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, len: 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, len: skb->len + rep_len - match_len); |
55 | } |
56 | |
57 | if (nf_ct_l3num(ct: (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: 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 ) |
68 | { |
69 | if (skb->len + extra > 65535) |
70 | return false; |
71 | |
72 | if (pskb_expand_head(skb, nhead: 0, ntail: 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, write_len: skb->len)) |
99 | return false; |
100 | |
101 | if (rep_len > match_len && |
102 | rep_len - match_len > skb_tailroom(skb) && |
103 | !enlarge_skb(skb, extra: rep_len - match_len)) |
104 | return false; |
105 | |
106 | tcph = (void *)skb->data + protoff; |
107 | |
108 | oldlen = skb->len - protoff; |
109 | mangle_contents(skb, dataoff: 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, nfproto: nf_ct_l3num(ct), IPPROTO_TCP, |
115 | data: tcph, check: &tcph->check, datalen, oldlen); |
116 | |
117 | if (adjust && rep_len != match_len) |
118 | nf_ct_seqadj_set(ct, ctinfo, seq: tcph->seq, |
119 | off: (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, write_len: skb->len)) |
149 | return false; |
150 | |
151 | if (rep_len > match_len && |
152 | rep_len - match_len > skb_tailroom(skb) && |
153 | !enlarge_skb(skb, extra: rep_len - match_len)) |
154 | return false; |
155 | |
156 | udph = (void *)skb->data + protoff; |
157 | |
158 | oldlen = skb->len - protoff; |
159 | mangle_contents(skb, dataoff: 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, nfproto: nf_ct_l3num(ct), IPPROTO_UDP, |
171 | data: udph, check: &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: &range, maniptype: 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: &range, maniptype: NF_NAT_MANIP_DST); |
199 | } |
200 | EXPORT_SYMBOL(nf_nat_follow_master); |
201 | |
202 | u16 nf_nat_exp_find_port(struct nf_conntrack_expect *exp, u16 port) |
203 | { |
204 | static const unsigned int max_attempts = 128; |
205 | int range, attempts_left; |
206 | u16 min = port; |
207 | |
208 | range = USHRT_MAX - port; |
209 | attempts_left = range; |
210 | |
211 | if (attempts_left > max_attempts) |
212 | attempts_left = max_attempts; |
213 | |
214 | /* Try to get same port: if not, try to change it. */ |
215 | for (;;) { |
216 | int res; |
217 | |
218 | exp->tuple.dst.u.tcp.port = htons(port); |
219 | res = nf_ct_expect_related(expect: exp, flags: 0); |
220 | if (res == 0) |
221 | return port; |
222 | |
223 | if (res != -EBUSY || (--attempts_left < 0)) |
224 | break; |
225 | |
226 | port = min + get_random_u32_below(ceil: range); |
227 | } |
228 | |
229 | return 0; |
230 | } |
231 | EXPORT_SYMBOL_GPL(nf_nat_exp_find_port); |
232 | |