sysdeps/unix/sysv/linux/check_pf.c

   1 /* Determine protocol families for which interfaces exist.  Linux version.
   2    Copyright (C) 2003-2024 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 static inline uint32_t
  70 get_nl_timestamp (void)
  71 {
  72 #if defined USE_NSCD
  73   return __nscd_get_nl_timestamp ();
  74 #else
  75   return 0;
  76 #endif
  77 }
  78
  79 static inline bool
  80 cache_valid_p (void)
  81 {
  82   if (cache != NULL)
  83     {
  84       uint32_t timestamp = get_nl_timestamp ();
  85       return timestamp != 0 && cache->timestamp == timestamp;
  86     }
  87   return false;
  88 }
  89
  90
  91 static struct cached_data *
  92 make_request (int fd, pid_t pid)
  93 {
  94   struct cached_data *result = NULL;
  95
  96   size_t result_len = 0;
  97   size_t result_cap = 32;
  98
  99   struct req
 100   {
 101     struct nlmsghdr nlh;
 102     struct rtgenmsg g;
 103     /* struct rtgenmsg consists of a single byte.  This means there
 104        are three bytes of padding included in the REQ definition.
 105        We make them explicit here.  */
 106     char pad[3];
 107   } req;
 108   struct sockaddr_nl nladdr;
 109
 110   req.nlh.nlmsg_len = sizeof (req);
 111   req.nlh.nlmsg_type = RTM_GETADDR;
 112   req.nlh.nlmsg_flags = NLM_F_ROOT | NLM_F_MATCH | NLM_F_REQUEST;
 113   req.nlh.nlmsg_pid = 0;
 114   req.nlh.nlmsg_seq = time_now ();
 115   req.g.rtgen_family = AF_UNSPEC;
 116
 117   assert (sizeof (req) - offsetof (struct req, pad) == 3);
 118   memset (req.pad, '\0', sizeof (req.pad));
 119
 120   memset (&nladdr, '\0', sizeof (nladdr));
 121   nladdr.nl_family = AF_NETLINK;
 122
 123 #ifdef PAGE_SIZE
 124   const size_t buf_size = PAGE_SIZE;
 125 #else
 126   const size_t buf_size = 4096;
 127 #endif
 128   char buf[buf_size];
 129
 130   struct iovec iov = { buf, buf_size };
 131
 132   if (TEMP_FAILURE_RETRY (__sendto (fd, (void *) &req, sizeof (req), 0,
 133                                     (struct sockaddr *) &nladdr,
 134                                     sizeof (nladdr))) < 0)
 135     goto out_fail;
 136
 137   bool done = false;
 138
 139   bool seen_ipv4 = false;
 140   bool seen_ipv6 = false;
 141
 142   do
 143     {
 144       struct msghdr msg =
 145         {
 146           .msg_name = (void *) &nladdr,
 147           .msg_namelen =  sizeof (nladdr),
 148           .msg_iov = &iov,
 149           .msg_iovlen = 1,
 150           .msg_control = NULL,
 151           .msg_controllen = 0,
 152           .msg_flags = 0
 153         };
 154
 155       ssize_t read_len = TEMP_FAILURE_RETRY (__recvmsg (fd, &msg, 0));
 156       __netlink_assert_response (fd, read_len);
 157       if (read_len < 0)
 158         goto out_fail;
 159
 160       if (msg.msg_flags & MSG_TRUNC)
 161         goto out_fail;
 162
 163       struct nlmsghdr *nlmh;
 164       for (nlmh = (struct nlmsghdr *) buf;
 165            NLMSG_OK (nlmh, (size_t) read_len);
 166            nlmh = (struct nlmsghdr *) NLMSG_NEXT (nlmh, read_len))
 167         {
 168           if (nladdr.nl_pid != 0 || (pid_t) nlmh->nlmsg_pid != pid
 169               || nlmh->nlmsg_seq != req.nlh.nlmsg_seq)
 170             continue;
 171
 172           if (nlmh->nlmsg_type == RTM_NEWADDR)
 173             {
 174               struct ifaddrmsg *ifam = (struct ifaddrmsg *) NLMSG_DATA (nlmh);
 175               struct rtattr *rta = IFA_RTA (ifam);
 176               size_t len = nlmh->nlmsg_len - NLMSG_LENGTH (sizeof (*ifam));
 177
 178               if (ifam->ifa_family != AF_INET
 179                   && ifam->ifa_family != AF_INET6)
 180                 continue;
 181
 182               const void *local = NULL;
 183               const void *address = NULL;
 184               while (RTA_OK (rta, len))
 185                 {
 186                   switch (rta->rta_type)
 187                     {
 188                     case IFA_LOCAL:
 189                       local = RTA_DATA (rta);
 190                       break;
 191
 192                     case IFA_ADDRESS:
 193                       address = RTA_DATA (rta);
 194                       goto out;
 195                     }
 196
 197                   rta = RTA_NEXT (rta, len);
 198                 }
 199
 200               if (local != NULL)
 201                 {
 202                   address = local;
 203                 out:
 204                   if (ifam->ifa_family == AF_INET)
 205                     {
 206                       if (*(const in_addr_t *) address
 207                           != htonl (INADDR_LOOPBACK))
 208                         seen_ipv4 = true;
 209                     }
 210                   else
 211                     {
 212                       if (!IN6_IS_ADDR_LOOPBACK (address))
 213                         seen_ipv6 = true;
 214                     }
 215                 }
 216
 217               if (result_len == 0 || result_len == result_cap)
 218                 {
 219                   result_cap = 2 * result_cap;
 220                   result = realloc (result, sizeof (*result)
 221                                     + result_cap
 222                                       * sizeof (struct in6addrinfo));
 223                 }
 224
 225               if (!result)
 226                 goto out_fail;
 227
 228               struct in6addrinfo *info = &result->in6ai[result_len++];
 229
 230               info->flags = (((ifam->ifa_flags
 231                                & (IFA_F_DEPRECATED | IFA_F_OPTIMISTIC))
 232                               ? in6ai_deprecated : 0)
 233                              | ((ifam->ifa_flags & IFA_F_HOMEADDRESS)
 234                                  ? in6ai_homeaddress : 0));
 235               info->prefixlen = ifam->ifa_prefixlen;
 236               info->index = ifam->ifa_index;
 237               if (ifam->ifa_family == AF_INET)
 238                 {
 239                   info->addr[0] = 0;
 240                   info->addr[1] = 0;
 241                   info->addr[2] = htonl (0xffff);
 242                   info->addr[3] = *(const in_addr_t *) address;
 243                 }
 244               else
 245                 memcpy (info->addr, address, sizeof (info->addr));
 246             }
 247           else if (nlmh->nlmsg_type == NLMSG_DONE)
 248             /* We found the end, leave the loop.  */
 249             done = true;
 250         }
 251     }
 252   while (! done);
 253
 254   if (seen_ipv6 && result != NULL)
 255     {
 256       result->timestamp = get_nl_timestamp ();
 257       result->usecnt = 2;
 258       result->seen_ipv4 = seen_ipv4;
 259       result->seen_ipv6 = true;
 260       result->in6ailen = result_len;
 261     }
 262   else
 263     {
 264       free (result);
 265
 266       atomic_fetch_add_relaxed (&noai6ai_cached.usecnt, 2);
 267       noai6ai_cached.seen_ipv4 = seen_ipv4;
 268       noai6ai_cached.seen_ipv6 = seen_ipv6;
 269       result = &noai6ai_cached;
 270     }
 271
 272   return result;
 273
 274  out_fail:
 275
 276   free (result);
 277   return NULL;
 278 }
 279
 280 #ifdef __EXCEPTIONS
 281 static void
 282 cancel_handler (void *arg __attribute__((unused)))
 283 {
 284   /* Release the lock.  */
 285   __libc_lock_unlock (lock);
 286 }
 287 #endif
 288
 289 void
 290 attribute_hidden
 291 __check_pf (bool *seen_ipv4, bool *seen_ipv6,
 292             struct in6addrinfo **in6ai, size_t *in6ailen)
 293 {
 294   *in6ai = NULL;
 295   *in6ailen = 0;
 296
 297   struct cached_data *olddata = NULL;
 298   struct cached_data *data = NULL;
 299
 300 #ifdef __EXCEPTIONS
 301   /* Make sure that lock is released when the thread is cancelled.  */
 302   __libc_cleanup_push (cancel_handler, NULL);
 303 #endif
 304   __libc_lock_lock (lock);
 305
 306   if (cache_valid_p ())
 307     {
 308       data = cache;
 309       atomic_fetch_add_relaxed (&cache->usecnt, 1);
 310     }
 311   else
 312     {
 313       int fd = __socket (PF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
 314
 315       if (__glibc_likely (fd >= 0))
 316         {
 317           struct sockaddr_nl nladdr;
 318           memset (&nladdr, '\0', sizeof (nladdr));
 319           nladdr.nl_family = AF_NETLINK;
 320
 321           socklen_t addr_len = sizeof (nladdr);
 322
 323           if (__bind (fd, (struct sockaddr *) &nladdr, sizeof (nladdr)) == 0
 324               && __getsockname (fd, (struct sockaddr *) &nladdr,
 325                                 &addr_len) == 0)
 326             data = make_request (fd, nladdr.nl_pid);
 327
 328           __close_nocancel_nostatus (fd);
 329         }
 330
 331       if (data != NULL)
 332         {
 333           olddata = cache;
 334           cache = data;
 335         }
 336     }
 337
 338 #ifdef __EXCEPTIONS
 339   __libc_cleanup_pop (0);
 340 #endif
 341   __libc_lock_unlock (lock);
 342
 343   if (data != NULL)
 344     {
 345       /* It worked.  */
 346       *seen_ipv4 = data->seen_ipv4;
 347       *seen_ipv6 = data->seen_ipv6;
 348       *in6ailen = data->in6ailen;
 349       *in6ai = data->in6ai;
 350
 351       if (olddata != NULL && olddata->usecnt > 0
 352           && atomic_fetch_add_relaxed (&olddata->usecnt, -1) == 1)
 353         free (olddata);
 354
 355       return;
 356     }
 357
 358   /* We cannot determine what interfaces are available.  Be
 359      pessimistic.  */
 360   *seen_ipv4 = true;
 361   *seen_ipv6 = true;
 362 }
 363
 364 /* Free the cache if it has been allocated.  */
 365 void
 366 __check_pf_freemem (void)
 367 {
 368   if (cache)
 369     __free_in6ai (cache->in6ai);
 370 }
 371
 372 void
 373 __free_in6ai (struct in6addrinfo *ai)
 374 {
 375   if (ai != NULL)
 376     {
 377       struct cached_data *data =
 378         (struct cached_data *) ((char *) ai
 379                                 - offsetof (struct cached_data, in6ai));
 380
 381       if (atomic_fetch_add_relaxed (&data->usecnt, -1) == 1)
 382         {
 383           __libc_lock_lock (lock);
 384
 385           if (data->usecnt == 0)
 386             /* Still unused.  */
 387             free (data);
 388
 389           __libc_lock_unlock (lock);
 390         }
 391     }
 392 }