glibc/resolv/res_libc.c

/* Definitions related to res_init linked into libc instead of libresolv.
   Copyright (C) 1995-2017 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

/*
 * Copyright (c) 1995-1999 by Internet Software Consortium.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

#include <atomic.h>
#include <limits.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include <libc-lock.h>
#include <resolv-internal.h>

/* We have atomic increment operations on 64-bit platforms.  */
#if __WORDSIZE == 64
# define atomicinclock(lock) (void) 0
# define atomicincunlock(lock) (void) 0
# define atomicinc(var) catomic_increment (&(var))
#else
__libc_lock_define_initialized (static, lock);
# define atomicinclock(lock) __libc_lock_lock (lock)
# define atomicincunlock(lock) __libc_lock_unlock (lock)
# define atomicinc(var) ++var
#endif

int
res_init (void)
{
  /* These three fields used to be statically initialized.  This made
     it hard to use this code in a shared library.  It is necessary,
     now that we're doing dynamic initialization here, that we
     preserve the old semantics: if an application modifies one of
     these three fields of _res before res_init is called,
     res_init will not alter them.  Of course, if an application is
     setting them to _zero_ before calling res_init, hoping to
     override what used to be the static default, we can't detect it
     and unexpected results will follow.  Zero for any of these fields
     would make no sense, so one can safely assume that the
     applications were already getting unexpected results.

     _res.options is tricky since some apps were known to diddle the
     bits before res_init was first called. We can't replicate that
     semantic with dynamic initialization (they may have turned bits
     off that are set in RES_DEFAULT).  Our solution is to declare
     such applications "broken".  They could fool us by setting
     RES_INIT but none do (yet).  */
  if (!_res.retrans)
    _res.retrans = RES_TIMEOUT;
  if (!_res.retry)
    _res.retry = RES_DFLRETRY;
  if (!(_res.options & RES_INIT))
    _res.options = RES_DEFAULT;
  else if (_res.nscount > 0)
    __res_iclose (&_res, true); /* Close any VC sockets.  */

  /* This one used to initialize implicitly to zero, so unless the app
     has set it to something in particular, we can randomize it *
     now.  */
  if (!_res.id)
    _res.id = res_randomid ();

  atomicinclock (lock);
  /* Request all threads to re-initialize their resolver states,
     resolv.conf might have changed.  */
  atomicinc (__res_initstamp);
  atomicincunlock (lock);

  return __res_vinit (&_res, 1);
}

/* Initialize *RESP if RES_INIT is not yet set in RESP->options, or if
   res_init in some other thread requested re-initializing.  */
int
__res_maybe_init (res_state resp, int preinit)
{
  if (resp->options & RES_INIT)
    {
      if (__res_initstamp != resp->_u._ext.initstamp)
        {
          if (resp->nscount > 0)
            __res_iclose (resp, true);
          return __res_vinit (resp, 1);
        }
      return 0;
    }
  else if (preinit)
    {
      if (!resp->retrans)
        resp->retrans = RES_TIMEOUT;
      if (!resp->retry)
        resp->retry = RES_DFLRETRY;
      resp->options = RES_DEFAULT;
      if (!resp->id)
        resp->id = res_randomid ();
      return __res_vinit (resp, 1);
    }
  else
    return __res_ninit (resp);
}
libc_hidden_def (__res_maybe_init)

/* This needs to be after the use of _res in res_init, above.  */
#undef _res

/* The resolver state for use by single-threaded programs.
   This differs from plain `struct __res_state _res;' in that it doesn't
   create a common definition, but a plain symbol that resides in .bss,
   which can have an alias.  */
struct __res_state _res __attribute__ ((nocommon));

#undef __resp
__thread struct __res_state *__resp = &_res;
extern __thread struct __res_state *__libc_resp
  __attribute__ ((alias ("__resp"))) attribute_hidden;

#include <shlib-compat.h>

/* We declare this with compat_symbol so that it's not
   visible at link time.  Programs must use the accessor functions.  */
#ifdef SHARED
compat_symbol (libc, _res, _res, GLIBC_2_0);
#endif

#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_2)
# undef res_init
extern int __res_init_weak (void);
weak_extern (__res_init_weak);
strong_alias (__res_init, __res_init_weak);
compat_symbol (libc, __res_init_weak, res_init, GLIBC_2_0);
#endif