1// SPDX-License-Identifier: GPL-2.0-only
2/* (C) 1999-2001 Paul `Rusty' Russell
3 * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
4 */
5
6#include <linux/module.h>
7#include <net/ipv6.h>
8#include <net/ip6_route.h>
9#include <net/ip6_fib.h>
10#include <net/ip6_checksum.h>
11#include <net/netfilter/ipv6/nf_reject.h>
12#include <linux/netfilter_ipv6.h>
13#include <linux/netfilter_bridge.h>
14
15static bool nf_reject_v6_csum_ok(struct sk_buff *skb, int hook)
16{
17 const struct ipv6hdr *ip6h = ipv6_hdr(skb);
18 int thoff;
19 __be16 fo;
20 u8 proto = ip6h->nexthdr;
21
22 if (skb_csum_unnecessary(skb))
23 return true;
24
25 if (ip6h->payload_len &&
26 pskb_trim_rcsum(skb, ntohs(ip6h->payload_len) + sizeof(*ip6h)))
27 return false;
28
29 ip6h = ipv6_hdr(skb);
30 thoff = ipv6_skip_exthdr(skb, start: ((u8*)(ip6h+1) - skb->data), nexthdrp: &proto, frag_offp: &fo);
31 if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
32 return false;
33
34 if (!nf_reject_verify_csum(skb, dataoff: thoff, proto))
35 return true;
36
37 return nf_ip6_checksum(skb, hook, dataoff: thoff, protocol: proto) == 0;
38}
39
40static int nf_reject_ip6hdr_validate(struct sk_buff *skb)
41{
42 struct ipv6hdr *hdr;
43 u32 pkt_len;
44
45 if (!pskb_may_pull(skb, len: sizeof(struct ipv6hdr)))
46 return 0;
47
48 hdr = ipv6_hdr(skb);
49 if (hdr->version != 6)
50 return 0;
51
52 pkt_len = ntohs(hdr->payload_len);
53 if (pkt_len + sizeof(struct ipv6hdr) > skb->len)
54 return 0;
55
56 return 1;
57}
58
59struct sk_buff *nf_reject_skb_v6_tcp_reset(struct net *net,
60 struct sk_buff *oldskb,
61 const struct net_device *dev,
62 int hook)
63{
64 struct sk_buff *nskb;
65 const struct tcphdr *oth;
66 struct tcphdr _oth;
67 unsigned int otcplen;
68 struct ipv6hdr *nip6h;
69
70 if (!nf_reject_ip6hdr_validate(skb: oldskb))
71 return NULL;
72
73 oth = nf_reject_ip6_tcphdr_get(oldskb, otcph: &_oth, otcplen: &otcplen, hook);
74 if (!oth)
75 return NULL;
76
77 nskb = alloc_skb(size: sizeof(struct ipv6hdr) + sizeof(struct tcphdr) +
78 LL_MAX_HEADER, GFP_ATOMIC);
79 if (!nskb)
80 return NULL;
81
82 nskb->dev = (struct net_device *)dev;
83
84 skb_reserve(skb: nskb, LL_MAX_HEADER);
85 nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
86 READ_ONCE(net->ipv6.devconf_all->hop_limit));
87 nf_reject_ip6_tcphdr_put(nskb, oldskb, oth, otcplen);
88 nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
89
90 return nskb;
91}
92EXPORT_SYMBOL_GPL(nf_reject_skb_v6_tcp_reset);
93
94struct sk_buff *nf_reject_skb_v6_unreach(struct net *net,
95 struct sk_buff *oldskb,
96 const struct net_device *dev,
97 int hook, u8 code)
98{
99 struct sk_buff *nskb;
100 struct ipv6hdr *nip6h;
101 struct icmp6hdr *icmp6h;
102 unsigned int len;
103
104 if (!nf_reject_ip6hdr_validate(skb: oldskb))
105 return NULL;
106
107 /* Include "As much of invoking packet as possible without the ICMPv6
108 * packet exceeding the minimum IPv6 MTU" in the ICMP payload.
109 */
110 len = min_t(unsigned int, 1220, oldskb->len);
111
112 if (!pskb_may_pull(skb: oldskb, len))
113 return NULL;
114
115 if (!nf_reject_v6_csum_ok(skb: oldskb, hook))
116 return NULL;
117
118 nskb = alloc_skb(size: sizeof(struct ipv6hdr) + sizeof(struct icmp6hdr) +
119 LL_MAX_HEADER + len, GFP_ATOMIC);
120 if (!nskb)
121 return NULL;
122
123 nskb->dev = (struct net_device *)dev;
124
125 skb_reserve(skb: nskb, LL_MAX_HEADER);
126 nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_ICMPV6,
127 READ_ONCE(net->ipv6.devconf_all->hop_limit));
128
129 skb_reset_transport_header(skb: nskb);
130 icmp6h = skb_put_zero(skb: nskb, len: sizeof(struct icmp6hdr));
131 icmp6h->icmp6_type = ICMPV6_DEST_UNREACH;
132 icmp6h->icmp6_code = code;
133
134 skb_put_data(skb: nskb, data: skb_network_header(skb: oldskb), len);
135 nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
136
137 icmp6h->icmp6_cksum =
138 csum_ipv6_magic(saddr: &nip6h->saddr, daddr: &nip6h->daddr,
139 len: nskb->len - sizeof(struct ipv6hdr),
140 IPPROTO_ICMPV6,
141 sum: csum_partial(buff: icmp6h,
142 len: nskb->len - sizeof(struct ipv6hdr),
143 sum: 0));
144
145 return nskb;
146}
147EXPORT_SYMBOL_GPL(nf_reject_skb_v6_unreach);
148
149const struct tcphdr *nf_reject_ip6_tcphdr_get(struct sk_buff *oldskb,
150 struct tcphdr *otcph,
151 unsigned int *otcplen, int hook)
152{
153 const struct ipv6hdr *oip6h = ipv6_hdr(skb: oldskb);
154 u8 proto;
155 __be16 frag_off;
156 int tcphoff;
157
158 proto = oip6h->nexthdr;
159 tcphoff = ipv6_skip_exthdr(oldskb, start: ((u8 *)(oip6h + 1) - oldskb->data),
160 nexthdrp: &proto, frag_offp: &frag_off);
161
162 if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
163 pr_debug("Cannot get TCP header.\n");
164 return NULL;
165 }
166
167 *otcplen = oldskb->len - tcphoff;
168
169 /* IP header checks: fragment, too short. */
170 if (proto != IPPROTO_TCP || *otcplen < sizeof(struct tcphdr)) {
171 pr_debug("proto(%d) != IPPROTO_TCP or too short (len = %d)\n",
172 proto, *otcplen);
173 return NULL;
174 }
175
176 otcph = skb_header_pointer(skb: oldskb, offset: tcphoff, len: sizeof(struct tcphdr),
177 buffer: otcph);
178 if (otcph == NULL)
179 return NULL;
180
181 /* No RST for RST. */
182 if (otcph->rst) {
183 pr_debug("RST is set\n");
184 return NULL;
185 }
186
187 /* Check checksum. */
188 if (nf_ip6_checksum(skb: oldskb, hook, dataoff: tcphoff, IPPROTO_TCP)) {
189 pr_debug("TCP checksum is invalid\n");
190 return NULL;
191 }
192
193 return otcph;
194}
195EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_get);
196
197struct ipv6hdr *nf_reject_ip6hdr_put(struct sk_buff *nskb,
198 const struct sk_buff *oldskb,
199 __u8 protocol, int hoplimit)
200{
201 struct ipv6hdr *ip6h;
202 const struct ipv6hdr *oip6h = ipv6_hdr(skb: oldskb);
203#define DEFAULT_TOS_VALUE 0x0U
204 const __u8 tclass = DEFAULT_TOS_VALUE;
205
206 skb_put(skb: nskb, len: sizeof(struct ipv6hdr));
207 skb_reset_network_header(skb: nskb);
208 ip6h = ipv6_hdr(skb: nskb);
209 ip6_flow_hdr(hdr: ip6h, tclass, flowlabel: 0);
210 ip6h->hop_limit = hoplimit;
211 ip6h->nexthdr = protocol;
212 ip6h->saddr = oip6h->daddr;
213 ip6h->daddr = oip6h->saddr;
214
215 nskb->protocol = htons(ETH_P_IPV6);
216
217 return ip6h;
218}
219EXPORT_SYMBOL_GPL(nf_reject_ip6hdr_put);
220
221void nf_reject_ip6_tcphdr_put(struct sk_buff *nskb,
222 const struct sk_buff *oldskb,
223 const struct tcphdr *oth, unsigned int otcplen)
224{
225 struct tcphdr *tcph;
226 int needs_ack;
227
228 skb_reset_transport_header(skb: nskb);
229 tcph = skb_put(skb: nskb, len: sizeof(struct tcphdr));
230 /* Truncate to length (no data) */
231 tcph->doff = sizeof(struct tcphdr)/4;
232 tcph->source = oth->dest;
233 tcph->dest = oth->source;
234
235 if (oth->ack) {
236 needs_ack = 0;
237 tcph->seq = oth->ack_seq;
238 tcph->ack_seq = 0;
239 } else {
240 needs_ack = 1;
241 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
242 otcplen - (oth->doff<<2));
243 tcph->seq = 0;
244 }
245
246 /* Reset flags */
247 ((u_int8_t *)tcph)[13] = 0;
248 tcph->rst = 1;
249 tcph->ack = needs_ack;
250 tcph->window = 0;
251 tcph->urg_ptr = 0;
252 tcph->check = 0;
253
254 /* Adjust TCP checksum */
255 tcph->check = csum_ipv6_magic(saddr: &ipv6_hdr(skb: nskb)->saddr,
256 daddr: &ipv6_hdr(skb: nskb)->daddr,
257 len: sizeof(struct tcphdr), IPPROTO_TCP,
258 sum: csum_partial(buff: tcph,
259 len: sizeof(struct tcphdr), sum: 0));
260}
261EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_put);
262
263static int nf_reject6_fill_skb_dst(struct sk_buff *skb_in)
264{
265 struct dst_entry *dst = NULL;
266 struct flowi fl;
267
268 memset(&fl, 0, sizeof(struct flowi));
269 fl.u.ip6.daddr = ipv6_hdr(skb: skb_in)->saddr;
270 nf_ip6_route(net: dev_net(dev: skb_in->dev), dst: &dst, fl: &fl, strict: false);
271 if (!dst)
272 return -1;
273
274 skb_dst_set(skb: skb_in, dst);
275 return 0;
276}
277
278void nf_send_reset6(struct net *net, struct sock *sk, struct sk_buff *oldskb,
279 int hook)
280{
281 struct sk_buff *nskb;
282 struct tcphdr _otcph;
283 const struct tcphdr *otcph;
284 unsigned int otcplen, hh_len;
285 const struct ipv6hdr *oip6h = ipv6_hdr(skb: oldskb);
286 struct ipv6hdr *ip6h;
287 struct dst_entry *dst = NULL;
288 struct flowi6 fl6;
289
290 if ((!(ipv6_addr_type(addr: &oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
291 (!(ipv6_addr_type(addr: &oip6h->daddr) & IPV6_ADDR_UNICAST))) {
292 pr_debug("addr is not unicast.\n");
293 return;
294 }
295
296 otcph = nf_reject_ip6_tcphdr_get(oldskb, &_otcph, &otcplen, hook);
297 if (!otcph)
298 return;
299
300 memset(&fl6, 0, sizeof(fl6));
301 fl6.flowi6_proto = IPPROTO_TCP;
302 fl6.saddr = oip6h->daddr;
303 fl6.daddr = oip6h->saddr;
304 fl6.fl6_sport = otcph->dest;
305 fl6.fl6_dport = otcph->source;
306
307 if (hook == NF_INET_PRE_ROUTING || hook == NF_INET_INGRESS) {
308 nf_ip6_route(net, dst: &dst, fl: flowi6_to_flowi(fl6: &fl6), strict: false);
309 if (!dst)
310 return;
311 skb_dst_set(skb: oldskb, dst);
312 }
313
314 fl6.flowi6_oif = l3mdev_master_ifindex(dev: skb_dst(skb: oldskb)->dev);
315 fl6.flowi6_mark = IP6_REPLY_MARK(net, oldskb->mark);
316 security_skb_classify_flow(skb: oldskb, flic: flowi6_to_flowi_common(fl6: &fl6));
317 dst = ip6_route_output(net, NULL, fl6: &fl6);
318 if (dst->error) {
319 dst_release(dst);
320 return;
321 }
322 dst = xfrm_lookup(net, dst_orig: dst, fl: flowi6_to_flowi(fl6: &fl6), NULL, flags: 0);
323 if (IS_ERR(ptr: dst))
324 return;
325
326 hh_len = (dst->dev->hard_header_len + 15)&~15;
327 nskb = alloc_skb(size: hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
328 + sizeof(struct tcphdr) + dst->trailer_len,
329 GFP_ATOMIC);
330
331 if (!nskb) {
332 net_dbg_ratelimited("cannot alloc skb\n");
333 dst_release(dst);
334 return;
335 }
336
337 skb_dst_set(skb: nskb, dst);
338
339 nskb->mark = fl6.flowi6_mark;
340
341 skb_reserve(skb: nskb, len: hh_len + dst->header_len);
342 ip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
343 ip6_dst_hoplimit(dst));
344 nf_reject_ip6_tcphdr_put(nskb, oldskb, otcph, otcplen);
345
346 nf_ct_attach(nskb, oldskb);
347 nf_ct_set_closing(nfct: skb_nfct(skb: oldskb));
348
349#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
350 /* If we use ip6_local_out for bridged traffic, the MAC source on
351 * the RST will be ours, instead of the destination's. This confuses
352 * some routers/firewalls, and they drop the packet. So we need to
353 * build the eth header using the original destination's MAC as the
354 * source, and send the RST packet directly.
355 */
356 if (nf_bridge_info_exists(skb: oldskb)) {
357 struct ethhdr *oeth = eth_hdr(skb: oldskb);
358 struct net_device *br_indev;
359
360 br_indev = nf_bridge_get_physindev(skb: oldskb, net);
361 if (!br_indev) {
362 kfree_skb(skb: nskb);
363 return;
364 }
365
366 nskb->dev = br_indev;
367 nskb->protocol = htons(ETH_P_IPV6);
368 ip6h->payload_len = htons(sizeof(struct tcphdr));
369 if (dev_hard_header(skb: nskb, dev: nskb->dev, ntohs(nskb->protocol),
370 daddr: oeth->h_source, saddr: oeth->h_dest, len: nskb->len) < 0) {
371 kfree_skb(skb: nskb);
372 return;
373 }
374 dev_queue_xmit(skb: nskb);
375 } else
376#endif
377 ip6_local_out(net, sk, skb: nskb);
378}
379EXPORT_SYMBOL_GPL(nf_send_reset6);
380
381static bool reject6_csum_ok(struct sk_buff *skb, int hook)
382{
383 const struct ipv6hdr *ip6h = ipv6_hdr(skb);
384 int thoff;
385 __be16 fo;
386 u8 proto;
387
388 if (skb_csum_unnecessary(skb))
389 return true;
390
391 proto = ip6h->nexthdr;
392 thoff = ipv6_skip_exthdr(skb, start: ((u8 *)(ip6h + 1) - skb->data), nexthdrp: &proto, frag_offp: &fo);
393
394 if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
395 return false;
396
397 if (!nf_reject_verify_csum(skb, dataoff: thoff, proto))
398 return true;
399
400 return nf_ip6_checksum(skb, hook, dataoff: thoff, protocol: proto) == 0;
401}
402
403void nf_send_unreach6(struct net *net, struct sk_buff *skb_in,
404 unsigned char code, unsigned int hooknum)
405{
406 if (!reject6_csum_ok(skb: skb_in, hook: hooknum))
407 return;
408
409 if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
410 skb_in->dev = net->loopback_dev;
411
412 if ((hooknum == NF_INET_PRE_ROUTING || hooknum == NF_INET_INGRESS) &&
413 nf_reject6_fill_skb_dst(skb_in) < 0)
414 return;
415
416 icmpv6_send(skb: skb_in, ICMPV6_DEST_UNREACH, code, info: 0);
417}
418EXPORT_SYMBOL_GPL(nf_send_unreach6);
419
420MODULE_LICENSE("GPL");
421MODULE_DESCRIPTION("IPv6 packet rejection core");
422

source code of linux/net/ipv6/netfilter/nf_reject_ipv6.c