1
2
3
4
5
6#include <linux/module.h>
7#include <net/ip.h>
8#include <net/tcp.h>
9#include <net/route.h>
10#include <net/dst.h>
11#include <net/netfilter/ipv4/nf_reject.h>
12#include <linux/netfilter_ipv4.h>
13#include <linux/netfilter_bridge.h>
14
15static int nf_reject_iphdr_validate(struct sk_buff *skb)
16{
17 struct iphdr *iph;
18 u32 len;
19
20 if (!pskb_may_pull(skb, sizeof(struct iphdr)))
21 return 0;
22
23 iph = ip_hdr(skb);
24 if (iph->ihl < 5 || iph->version != 4)
25 return 0;
26
27 len = ntohs(iph->tot_len);
28 if (skb->len < len)
29 return 0;
30 else if (len < (iph->ihl*4))
31 return 0;
32
33 if (!pskb_may_pull(skb, iph->ihl*4))
34 return 0;
35
36 return 1;
37}
38
39struct sk_buff *nf_reject_skb_v4_tcp_reset(struct net *net,
40 struct sk_buff *oldskb,
41 const struct net_device *dev,
42 int hook)
43{
44 const struct tcphdr *oth;
45 struct sk_buff *nskb;
46 struct iphdr *niph;
47 struct tcphdr _oth;
48
49 if (!nf_reject_iphdr_validate(oldskb))
50 return NULL;
51
52 oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
53 if (!oth)
54 return NULL;
55
56 nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
57 LL_MAX_HEADER, GFP_ATOMIC);
58 if (!nskb)
59 return NULL;
60
61 nskb->dev = (struct net_device *)dev;
62
63 skb_reserve(nskb, LL_MAX_HEADER);
64 niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
65 READ_ONCE(net->ipv4.sysctl_ip_default_ttl));
66 nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
67 niph->tot_len = htons(nskb->len);
68 ip_send_check(niph);
69
70 return nskb;
71}
72EXPORT_SYMBOL_GPL(nf_reject_skb_v4_tcp_reset);
73
74struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
75 struct sk_buff *oldskb,
76 const struct net_device *dev,
77 int hook, u8 code)
78{
79 struct sk_buff *nskb;
80 struct iphdr *niph;
81 struct icmphdr *icmph;
82 unsigned int len;
83 int dataoff;
84 __wsum csum;
85 u8 proto;
86
87 if (!nf_reject_iphdr_validate(oldskb))
88 return NULL;
89
90
91 if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
92 return NULL;
93
94
95 len = min_t(unsigned int, 536, oldskb->len);
96
97 if (!pskb_may_pull(oldskb, len))
98 return NULL;
99
100 if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
101 return NULL;
102
103 dataoff = ip_hdrlen(oldskb);
104 proto = ip_hdr(oldskb)->protocol;
105
106 if (!skb_csum_unnecessary(oldskb) &&
107 nf_reject_verify_csum(oldskb, dataoff, proto) &&
108 nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), proto))
109 return NULL;
110
111 nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct icmphdr) +
112 LL_MAX_HEADER + len, GFP_ATOMIC);
113 if (!nskb)
114 return NULL;
115
116 nskb->dev = (struct net_device *)dev;
117
118 skb_reserve(nskb, LL_MAX_HEADER);
119 niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_ICMP,
120 READ_ONCE(net->ipv4.sysctl_ip_default_ttl));
121
122 skb_reset_transport_header(nskb);
123 icmph = skb_put_zero(nskb, sizeof(struct icmphdr));
124 icmph->type = ICMP_DEST_UNREACH;
125 icmph->code = code;
126
127 skb_put_data(nskb, skb_network_header(oldskb), len);
128
129 csum = csum_partial((void *)icmph, len + sizeof(struct icmphdr), 0);
130 icmph->checksum = csum_fold(csum);
131
132 niph->tot_len = htons(nskb->len);
133 ip_send_check(niph);
134
135 return nskb;
136}
137EXPORT_SYMBOL_GPL(nf_reject_skb_v4_unreach);
138
139const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,
140 struct tcphdr *_oth, int hook)
141{
142 const struct tcphdr *oth;
143
144
145 if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
146 return NULL;
147
148 if (ip_hdr(oldskb)->protocol != IPPROTO_TCP)
149 return NULL;
150
151 oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
152 sizeof(struct tcphdr), _oth);
153 if (oth == NULL)
154 return NULL;
155
156
157 if (oth->rst)
158 return NULL;
159
160
161 if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
162 return NULL;
163
164 return oth;
165}
166EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);
167
168struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,
169 const struct sk_buff *oldskb,
170 __u8 protocol, int ttl)
171{
172 struct iphdr *niph, *oiph = ip_hdr(oldskb);
173
174 skb_reset_network_header(nskb);
175 niph = skb_put(nskb, sizeof(struct iphdr));
176 niph->version = 4;
177 niph->ihl = sizeof(struct iphdr) / 4;
178 niph->tos = 0;
179 niph->id = 0;
180 niph->frag_off = htons(IP_DF);
181 niph->protocol = protocol;
182 niph->check = 0;
183 niph->saddr = oiph->daddr;
184 niph->daddr = oiph->saddr;
185 niph->ttl = ttl;
186
187 nskb->protocol = htons(ETH_P_IP);
188
189 return niph;
190}
191EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);
192
193void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,
194 const struct tcphdr *oth)
195{
196 struct iphdr *niph = ip_hdr(nskb);
197 struct tcphdr *tcph;
198
199 skb_reset_transport_header(nskb);
200 tcph = skb_put_zero(nskb, sizeof(struct tcphdr));
201 tcph->source = oth->dest;
202 tcph->dest = oth->source;
203 tcph->doff = sizeof(struct tcphdr) / 4;
204
205 if (oth->ack) {
206 tcph->seq = oth->ack_seq;
207 } else {
208 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
209 oldskb->len - ip_hdrlen(oldskb) -
210 (oth->doff << 2));
211 tcph->ack = 1;
212 }
213
214 tcph->rst = 1;
215 tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
216 niph->daddr, 0);
217 nskb->ip_summed = CHECKSUM_PARTIAL;
218 nskb->csum_start = (unsigned char *)tcph - nskb->head;
219 nskb->csum_offset = offsetof(struct tcphdr, check);
220}
221EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);
222
223static int nf_reject_fill_skb_dst(struct sk_buff *skb_in)
224{
225 struct dst_entry *dst = NULL;
226 struct flowi fl;
227
228 memset(&fl, 0, sizeof(struct flowi));
229 fl.u.ip4.daddr = ip_hdr(skb_in)->saddr;
230 nf_ip_route(dev_net(skb_in->dev), &dst, &fl, false);
231 if (!dst)
232 return -1;
233
234 skb_dst_set(skb_in, dst);
235 return 0;
236}
237
238
239void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
240 int hook)
241{
242 struct net_device *br_indev __maybe_unused;
243 struct sk_buff *nskb;
244 struct iphdr *niph;
245 const struct tcphdr *oth;
246 struct tcphdr _oth;
247
248 oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
249 if (!oth)
250 return;
251
252 if ((hook == NF_INET_PRE_ROUTING || hook == NF_INET_INGRESS) &&
253 nf_reject_fill_skb_dst(oldskb) < 0)
254 return;
255
256 if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
257 return;
258
259 nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
260 LL_MAX_HEADER, GFP_ATOMIC);
261 if (!nskb)
262 return;
263
264
265 skb_dst_set_noref(nskb, skb_dst(oldskb));
266
267 nskb->mark = IP4_REPLY_MARK(net, oldskb->mark);
268
269 skb_reserve(nskb, LL_MAX_HEADER);
270 niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
271 ip4_dst_hoplimit(skb_dst(nskb)));
272 nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
273 if (ip_route_me_harder(net, sk, nskb, RTN_UNSPEC))
274 goto free_nskb;
275
276 niph = ip_hdr(nskb);
277
278
279 if (nskb->len > dst_mtu(skb_dst(nskb)))
280 goto free_nskb;
281
282 nf_ct_attach(nskb, oldskb);
283
284#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
285
286
287
288
289
290
291 br_indev = nf_bridge_get_physindev(oldskb);
292 if (br_indev) {
293 struct ethhdr *oeth = eth_hdr(oldskb);
294
295 nskb->dev = br_indev;
296 niph->tot_len = htons(nskb->len);
297 ip_send_check(niph);
298 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
299 oeth->h_source, oeth->h_dest, nskb->len) < 0)
300 goto free_nskb;
301 dev_queue_xmit(nskb);
302 } else
303#endif
304 ip_local_out(net, nskb->sk, nskb);
305
306 return;
307
308 free_nskb:
309 kfree_skb(nskb);
310}
311EXPORT_SYMBOL_GPL(nf_send_reset);
312
313void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
314{
315 struct iphdr *iph = ip_hdr(skb_in);
316 int dataoff = ip_hdrlen(skb_in);
317 u8 proto = iph->protocol;
318
319 if (iph->frag_off & htons(IP_OFFSET))
320 return;
321
322 if ((hook == NF_INET_PRE_ROUTING || hook == NF_INET_INGRESS) &&
323 nf_reject_fill_skb_dst(skb_in) < 0)
324 return;
325
326 if (skb_csum_unnecessary(skb_in) ||
327 !nf_reject_verify_csum(skb_in, dataoff, proto)) {
328 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
329 return;
330 }
331
332 if (nf_ip_checksum(skb_in, hook, dataoff, proto) == 0)
333 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
334}
335EXPORT_SYMBOL_GPL(nf_send_unreach);
336
337MODULE_LICENSE("GPL");
338
