Linux-libre 5.4.47-gnu
[librecmc/linux-libre.git] / net / netfilter / nf_nat_helper.c
1 // SPDX-License-Identifier: GPL-2.0-only
2 /* nf_nat_helper.c - generic support functions for NAT helpers
3  *
4  * (C) 2000-2002 Harald Welte <laforge@netfilter.org>
5  * (C) 2003-2006 Netfilter Core Team <coreteam@netfilter.org>
6  * (C) 2007-2012 Patrick McHardy <kaber@trash.net>
7  */
8 #include <linux/module.h>
9 #include <linux/gfp.h>
10 #include <linux/types.h>
11 #include <linux/skbuff.h>
12 #include <linux/tcp.h>
13 #include <linux/udp.h>
14 #include <net/tcp.h>
15
16 #include <net/netfilter/nf_conntrack.h>
17 #include <net/netfilter/nf_conntrack_helper.h>
18 #include <net/netfilter/nf_conntrack_ecache.h>
19 #include <net/netfilter/nf_conntrack_expect.h>
20 #include <net/netfilter/nf_conntrack_seqadj.h>
21 #include <net/netfilter/nf_nat.h>
22 #include <net/netfilter/nf_nat_helper.h>
23
24 /* Frobs data inside this packet, which is linear. */
25 static void mangle_contents(struct sk_buff *skb,
26                             unsigned int dataoff,
27                             unsigned int match_offset,
28                             unsigned int match_len,
29                             const char *rep_buffer,
30                             unsigned int rep_len)
31 {
32         unsigned char *data;
33
34         SKB_LINEAR_ASSERT(skb);
35         data = skb_network_header(skb) + dataoff;
36
37         /* move post-replacement */
38         memmove(data + match_offset + rep_len,
39                 data + match_offset + match_len,
40                 skb_tail_pointer(skb) - (skb_network_header(skb) + dataoff +
41                              match_offset + match_len));
42
43         /* insert data from buffer */
44         memcpy(data + match_offset, rep_buffer, rep_len);
45
46         /* update skb info */
47         if (rep_len > match_len) {
48                 pr_debug("nf_nat_mangle_packet: Extending packet by "
49                          "%u from %u bytes\n", rep_len - match_len, skb->len);
50                 skb_put(skb, rep_len - match_len);
51         } else {
52                 pr_debug("nf_nat_mangle_packet: Shrinking packet from "
53                          "%u from %u bytes\n", match_len - rep_len, skb->len);
54                 __skb_trim(skb, skb->len + rep_len - match_len);
55         }
56
57         if (nf_ct_l3num((struct nf_conn *)skb_nfct(skb)) == NFPROTO_IPV4) {
58                 /* fix IP hdr checksum information */
59                 ip_hdr(skb)->tot_len = htons(skb->len);
60                 ip_send_check(ip_hdr(skb));
61         } else
62                 ipv6_hdr(skb)->payload_len =
63                         htons(skb->len - sizeof(struct ipv6hdr));
64 }
65
66 /* Unusual, but possible case. */
67 static bool enlarge_skb(struct sk_buff *skb, unsigned int extra)
68 {
69         if (skb->len + extra > 65535)
70                 return false;
71
72         if (pskb_expand_head(skb, 0, extra - skb_tailroom(skb), GFP_ATOMIC))
73                 return false;
74
75         return true;
76 }
77
78 /* Generic function for mangling variable-length address changes inside
79  * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
80  * command in FTP).
81  *
82  * Takes care about all the nasty sequence number changes, checksumming,
83  * skb enlargement, ...
84  *
85  * */
86 bool __nf_nat_mangle_tcp_packet(struct sk_buff *skb,
87                                 struct nf_conn *ct,
88                                 enum ip_conntrack_info ctinfo,
89                                 unsigned int protoff,
90                                 unsigned int match_offset,
91                                 unsigned int match_len,
92                                 const char *rep_buffer,
93                                 unsigned int rep_len, bool adjust)
94 {
95         struct tcphdr *tcph;
96         int oldlen, datalen;
97
98         if (skb_ensure_writable(skb, skb->len))
99                 return false;
100
101         if (rep_len > match_len &&
102             rep_len - match_len > skb_tailroom(skb) &&
103             !enlarge_skb(skb, rep_len - match_len))
104                 return false;
105
106         tcph = (void *)skb->data + protoff;
107
108         oldlen = skb->len - protoff;
109         mangle_contents(skb, protoff + tcph->doff*4,
110                         match_offset, match_len, rep_buffer, rep_len);
111
112         datalen = skb->len - protoff;
113
114         nf_nat_csum_recalc(skb, nf_ct_l3num(ct), IPPROTO_TCP,
115                            tcph, &tcph->check, datalen, oldlen);
116
117         if (adjust && rep_len != match_len)
118                 nf_ct_seqadj_set(ct, ctinfo, tcph->seq,
119                                  (int)rep_len - (int)match_len);
120
121         return true;
122 }
123 EXPORT_SYMBOL(__nf_nat_mangle_tcp_packet);
124
125 /* Generic function for mangling variable-length address changes inside
126  * NATed UDP connections (like the CONNECT DATA XXXXX MESG XXXXX INDEX XXXXX
127  * command in the Amanda protocol)
128  *
129  * Takes care about all the nasty sequence number changes, checksumming,
130  * skb enlargement, ...
131  *
132  * XXX - This function could be merged with nf_nat_mangle_tcp_packet which
133  *       should be fairly easy to do.
134  */
135 bool
136 nf_nat_mangle_udp_packet(struct sk_buff *skb,
137                          struct nf_conn *ct,
138                          enum ip_conntrack_info ctinfo,
139                          unsigned int protoff,
140                          unsigned int match_offset,
141                          unsigned int match_len,
142                          const char *rep_buffer,
143                          unsigned int rep_len)
144 {
145         struct udphdr *udph;
146         int datalen, oldlen;
147
148         if (skb_ensure_writable(skb, skb->len))
149                 return false;
150
151         if (rep_len > match_len &&
152             rep_len - match_len > skb_tailroom(skb) &&
153             !enlarge_skb(skb, rep_len - match_len))
154                 return false;
155
156         udph = (void *)skb->data + protoff;
157
158         oldlen = skb->len - protoff;
159         mangle_contents(skb, protoff + sizeof(*udph),
160                         match_offset, match_len, rep_buffer, rep_len);
161
162         /* update the length of the UDP packet */
163         datalen = skb->len - protoff;
164         udph->len = htons(datalen);
165
166         /* fix udp checksum if udp checksum was previously calculated */
167         if (!udph->check && skb->ip_summed != CHECKSUM_PARTIAL)
168                 return true;
169
170         nf_nat_csum_recalc(skb, nf_ct_l3num(ct), IPPROTO_UDP,
171                            udph, &udph->check, datalen, oldlen);
172
173         return true;
174 }
175 EXPORT_SYMBOL(nf_nat_mangle_udp_packet);
176
177 /* Setup NAT on this expected conntrack so it follows master. */
178 /* If we fail to get a free NAT slot, we'll get dropped on confirm */
179 void nf_nat_follow_master(struct nf_conn *ct,
180                           struct nf_conntrack_expect *exp)
181 {
182         struct nf_nat_range2 range;
183
184         /* This must be a fresh one. */
185         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
186
187         /* Change src to where master sends to */
188         range.flags = NF_NAT_RANGE_MAP_IPS;
189         range.min_addr = range.max_addr
190                 = ct->master->tuplehash[!exp->dir].tuple.dst.u3;
191         nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
192
193         /* For DST manip, map port here to where it's expected. */
194         range.flags = (NF_NAT_RANGE_MAP_IPS | NF_NAT_RANGE_PROTO_SPECIFIED);
195         range.min_proto = range.max_proto = exp->saved_proto;
196         range.min_addr = range.max_addr
197                 = ct->master->tuplehash[!exp->dir].tuple.src.u3;
198         nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST);
199 }
200 EXPORT_SYMBOL(nf_nat_follow_master);