1 /*
2 * Copyright 2011 Daniel Drown
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 *
16 * ipv6.c - takes ipv6 packets, finds their headers, and then calls translation functions on them
17 */
18 #include <string.h>
19
20 #include <arpa/inet.h>
21
22 #include "translate.h"
23 #include "checksum.h"
24 #include "logging.h"
25 #include "dump.h"
26 #include "config.h"
27 #include "debug.h"
28
29 /* function: icmp6_packet
30 * takes an icmp6 packet and sets it up for translation
31 * out - output packet
32 * icmp6 - pointer to icmp6 header in packet
33 * checksum - pseudo-header checksum (unused)
34 * len - size of ip payload
35 * returns: the highest position in the output clat_packet that's filled in
36 */
icmp6_packet(clat_packet out,int pos,const struct icmp6_hdr * icmp6,size_t len)37 int icmp6_packet(clat_packet out, int pos, const struct icmp6_hdr *icmp6, size_t len) {
38 const char *payload;
39 size_t payload_size;
40
41 if(len < sizeof(struct icmp6_hdr)) {
42 logmsg_dbg(ANDROID_LOG_ERROR, "icmp6_packet/(too small)");
43 return 0;
44 }
45
46 payload = (const char *) (icmp6 + 1);
47 payload_size = len - sizeof(struct icmp6_hdr);
48
49 return icmp6_to_icmp(out, pos, icmp6, payload, payload_size);
50 }
51
52 /* function: log_bad_address
53 * logs a bad address to android's log buffer if debugging is turned on
54 * fmt - printf-style format, use %s to place the address
55 * badaddr - the bad address in question
56 */
57 #if CLAT_DEBUG
log_bad_address(const char * fmt,const struct in6_addr * src,const struct in6_addr * dst)58 void log_bad_address(const char *fmt, const struct in6_addr *src, const struct in6_addr *dst) {
59 char srcstr[INET6_ADDRSTRLEN];
60 char dststr[INET6_ADDRSTRLEN];
61
62 inet_ntop(AF_INET6, src, srcstr, sizeof(srcstr));
63 inet_ntop(AF_INET6, dst, dststr, sizeof(dststr));
64 logmsg_dbg(ANDROID_LOG_ERROR, fmt, srcstr, dststr);
65 }
66 #else
67 #define log_bad_address(fmt, src, dst)
68 #endif
69
70 /* function: ipv6_packet
71 * takes an ipv6 packet and hands it off to the layer 4 protocol function
72 * out - output packet
73 * packet - packet data
74 * len - size of packet
75 * returns: the highest position in the output clat_packet that's filled in
76 */
ipv6_packet(clat_packet out,int pos,const char * packet,size_t len)77 int ipv6_packet(clat_packet out, int pos, const char *packet, size_t len) {
78 const struct ip6_hdr *ip6 = (struct ip6_hdr *) packet;
79 struct iphdr *ip_targ = (struct iphdr *) out[pos].iov_base;
80 struct ip6_frag *frag_hdr = NULL;
81 uint8_t protocol;
82 const char *next_header;
83 size_t len_left;
84 uint32_t old_sum, new_sum;
85 int iov_len;
86
87 if(len < sizeof(struct ip6_hdr)) {
88 logmsg_dbg(ANDROID_LOG_ERROR, "ipv6_packet/too short for an ip6 header: %d", len);
89 return 0;
90 }
91
92 if(IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst)) {
93 log_bad_address("ipv6_packet/multicast %s->%s", &ip6->ip6_src, &ip6->ip6_dst);
94 return 0; // silently ignore
95 }
96
97 // If the packet is not from the plat subnet to the local subnet, or vice versa, drop it, unless
98 // it's an ICMP packet (which can come from anywhere). We do not send IPv6 packets from the plat
99 // subnet to the local subnet, but these can appear as inner packets in ICMP errors, so we need
100 // to translate them. We accept third-party ICMPv6 errors, even though their source addresses
101 // cannot be translated, so that things like unreachables and traceroute will work. fill_ip_header
102 // takes care of faking a source address for them.
103 if (!(is_in_plat_subnet(&ip6->ip6_src) &&
104 IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &Global_Clatd_Config.ipv6_local_subnet)) &&
105 !(is_in_plat_subnet(&ip6->ip6_dst) &&
106 IN6_ARE_ADDR_EQUAL(&ip6->ip6_src, &Global_Clatd_Config.ipv6_local_subnet)) &&
107 ip6->ip6_nxt != IPPROTO_ICMPV6) {
108 log_bad_address("ipv6_packet/wrong source address: %s->%s", &ip6->ip6_src, &ip6->ip6_dst);
109 return 0;
110 }
111
112 next_header = packet + sizeof(struct ip6_hdr);
113 len_left = len - sizeof(struct ip6_hdr);
114
115 protocol = ip6->ip6_nxt;
116
117 /* Fill in the IPv4 header. We need to do this before we translate the packet because TCP and
118 * UDP include parts of the IP header in the checksum. Set the length to zero because we don't
119 * know it yet.
120 */
121 fill_ip_header(ip_targ, 0, protocol, ip6);
122 out[pos].iov_len = sizeof(struct iphdr);
123
124 // If there's a Fragment header, parse it and decide what the next header is.
125 // Do this before calculating the pseudo-header checksum because it updates the next header value.
126 if (protocol == IPPROTO_FRAGMENT) {
127 frag_hdr = (struct ip6_frag *) next_header;
128 if (len_left < sizeof(*frag_hdr)) {
129 logmsg_dbg(ANDROID_LOG_ERROR, "ipv6_packet/too short for fragment header: %d", len);
130 return 0;
131 }
132
133 next_header += sizeof(*frag_hdr);
134 len_left -= sizeof(*frag_hdr);
135
136 protocol = parse_frag_header(frag_hdr, ip_targ);
137 }
138
139 // ICMP and ICMPv6 have different protocol numbers.
140 if (protocol == IPPROTO_ICMPV6) {
141 protocol = IPPROTO_ICMP;
142 ip_targ->protocol = IPPROTO_ICMP;
143 }
144
145 /* Calculate the pseudo-header checksum.
146 * Technically, the length that is used in the pseudo-header checksum is the transport layer
147 * length, which is not the same as len_left in the case of fragmented packets. But since
148 * translation does not change the transport layer length, the checksum is unaffected.
149 */
150 old_sum = ipv6_pseudo_header_checksum(ip6, len_left, protocol);
151 new_sum = ipv4_pseudo_header_checksum(ip_targ, len_left);
152
153 // Does not support IPv6 extension headers except Fragment.
154 if (frag_hdr && (frag_hdr->ip6f_offlg & IP6F_OFF_MASK)) {
155 iov_len = generic_packet(out, pos + 2, next_header, len_left);
156 } else if (protocol == IPPROTO_ICMP) {
157 iov_len = icmp6_packet(out, pos + 2, (const struct icmp6_hdr *) next_header, len_left);
158 } else if (protocol == IPPROTO_TCP) {
159 iov_len = tcp_packet(out, pos + 2, (const struct tcphdr *) next_header, old_sum, new_sum,
160 len_left);
161 } else if (protocol == IPPROTO_UDP) {
162 iov_len = udp_packet(out, pos + 2, (const struct udphdr *) next_header, old_sum, new_sum,
163 len_left);
164 } else if (protocol == IPPROTO_GRE) {
165 iov_len = generic_packet(out, pos + 2, next_header, len_left);
166 } else {
167 #if CLAT_DEBUG
168 logmsg(ANDROID_LOG_ERROR, "ipv6_packet/unknown next header type: %x", ip6->ip6_nxt);
169 logcat_hexdump("ipv6/nxthdr", packet, len);
170 #endif
171 return 0;
172 }
173
174 // Set the length and calculate the checksum.
175 ip_targ->tot_len = htons(ntohs(ip_targ->tot_len) + packet_length(out, pos));
176 ip_targ->check = ip_checksum(ip_targ, sizeof(struct iphdr));
177 return iov_len;
178 }
179