net/ipv4/netfilter/nf_reject_ipv4.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/ip.h>
   8 #include <net/tcp.h>
   9 #include <net/route.h>
  10 #include <net/dst.h>
  11 #include <net/netfilter/ipv4/nf_reject.h>
  12 #include <linux/netfilter_ipv4.h>
  13 #include <linux/netfilter_bridge.h>
  14
  15 static int nf_reject_iphdr_validate(struct sk_buff *skb)
  16 {
  17         struct iphdr *iph;
  18         u32 len;
  19
  20         if (!pskb_may_pull(skb, sizeof(struct iphdr)))
  21                 return 0;
  22
  23         iph = ip_hdr(skb);
  24         if (iph->ihl < 5 || iph->version != 4)
  25                 return 0;
  26
  27         len = ntohs(iph->tot_len);
  28         if (skb->len < len)
  29                 return 0;
  30         else if (len < (iph->ihl*4))
  31                 return 0;
  32
  33         if (!pskb_may_pull(skb, iph->ihl*4))
  34                 return 0;
  35
  36         return 1;
  37 }
  38
  39 struct sk_buff *nf_reject_skb_v4_tcp_reset(struct net *net,
  40                                            struct sk_buff *oldskb,
  41                                            const struct net_device *dev,
  42                                            int hook)
  43 {
  44         const struct tcphdr *oth;
  45         struct sk_buff *nskb;
  46         struct iphdr *niph;
  47         struct tcphdr _oth;
  48
  49         if (!nf_reject_iphdr_validate(oldskb))
  50                 return NULL;
  51
  52         oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
  53         if (!oth)
  54                 return NULL;
  55
  56         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
  57                          LL_MAX_HEADER, GFP_ATOMIC);
  58         if (!nskb)
  59                 return NULL;
  60
  61         nskb->dev = (struct net_device *)dev;
  62
  63         skb_reserve(nskb, LL_MAX_HEADER);
  64         niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
  65                                    READ_ONCE(net->ipv4.sysctl_ip_default_ttl));
  66         nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
  67         niph->tot_len = htons(nskb->len);
  68         ip_send_check(niph);
  69
  70         return nskb;
  71 }
  72 EXPORT_SYMBOL_GPL(nf_reject_skb_v4_tcp_reset);
  73
  74 struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
  75                                          struct sk_buff *oldskb,
  76                                          const struct net_device *dev,
  77                                          int hook, u8 code)
  78 {
  79         struct sk_buff *nskb;
  80         struct iphdr *niph;
  81         struct icmphdr *icmph;
  82         unsigned int len;
  83         int dataoff;
  84         __wsum csum;
  85         u8 proto;
  86
  87         if (!nf_reject_iphdr_validate(oldskb))
  88                 return NULL;
  89
  90         /* IP header checks: fragment. */
  91         if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
  92                 return NULL;
  93
  94         /* RFC says return as much as we can without exceeding 576 bytes. */
  95         len = min_t(unsigned int, 536, oldskb->len);
  96
  97         if (!pskb_may_pull(oldskb, len))
  98                 return NULL;
  99
 100         if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
 101                 return NULL;
 102
 103         dataoff = ip_hdrlen(oldskb);
 104         proto = ip_hdr(oldskb)->protocol;
 105
 106         if (!skb_csum_unnecessary(oldskb) &&
 107             nf_reject_verify_csum(oldskb, dataoff, proto) &&
 108             nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), proto))
 109                 return NULL;
 110
 111         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct icmphdr) +
 112                          LL_MAX_HEADER + len, GFP_ATOMIC);
 113         if (!nskb)
 114                 return NULL;
 115
 116         nskb->dev = (struct net_device *)dev;
 117
 118         skb_reserve(nskb, LL_MAX_HEADER);
 119         niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_ICMP,
 120                                    READ_ONCE(net->ipv4.sysctl_ip_default_ttl));
 121
 122         skb_reset_transport_header(nskb);
 123         icmph = skb_put_zero(nskb, sizeof(struct icmphdr));
 124         icmph->type     = ICMP_DEST_UNREACH;
 125         icmph->code     = code;
 126
 127         skb_put_data(nskb, skb_network_header(oldskb), len);
 128
 129         csum = csum_partial((void *)icmph, len + sizeof(struct icmphdr), 0);
 130         icmph->checksum = csum_fold(csum);
 131
 132         niph->tot_len   = htons(nskb->len);
 133         ip_send_check(niph);
 134
 135         return nskb;
 136 }
 137 EXPORT_SYMBOL_GPL(nf_reject_skb_v4_unreach);
 138
 139 const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,
 140                                              struct tcphdr *_oth, int hook)
 141 {
 142         const struct tcphdr *oth;
 143
 144         /* IP header checks: fragment. */
 145         if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
 146                 return NULL;
 147
 148         if (ip_hdr(oldskb)->protocol != IPPROTO_TCP)
 149                 return NULL;
 150
 151         oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
 152                                  sizeof(struct tcphdr), _oth);
 153         if (oth == NULL)
 154                 return NULL;
 155
 156         /* No RST for RST. */
 157         if (oth->rst)
 158                 return NULL;
 159
 160         /* Check checksum */
 161         if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
 162                 return NULL;
 163
 164         return oth;
 165 }
 166 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);
 167
 168 struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,
 169                                   const struct sk_buff *oldskb,
 170                                   __u8 protocol, int ttl)
 171 {
 172         struct iphdr *niph, *oiph = ip_hdr(oldskb);
 173
 174         skb_reset_network_header(nskb);
 175         niph = skb_put(nskb, sizeof(struct iphdr));
 176         niph->version   = 4;
 177         niph->ihl       = sizeof(struct iphdr) / 4;
 178         niph->tos       = 0;
 179         niph->id        = 0;
 180         niph->frag_off  = htons(IP_DF);
 181         niph->protocol  = protocol;
 182         niph->check     = 0;
 183         niph->saddr     = oiph->daddr;
 184         niph->daddr     = oiph->saddr;
 185         niph->ttl       = ttl;
 186
 187         nskb->protocol = htons(ETH_P_IP);
 188
 189         return niph;
 190 }
 191 EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);
 192
 193 void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,
 194                           const struct tcphdr *oth)
 195 {
 196         struct iphdr *niph = ip_hdr(nskb);
 197         struct tcphdr *tcph;
 198
 199         skb_reset_transport_header(nskb);
 200         tcph = skb_put_zero(nskb, sizeof(struct tcphdr));
 201         tcph->source    = oth->dest;
 202         tcph->dest      = oth->source;
 203         tcph->doff      = sizeof(struct tcphdr) / 4;
 204
 205         if (oth->ack) {
 206                 tcph->seq = oth->ack_seq;
 207         } else {
 208                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
 209                                       oldskb->len - ip_hdrlen(oldskb) -
 210                                       (oth->doff << 2));
 211                 tcph->ack = 1;
 212         }
 213
 214         tcph->rst       = 1;
 215         tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
 216                                     niph->daddr, 0);
 217         nskb->ip_summed = CHECKSUM_PARTIAL;
 218         nskb->csum_start = (unsigned char *)tcph - nskb->head;
 219         nskb->csum_offset = offsetof(struct tcphdr, check);
 220 }
 221 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);
 222
 223 static int nf_reject_fill_skb_dst(struct sk_buff *skb_in)
 224 {
 225         struct dst_entry *dst = NULL;
 226         struct flowi fl;
 227
 228         memset(&fl, 0, sizeof(struct flowi));
 229         fl.u.ip4.daddr = ip_hdr(skb_in)->saddr;
 230         nf_ip_route(dev_net(skb_in->dev), &dst, &fl, false);
 231         if (!dst)
 232                 return -1;
 233
 234         skb_dst_set(skb_in, dst);
 235         return 0;
 236 }
 237
 238 /* Send RST reply */
 239 void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
 240                    int hook)
 241 {
 242         struct sk_buff *nskb;
 243         struct iphdr *niph;
 244         const struct tcphdr *oth;
 245         struct tcphdr _oth;
 246
 247         oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
 248         if (!oth)
 249                 return;
 250
 251         if ((hook == NF_INET_PRE_ROUTING || hook == NF_INET_INGRESS) &&
 252             nf_reject_fill_skb_dst(oldskb) < 0)
 253                 return;
 254
 255         if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
 256                 return;
 257
 258         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
 259                          LL_MAX_HEADER, GFP_ATOMIC);
 260         if (!nskb)
 261                 return;
 262
 263         /* ip_route_me_harder expects skb->dst to be set */
 264         skb_dst_set_noref(nskb, skb_dst(oldskb));
 265
 266         nskb->mark = IP4_REPLY_MARK(net, oldskb->mark);
 267
 268         skb_reserve(nskb, LL_MAX_HEADER);
 269         niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
 270                                    ip4_dst_hoplimit(skb_dst(nskb)));
 271         nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
 272         if (ip_route_me_harder(net, sk, nskb, RTN_UNSPEC))
 273                 goto free_nskb;
 274
 275         niph = ip_hdr(nskb);
 276
 277         /* "Never happens" */
 278         if (nskb->len > dst_mtu(skb_dst(nskb)))
 279                 goto free_nskb;
 280
 281         nf_ct_attach(nskb, oldskb);
 282         nf_ct_set_closing(skb_nfct(oldskb));
 283
 284 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 285         /* If we use ip_local_out for bridged traffic, the MAC source on
 286          * the RST will be ours, instead of the destination's.  This confuses
 287          * some routers/firewalls, and they drop the packet.  So we need to
 288          * build the eth header using the original destination's MAC as the
 289          * source, and send the RST packet directly.
 290          */
 291         if (nf_bridge_info_exists(oldskb)) {
 292                 struct ethhdr *oeth = eth_hdr(oldskb);
 293                 struct net_device *br_indev;
 294
 295                 br_indev = nf_bridge_get_physindev(oldskb, net);
 296                 if (!br_indev)
 297                         goto free_nskb;
 298
 299                 nskb->dev = br_indev;
 300                 niph->tot_len = htons(nskb->len);
 301                 ip_send_check(niph);
 302                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 303                                     oeth->h_source, oeth->h_dest, nskb->len) < 0)
 304                         goto free_nskb;
 305                 dev_queue_xmit(nskb);
 306         } else
 307 #endif
 308                 ip_local_out(net, nskb->sk, nskb);
 309
 310         return;
 311
 312  free_nskb:
 313         kfree_skb(nskb);
 314 }
 315 EXPORT_SYMBOL_GPL(nf_send_reset);
 316
 317 void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
 318 {
 319         struct iphdr *iph = ip_hdr(skb_in);
 320         int dataoff = ip_hdrlen(skb_in);
 321         u8 proto = iph->protocol;
 322
 323         if (iph->frag_off & htons(IP_OFFSET))
 324                 return;
 325
 326         if ((hook == NF_INET_PRE_ROUTING || hook == NF_INET_INGRESS) &&
 327             nf_reject_fill_skb_dst(skb_in) < 0)
 328                 return;
 329
 330         if (skb_csum_unnecessary(skb_in) ||
 331             !nf_reject_verify_csum(skb_in, dataoff, proto)) {
 332                 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 333                 return;
 334         }
 335
 336         if (nf_ip_checksum(skb_in, hook, dataoff, proto) == 0)
 337                 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 338 }
 339 EXPORT_SYMBOL_GPL(nf_send_unreach);
 340
 341 MODULE_LICENSE("GPL");