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 <linux/netfilter_ipv4.h>
  15 #include <net/netfilter/ipv4/nf_reject.h>
  16
  17 const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,
  18                                              struct tcphdr *_oth, int hook)
  19 {
  20         const struct tcphdr *oth;
  21
  22         /* IP header checks: fragment. */
  23         if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
  24                 return NULL;
  25
  26         oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
  27                                  sizeof(struct tcphdr), _oth);
  28         if (oth == NULL)
  29                 return NULL;
  30
  31         /* No RST for RST. */
  32         if (oth->rst)
  33                 return NULL;
  34
  35         /* Check checksum */
  36         if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
  37                 return NULL;
  38
  39         return oth;
  40 }
  41 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);
  42
  43 struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,
  44                                   const struct sk_buff *oldskb,
  45                                   __be16 protocol, int ttl)
  46 {
  47         struct iphdr *niph, *oiph = ip_hdr(oldskb);
  48
  49         skb_reset_network_header(nskb);
  50         niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
  51         niph->version   = 4;
  52         niph->ihl       = sizeof(struct iphdr) / 4;
  53         niph->tos       = 0;
  54         niph->id        = 0;
  55         niph->frag_off  = htons(IP_DF);
  56         niph->protocol  = protocol;
  57         niph->check     = 0;
  58         niph->saddr     = oiph->daddr;
  59         niph->daddr     = oiph->saddr;
  60         niph->ttl       = ttl;
  61
  62         nskb->protocol = htons(ETH_P_IP);
  63
  64         return niph;
  65 }
  66 EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);
  67
  68 void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,
  69                           const struct tcphdr *oth)
  70 {
  71         struct iphdr *niph = ip_hdr(nskb);
  72         struct tcphdr *tcph;
  73
  74         skb_reset_transport_header(nskb);
  75         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
  76         memset(tcph, 0, sizeof(*tcph));
  77         tcph->source    = oth->dest;
  78         tcph->dest      = oth->source;
  79         tcph->doff      = sizeof(struct tcphdr) / 4;
  80
  81         if (oth->ack) {
  82                 tcph->seq = oth->ack_seq;
  83         } else {
  84                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
  85                                       oldskb->len - ip_hdrlen(oldskb) -
  86                                       (oth->doff << 2));
  87                 tcph->ack = 1;
  88         }
  89
  90         tcph->rst       = 1;
  91         tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
  92                                     niph->daddr, 0);
  93         nskb->ip_summed = CHECKSUM_PARTIAL;
  94         nskb->csum_start = (unsigned char *)tcph - nskb->head;
  95         nskb->csum_offset = offsetof(struct tcphdr, check);
  96 }
  97 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);
  98
  99 /* Send RST reply */
 100 void nf_send_reset(struct sk_buff *oldskb, int hook)
 101 {
 102         struct sk_buff *nskb;
 103         const struct iphdr *oiph;
 104         struct iphdr *niph;
 105         const struct tcphdr *oth;
 106         struct tcphdr _oth;
 107
 108         oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
 109         if (!oth)
 110                 return;
 111
 112         if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
 113                 return;
 114
 115         oiph = ip_hdr(oldskb);
 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         skb_reserve(nskb, LL_MAX_HEADER);
 126         niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
 127                                    ip4_dst_hoplimit(skb_dst(nskb)));
 128         nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
 129
 130         if (ip_route_me_harder(nskb, RTN_UNSPEC))
 131                 goto free_nskb;
 132
 133         /* "Never happens" */
 134         if (nskb->len > dst_mtu(skb_dst(nskb)))
 135                 goto free_nskb;
 136
 137         nf_ct_attach(nskb, oldskb);
 138
 139 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 140         /* If we use ip_local_out for bridged traffic, the MAC source on
 141          * the RST will be ours, instead of the destination's.  This confuses
 142          * some routers/firewalls, and they drop the packet.  So we need to
 143          * build the eth header using the original destination's MAC as the
 144          * source, and send the RST packet directly.
 145          */
 146         if (oldskb->nf_bridge) {
 147                 struct ethhdr *oeth = eth_hdr(oldskb);
 148                 nskb->dev = oldskb->nf_bridge->physindev;
 149                 niph->tot_len = htons(nskb->len);
 150                 ip_send_check(niph);
 151                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 152                                     oeth->h_source, oeth->h_dest, nskb->len) < 0)
 153                         goto free_nskb;
 154                 dev_queue_xmit(nskb);
 155         } else
 156 #endif
 157                 ip_local_out(nskb);
 158
 159         return;
 160
 161  free_nskb:
 162         kfree_skb(nskb);
 163 }
 164 EXPORT_SYMBOL_GPL(nf_send_reset);
 165
 166 MODULE_LICENSE("GPL");