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,clat_packet_index pos,const struct icmp6_hdr * icmp6,size_t len)37 int icmp6_packet(clat_packet out, clat_packet_index pos, const struct icmp6_hdr *icmp6,
38 size_t len) {
39 const uint8_t *payload;
40 size_t payload_size;
41
42 if(len < sizeof(struct icmp6_hdr)) {
43 logmsg_dbg(ANDROID_LOG_ERROR, "icmp6_packet/(too small)");
44 return 0;
45 }
46
47 payload = (const uint8_t *) (icmp6 + 1);
48 payload_size = len - sizeof(struct icmp6_hdr);
49
50 return icmp6_to_icmp(out, pos, icmp6, payload, payload_size);
51 }
52
53 /* function: log_bad_address
54 * logs a bad address to android's log buffer if debugging is turned on
55 * fmt - printf-style format, use %s to place the address
56 * badaddr - the bad address in question
57 */
58 #if CLAT_DEBUG
log_bad_address(const char * fmt,const struct in6_addr * src,const struct in6_addr * dst)59 void log_bad_address(const char *fmt, const struct in6_addr *src, const struct in6_addr *dst) {
60 char srcstr[INET6_ADDRSTRLEN];
61 char dststr[INET6_ADDRSTRLEN];
62
63 inet_ntop(AF_INET6, src, srcstr, sizeof(srcstr));
64 inet_ntop(AF_INET6, dst, dststr, sizeof(dststr));
65 logmsg_dbg(ANDROID_LOG_ERROR, fmt, srcstr, dststr);
66 }
67 #else
68 #define log_bad_address(fmt, src, dst)
69 #endif
70
71 /* function: ipv6_packet
72 * takes an ipv6 packet and hands it off to the layer 4 protocol function
73 * out - output packet
74 * packet - packet data
75 * len - size of packet
76 * returns: the highest position in the output clat_packet that's filled in
77 */
ipv6_packet(clat_packet out,clat_packet_index pos,const uint8_t * packet,size_t len)78 int ipv6_packet(clat_packet out, clat_packet_index pos, const uint8_t *packet, size_t len) {
79 const struct ip6_hdr *ip6 = (struct ip6_hdr *) packet;
80 struct iphdr *ip_targ = (struct iphdr *) out[pos].iov_base;
81 struct ip6_frag *frag_hdr = NULL;
82 uint8_t protocol;
83 const uint8_t *next_header;
84 size_t len_left;
85 uint32_t old_sum, new_sum;
86 int iov_len;
87
88 if(len < sizeof(struct ip6_hdr)) {
89 logmsg_dbg(ANDROID_LOG_ERROR, "ipv6_packet/too short for an ip6 header: %d", len);
90 return 0;
91 }
92
93 if(IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst)) {
94 log_bad_address("ipv6_packet/multicast %s->%s", &ip6->ip6_src, &ip6->ip6_dst);
95 return 0; // silently ignore
96 }
97
98 // If the packet is not from the plat subnet to the local subnet, or vice versa, drop it, unless
99 // it's an ICMP packet (which can come from anywhere). We do not send IPv6 packets from the plat
100 // subnet to the local subnet, but these can appear as inner packets in ICMP errors, so we need
101 // to translate them. We accept third-party ICMPv6 errors, even though their source addresses
102 // cannot be translated, so that things like unreachables and traceroute will work. fill_ip_header
103 // takes care of faking a source address for them.
104 if (!(is_in_plat_subnet(&ip6->ip6_src) &&
105 IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &Global_Clatd_Config.ipv6_local_subnet)) &&
106 !(is_in_plat_subnet(&ip6->ip6_dst) &&
107 IN6_ARE_ADDR_EQUAL(&ip6->ip6_src, &Global_Clatd_Config.ipv6_local_subnet)) &&
108 ip6->ip6_nxt != IPPROTO_ICMPV6) {
109 log_bad_address("ipv6_packet/wrong source address: %s->%s", &ip6->ip6_src, &ip6->ip6_dst);
110 return 0;
111 }
112
113 next_header = packet + sizeof(struct ip6_hdr);
114 len_left = len - sizeof(struct ip6_hdr);
115
116 protocol = ip6->ip6_nxt;
117
118 /* Fill in the IPv4 header. We need to do this before we translate the packet because TCP and
119 * UDP include parts of the IP header in the checksum. Set the length to zero because we don't
120 * know it yet.
121 */
122 fill_ip_header(ip_targ, 0, protocol, ip6);
123 out[pos].iov_len = sizeof(struct iphdr);
124
125 // If there's a Fragment header, parse it and decide what the next header is.
126 // Do this before calculating the pseudo-header checksum because it updates the next header value.
127 if (protocol == IPPROTO_FRAGMENT) {
128 frag_hdr = (struct ip6_frag *) next_header;
129 if (len_left < sizeof(*frag_hdr)) {
130 logmsg_dbg(ANDROID_LOG_ERROR, "ipv6_packet/too short for fragment header: %d", len);
131 return 0;
132 }
133
134 next_header += sizeof(*frag_hdr);
135 len_left -= sizeof(*frag_hdr);
136
137 protocol = parse_frag_header(frag_hdr, ip_targ);
138 }
139
140 // ICMP and ICMPv6 have different protocol numbers.
141 if (protocol == IPPROTO_ICMPV6) {
142 protocol = IPPROTO_ICMP;
143 ip_targ->protocol = IPPROTO_ICMP;
144 }
145
146 /* Calculate the pseudo-header checksum.
147 * Technically, the length that is used in the pseudo-header checksum is the transport layer
148 * length, which is not the same as len_left in the case of fragmented packets. But since
149 * translation does not change the transport layer length, the checksum is unaffected.
150 */
151 old_sum = ipv6_pseudo_header_checksum(ip6, len_left, protocol);
152 new_sum = ipv4_pseudo_header_checksum(ip_targ, len_left);
153
154 // Does not support IPv6 extension headers except Fragment.
155 if (frag_hdr && (frag_hdr->ip6f_offlg & IP6F_OFF_MASK)) {
156 iov_len = generic_packet(out, pos + 2, next_header, len_left);
157 } else if (protocol == IPPROTO_ICMP) {
158 iov_len = icmp6_packet(out, pos + 2, (const struct icmp6_hdr *) next_header, len_left);
159 } else if (protocol == IPPROTO_TCP) {
160 iov_len = tcp_packet(out, pos + 2, (const struct tcphdr *) next_header, old_sum, new_sum,
161 len_left);
162 } else if (protocol == IPPROTO_UDP) {
163 iov_len = udp_packet(out, pos + 2, (const struct udphdr *) next_header, old_sum, new_sum,
164 len_left);
165 } else if (protocol == IPPROTO_GRE) {
166 iov_len = generic_packet(out, pos + 2, next_header, len_left);
167 } else {
168 #if CLAT_DEBUG
169 logmsg(ANDROID_LOG_ERROR, "ipv6_packet/unknown next header type: %x", ip6->ip6_nxt);
170 logcat_hexdump("ipv6/nxthdr", packet, len);
171 #endif
172 return 0;
173 }
174
175 // Set the length and calculate the checksum.
176 ip_targ->tot_len = htons(ntohs(ip_targ->tot_len) + packet_length(out, pos));
177 ip_targ->check = ip_checksum(ip_targ, sizeof(struct iphdr));
178 return iov_len;
179 }
180