1 /* Determine protocol families for which interfaces exist. Linux version.
2 Copyright (C) 2003-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 #include <assert.h>
20 #include <errno.h>
21 #include <ifaddrs.h>
22 #include <netdb.h>
23 #include <stddef.h>
24 #include <string.h>
25 #include <time.h>
26 #include <unistd.h>
27 #include <stdint.h>
28 #include <sys/socket.h>
29
30 #include <asm/types.h>
31 #include <linux/netlink.h>
32 #include <linux/rtnetlink.h>
33
34 #include <not-cancel.h>
35 #include <libc-lock.h>
36 #include <atomic.h>
37 #include <nscd/nscd-client.h>
38
39 #include "netlinkaccess.h"
40
41 #ifndef IFA_F_HOMEADDRESS
42 # define IFA_F_HOMEADDRESS 0
43 #endif
44 #ifndef IFA_F_OPTIMISTIC
45 # define IFA_F_OPTIMISTIC 0
46 #endif
47
48
49 struct cached_data
50 {
51 uint32_t timestamp;
52 uint32_t usecnt;
53 bool seen_ipv4;
54 bool seen_ipv6;
55 size_t in6ailen;
56 struct in6addrinfo in6ai[0];
57 };
58
59 static struct cached_data noai6ai_cached =
60 {
61 .usecnt = 1, /* Make sure we never try to delete this entry. */
62 .in6ailen = 0
63 };
64
65 static struct cached_data *cache;
66 __libc_lock_define_initialized (static, lock);
67
68
69 #if IS_IN (nscd)
70 static uint32_t nl_timestamp;
71
72 uint32_t
73 __bump_nl_timestamp (void)
74 {
75 if (atomic_fetch_add_relaxed (&nl_timestamp, 1) + 1 == 0)
76 atomic_fetch_add_relaxed (&nl_timestamp, 1);
77
78 return nl_timestamp;
79 }
80 #endif
81
82 static inline uint32_t
83 get_nl_timestamp (void)
84 {
85 #if IS_IN (nscd)
86 return nl_timestamp;
87 #elif defined USE_NSCD
88 return __nscd_get_nl_timestamp ();
89 #else
90 return 0;
91 #endif
92 }
93
94 static inline bool
95 cache_valid_p (void)
96 {
97 if (cache != NULL)
98 {
99 uint32_t timestamp = get_nl_timestamp ();
100 return timestamp != 0 && cache->timestamp == timestamp;
101 }
102 return false;
103 }
104
105
106 static struct cached_data *
107 make_request (int fd, pid_t pid)
108 {
109 struct cached_data *result = NULL;
110
111 size_t result_len = 0;
112 size_t result_cap = 32;
113
114 struct req
115 {
116 struct nlmsghdr nlh;
117 struct rtgenmsg g;
118 /* struct rtgenmsg consists of a single byte. This means there
119 are three bytes of padding included in the REQ definition.
120 We make them explicit here. */
121 char pad[3];
122 } req;
123 struct sockaddr_nl nladdr;
124
125 req.nlh.nlmsg_len = sizeof (req);
126 req.nlh.nlmsg_type = RTM_GETADDR;
127 req.nlh.nlmsg_flags = NLM_F_ROOT | NLM_F_MATCH | NLM_F_REQUEST;
128 req.nlh.nlmsg_pid = 0;
129 req.nlh.nlmsg_seq = time_now ();
130 req.g.rtgen_family = AF_UNSPEC;
131
132 assert (sizeof (req) - offsetof (struct req, pad) == 3);
133 memset (req.pad, '\0', sizeof (req.pad));
134
135 memset (&nladdr, '\0', sizeof (nladdr));
136 nladdr.nl_family = AF_NETLINK;
137
138 #ifdef PAGE_SIZE
139 const size_t buf_size = PAGE_SIZE;
140 #else
141 const size_t buf_size = 4096;
142 #endif
143 char buf[buf_size];
144
145 struct iovec iov = { buf, buf_size };
146
147 if (TEMP_FAILURE_RETRY (__sendto (fd, (void *) &req, sizeof (req), 0,
148 (struct sockaddr *) &nladdr,
149 sizeof (nladdr))) < 0)
150 goto out_fail;
151
152 bool done = false;
153
154 bool seen_ipv4 = false;
155 bool seen_ipv6 = false;
156
157 do
158 {
159 struct msghdr msg =
160 {
161 .msg_name = (void *) &nladdr,
162 .msg_namelen = sizeof (nladdr),
163 .msg_iov = &iov,
164 .msg_iovlen = 1,
165 .msg_control = NULL,
166 .msg_controllen = 0,
167 .msg_flags = 0
168 };
169
170 ssize_t read_len = TEMP_FAILURE_RETRY (__recvmsg (fd, &msg, 0));
171 __netlink_assert_response (fd, read_len);
172 if (read_len < 0)
173 goto out_fail;
174
175 if (msg.msg_flags & MSG_TRUNC)
176 goto out_fail;
177
178 struct nlmsghdr *nlmh;
179 for (nlmh = (struct nlmsghdr *) buf;
180 NLMSG_OK (nlmh, (size_t) read_len);
181 nlmh = (struct nlmsghdr *) NLMSG_NEXT (nlmh, read_len))
182 {
183 if (nladdr.nl_pid != 0 || (pid_t) nlmh->nlmsg_pid != pid
184 || nlmh->nlmsg_seq != req.nlh.nlmsg_seq)
185 continue;
186
187 if (nlmh->nlmsg_type == RTM_NEWADDR)
188 {
189 struct ifaddrmsg *ifam = (struct ifaddrmsg *) NLMSG_DATA (nlmh);
190 struct rtattr *rta = IFA_RTA (ifam);
191 size_t len = nlmh->nlmsg_len - NLMSG_LENGTH (sizeof (*ifam));
192
193 if (ifam->ifa_family != AF_INET
194 && ifam->ifa_family != AF_INET6)
195 continue;
196
197 const void *local = NULL;
198 const void *address = NULL;
199 while (RTA_OK (rta, len))
200 {
201 switch (rta->rta_type)
202 {
203 case IFA_LOCAL:
204 local = RTA_DATA (rta);
205 break;
206
207 case IFA_ADDRESS:
208 address = RTA_DATA (rta);
209 goto out;
210 }
211
212 rta = RTA_NEXT (rta, len);
213 }
214
215 if (local != NULL)
216 {
217 address = local;
218 out:
219 if (ifam->ifa_family == AF_INET)
220 {
221 if (*(const in_addr_t *) address
222 != htonl (INADDR_LOOPBACK))
223 seen_ipv4 = true;
224 }
225 else
226 {
227 if (!IN6_IS_ADDR_LOOPBACK (address))
228 seen_ipv6 = true;
229 }
230 }
231
232 if (result_len == 0 || result_len == result_cap)
233 {
234 result_cap = 2 * result_cap;
235 result = realloc (result, sizeof (*result)
236 + result_cap
237 * sizeof (struct in6addrinfo));
238 }
239
240 if (!result)
241 goto out_fail;
242
243 struct in6addrinfo *info = &result->in6ai[result_len++];
244
245 info->flags = (((ifam->ifa_flags
246 & (IFA_F_DEPRECATED | IFA_F_OPTIMISTIC))
247 ? in6ai_deprecated : 0)
248 | ((ifam->ifa_flags & IFA_F_HOMEADDRESS)
249 ? in6ai_homeaddress : 0));
250 info->prefixlen = ifam->ifa_prefixlen;
251 info->index = ifam->ifa_index;
252 if (ifam->ifa_family == AF_INET)
253 {
254 info->addr[0] = 0;
255 info->addr[1] = 0;
256 info->addr[2] = htonl (0xffff);
257 info->addr[3] = *(const in_addr_t *) address;
258 }
259 else
260 memcpy (info->addr, address, sizeof (info->addr));
261 }
262 else if (nlmh->nlmsg_type == NLMSG_DONE)
263 /* We found the end, leave the loop. */
264 done = true;
265 }
266 }
267 while (! done);
268
269 if (seen_ipv6 && result != NULL)
270 {
271 result->timestamp = get_nl_timestamp ();
272 result->usecnt = 2;
273 result->seen_ipv4 = seen_ipv4;
274 result->seen_ipv6 = true;
275 result->in6ailen = result_len;
276 }
277 else
278 {
279 free (result);
280
281 atomic_fetch_add_relaxed (&noai6ai_cached.usecnt, 2);
282 noai6ai_cached.seen_ipv4 = seen_ipv4;
283 noai6ai_cached.seen_ipv6 = seen_ipv6;
284 result = &noai6ai_cached;
285 }
286
287 return result;
288
289 out_fail:
290
291 free (result);
292 return NULL;
293 }
294
295 #ifdef __EXCEPTIONS
296 static void
297 cancel_handler (void *arg __attribute__((unused)))
298 {
299 /* Release the lock. */
300 __libc_lock_unlock (lock);
301 }
302 #endif
303
304 void
305 attribute_hidden
306 __check_pf (bool *seen_ipv4, bool *seen_ipv6,
307 struct in6addrinfo **in6ai, size_t *in6ailen)
308 {
309 *in6ai = NULL;
310 *in6ailen = 0;
311
312 struct cached_data *olddata = NULL;
313 struct cached_data *data = NULL;
314
315 #ifdef __EXCEPTIONS
316 /* Make sure that lock is released when the thread is cancelled. */
317 __libc_cleanup_push (cancel_handler, NULL);
318 #endif
319 __libc_lock_lock (lock);
320
321 if (cache_valid_p ())
322 {
323 data = cache;
324 atomic_fetch_add_relaxed (&cache->usecnt, 1);
325 }
326 else
327 {
328 int fd = __socket (PF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
329
330 if (__glibc_likely (fd >= 0))
331 {
332 struct sockaddr_nl nladdr;
333 memset (&nladdr, '\0', sizeof (nladdr));
334 nladdr.nl_family = AF_NETLINK;
335
336 socklen_t addr_len = sizeof (nladdr);
337
338 if (__bind (fd, (struct sockaddr *) &nladdr, sizeof (nladdr)) == 0
339 && __getsockname (fd, (struct sockaddr *) &nladdr,
340 &addr_len) == 0)
341 data = make_request (fd, nladdr.nl_pid);
342
343 __close_nocancel_nostatus (fd);
344 }
345
346 if (data != NULL)
347 {
348 olddata = cache;
349 cache = data;
350 }
351 }
352
353 #ifdef __EXCEPTIONS
354 __libc_cleanup_pop (0);
355 #endif
356 __libc_lock_unlock (lock);
357
358 if (data != NULL)
359 {
360 /* It worked. */
361 *seen_ipv4 = data->seen_ipv4;
362 *seen_ipv6 = data->seen_ipv6;
363 *in6ailen = data->in6ailen;
364 *in6ai = data->in6ai;
365
366 if (olddata != NULL && olddata->usecnt > 0
367 && atomic_fetch_add_relaxed (&olddata->usecnt, -1) == 1)
368 free (olddata);
369
370 return;
371 }
372
373 /* We cannot determine what interfaces are available. Be
374 pessimistic. */
375 *seen_ipv4 = true;
376 *seen_ipv6 = true;
377 }
378
379 /* Free the cache if it has been allocated. */
380 void
381 __check_pf_freemem (void)
382 {
383 if (cache)
384 __free_in6ai (cache->in6ai);
385 }
386
387 void
388 __free_in6ai (struct in6addrinfo *ai)
389 {
390 if (ai != NULL)
391 {
392 struct cached_data *data =
393 (struct cached_data *) ((char *) ai
394 - offsetof (struct cached_data, in6ai));
395
396 if (atomic_fetch_add_relaxed (&data->usecnt, -1) == 1)
397 {
398 __libc_lock_lock (lock);
399
400 if (data->usecnt == 0)
401 /* Still unused. */
402 free (data);
403
404 __libc_lock_unlock (lock);
405 }
406 }
407 }