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 <net/netfilter/ipv4/nf_reject.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         oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
  28                                  sizeof(struct tcphdr), _oth);
  29         if (oth == NULL)
  30                 return NULL;
  31
  32         /* No RST for RST. */
  33         if (oth->rst)
  34                 return NULL;
  35
  36         /* Check checksum */
  37         if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
  38                 return NULL;
  39
  40         return oth;
  41 }
  42 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);
  43
  44 struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,
  45                                   const struct sk_buff *oldskb,
  46                                   __be16 protocol, int ttl)
  47 {
  48         struct iphdr *niph, *oiph = ip_hdr(oldskb);
  49
  50         skb_reset_network_header(nskb);
  51         niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
  52         niph->version   = 4;
  53         niph->ihl       = sizeof(struct iphdr) / 4;
  54         niph->tos       = 0;
  55         niph->id        = 0;
  56         niph->frag_off  = htons(IP_DF);
  57         niph->protocol  = protocol;
  58         niph->check     = 0;
  59         niph->saddr     = oiph->daddr;
  60         niph->daddr     = oiph->saddr;
  61         niph->ttl       = ttl;
  62
  63         nskb->protocol = htons(ETH_P_IP);
  64
  65         return niph;
  66 }
  67 EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);
  68
  69 void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,
  70                           const struct tcphdr *oth)
  71 {
  72         struct iphdr *niph = ip_hdr(nskb);
  73         struct tcphdr *tcph;
  74
  75         skb_reset_transport_header(nskb);
  76         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
  77         memset(tcph, 0, sizeof(*tcph));
  78         tcph->source    = oth->dest;
  79         tcph->dest      = oth->source;
  80         tcph->doff      = sizeof(struct tcphdr) / 4;
  81
  82         if (oth->ack) {
  83                 tcph->seq = oth->ack_seq;
  84         } else {
  85                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
  86                                       oldskb->len - ip_hdrlen(oldskb) -
  87                                       (oth->doff << 2));
  88                 tcph->ack = 1;
  89         }
  90
  91         tcph->rst       = 1;
  92         tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
  93                                     niph->daddr, 0);
  94         nskb->ip_summed = CHECKSUM_PARTIAL;
  95         nskb->csum_start = (unsigned char *)tcph - nskb->head;
  96         nskb->csum_offset = offsetof(struct tcphdr, check);
  97 }
  98 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);
  99
 100 /* Send RST reply */
 101 void nf_send_reset(struct sk_buff *oldskb, int hook)
 102 {
 103         struct sk_buff *nskb;
 104         const struct iphdr *oiph;
 105         struct iphdr *niph;
 106         const struct tcphdr *oth;
 107         struct tcphdr _oth;
 108
 109         oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
 110         if (!oth)
 111                 return;
 112
 113         if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
 114                 return;
 115
 116         oiph = ip_hdr(oldskb);
 117
 118         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
 119                          LL_MAX_HEADER, GFP_ATOMIC);
 120         if (!nskb)
 121                 return;
 122
 123         /* ip_route_me_harder expects skb->dst to be set */
 124         skb_dst_set_noref(nskb, skb_dst(oldskb));
 125
 126         skb_reserve(nskb, LL_MAX_HEADER);
 127         niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
 128                                    ip4_dst_hoplimit(skb_dst(nskb)));
 129         nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
 130
 131         if (ip_route_me_harder(nskb, RTN_UNSPEC))
 132                 goto free_nskb;
 133
 134         /* "Never happens" */
 135         if (nskb->len > dst_mtu(skb_dst(nskb)))
 136                 goto free_nskb;
 137
 138         nf_ct_attach(nskb, oldskb);
 139
 140 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 141         /* If we use ip_local_out for bridged traffic, the MAC source on
 142          * the RST will be ours, instead of the destination's.  This confuses
 143          * some routers/firewalls, and they drop the packet.  So we need to
 144          * build the eth header using the original destination's MAC as the
 145          * source, and send the RST packet directly.
 146          */
 147         if (oldskb->nf_bridge) {
 148                 struct ethhdr *oeth = eth_hdr(oldskb);
 149                 nskb->dev = oldskb->nf_bridge->physindev;
 150                 niph->tot_len = htons(nskb->len);
 151                 ip_send_check(niph);
 152                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 153                                     oeth->h_source, oeth->h_dest, nskb->len) < 0)
 154                         goto free_nskb;
 155                 dev_queue_xmit(nskb);
 156         } else
 157 #endif
 158                 ip_local_out(nskb);
 159
 160         return;
 161
 162  free_nskb:
 163         kfree_skb(nskb);
 164 }
 165 EXPORT_SYMBOL_GPL(nf_send_reset);
 166
 167 MODULE_LICENSE("GPL");