include/net/netfilter/ipv4/nf_reject.h

   1 #ifndef _IPV4_NF_REJECT_H
   2 #define _IPV4_NF_REJECT_H
   3
   4 #include <net/ip.h>
   5 #include <net/tcp.h>
   6 #include <net/route.h>
   7 #include <net/dst.h>
   8
   9 static inline void nf_send_unreach(struct sk_buff *skb_in, int code)
  10 {
  11         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
  12 }
  13
  14 /* Send RST reply */
  15 static void nf_send_reset(struct sk_buff *oldskb, int hook)
  16 {
  17         struct sk_buff *nskb;
  18         const struct iphdr *oiph;
  19         struct iphdr *niph;
  20         const struct tcphdr *oth;
  21         struct tcphdr _otcph, *tcph;
  22
  23         /* IP header checks: fragment. */
  24         if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
  25                 return;
  26
  27         oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
  28                                  sizeof(_otcph), &_otcph);
  29         if (oth == NULL)
  30                 return;
  31
  32         /* No RST for RST. */
  33         if (oth->rst)
  34                 return;
  35
  36         if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
  37                 return;
  38
  39         /* Check checksum */
  40         if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
  41                 return;
  42         oiph = ip_hdr(oldskb);
  43
  44         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
  45                          LL_MAX_HEADER, GFP_ATOMIC);
  46         if (!nskb)
  47                 return;
  48
  49         skb_reserve(nskb, LL_MAX_HEADER);
  50
  51         skb_reset_network_header(nskb);
  52         niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
  53         niph->version   = 4;
  54         niph->ihl       = sizeof(struct iphdr) / 4;
  55         niph->tos       = 0;
  56         niph->id        = 0;
  57         niph->frag_off  = htons(IP_DF);
  58         niph->protocol  = IPPROTO_TCP;
  59         niph->check     = 0;
  60         niph->saddr     = oiph->daddr;
  61         niph->daddr     = oiph->saddr;
  62
  63         skb_reset_transport_header(nskb);
  64         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
  65         memset(tcph, 0, sizeof(*tcph));
  66         tcph->source    = oth->dest;
  67         tcph->dest      = oth->source;
  68         tcph->doff      = sizeof(struct tcphdr) / 4;
  69
  70         if (oth->ack)
  71                 tcph->seq = oth->ack_seq;
  72         else {
  73                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
  74                                       oldskb->len - ip_hdrlen(oldskb) -
  75                                       (oth->doff << 2));
  76                 tcph->ack = 1;
  77         }
  78
  79         tcph->rst       = 1;
  80         tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
  81                                     niph->daddr, 0);
  82         nskb->ip_summed = CHECKSUM_PARTIAL;
  83         nskb->csum_start = (unsigned char *)tcph - nskb->head;
  84         nskb->csum_offset = offsetof(struct tcphdr, check);
  85
  86         /* ip_route_me_harder expects skb->dst to be set */
  87         skb_dst_set_noref(nskb, skb_dst(oldskb));
  88
  89         nskb->protocol = htons(ETH_P_IP);
  90         if (ip_route_me_harder(nskb, RTN_UNSPEC))
  91                 goto free_nskb;
  92
  93         niph->ttl       = ip4_dst_hoplimit(skb_dst(nskb));
  94
  95         /* "Never happens" */
  96         if (nskb->len > dst_mtu(skb_dst(nskb)))
  97                 goto free_nskb;
  98
  99         nf_ct_attach(nskb, oldskb);
 100
 101 #ifdef CONFIG_BRIDGE_NETFILTER
 102         /* If we use ip_local_out for bridged traffic, the MAC source on
 103          * the RST will be ours, instead of the destination's.  This confuses
 104          * some routers/firewalls, and they drop the packet.  So we need to
 105          * build the eth header using the original destination's MAC as the
 106          * source, and send the RST packet directly.
 107          */
 108         if (oldskb->nf_bridge) {
 109                 struct ethhdr *oeth = eth_hdr(oldskb);
 110                 nskb->dev = oldskb->nf_bridge->physindev;
 111                 niph->tot_len = htons(nskb->len);
 112                 ip_send_check(niph);
 113                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 114                                     oeth->h_source, oeth->h_dest, nskb->len) < 0)
 115                         goto free_nskb;
 116                 dev_queue_xmit(nskb);
 117         } else
 118 #endif
 119                 ip_local_out(nskb);
 120
 121         return;
 122
 123  free_nskb:
 124         kfree_skb(nskb);
 125 }
 126
 127
 128 #endif /* _IPV4_NF_REJECT_H */