resolv/res_libc.c

   1 /* Definitions related to res_init linked into libc instead of libresolv.
   2    Copyright (C) 1995-2017 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 /*
  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 /* We have atomic increment operations on 64-bit platforms.  */
  46 #if __WORDSIZE == 64
  47 # define atomicinclock(lock) (void) 0
  48 # define atomicincunlock(lock) (void) 0
  49 # define atomicinc(var) catomic_increment (&(var))
  50 #else
  51 __libc_lock_define_initialized (static, lock);
  52 # define atomicinclock(lock) __libc_lock_lock (lock)
  53 # define atomicincunlock(lock) __libc_lock_unlock (lock)
  54 # define atomicinc(var) ++var
  55 #endif
  56
  57 int
  58 res_init (void)
  59 {
  60   /* These three fields used to be statically initialized.  This made
  61      it hard to use this code in a shared library.  It is necessary,
  62      now that we're doing dynamic initialization here, that we
  63      preserve the old semantics: if an application modifies one of
  64      these three fields of _res before res_init is called,
  65      res_init will not alter them.  Of course, if an application is
  66      setting them to _zero_ before calling res_init, hoping to
  67      override what used to be the static default, we can't detect it
  68      and unexpected results will follow.  Zero for any of these fields
  69      would make no sense, so one can safely assume that the
  70      applications were already getting unexpected results.
  71
  72      _res.options is tricky since some apps were known to diddle the
  73      bits before res_init was first called. We can't replicate that
  74      semantic with dynamic initialization (they may have turned bits
  75      off that are set in RES_DEFAULT).  Our solution is to declare
  76      such applications "broken".  They could fool us by setting
  77      RES_INIT but none do (yet).  */
  78   if (!_res.retrans)
  79     _res.retrans = RES_TIMEOUT;
  80   if (!_res.retry)
  81     _res.retry = RES_DFLRETRY;
  82   if (!(_res.options & RES_INIT))
  83     _res.options = RES_DEFAULT;
  84   else if (_res.nscount > 0)
  85     __res_iclose (&_res, true); /* Close any VC sockets.  */
  86
  87   /* This one used to initialize implicitly to zero, so unless the app
  88      has set it to something in particular, we can randomize it *
  89      now.  */
  90   if (!_res.id)
  91     _res.id = res_randomid ();
  92
  93   atomicinclock (lock);
  94   /* Request all threads to re-initialize their resolver states,
  95      resolv.conf might have changed.  */
  96   atomicinc (__res_initstamp);
  97   atomicincunlock (lock);
  98
  99   return __res_vinit (&_res, 1);
 100 }
 101
 102 /* Initialize *RESP if RES_INIT is not yet set in RESP->options, or if
 103    res_init in some other thread requested re-initializing.  */
 104 int
 105 __res_maybe_init (res_state resp, int preinit)
 106 {
 107   if (resp->options & RES_INIT)
 108     {
 109       if (__res_initstamp != resp->_u._ext.initstamp)
 110         {
 111           if (resp->nscount > 0)
 112             __res_iclose (resp, true);
 113           return __res_vinit (resp, 1);
 114         }
 115       return 0;
 116     }
 117   else if (preinit)
 118     {
 119       if (!resp->retrans)
 120         resp->retrans = RES_TIMEOUT;
 121       if (!resp->retry)
 122         resp->retry = RES_DFLRETRY;
 123       resp->options = RES_DEFAULT;
 124       if (!resp->id)
 125         resp->id = res_randomid ();
 126       return __res_vinit (resp, 1);
 127     }
 128   else
 129     return __res_ninit (resp);
 130 }
 131 libc_hidden_def (__res_maybe_init)
 132 \f
 133 /* This needs to be after the use of _res in res_init, above.  */
 134 #undef _res
 135
 136 /* The resolver state for use by single-threaded programs.
 137    This differs from plain `struct __res_state _res;' in that it doesn't
 138    create a common definition, but a plain symbol that resides in .bss,
 139    which can have an alias.  */
 140 struct __res_state _res __attribute__ ((nocommon));
 141
 142 #undef __resp
 143 __thread struct __res_state *__resp = &_res;
 144 extern __thread struct __res_state *__libc_resp
 145   __attribute__ ((alias ("__resp"))) attribute_hidden;
 146
 147 #include <shlib-compat.h>
 148
 149 /* We declare this with compat_symbol so that it's not
 150    visible at link time.  Programs must use the accessor functions.  */
 151 #ifdef SHARED
 152 compat_symbol (libc, _res, _res, GLIBC_2_0);
 153 #endif
 154
 155 #if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_2)
 156 # undef res_init
 157 extern int __res_init_weak (void);
 158 weak_extern (__res_init_weak);
 159 strong_alias (__res_init, __res_init_weak);
 160 compat_symbol (libc, __res_init_weak, res_init, GLIBC_2_0);
 161 #endif