net/ipv4/netfilter/nf_reject_ipv4.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/ip.h>
  11 #include <net/tcp.h>
  12 #include <net/route.h>
  13 #include <net/dst.h>
  14 #include <net/netfilter/ipv4/nf_reject.h>
  15 #include <linux/netfilter_ipv4.h>
  16 #include <linux/netfilter_bridge.h>
  17
  18 const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,
  19                                              struct tcphdr *_oth, int hook)
  20 {
  21         const struct tcphdr *oth;
  22
  23         /* IP header checks: fragment. */
  24         if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
  25                 return NULL;
  26
  27         if (ip_hdr(oldskb)->protocol != IPPROTO_TCP)
  28                 return NULL;
  29
  30         oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
  31                                  sizeof(struct tcphdr), _oth);
  32         if (oth == NULL)
  33                 return NULL;
  34
  35         /* No RST for RST. */
  36         if (oth->rst)
  37                 return NULL;
  38
  39         /* Check checksum */
  40         if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
  41                 return NULL;
  42
  43         return oth;
  44 }
  45 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);
  46
  47 struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,
  48                                   const struct sk_buff *oldskb,
  49                                   __u8 protocol, int ttl)
  50 {
  51         struct iphdr *niph, *oiph = ip_hdr(oldskb);
  52
  53         skb_reset_network_header(nskb);
  54         niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
  55         niph->version   = 4;
  56         niph->ihl       = sizeof(struct iphdr) / 4;
  57         niph->tos       = 0;
  58         niph->id        = 0;
  59         niph->frag_off  = htons(IP_DF);
  60         niph->protocol  = protocol;
  61         niph->check     = 0;
  62         niph->saddr     = oiph->daddr;
  63         niph->daddr     = oiph->saddr;
  64         niph->ttl       = ttl;
  65
  66         nskb->protocol = htons(ETH_P_IP);
  67
  68         return niph;
  69 }
  70 EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);
  71
  72 void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,
  73                           const struct tcphdr *oth)
  74 {
  75         struct iphdr *niph = ip_hdr(nskb);
  76         struct tcphdr *tcph;
  77
  78         skb_reset_transport_header(nskb);
  79         tcph = skb_put_zero(nskb, sizeof(struct tcphdr));
  80         tcph->source    = oth->dest;
  81         tcph->dest      = oth->source;
  82         tcph->doff      = sizeof(struct tcphdr) / 4;
  83
  84         if (oth->ack) {
  85                 tcph->seq = oth->ack_seq;
  86         } else {
  87                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
  88                                       oldskb->len - ip_hdrlen(oldskb) -
  89                                       (oth->doff << 2));
  90                 tcph->ack = 1;
  91         }
  92
  93         tcph->rst       = 1;
  94         tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
  95                                     niph->daddr, 0);
  96         nskb->ip_summed = CHECKSUM_PARTIAL;
  97         nskb->csum_start = (unsigned char *)tcph - nskb->head;
  98         nskb->csum_offset = offsetof(struct tcphdr, check);
  99 }
 100 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);
 101
 102 /* Send RST reply */
 103 void nf_send_reset(struct net *net, struct sk_buff *oldskb, int hook)
 104 {
 105         struct sk_buff *nskb;
 106         struct iphdr *niph;
 107         const struct tcphdr *oth;
 108         struct tcphdr _oth;
 109
 110         oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
 111         if (!oth)
 112                 return;
 113
 114         if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
 115                 return;
 116
 117         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
 118                          LL_MAX_HEADER, GFP_ATOMIC);
 119         if (!nskb)
 120                 return;
 121
 122         /* ip_route_me_harder expects skb->dst to be set */
 123         skb_dst_set_noref(nskb, skb_dst(oldskb));
 124
 125         nskb->mark = IP4_REPLY_MARK(net, oldskb->mark);
 126
 127         skb_reserve(nskb, LL_MAX_HEADER);
 128         niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
 129                                    ip4_dst_hoplimit(skb_dst(nskb)));
 130         nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
 131
 132         if (ip_route_me_harder(net, nskb, RTN_UNSPEC))
 133                 goto free_nskb;
 134
 135         /* "Never happens" */
 136         if (nskb->len > dst_mtu(skb_dst(nskb)))
 137                 goto free_nskb;
 138
 139         nf_ct_attach(nskb, oldskb);
 140
 141 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 142         /* If we use ip_local_out for bridged traffic, the MAC source on
 143          * the RST will be ours, instead of the destination's.  This confuses
 144          * some routers/firewalls, and they drop the packet.  So we need to
 145          * build the eth header using the original destination's MAC as the
 146          * source, and send the RST packet directly.
 147          */
 148         if (oldskb->nf_bridge) {
 149                 struct ethhdr *oeth = eth_hdr(oldskb);
 150
 151                 nskb->dev = nf_bridge_get_physindev(oldskb);
 152                 niph->tot_len = htons(nskb->len);
 153                 ip_send_check(niph);
 154                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 155                                     oeth->h_source, oeth->h_dest, nskb->len) < 0)
 156                         goto free_nskb;
 157                 dev_queue_xmit(nskb);
 158         } else
 159 #endif
 160                 ip_local_out(net, nskb->sk, nskb);
 161
 162         return;
 163
 164  free_nskb:
 165         kfree_skb(nskb);
 166 }
 167 EXPORT_SYMBOL_GPL(nf_send_reset);
 168
 169 void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
 170 {
 171         struct iphdr *iph = ip_hdr(skb_in);
 172         u8 proto;
 173
 174         if (iph->frag_off & htons(IP_OFFSET))
 175                 return;
 176
 177         if (skb_csum_unnecessary(skb_in)) {
 178                 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 179                 return;
 180         }
 181
 182         if (iph->protocol == IPPROTO_TCP || iph->protocol == IPPROTO_UDP)
 183                 proto = iph->protocol;
 184         else
 185                 proto = 0;
 186
 187         if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), proto) == 0)
 188                 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 189 }
 190 EXPORT_SYMBOL_GPL(nf_send_unreach);
 191
 192 MODULE_LICENSE("GPL");