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 <linux/netfilter_ipv4.h>
15 #include <net/netfilter/ipv4/nf_reject.h>
16
nf_reject_ip_tcphdr_get(struct sk_buff * oldskb,struct tcphdr * _oth,int hook)17 const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,
18 struct tcphdr *_oth, int hook)
19 {
20 const struct tcphdr *oth;
21
22 /* IP header checks: fragment. */
23 if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
24 return NULL;
25
26 oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
27 sizeof(struct tcphdr), _oth);
28 if (oth == NULL)
29 return NULL;
30
31 /* No RST for RST. */
32 if (oth->rst)
33 return NULL;
34
35 /* Check checksum */
36 if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
37 return NULL;
38
39 return oth;
40 }
41 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);
42
nf_reject_iphdr_put(struct sk_buff * nskb,const struct sk_buff * oldskb,__be16 protocol,int ttl)43 struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,
44 const struct sk_buff *oldskb,
45 __be16 protocol, int ttl)
46 {
47 struct iphdr *niph, *oiph = ip_hdr(oldskb);
48
49 skb_reset_network_header(nskb);
50 niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
51 niph->version = 4;
52 niph->ihl = sizeof(struct iphdr) / 4;
53 niph->tos = 0;
54 niph->id = 0;
55 niph->frag_off = htons(IP_DF);
56 niph->protocol = protocol;
57 niph->check = 0;
58 niph->saddr = oiph->daddr;
59 niph->daddr = oiph->saddr;
60 niph->ttl = ttl;
61
62 nskb->protocol = htons(ETH_P_IP);
63
64 return niph;
65 }
66 EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);
67
nf_reject_ip_tcphdr_put(struct sk_buff * nskb,const struct sk_buff * oldskb,const struct tcphdr * oth)68 void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,
69 const struct tcphdr *oth)
70 {
71 struct iphdr *niph = ip_hdr(nskb);
72 struct tcphdr *tcph;
73
74 skb_reset_transport_header(nskb);
75 tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
76 memset(tcph, 0, sizeof(*tcph));
77 tcph->source = oth->dest;
78 tcph->dest = oth->source;
79 tcph->doff = sizeof(struct tcphdr) / 4;
80
81 if (oth->ack) {
82 tcph->seq = oth->ack_seq;
83 } else {
84 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
85 oldskb->len - ip_hdrlen(oldskb) -
86 (oth->doff << 2));
87 tcph->ack = 1;
88 }
89
90 tcph->rst = 1;
91 tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
92 niph->daddr, 0);
93 nskb->ip_summed = CHECKSUM_PARTIAL;
94 nskb->csum_start = (unsigned char *)tcph - nskb->head;
95 nskb->csum_offset = offsetof(struct tcphdr, check);
96 }
97 EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);
98
99 /* Send RST reply */
nf_send_reset(struct sk_buff * oldskb,int hook)100 void nf_send_reset(struct sk_buff *oldskb, int hook)
101 {
102 struct sk_buff *nskb;
103 const struct iphdr *oiph;
104 struct iphdr *niph;
105 const struct tcphdr *oth;
106 struct tcphdr _oth;
107
108 oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
109 if (!oth)
110 return;
111
112 if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
113 return;
114
115 oiph = ip_hdr(oldskb);
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 skb_reserve(nskb, LL_MAX_HEADER);
126 niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
127 ip4_dst_hoplimit(skb_dst(nskb)));
128 nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
129
130 if (ip_route_me_harder(nskb, RTN_UNSPEC))
131 goto free_nskb;
132
133 /* "Never happens" */
134 if (nskb->len > dst_mtu(skb_dst(nskb)))
135 goto free_nskb;
136
137 nf_ct_attach(nskb, oldskb);
138
139 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
140 /* If we use ip_local_out for bridged traffic, the MAC source on
141 * the RST will be ours, instead of the destination's. This confuses
142 * some routers/firewalls, and they drop the packet. So we need to
143 * build the eth header using the original destination's MAC as the
144 * source, and send the RST packet directly.
145 */
146 if (oldskb->nf_bridge) {
147 struct ethhdr *oeth = eth_hdr(oldskb);
148 nskb->dev = oldskb->nf_bridge->physindev;
149 niph->tot_len = htons(nskb->len);
150 ip_send_check(niph);
151 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
152 oeth->h_source, oeth->h_dest, nskb->len) < 0)
153 goto free_nskb;
154 dev_queue_xmit(nskb);
155 } else
156 #endif
157 ip_local_out(nskb);
158
159 return;
160
161 free_nskb:
162 kfree_skb(nskb);
163 }
164 EXPORT_SYMBOL_GPL(nf_send_reset);
165
166 MODULE_LICENSE("GPL");
167