6h->payload_len = htons(sizeof(struct tcphdr));
 228                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 229                                     oeth->h_source, oeth->h_dest, nskb->len) < 0) {
 230                         kfree_skb(nskb);
 231                         return;
 232                 }
 233                 dev_queue_xmit(nskb);
 234         } else
 235 #endif
 236                 ip6_local_out(net, nskb->sk, nskb);
 237 }
 238 EXPORT_SYMBOL_GPL(nf_send_reset6);
 239
 240 static bool reject6_csum_ok(struct sk_buff *skb, int hook)
 241 {
 242         const struct ipv6hdr *ip6h = ipv6_hdr(skb);
 243         int thoff;
 244         __be16 fo;
 245         u8 proto;
 246
 247         if (skb_csum_unnecessary(skb))
 248                 return true;
 249
 250         proto = ip6h->nexthdr;
 251         thoff = ipv6_skip_exthdr(skb, ((u8 *)(ip6h + 1) - skb->data), &proto, &fo);
 252
 253         if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
 254                 return false;
 255
 256         if (!nf_reject_verify_csum(proto))
 257                 return true;
 258
 259         return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
 260 }
 261
 262 void nf_send_unreach6(struct net *net, struct sk_buff *skb_in,
 263                       unsigned char code, unsigned int hooknum)
 264 {
 265         if (!reject6_csum_ok(skb_in, hooknum))
 266                 return;
 267
 268         if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 269                 skb_in->dev = net->loopback_dev;
 270
 271         if (hooknum == NF_INET_PRE_ROUTING && nf_reject6_fill_skb_dst(skb_in))
 272                 return;
 273
 274         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
 275 }
 276 EXPORT_SYMBOL_GPL(nf_send_unreach6);
 277
 278 MODULE_LICENSE("GPL");