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
18const 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}
45EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);
46
47struct 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}
70EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);
71
72void 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}
100EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);
101
102/* Send RST reply */
103void nf_send_reset(struct net *net, struct sk_buff *oldskb, int hook)
104{
105 struct net_device *br_indev __maybe_unused;
106 struct sk_buff *nskb;
107 struct iphdr *niph;
108 const struct tcphdr *oth;
109 struct tcphdr _oth;
110
111 oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
112 if (!oth)
113 return;
114
115 if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
116 return;
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 nskb->mark = IP4_REPLY_MARK(net, oldskb->mark);
127
128 skb_reserve(nskb, LL_MAX_HEADER);
129 niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
130 ip4_dst_hoplimit(skb_dst(nskb)));
131 nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
132
133 if (ip_route_me_harder(net, nskb, RTN_UNSPEC))
134 goto free_nskb;
135
136 niph = ip_hdr(nskb);
137
138 /* "Never happens" */
139 if (nskb->len > dst_mtu(skb_dst(nskb)))
140 goto free_nskb;
141
142 nf_ct_attach(nskb, oldskb);
143
144#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
145 /* If we use ip_local_out for bridged traffic, the MAC source on
146 * the RST will be ours, instead of the destination's. This confuses
147 * some routers/firewalls, and they drop the packet. So we need to
148 * build the eth header using the original destination's MAC as the
149 * source, and send the RST packet directly.
150 */
151 br_indev = nf_bridge_get_physindev(oldskb);
152 if (br_indev) {
153 struct ethhdr *oeth = eth_hdr(oldskb);
154
155 nskb->dev = br_indev;
156 niph->tot_len = htons(nskb->len);
157 ip_send_check(niph);
158 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
159 oeth->h_source, oeth->h_dest, nskb->len) < 0)
160 goto free_nskb;
161 dev_queue_xmit(nskb);
162 } else
163#endif
164 ip_local_out(net, nskb->sk, nskb);
165
166 return;
167
168 free_nskb:
169 kfree_skb(nskb);
170}
171EXPORT_SYMBOL_GPL(nf_send_reset);
172
173void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
174{
175 struct iphdr *iph = ip_hdr(skb_in);
176 u8 proto = iph->protocol;
177
178 if (iph->frag_off & htons(IP_OFFSET))
179 return;
180
181 if (skb_csum_unnecessary(skb_in) || !nf_reject_verify_csum(proto)) {
182 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
183 return;
184 }
185
186 if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), proto) == 0)
187 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
188}
189EXPORT_SYMBOL_GPL(nf_send_unreach);
190
191MODULE_LICENSE("GPL");
192