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Linux/net/ipv6/netfilter/nf_reject_ipv6.c

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  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 
 15 const struct tcphdr *nf_reject_ip6_tcphdr_get(struct sk_buff *oldskb,
 16                                               struct tcphdr *otcph,
 17                                               unsigned int *otcplen, int hook)
 18 {
 19         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
 20         u8 proto;
 21         __be16 frag_off;
 22         int tcphoff;
 23 
 24         proto = oip6h->nexthdr;
 25         tcphoff = ipv6_skip_exthdr(oldskb, ((u8 *)(oip6h + 1) - oldskb->data),
 26                                    &proto, &frag_off);
 27 
 28         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
 29                 pr_debug("Cannot get TCP header.\n");
 30                 return NULL;
 31         }
 32 
 33         *otcplen = oldskb->len - tcphoff;
 34 
 35         /* IP header checks: fragment, too short. */
 36         if (proto != IPPROTO_TCP || *otcplen < sizeof(struct tcphdr)) {
 37                 pr_debug("proto(%d) != IPPROTO_TCP or too short (len = %d)\n",
 38                          proto, *otcplen);
 39                 return NULL;
 40         }
 41 
 42         otcph = skb_header_pointer(oldskb, tcphoff, sizeof(struct tcphdr),
 43                                    otcph);
 44         if (otcph == NULL)
 45                 return NULL;
 46 
 47         /* No RST for RST. */
 48         if (otcph->rst) {
 49                 pr_debug("RST is set\n");
 50                 return NULL;
 51         }
 52 
 53         /* Check checksum. */
 54         if (nf_ip6_checksum(oldskb, hook, tcphoff, IPPROTO_TCP)) {
 55                 pr_debug("TCP checksum is invalid\n");
 56                 return NULL;
 57         }
 58 
 59         return otcph;
 60 }
 61 EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_get);
 62 
 63 struct ipv6hdr *nf_reject_ip6hdr_put(struct sk_buff *nskb,
 64                                      const struct sk_buff *oldskb,
 65                                      __u8 protocol, int hoplimit)
 66 {
 67         struct ipv6hdr *ip6h;
 68         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
 69 #define DEFAULT_TOS_VALUE       0x0U
 70         const __u8 tclass = DEFAULT_TOS_VALUE;
 71 
 72         skb_put(nskb, sizeof(struct ipv6hdr));
 73         skb_reset_network_header(nskb);
 74         ip6h = ipv6_hdr(nskb);
 75         ip6_flow_hdr(ip6h, tclass, 0);
 76         ip6h->hop_limit = hoplimit;
 77         ip6h->nexthdr = protocol;
 78         ip6h->saddr = oip6h->daddr;
 79         ip6h->daddr = oip6h->saddr;
 80 
 81         nskb->protocol = htons(ETH_P_IPV6);
 82 
 83         return ip6h;
 84 }
 85 EXPORT_SYMBOL_GPL(nf_reject_ip6hdr_put);
 86 
 87 void nf_reject_ip6_tcphdr_put(struct sk_buff *nskb,
 88                               const struct sk_buff *oldskb,
 89                               const struct tcphdr *oth, unsigned int otcplen)
 90 {
 91         struct tcphdr *tcph;
 92         int needs_ack;
 93 
 94         skb_reset_transport_header(nskb);
 95         tcph = skb_put(nskb, sizeof(struct tcphdr));
 96         /* Truncate to length (no data) */
 97         tcph->doff = sizeof(struct tcphdr)/4;
 98         tcph->source = oth->dest;
 99         tcph->dest = oth->source;
100 
101         if (oth->ack) {
102                 needs_ack = 0;
103                 tcph->seq = oth->ack_seq;
104                 tcph->ack_seq = 0;
105         } else {
106                 needs_ack = 1;
107                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
108                                       otcplen - (oth->doff<<2));
109                 tcph->seq = 0;
110         }
111 
112         /* Reset flags */
113         ((u_int8_t *)tcph)[13] = 0;
114         tcph->rst = 1;
115         tcph->ack = needs_ack;
116         tcph->window = 0;
117         tcph->urg_ptr = 0;
118         tcph->check = 0;
119 
120         /* Adjust TCP checksum */
121         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
122                                       &ipv6_hdr(nskb)->daddr,
123                                       sizeof(struct tcphdr), IPPROTO_TCP,
124                                       csum_partial(tcph,
125                                                    sizeof(struct tcphdr), 0));
126 }
127 EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_put);
128 
129 static int nf_reject6_fill_skb_dst(struct sk_buff *skb_in)
130 {
131         struct dst_entry *dst = NULL;
132         struct flowi fl;
133 
134         memset(&fl, 0, sizeof(struct flowi));
135         fl.u.ip6.daddr = ipv6_hdr(skb_in)->saddr;
136         nf_ip6_route(dev_net(skb_in->dev), &dst, &fl, false);
137         if (!dst)
138                 return -1;
139 
140         skb_dst_set(skb_in, dst);
141         return 0;
142 }
143 
144 void nf_send_reset6(struct net *net, struct sk_buff *oldskb, int hook)
145 {
146         struct net_device *br_indev __maybe_unused;
147         struct sk_buff *nskb;
148         struct tcphdr _otcph;
149         const struct tcphdr *otcph;
150         unsigned int otcplen, hh_len;
151         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
152         struct ipv6hdr *ip6h;
153         struct dst_entry *dst = NULL;
154         struct flowi6 fl6;
155 
156         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
157             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
158                 pr_debug("addr is not unicast.\n");
159                 return;
160         }
161 
162         otcph = nf_reject_ip6_tcphdr_get(oldskb, &_otcph, &otcplen, hook);
163         if (!otcph)
164                 return;
165 
166         memset(&fl6, 0, sizeof(fl6));
167         fl6.flowi6_proto = IPPROTO_TCP;
168         fl6.saddr = oip6h->daddr;
169         fl6.daddr = oip6h->saddr;
170         fl6.fl6_sport = otcph->dest;
171         fl6.fl6_dport = otcph->source;
172 
173         if (hook == NF_INET_PRE_ROUTING) {
174                 nf_ip6_route(net, &dst, flowi6_to_flowi(&fl6), false);
175                 if (!dst)
176                         return;
177                 skb_dst_set(oldskb, dst);
178         }
179 
180         fl6.flowi6_oif = l3mdev_master_ifindex(skb_dst(oldskb)->dev);
181         fl6.flowi6_mark = IP6_REPLY_MARK(net, oldskb->mark);
182         security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
183         dst = ip6_route_output(net, NULL, &fl6);
184         if (dst->error) {
185                 dst_release(dst);
186                 return;
187         }
188         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
189         if (IS_ERR(dst))
190                 return;
191 
192         hh_len = (dst->dev->hard_header_len + 15)&~15;
193         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
194                          + sizeof(struct tcphdr) + dst->trailer_len,
195                          GFP_ATOMIC);
196 
197         if (!nskb) {
198                 net_dbg_ratelimited("cannot alloc skb\n");
199                 dst_release(dst);
200                 return;
201         }
202 
203         skb_dst_set(nskb, dst);
204 
205         nskb->mark = fl6.flowi6_mark;
206 
207         skb_reserve(nskb, hh_len + dst->header_len);
208         ip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
209                                     ip6_dst_hoplimit(dst));
210         nf_reject_ip6_tcphdr_put(nskb, oldskb, otcph, otcplen);
211 
212         nf_ct_attach(nskb, oldskb);
213 
214 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
215         /* If we use ip6_local_out for bridged traffic, the MAC source on
216          * the RST will be ours, instead of the destination's.  This confuses
217          * some routers/firewalls, and they drop the packet.  So we need to
218          * build the eth header using the original destination's MAC as the
219          * source, and send the RST packet directly.
220          */
221         br_indev = nf_bridge_get_physindev(oldskb);
222         if (br_indev) {
223                 struct ethhdr *oeth = eth_hdr(oldskb);
224 
225                 nskb->dev = br_indev;
226                 nskb->protocol = htons(ETH_P_IPV6);
227                 ip6h->payload_len = htons(sizeof(struct tcphdr));
228                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
229                                     oeth->h_source, oeth->h_dest, nskb->len) < 0) {
230                         kfree_skb(nskb);
231                         return;
232                 }
233                 dev_queue_xmit(nskb);
234         } else
235 #endif
236                 ip6_local_out(net, nskb->sk, nskb);
237 }
238 EXPORT_SYMBOL_GPL(nf_send_reset6);
239 
240 static bool reject6_csum_ok(struct sk_buff *skb, int hook)
241 {
242         const struct ipv6hdr *ip6h = ipv6_hdr(skb);
243         int thoff;
244         __be16 fo;
245         u8 proto;
246 
247         if (skb_csum_unnecessary(skb))
248                 return true;
249 
250         proto = ip6h->nexthdr;
251         thoff = ipv6_skip_exthdr(skb, ((u8 *)(ip6h + 1) - skb->data), &proto, &fo);
252 
253         if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
254                 return false;
255 
256         if (!nf_reject_verify_csum(proto))
257                 return true;
258 
259         return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
260 }
261 
262 void nf_send_unreach6(struct net *net, struct sk_buff *skb_in,
263                       unsigned char code, unsigned int hooknum)
264 {
265         if (!reject6_csum_ok(skb_in, hooknum))
266                 return;
267 
268         if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
269                 skb_in->dev = net->loopback_dev;
270 
271         if (hooknum == NF_INET_PRE_ROUTING && nf_reject6_fill_skb_dst(skb_in))
272                 return;
273 
274         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
275 }
276 EXPORT_SYMBOL_GPL(nf_send_unreach6);
277 
278 MODULE_LICENSE("GPL");
279 

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