sysdeps/unix/sysv/linux/check_pf.c

   1 /* Determine protocol families for which interfaces exist.  Linux version.
   2    Copyright (C) 2003-2014 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    <http://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 <kernel-features.h>
  36 #include <bits/libc-lock.h>
  37 #include <atomic.h>
  38 #include <nscd/nscd-client.h>
  39
  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 libc_freeres_ptr (static struct cached_data *cache);
  66 __libc_lock_define_initialized (static, lock);
  67
  68
  69 #ifdef IS_IN_nscd
  70 static uint32_t nl_timestamp;
  71
  72 uint32_t
  73 __bump_nl_timestamp (void)
  74 {
  75   if (atomic_increment_val (&nl_timestamp) == 0)
  76     atomic_increment (&nl_timestamp);
  77
  78   return nl_timestamp;
  79 }
  80 #endif
  81
  82 static inline uint32_t
  83 get_nl_timestamp (void)
  84 {
  85 #ifdef 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 req
 110   {
 111     struct nlmsghdr nlh;
 112     struct rtgenmsg g;
 113     /* struct rtgenmsg consists of a single byte.  This means there
 114        are three bytes of padding included in the REQ definition.
 115        We make them explicit here.  */
 116     char pad[3];
 117   } req;
 118   struct sockaddr_nl nladdr;
 119
 120   req.nlh.nlmsg_len = sizeof (req);
 121   req.nlh.nlmsg_type = RTM_GETADDR;
 122   req.nlh.nlmsg_flags = NLM_F_ROOT | NLM_F_MATCH | NLM_F_REQUEST;
 123   req.nlh.nlmsg_pid = 0;
 124   req.nlh.nlmsg_seq = time (NULL);
 125   req.g.rtgen_family = AF_UNSPEC;
 126
 127   assert (sizeof (req) - offsetof (struct req, pad) == 3);
 128   memset (req.pad, '\0', sizeof (req.pad));
 129
 130   memset (&nladdr, '\0', sizeof (nladdr));
 131   nladdr.nl_family = AF_NETLINK;
 132
 133 #ifdef PAGE_SIZE
 134   /* Help the compiler optimize out the malloc call if PAGE_SIZE
 135      is constant and smaller or equal to PTHREAD_STACK_MIN/4.  */
 136   const size_t buf_size = PAGE_SIZE;
 137 #else
 138   const size_t buf_size = __getpagesize ();
 139 #endif
 140   bool use_malloc = false;
 141   char *buf;
 142
 143   if (__libc_use_alloca (buf_size))
 144     buf = alloca (buf_size);
 145   else
 146     {
 147       buf = malloc (buf_size);
 148       if (buf != NULL)
 149         use_malloc = true;
 150       else
 151         goto out_fail;
 152     }
 153
 154   struct iovec iov = { buf, buf_size };
 155
 156   if (TEMP_FAILURE_RETRY (__sendto (fd, (void *) &req, sizeof (req), 0,
 157                                     (struct sockaddr *) &nladdr,
 158                                     sizeof (nladdr))) < 0)
 159     goto out_fail;
 160
 161   bool done = false;
 162   struct in6ailist
 163   {
 164     struct in6addrinfo info;
 165     struct in6ailist *next;
 166   } *in6ailist = NULL;
 167   size_t in6ailistlen = 0;
 168   bool seen_ipv4 = false;
 169   bool seen_ipv6 = false;
 170
 171   do
 172     {
 173       struct msghdr msg =
 174         {
 175           (void *) &nladdr, sizeof (nladdr),
 176           &iov, 1,
 177           NULL, 0,
 178           0
 179         };
 180
 181       ssize_t read_len = TEMP_FAILURE_RETRY (__recvmsg (fd, &msg, 0));
 182       if (read_len < 0)
 183         goto out_fail;
 184
 185       if (msg.msg_flags & MSG_TRUNC)
 186         goto out_fail;
 187
 188       struct nlmsghdr *nlmh;
 189       for (nlmh = (struct nlmsghdr *) buf;
 190            NLMSG_OK (nlmh, (size_t) read_len);
 191            nlmh = (struct nlmsghdr *) NLMSG_NEXT (nlmh, read_len))
 192         {
 193           if (nladdr.nl_pid != 0 || (pid_t) nlmh->nlmsg_pid != pid
 194               || nlmh->nlmsg_seq != req.nlh.nlmsg_seq)
 195             continue;
 196
 197           if (nlmh->nlmsg_type == RTM_NEWADDR)
 198             {
 199               struct ifaddrmsg *ifam = (struct ifaddrmsg *) NLMSG_DATA (nlmh);
 200               struct rtattr *rta = IFA_RTA (ifam);
 201               size_t len = nlmh->nlmsg_len - NLMSG_LENGTH (sizeof (*ifam));
 202
 203               if (ifam->ifa_family != AF_INET
 204                   && ifam->ifa_family != AF_INET6)
 205                 continue;
 206
 207               const void *local = NULL;
 208               const void *address = NULL;
 209               while (RTA_OK (rta, len))
 210                 {
 211                   switch (rta->rta_type)
 212                     {
 213                     case IFA_LOCAL:
 214                       local = RTA_DATA (rta);
 215                       break;
 216
 217                     case IFA_ADDRESS:
 218                       address = RTA_DATA (rta);
 219                       goto out;
 220                     }
 221
 222                   rta = RTA_NEXT (rta, len);
 223                 }
 224
 225               if (local != NULL)
 226                 {
 227                   address = local;
 228                 out:
 229                   if (ifam->ifa_family == AF_INET)
 230                     {
 231                       if (*(const in_addr_t *) address
 232                           != htonl (INADDR_LOOPBACK))
 233                         seen_ipv4 = true;
 234                     }
 235                   else
 236                     {
 237                       if (!IN6_IS_ADDR_LOOPBACK (address))
 238                         seen_ipv6 = true;
 239                     }
 240                 }
 241
 242               struct in6ailist *newp = alloca (sizeof (*newp));
 243               newp->info.flags = (((ifam->ifa_flags
 244                                     & (IFA_F_DEPRECATED
 245                                        | IFA_F_OPTIMISTIC))
 246                                    ? in6ai_deprecated : 0)
 247                                   | ((ifam->ifa_flags
 248                                       & IFA_F_HOMEADDRESS)
 249                                      ? in6ai_homeaddress : 0));
 250               newp->info.prefixlen = ifam->ifa_prefixlen;
 251               newp->info.index = ifam->ifa_index;
 252               if (ifam->ifa_family == AF_INET)
 253                 {
 254                   newp->info.addr[0] = 0;
 255                   newp->info.addr[1] = 0;
 256                   newp->info.addr[2] = htonl (0xffff);
 257                   newp->info.addr[3] = *(const in_addr_t *) address;
 258                 }
 259               else
 260                 memcpy (newp->info.addr, address, sizeof (newp->info.addr));
 261               newp->next = in6ailist;
 262               in6ailist = newp;
 263               ++in6ailistlen;
 264             }
 265           else if (nlmh->nlmsg_type == NLMSG_DONE)
 266             /* We found the end, leave the loop.  */
 267             done = true;
 268         }
 269     }
 270   while (! done);
 271
 272   struct cached_data *result;
 273   if (seen_ipv6 && in6ailist != NULL)
 274     {
 275       result = malloc (sizeof (*result)
 276                        + in6ailistlen * sizeof (struct in6addrinfo));
 277       if (result == NULL)
 278         goto out_fail;
 279
 280       result->timestamp = get_nl_timestamp ();
 281       result->usecnt = 2;
 282       result->seen_ipv4 = seen_ipv4;
 283       result->seen_ipv6 = true;
 284       result->in6ailen = in6ailistlen;
 285
 286       do
 287         {
 288           result->in6ai[--in6ailistlen] = in6ailist->info;
 289           in6ailist = in6ailist->next;
 290         }
 291       while (in6ailist != NULL);
 292     }
 293   else
 294     {
 295       atomic_add (&noai6ai_cached.usecnt, 2);
 296       noai6ai_cached.seen_ipv4 = seen_ipv4;
 297       noai6ai_cached.seen_ipv6 = seen_ipv6;
 298       result = &noai6ai_cached;
 299     }
 300
 301   if (use_malloc)
 302     free (buf);
 303   return result;
 304
 305 out_fail:
 306   if (use_malloc)
 307     free (buf);
 308   return NULL;
 309 }
 310
 311
 312 void
 313 attribute_hidden
 314 __check_pf (bool *seen_ipv4, bool *seen_ipv6,
 315             struct in6addrinfo **in6ai, size_t *in6ailen)
 316 {
 317   *in6ai = NULL;
 318   *in6ailen = 0;
 319
 320   struct cached_data *olddata = NULL;
 321   struct cached_data *data = NULL;
 322
 323   __libc_lock_lock (lock);
 324
 325   if (cache_valid_p ())
 326     {
 327       data = cache;
 328       atomic_increment (&cache->usecnt);
 329     }
 330   else
 331     {
 332       int fd = __socket (PF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
 333
 334       if (__builtin_expect (fd >= 0, 1))
 335         {
 336           struct sockaddr_nl nladdr;
 337           memset (&nladdr, '\0', sizeof (nladdr));
 338           nladdr.nl_family = AF_NETLINK;
 339
 340           socklen_t addr_len = sizeof (nladdr);
 341
 342           if (__bind (fd, (struct sockaddr *) &nladdr, sizeof (nladdr)) == 0
 343               && __getsockname (fd, (struct sockaddr *) &nladdr,
 344                                 &addr_len) == 0)
 345             data = make_request (fd, nladdr.nl_pid);
 346
 347           close_not_cancel_no_status (fd);
 348         }
 349
 350       if (data != NULL)
 351         {
 352           olddata = cache;
 353           cache = data;
 354         }
 355     }
 356
 357   __libc_lock_unlock (lock);
 358
 359   if (data != NULL)
 360     {
 361       /* It worked.  */
 362       *seen_ipv4 = data->seen_ipv4;
 363       *seen_ipv6 = data->seen_ipv6;
 364       *in6ailen = data->in6ailen;
 365       *in6ai = data->in6ai;
 366
 367       if (olddata != NULL && olddata->usecnt > 0
 368           && atomic_add_zero (&olddata->usecnt, -1))
 369         free (olddata);
 370
 371       return;
 372     }
 373
 374   /* We cannot determine what interfaces are available.  Be
 375      pessimistic.  */
 376   *seen_ipv4 = true;
 377   *seen_ipv6 = true;
 378 }
 379
 380
 381 void
 382 __free_in6ai (struct in6addrinfo *ai)
 383 {
 384   if (ai != NULL)
 385     {
 386       struct cached_data *data =
 387         (struct cached_data *) ((char *) ai
 388                                 - offsetof (struct cached_data, in6ai));
 389
 390       if (atomic_add_zero (&data->usecnt, -1))
 391         {
 392           __libc_lock_lock (lock);
 393
 394           if (data->usecnt == 0)
 395             /* Still unused.  */
 396             free (data);
 397
 398           __libc_lock_unlock (lock);
 399         }
 400     }
 401 }