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 * config.c - configuration settings
17 */
18
19#include <string.h>
20#include <stdlib.h>
21#include <arpa/inet.h>
22#include <stdio.h>
23#include <limits.h>
24#include <errno.h>
25#include <unistd.h>
26
27#include <cutils/config_utils.h>
28#include <netutils/ifc.h>
29
30#include "config.h"
31#include "dns64.h"
32#include "logging.h"
33#include "getaddr.h"
34#include "clatd.h"
35#include "checksum.h"
36
37struct clat_config Global_Clatd_Config;
38
39/* function: config_item_str
40 * locates the config item and returns the pointer to a string, or NULL on failure.  Caller frees pointer
41 * root       - parsed configuration
42 * item_name  - name of config item to locate
43 * defaultvar - value to use if config item isn't present
44 */
45char *config_item_str(cnode *root, const char *item_name, const char *defaultvar) {
46  const char *tmp;
47
48  if(!(tmp = config_str(root, item_name, defaultvar))) {
49    logmsg(ANDROID_LOG_FATAL,"%s config item needed",item_name);
50    return NULL;
51  }
52  return strdup(tmp);
53}
54
55/* function: config_item_int16_t
56 * locates the config item, parses the integer, and returns the pointer ret_val_ptr, or NULL on failure
57 * root        - parsed configuration
58 * item_name   - name of config item to locate
59 * defaultvar  - value to use if config item isn't present
60 * ret_val_ptr - pointer for return value storage
61 */
62int16_t *config_item_int16_t(cnode *root, const char *item_name, const char *defaultvar, int16_t *ret_val_ptr) {
63  const char *tmp;
64  char *endptr;
65  long int conf_int;
66
67  if(!(tmp = config_str(root, item_name, defaultvar))) {
68    logmsg(ANDROID_LOG_FATAL,"%s config item needed",item_name);
69    return NULL;
70  }
71
72  errno = 0;
73  conf_int = strtol(tmp,&endptr,10);
74  if(errno > 0) {
75    logmsg(ANDROID_LOG_FATAL,"%s config item is not numeric: %s (error=%s)",item_name,tmp,strerror(errno));
76    return NULL;
77  }
78  if(endptr == tmp || *tmp == '\0') {
79    logmsg(ANDROID_LOG_FATAL,"%s config item is not numeric: %s",item_name,tmp);
80    return NULL;
81  }
82  if(*endptr != '\0') {
83    logmsg(ANDROID_LOG_FATAL,"%s config item contains non-numeric characters: %s",item_name,endptr);
84    return NULL;
85  }
86  if(conf_int > INT16_MAX || conf_int < INT16_MIN) {
87    logmsg(ANDROID_LOG_FATAL,"%s config item is too big/small: %d",item_name,conf_int);
88    return NULL;
89  }
90  *ret_val_ptr = conf_int;
91  return ret_val_ptr;
92}
93
94/* function: config_item_ip
95 * locates the config item, parses the ipv4 address, and returns the pointer ret_val_ptr, or NULL on failure
96 * root        - parsed configuration
97 * item_name   - name of config item to locate
98 * defaultvar  - value to use if config item isn't present
99 * ret_val_ptr - pointer for return value storage
100 */
101struct in_addr *config_item_ip(cnode *root, const char *item_name, const char *defaultvar, struct in_addr *ret_val_ptr) {
102  const char *tmp;
103  int status;
104
105  if(!(tmp = config_str(root, item_name, defaultvar))) {
106    logmsg(ANDROID_LOG_FATAL,"%s config item needed",item_name);
107    return NULL;
108  }
109
110  status = inet_pton(AF_INET, tmp, ret_val_ptr);
111  if(status <= 0) {
112    logmsg(ANDROID_LOG_FATAL,"invalid IPv4 address specified for %s: %s", item_name, tmp);
113    return NULL;
114  }
115
116  return ret_val_ptr;
117}
118
119/* function: config_item_ip6
120 * locates the config item, parses the ipv6 address, and returns the pointer ret_val_ptr, or NULL on failure
121 * root        - parsed configuration
122 * item_name   - name of config item to locate
123 * defaultvar  - value to use if config item isn't present
124 * ret_val_ptr - pointer for return value storage
125 */
126struct in6_addr *config_item_ip6(cnode *root, const char *item_name, const char *defaultvar, struct in6_addr *ret_val_ptr) {
127  const char *tmp;
128  int status;
129
130  if(!(tmp = config_str(root, item_name, defaultvar))) {
131    logmsg(ANDROID_LOG_FATAL,"%s config item needed",item_name);
132    return NULL;
133  }
134
135  status = inet_pton(AF_INET6, tmp, ret_val_ptr);
136  if(status <= 0) {
137    logmsg(ANDROID_LOG_FATAL,"invalid IPv6 address specified for %s: %s", item_name, tmp);
138    return NULL;
139  }
140
141  return ret_val_ptr;
142}
143
144/* function: free_config
145 * frees the memory used by the global config variable
146 */
147void free_config() {
148  if(Global_Clatd_Config.plat_from_dns64_hostname) {
149    free(Global_Clatd_Config.plat_from_dns64_hostname);
150    Global_Clatd_Config.plat_from_dns64_hostname = NULL;
151  }
152}
153
154/* function: ipv6_prefix_equal
155 * compares the prefixes two ipv6 addresses. assumes the prefix lengths are both /64.
156 * a1 - first address
157 * a2 - second address
158 * returns: 0 if the subnets are different, 1 if they are the same.
159 */
160int ipv6_prefix_equal(struct in6_addr *a1, struct in6_addr *a2) {
161    return !memcmp(a1, a2, 8);
162}
163
164/* function: dns64_detection
165 * does dns lookups to set the plat subnet or exits on failure, waits forever for a dns response with a query backoff timer
166 * net_id - (optional) netId to use, NETID_UNSET indicates use of default network
167 */
168void dns64_detection(unsigned net_id) {
169  int backoff_sleep, status;
170  struct in6_addr tmp_ptr;
171
172  backoff_sleep = 1;
173
174  while(1) {
175    status = plat_prefix(Global_Clatd_Config.plat_from_dns64_hostname,net_id,&tmp_ptr);
176    if(status > 0) {
177      memcpy(&Global_Clatd_Config.plat_subnet, &tmp_ptr, sizeof(struct in6_addr));
178      return;
179    }
180    logmsg(ANDROID_LOG_WARN, "dns64_detection -- error, sleeping for %d seconds", backoff_sleep);
181    sleep(backoff_sleep);
182    backoff_sleep *= 2;
183    if(backoff_sleep >= 120) {
184      backoff_sleep = 120;
185    }
186  }
187}
188
189/* function: gen_random_iid
190 * picks a random interface ID that is checksum neutral with the IPv4 address and the NAT64 prefix
191 * myaddr            - IPv6 address to write to
192 * ipv4_local_subnet - clat IPv4 address
193 * plat_subnet       - NAT64 prefix
194 */
195void gen_random_iid(struct in6_addr *myaddr, struct in_addr *ipv4_local_subnet,
196                    struct in6_addr *plat_subnet) {
197  // Fill last 8 bytes of IPv6 address with random bits.
198  arc4random_buf(&myaddr->s6_addr[8], 8);
199
200  // Make the IID checksum-neutral. That is, make it so that:
201  //   checksum(Local IPv4 | Remote IPv4) = checksum(Local IPv6 | Remote IPv6)
202  // in other words (because remote IPv6 = NAT64 prefix | Remote IPv4):
203  //   checksum(Local IPv4) = checksum(Local IPv6 | NAT64 prefix)
204  // Do this by adjusting the two bytes in the middle of the IID.
205
206  uint16_t middlebytes = (myaddr->s6_addr[11] << 8) + myaddr->s6_addr[12];
207
208  uint32_t c1 = ip_checksum_add(0, ipv4_local_subnet, sizeof(*ipv4_local_subnet));
209  uint32_t c2 = ip_checksum_add(0, plat_subnet, sizeof(*plat_subnet)) +
210                ip_checksum_add(0, myaddr, sizeof(*myaddr));
211
212  uint16_t delta = ip_checksum_adjust(middlebytes, c1, c2);
213  myaddr->s6_addr[11] = delta >> 8;
214  myaddr->s6_addr[12] = delta & 0xff;
215}
216
217// Factored out to a separate function for testability.
218int connect_is_ipv4_address_free(in_addr_t addr) {
219  int s = socket(AF_INET, SOCK_DGRAM, 0);
220  if (s == -1) {
221    return 0;
222  }
223
224  // Attempt to connect to the address. If the connection succeeds and getsockname returns the same
225  // the address then the address is already assigned to the system and we can't use it.
226  struct sockaddr_in sin = { .sin_family = AF_INET, .sin_addr = { addr }, .sin_port = 53 };
227  socklen_t len = sizeof(sin);
228  int inuse = connect(s, (struct sockaddr *) &sin, sizeof(sin)) == 0 &&
229              getsockname(s, (struct sockaddr *) &sin, &len) == 0 &&
230              (size_t) len >= sizeof(sin) &&
231              sin.sin_addr.s_addr == addr;
232
233  close(s);
234  return !inuse;
235}
236
237addr_free_func config_is_ipv4_address_free = connect_is_ipv4_address_free;
238
239/* function: config_select_ipv4_address
240 * picks a free IPv4 address, starting from ip and trying all addresses in the prefix in order
241 * ip        - the IP address from the configuration file
242 * prefixlen - the length of the prefix from which addresses may be selected.
243 * returns: the IPv4 address, or INADDR_NONE if no addresses were available
244 */
245in_addr_t config_select_ipv4_address(const struct in_addr *ip, int16_t prefixlen) {
246  in_addr_t chosen = INADDR_NONE;
247
248  // Don't accept prefixes that are too large because we scan addresses one by one.
249  if (prefixlen < 16 || prefixlen > 32) {
250      return chosen;
251  }
252
253  // All these are in host byte order.
254  in_addr_t mask = 0xffffffff >> (32 - prefixlen) << (32 - prefixlen);
255  in_addr_t ipv4 = ntohl(ip->s_addr);
256  in_addr_t first_ipv4 = ipv4;
257  in_addr_t prefix = ipv4 & mask;
258
259  // Pick the first IPv4 address in the pool, wrapping around if necessary.
260  // So, for example, 192.0.0.4 -> 192.0.0.5 -> 192.0.0.6 -> 192.0.0.7 -> 192.0.0.0.
261  do {
262     if (config_is_ipv4_address_free(htonl(ipv4))) {
263       chosen = htonl(ipv4);
264       break;
265     }
266     ipv4 = prefix | ((ipv4 + 1) & ~mask);
267  } while (ipv4 != first_ipv4);
268
269  return chosen;
270}
271
272/* function: config_generate_local_ipv6_subnet
273 * generates the local ipv6 subnet when given the interface ip
274 * requires config.ipv6_host_id
275 * interface_ip - in: interface ip, out: local ipv6 host address
276 */
277void config_generate_local_ipv6_subnet(struct in6_addr *interface_ip) {
278  int i;
279
280  if (Global_Clatd_Config.use_dynamic_iid) {
281    /* Generate a random interface ID. */
282    gen_random_iid(interface_ip,
283                   &Global_Clatd_Config.ipv4_local_subnet,
284                   &Global_Clatd_Config.plat_subnet);
285  } else {
286    /* Use the specified interface ID. */
287    for(i = 2; i < 4; i++) {
288      interface_ip->s6_addr32[i] = Global_Clatd_Config.ipv6_host_id.s6_addr32[i];
289    }
290  }
291}
292
293/* function: read_config
294 * reads the config file and parses it into the global variable Global_Clatd_Config. returns 0 on failure, 1 on success
295 * file             - filename to parse
296 * uplink_interface - interface to use to reach the internet and supplier of address space
297 * plat_prefix      - (optional) plat prefix to use, otherwise follow config file
298 * net_id           - (optional) netId to use, NETID_UNSET indicates use of default network
299 */
300int read_config(const char *file, const char *uplink_interface, const char *plat_prefix,
301        unsigned net_id) {
302  cnode *root = config_node("", "");
303  void *tmp_ptr = NULL;
304  unsigned flags;
305
306  if(!root) {
307    logmsg(ANDROID_LOG_FATAL,"out of memory");
308    return 0;
309  }
310
311  memset(&Global_Clatd_Config, '\0', sizeof(Global_Clatd_Config));
312
313  config_load_file(root, file);
314  if(root->first_child == NULL) {
315    logmsg(ANDROID_LOG_FATAL,"Could not read config file %s", file);
316    goto failed;
317  }
318
319  Global_Clatd_Config.default_pdp_interface = strdup(uplink_interface);
320  if (!Global_Clatd_Config.default_pdp_interface)
321    goto failed;
322
323  if(!config_item_int16_t(root, "mtu", "-1", &Global_Clatd_Config.mtu))
324    goto failed;
325
326  if(!config_item_int16_t(root, "ipv4mtu", "-1", &Global_Clatd_Config.ipv4mtu))
327    goto failed;
328
329  if(!config_item_ip(root, "ipv4_local_subnet", DEFAULT_IPV4_LOCAL_SUBNET,
330                     &Global_Clatd_Config.ipv4_local_subnet))
331    goto failed;
332
333  if(!config_item_int16_t(root, "ipv4_local_prefixlen", DEFAULT_IPV4_LOCAL_PREFIXLEN,
334                          &Global_Clatd_Config.ipv4_local_prefixlen))
335    goto failed;
336
337  if(plat_prefix) { // plat subnet is coming from the command line
338    if(inet_pton(AF_INET6, plat_prefix, &Global_Clatd_Config.plat_subnet) <= 0) {
339      logmsg(ANDROID_LOG_FATAL,"invalid IPv6 address specified for plat prefix: %s", plat_prefix);
340      goto failed;
341    }
342  } else {
343    tmp_ptr = (void *)config_item_str(root, "plat_from_dns64", "yes");
344    if(!tmp_ptr || strcmp(tmp_ptr, "no") == 0) {
345      free(tmp_ptr);
346
347      if(!config_item_ip6(root, "plat_subnet", NULL, &Global_Clatd_Config.plat_subnet)) {
348        logmsg(ANDROID_LOG_FATAL, "plat_from_dns64 disabled, but no plat_subnet specified");
349        goto failed;
350      }
351    } else {
352      free(tmp_ptr);
353
354      if(!(Global_Clatd_Config.plat_from_dns64_hostname = config_item_str(root, "plat_from_dns64_hostname", DEFAULT_DNS64_DETECTION_HOSTNAME)))
355        goto failed;
356      dns64_detection(net_id);
357    }
358  }
359
360  if (!config_item_ip6(root, "ipv6_host_id", "::", &Global_Clatd_Config.ipv6_host_id))
361    goto failed;
362
363  /* In order to prevent multiple devices attempting to use the same clat address, never use a
364     statically-configured interface ID on a broadcast interface such as wifi. */
365  if (!IN6_IS_ADDR_UNSPECIFIED(&Global_Clatd_Config.ipv6_host_id)) {
366    ifc_init();
367    ifc_get_info(Global_Clatd_Config.default_pdp_interface, NULL, NULL, &flags);
368    ifc_close();
369    Global_Clatd_Config.use_dynamic_iid = (flags & IFF_BROADCAST) != 0;
370  } else {
371    Global_Clatd_Config.use_dynamic_iid = 1;
372  }
373
374  return 1;
375
376failed:
377  free(root);
378  free_config();
379  return 0;
380}
381
382/* function; dump_config
383 * prints the current config
384 */
385void dump_config() {
386  char charbuffer[INET6_ADDRSTRLEN];
387
388  logmsg(ANDROID_LOG_DEBUG,"mtu = %d",Global_Clatd_Config.mtu);
389  logmsg(ANDROID_LOG_DEBUG,"ipv4mtu = %d",Global_Clatd_Config.ipv4mtu);
390  logmsg(ANDROID_LOG_DEBUG,"ipv6_local_subnet = %s",inet_ntop(AF_INET6, &Global_Clatd_Config.ipv6_local_subnet, charbuffer, sizeof(charbuffer)));
391  logmsg(ANDROID_LOG_DEBUG,"ipv4_local_subnet = %s",inet_ntop(AF_INET, &Global_Clatd_Config.ipv4_local_subnet, charbuffer, sizeof(charbuffer)));
392  logmsg(ANDROID_LOG_DEBUG,"ipv4_local_prefixlen = %d", Global_Clatd_Config.ipv4_local_prefixlen);
393  logmsg(ANDROID_LOG_DEBUG,"plat_subnet = %s",inet_ntop(AF_INET6, &Global_Clatd_Config.plat_subnet, charbuffer, sizeof(charbuffer)));
394  logmsg(ANDROID_LOG_DEBUG,"default_pdp_interface = %s",Global_Clatd_Config.default_pdp_interface);
395}
396