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Linux/net/ipv4/netfilter/nf_reject_ipv4.c

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  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 = 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         niph = ip_hdr(nskb);
136 
137         /* "Never happens" */
138         if (nskb->len > dst_mtu(skb_dst(nskb)))
139                 goto free_nskb;
140 
141         nf_ct_attach(nskb, oldskb);
142 
143 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
144         /* If we use ip_local_out for bridged traffic, the MAC source on
145          * the RST will be ours, instead of the destination's.  This confuses
146          * some routers/firewalls, and they drop the packet.  So we need to
147          * build the eth header using the original destination's MAC as the
148          * source, and send the RST packet directly.
149          */
150         if (oldskb->nf_bridge) {
151                 struct ethhdr *oeth = eth_hdr(oldskb);
152 
153                 nskb->dev = nf_bridge_get_physindev(oldskb);
154                 niph->tot_len = htons(nskb->len);
155                 ip_send_check(niph);
156                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
157                                     oeth->h_source, oeth->h_dest, nskb->len) < 0)
158                         goto free_nskb;
159                 dev_queue_xmit(nskb);
160         } else
161 #endif
162                 ip_local_out(net, nskb->sk, nskb);
163 
164         return;
165 
166  free_nskb:
167         kfree_skb(nskb);
168 }
169 EXPORT_SYMBOL_GPL(nf_send_reset);
170 
171 void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
172 {
173         struct iphdr *iph = ip_hdr(skb_in);
174         u8 proto;
175 
176         if (iph->frag_off & htons(IP_OFFSET))
177                 return;
178 
179         if (skb_csum_unnecessary(skb_in)) {
180                 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
181                 return;
182         }
183 
184         if (iph->protocol == IPPROTO_TCP || iph->protocol == IPPROTO_UDP)
185                 proto = iph->protocol;
186         else
187                 proto = 0;
188 
189         if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), proto) == 0)
190                 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
191 }
192 EXPORT_SYMBOL_GPL(nf_send_unreach);
193 
194 MODULE_LICENSE("GPL");
195 

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