sysdeps/unix/sysv/linux/check_pf.c

   1 /* Determine protocol families for which interfaces exist.  Linux version.
   2    Copyright (C) 2003-2016 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 <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_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 #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 (NULL);
 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           (void *) &nladdr, sizeof (nladdr),
 162           &iov, 1,
 163           NULL, 0,
 164           0
 165         };
 166
 167       ssize_t read_len = TEMP_FAILURE_RETRY (__recvmsg (fd, &msg, 0));
 168       __netlink_assert_response (fd, read_len);
 169       if (read_len < 0)
 170         goto out_fail;
 171
 172       if (msg.msg_flags & MSG_TRUNC)
 173         goto out_fail;
 174
 175       struct nlmsghdr *nlmh;
 176       for (nlmh = (struct nlmsghdr *) buf;
 177            NLMSG_OK (nlmh, (size_t) read_len);
 178            nlmh = (struct nlmsghdr *) NLMSG_NEXT (nlmh, read_len))
 179         {
 180           if (nladdr.nl_pid != 0 || (pid_t) nlmh->nlmsg_pid != pid
 181               || nlmh->nlmsg_seq != req.nlh.nlmsg_seq)
 182             continue;
 183
 184           if (nlmh->nlmsg_type == RTM_NEWADDR)
 185             {
 186               struct ifaddrmsg *ifam = (struct ifaddrmsg *) NLMSG_DATA (nlmh);
 187               struct rtattr *rta = IFA_RTA (ifam);
 188               size_t len = nlmh->nlmsg_len - NLMSG_LENGTH (sizeof (*ifam));
 189
 190               if (ifam->ifa_family != AF_INET
 191                   && ifam->ifa_family != AF_INET6)
 192                 continue;
 193
 194               const void *local = NULL;
 195               const void *address = NULL;
 196               while (RTA_OK (rta, len))
 197                 {
 198                   switch (rta->rta_type)
 199                     {
 200                     case IFA_LOCAL:
 201                       local = RTA_DATA (rta);
 202                       break;
 203
 204                     case IFA_ADDRESS:
 205                       address = RTA_DATA (rta);
 206                       goto out;
 207                     }
 208
 209                   rta = RTA_NEXT (rta, len);
 210                 }
 211
 212               if (local != NULL)
 213                 {
 214                   address = local;
 215                 out:
 216                   if (ifam->ifa_family == AF_INET)
 217                     {
 218                       if (*(const in_addr_t *) address
 219                           != htonl (INADDR_LOOPBACK))
 220                         seen_ipv4 = true;
 221                     }
 222                   else
 223                     {
 224                       if (!IN6_IS_ADDR_LOOPBACK (address))
 225                         seen_ipv6 = true;
 226                     }
 227                 }
 228
 229               if (result_len == 0 || result_len == result_cap)
 230                 {
 231                   result_cap = 2 * result_cap;
 232                   result = realloc (result, sizeof (*result)
 233                                     + result_cap
 234                                       * sizeof (struct in6addrinfo));
 235                 }
 236
 237               if (!result)
 238                 goto out_fail;
 239
 240               struct in6addrinfo *info = &result->in6ai[result_len++];
 241
 242               info->flags = (((ifam->ifa_flags
 243                                & (IFA_F_DEPRECATED | IFA_F_OPTIMISTIC))
 244                               ? in6ai_deprecated : 0)
 245                              | ((ifam->ifa_flags & IFA_F_HOMEADDRESS)
 246                                  ? in6ai_homeaddress : 0));
 247               info->prefixlen = ifam->ifa_prefixlen;
 248               info->index = ifam->ifa_index;
 249               if (ifam->ifa_family == AF_INET)
 250                 {
 251                   info->addr[0] = 0;
 252                   info->addr[1] = 0;
 253                   info->addr[2] = htonl (0xffff);
 254                   info->addr[3] = *(const in_addr_t *) address;
 255                 }
 256               else
 257                 memcpy (info->addr, address, sizeof (info->addr));
 258             }
 259           else if (nlmh->nlmsg_type == NLMSG_DONE)
 260             /* We found the end, leave the loop.  */
 261             done = true;
 262         }
 263     }
 264   while (! done);
 265
 266   if (seen_ipv6 && result != NULL)
 267     {
 268       result->timestamp = get_nl_timestamp ();
 269       result->usecnt = 2;
 270       result->seen_ipv4 = seen_ipv4;
 271       result->seen_ipv6 = true;
 272       result->in6ailen = result_len;
 273     }
 274   else
 275     {
 276       free (result);
 277
 278       atomic_add (&noai6ai_cached.usecnt, 2);
 279       noai6ai_cached.seen_ipv4 = seen_ipv4;
 280       noai6ai_cached.seen_ipv6 = seen_ipv6;
 281       result = &noai6ai_cached;
 282     }
 283
 284   return result;
 285
 286  out_fail:
 287
 288   free (result);
 289   return NULL;
 290 }
 291
 292
 293 void
 294 attribute_hidden
 295 __check_pf (bool *seen_ipv4, bool *seen_ipv6,
 296             struct in6addrinfo **in6ai, size_t *in6ailen)
 297 {
 298   *in6ai = NULL;
 299   *in6ailen = 0;
 300
 301   struct cached_data *olddata = NULL;
 302   struct cached_data *data = NULL;
 303
 304   __libc_lock_lock (lock);
 305
 306   if (cache_valid_p ())
 307     {
 308       data = cache;
 309       atomic_increment (&cache->usecnt);
 310     }
 311   else
 312     {
 313       int fd = __socket (PF_NETLINK, SOCK_RAW, 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_not_cancel_no_status (fd);
 329         }
 330
 331       if (data != NULL)
 332         {
 333           olddata = cache;
 334           cache = data;
 335         }
 336     }
 337
 338   __libc_lock_unlock (lock);
 339
 340   if (data != NULL)
 341     {
 342       /* It worked.  */
 343       *seen_ipv4 = data->seen_ipv4;
 344       *seen_ipv6 = data->seen_ipv6;
 345       *in6ailen = data->in6ailen;
 346       *in6ai = data->in6ai;
 347
 348       if (olddata != NULL && olddata->usecnt > 0
 349           && atomic_add_zero (&olddata->usecnt, -1))
 350         free (olddata);
 351
 352       return;
 353     }
 354
 355   /* We cannot determine what interfaces are available.  Be
 356      pessimistic.  */
 357   *seen_ipv4 = true;
 358   *seen_ipv6 = true;
 359 }
 360
 361 /* Free the cache if it has been allocated.  */
 362 libc_freeres_fn (freecache)
 363 {
 364   if (cache)
 365     __free_in6ai (cache->in6ai);
 366 }
 367
 368 void
 369 __free_in6ai (struct in6addrinfo *ai)
 370 {
 371   if (ai != NULL)
 372     {
 373       struct cached_data *data =
 374         (struct cached_data *) ((char *) ai
 375                                 - offsetof (struct cached_data, in6ai));
 376
 377       if (atomic_add_zero (&data->usecnt, -1))
 378         {
 379           __libc_lock_lock (lock);
 380
 381           if (data->usecnt == 0)
 382             /* Still unused.  */
 383             free (data);
 384
 385           __libc_lock_unlock (lock);
 386         }
 387     }
 388 }