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 #include <net/netfilter/ipv4/nf_reject.h>
18
nf_reject_ip_tcphdr_get(struct sk_buff * oldskb,struct tcphdr * _oth,int hook)19 const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,
20 struct tcphdr *_oth, int hook)
21 {
22 const struct tcphdr *oth;
23
24 /* IP header checks: fragment. */
25 if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
26 return NULL;
27
28 oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
29 sizeof(struct tcphdr), _oth);
30 if (oth == NULL)
31 return NULL;
32
33 /* No RST for RST. */
34 if (oth->rst)
35 return NULL;
36
37 /* Check checksum */
38 if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
39 return NULL;
40
41 return oth;
42 }
43 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);
44
nf_reject_iphdr_put(struct sk_buff * nskb,const struct sk_buff * oldskb,__u8 protocol,int ttl)45 struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,
46 const struct sk_buff *oldskb,
47 __u8 protocol, int ttl)
48 {
49 struct iphdr *niph, *oiph = ip_hdr(oldskb);
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 = protocol;
59 niph->check = 0;
60 niph->saddr = oiph->daddr;
61 niph->daddr = oiph->saddr;
62 niph->ttl = ttl;
63
64 nskb->protocol = htons(ETH_P_IP);
65
66 return niph;
67 }
68 EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);
69
nf_reject_ip_tcphdr_put(struct sk_buff * nskb,const struct sk_buff * oldskb,const struct tcphdr * oth)70 void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,
71 const struct tcphdr *oth)
72 {
73 struct iphdr *niph = ip_hdr(nskb);
74 struct tcphdr *tcph;
75
76 skb_reset_transport_header(nskb);
77 tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
78 memset(tcph, 0, sizeof(*tcph));
79 tcph->source = oth->dest;
80 tcph->dest = oth->source;
81 tcph->doff = sizeof(struct tcphdr) / 4;
82
83 if (oth->ack) {
84 tcph->seq = oth->ack_seq;
85 } else {
86 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
87 oldskb->len - ip_hdrlen(oldskb) -
88 (oth->doff << 2));
89 tcph->ack = 1;
90 }
91
92 tcph->rst = 1;
93 tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
94 niph->daddr, 0);
95 nskb->ip_summed = CHECKSUM_PARTIAL;
96 nskb->csum_start = (unsigned char *)tcph - nskb->head;
97 nskb->csum_offset = offsetof(struct tcphdr, check);
98 }
99 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);
100
101 /* Send RST reply */
nf_send_reset(struct sk_buff * oldskb,int hook)102 void nf_send_reset(struct sk_buff *oldskb, int hook)
103 {
104 struct sk_buff *nskb;
105 const struct iphdr *oiph;
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 oiph = ip_hdr(oldskb);
118
119 nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
120 LL_MAX_HEADER, GFP_ATOMIC);
121 if (!nskb)
122 return;
123
124 /* ip_route_me_harder expects skb->dst to be set */
125 skb_dst_set_noref(nskb, skb_dst(oldskb));
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(nskb, RTN_UNSPEC))
133 goto free_nskb;
134
135 /* "Never happens" */
136 if (nskb->len > dst_mtu(skb_dst(nskb)))
137 goto free_nskb;
138
139 nf_ct_attach(nskb, oldskb);
140
141 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
142 /* If we use ip_local_out for bridged traffic, the MAC source on
143 * the RST will be ours, instead of the destination's. This confuses
144 * some routers/firewalls, and they drop the packet. So we need to
145 * build the eth header using the original destination's MAC as the
146 * source, and send the RST packet directly.
147 */
148 if (oldskb->nf_bridge) {
149 struct ethhdr *oeth = eth_hdr(oldskb);
150
151 nskb->dev = nf_bridge_get_physindev(oldskb);
152 niph->tot_len = htons(nskb->len);
153 ip_send_check(niph);
154 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
155 oeth->h_source, oeth->h_dest, nskb->len) < 0)
156 goto free_nskb;
157 dev_queue_xmit(nskb);
158 } else
159 #endif
160 ip_local_out(nskb);
161
162 return;
163
164 free_nskb:
165 kfree_skb(nskb);
166 }
167 EXPORT_SYMBOL_GPL(nf_send_reset);
168
nf_send_unreach(struct sk_buff * skb_in,int code,int hook)169 void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
170 {
171 struct iphdr *iph = ip_hdr(skb_in);
172 u8 proto;
173
174 if (skb_in->csum_bad || iph->frag_off & htons(IP_OFFSET))
175 return;
176
177 if (skb_csum_unnecessary(skb_in)) {
178 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
179 return;
180 }
181
182 if (iph->protocol == IPPROTO_TCP || iph->protocol == IPPROTO_UDP)
183 proto = iph->protocol;
184 else
185 proto = 0;
186
187 if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), proto) == 0)
188 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
189 }
190 EXPORT_SYMBOL_GPL(nf_send_unreach);
191
192 MODULE_LICENSE("GPL");
193