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 */
37int 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
59void 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 */
78int 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