1  /* Definitions related to res_init linked into libc instead of libresolv.
       2     Copyright (C) 1995-2023 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  /*
      20   * Copyright (c) 1995-1999 by Internet Software Consortium.
      21   *
      22   * Permission to use, copy, modify, and distribute this software for any
      23   * purpose with or without fee is hereby granted, provided that the above
      24   * copyright notice and this permission notice appear in all copies.
      25   *
      26   * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
      27   * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
      28   * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
      29   * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
      30   * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
      31   * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
      32   * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
      33   * SOFTWARE.
      34   */
      35  
      36  #include <atomic.h>
      37  #include <limits.h>
      38  #include <sys/types.h>
      39  #include <netinet/in.h>
      40  #include <arpa/nameser.h>
      41  #include <resolv.h>
      42  #include <libc-lock.h>
      43  #include <resolv-internal.h>
      44  
      45  int
      46  res_init (void)
      47  {
      48    /* These three fields used to be statically initialized.  This made
      49       it hard to use this code in a shared library.  It is necessary,
      50       now that we're doing dynamic initialization here, that we
      51       preserve the old semantics: if an application modifies one of
      52       these three fields of _res before res_init is called,
      53       res_init will not alter them.  Of course, if an application is
      54       setting them to _zero_ before calling res_init, hoping to
      55       override what used to be the static default, we can't detect it
      56       and unexpected results will follow.  Zero for any of these fields
      57       would make no sense, so one can safely assume that the
      58       applications were already getting unexpected results.
      59  
      60       _res.options is tricky since some apps were known to diddle the
      61       bits before res_init was first called. We can't replicate that
      62       semantic with dynamic initialization (they may have turned bits
      63       off that are set in RES_DEFAULT).  Our solution is to declare
      64       such applications "broken".  They could fool us by setting
      65       RES_INIT but none do (yet).  */
      66    if (!_res.retrans)
      67      _res.retrans = RES_TIMEOUT;
      68    if (!_res.retry)
      69      _res.retry = RES_DFLRETRY;
      70    if (!(_res.options & RES_INIT))
      71      _res.options = RES_DEFAULT;
      72    else if (_res.nscount > 0)
      73      __res_iclose (&_res, true); /* Close any VC sockets.  */
      74  
      75    /* This one used to initialize implicitly to zero, so unless the app
      76       has set it to something in particular, we can randomize it *
      77       now.  */
      78    if (!_res.id)
      79      _res.id = res_randomid ();
      80  
      81    return __res_vinit (&_res, 1);
      82  }
      83  
      84  /* This needs to be after the use of _res in res_init, above.  */
      85  #undef _res
      86  
      87  /* The resolver state for use by single-threaded programs.
      88     This differs from plain `struct __res_state _res;' in that it doesn't
      89     create a common definition, but a plain symbol that resides in .bss,
      90     which can have an alias.  */
      91  struct __res_state _res;
      92  
      93  #undef __resp
      94  __thread struct __res_state *__resp = &_res;
      95  extern __thread struct __res_state *__libc_resp
      96    __attribute__ ((alias ("__resp"))) attribute_hidden;
      97  
      98  #include <shlib-compat.h>
      99  
     100  /* We declare this with compat_symbol so that it's not
     101     visible at link time.  Programs must use the accessor functions.  */
     102  #ifdef SHARED
     103  compat_symbol (libc, _res, _res, GLIBC_2_0);
     104  #endif
     105  
     106  #if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_2)
     107  # undef res_init
     108  extern int __res_init_weak (void);
     109  weak_extern (__res_init_weak);
     110  strong_alias (__res_init, __res_init_weak);
     111  compat_symbol (libc, __res_init_weak, res_init, GLIBC_2_0);
     112  #endif