sysdeps/unix/sysv/linux/check_pf.c

   1 /* Determine protocol families for which interfaces exist.  Linux version.
   2    Copyright (C) 2003-2022 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_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_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
 296 void
 297 attribute_hidden
 298 __check_pf (bool *seen_ipv4, bool *seen_ipv6,
 299             struct in6addrinfo **in6ai, size_t *in6ailen)
 300 {
 301   *in6ai = NULL;
 302   *in6ailen = 0;
 303
 304   struct cached_data *olddata = NULL;
 305   struct cached_data *data = NULL;
 306
 307   __libc_lock_lock (lock);
 308
 309   if (cache_valid_p ())
 310     {
 311       data = cache;
 312       atomic_increment (&cache->usecnt);
 313     }
 314   else
 315     {
 316       int fd = __socket (PF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
 317
 318       if (__glibc_likely (fd >= 0))
 319         {
 320           struct sockaddr_nl nladdr;
 321           memset (&nladdr, '\0', sizeof (nladdr));
 322           nladdr.nl_family = AF_NETLINK;
 323
 324           socklen_t addr_len = sizeof (nladdr);
 325
 326           if (__bind (fd, (struct sockaddr *) &nladdr, sizeof (nladdr)) == 0
 327               && __getsockname (fd, (struct sockaddr *) &nladdr,
 328                                 &addr_len) == 0)
 329             data = make_request (fd, nladdr.nl_pid);
 330
 331           __close_nocancel_nostatus (fd);
 332         }
 333
 334       if (data != NULL)
 335         {
 336           olddata = cache;
 337           cache = data;
 338         }
 339     }
 340
 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 libc_freeres_fn (freecache)
 366 {
 367   if (cache)
 368     __free_in6ai (cache->in6ai);
 369 }
 370
 371 void
 372 __free_in6ai (struct in6addrinfo *ai)
 373 {
 374   if (ai != NULL)
 375     {
 376       struct cached_data *data =
 377         (struct cached_data *) ((char *) ai
 378                                 - offsetof (struct cached_data, in6ai));
 379
 380       if (atomic_fetch_add_relaxed (&data->usecnt, -1) == 1)
 381         {
 382           __libc_lock_lock (lock);
 383
 384           if (data->usecnt == 0)
 385             /* Still unused.  */
 386             free (data);
 387
 388           __libc_lock_unlock (lock);
 389         }
 390     }
 391 }