stdlib/setenv.c

   1 /* Copyright (C) 1992-2015 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #if HAVE_CONFIG_H
  19 # include <config.h>
  20 #endif
  21
  22 /* Pacify GCC; see the commentary about VALLEN below.  This is needed
  23    at least through GCC 4.9.2.  Pacify GCC for the entire file, as
  24    there seems to be no way to pacify GCC selectively, only for the
  25    place where it's needed.  Do not use DIAG_IGNORE_NEEDS_COMMENT
  26    here, as it's not defined yet.  */
  27 #if ((__GNUC__ << 16) + __GNUC_MINOR__) >= ((4 << 16) + 7)
  28 # pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
  29 #else
  30 # pragma GCC diagnostic ignored "-Wuninitialized"
  31 #endif
  32
  33 #include <errno.h>
  34 #if !_LIBC
  35 # if !defined errno && !defined HAVE_ERRNO_DECL
  36 extern int errno;
  37 # endif
  38 # define __set_errno(ev) ((errno) = (ev))
  39 #endif
  40
  41 #if _LIBC || HAVE_STDLIB_H
  42 # include <stdlib.h>
  43 #endif
  44 #if _LIBC || HAVE_STRING_H
  45 # include <string.h>
  46 #endif
  47 #if _LIBC || HAVE_UNISTD_H
  48 # include <unistd.h>
  49 #endif
  50
  51 #if !_LIBC
  52 # define __environ      environ
  53 # ifndef HAVE_ENVIRON_DECL
  54 extern char **environ;
  55 # endif
  56 #endif
  57
  58 #if _LIBC
  59 /* This lock protects against simultaneous modifications of `environ'.  */
  60 # include <bits/libc-lock.h>
  61 __libc_lock_define_initialized (static, envlock)
  62 # define LOCK   __libc_lock_lock (envlock)
  63 # define UNLOCK __libc_lock_unlock (envlock)
  64 #else
  65 # define LOCK
  66 # define UNLOCK
  67 #endif
  68
  69 /* In the GNU C library we must keep the namespace clean.  */
  70 #ifdef _LIBC
  71 # define setenv __setenv
  72 # define unsetenv __unsetenv
  73 # define clearenv __clearenv
  74 # define tfind __tfind
  75 # define tsearch __tsearch
  76 #endif
  77
  78 /* In the GNU C library implementation we try to be more clever and
  79    allow arbitrarily many changes of the environment given that the used
  80    values are from a small set.  Outside glibc this will eat up all
  81    memory after a while.  */
  82 #if defined _LIBC || (defined HAVE_SEARCH_H && defined HAVE_TSEARCH \
  83                       && defined __GNUC__)
  84 # define USE_TSEARCH    1
  85 # include <search.h>
  86
  87 /* This is a pointer to the root of the search tree with the known
  88    values.  */
  89 static void *known_values;
  90
  91 # define KNOWN_VALUE(Str) \
  92   ({                                                                          \
  93     void *value = tfind (Str, &known_values, (__compar_fn_t) strcmp);         \
  94     value != NULL ? *(char **) value : NULL;                                  \
  95   })
  96 # define STORE_VALUE(Str) \
  97   tsearch (Str, &known_values, (__compar_fn_t) strcmp)
  98
  99 #else
 100 # undef USE_TSEARCH
 101
 102 # define KNOWN_VALUE(Str) NULL
 103 # define STORE_VALUE(Str) do { } while (0)
 104
 105 #endif
 106
 107
 108 /* If this variable is not a null pointer we allocated the current
 109    environment.  */
 110 static char **last_environ;
 111
 112
 113 /* This function is used by `setenv' and `putenv'.  The difference between
 114    the two functions is that for the former must create a new string which
 115    is then placed in the environment, while the argument of `putenv'
 116    must be used directly.  This is all complicated by the fact that we try
 117    to reuse values once generated for a `setenv' call since we can never
 118    free the strings.  */
 119 int
 120 __add_to_environ (name, value, combined, replace)
 121      const char *name;
 122      const char *value;
 123      const char *combined;
 124      int replace;
 125 {
 126   char **ep;
 127   size_t size;
 128
 129   /* Compute lengths before locking, so that the critical section is
 130      less of a performance bottleneck.  VALLEN is needed only if
 131      COMBINED is null (unfortunately GCC is not smart enough to deduce
 132      this; see the #pragma at the start of this file).  Testing
 133      COMBINED instead of VALUE causes setenv (..., NULL, ...)  to dump
 134      core now instead of corrupting memory later.  */
 135   const size_t namelen = strlen (name);
 136   size_t vallen;
 137   if (combined == NULL)
 138     vallen = strlen (value) + 1;
 139
 140   LOCK;
 141
 142   /* We have to get the pointer now that we have the lock and not earlier
 143      since another thread might have created a new environment.  */
 144   ep = __environ;
 145
 146   size = 0;
 147   if (ep != NULL)
 148     {
 149       for (; *ep != NULL; ++ep)
 150         if (!strncmp (*ep, name, namelen) && (*ep)[namelen] == '=')
 151           break;
 152         else
 153           ++size;
 154     }
 155
 156   if (ep == NULL || __builtin_expect (*ep == NULL, 1))
 157     {
 158       char **new_environ;
 159
 160       /* We allocated this space; we can extend it.  */
 161       new_environ = (char **) realloc (last_environ,
 162                                        (size + 2) * sizeof (char *));
 163       if (new_environ == NULL)
 164         {
 165           UNLOCK;
 166           return -1;
 167         }
 168
 169       if (__environ != last_environ)
 170         memcpy ((char *) new_environ, (char *) __environ,
 171                 size * sizeof (char *));
 172
 173       new_environ[size] = NULL;
 174       new_environ[size + 1] = NULL;
 175       ep = new_environ + size;
 176
 177       last_environ = __environ = new_environ;
 178     }
 179   if (*ep == NULL || replace)
 180     {
 181       char *np;
 182
 183       /* Use the user string if given.  */
 184       if (combined != NULL)
 185         np = (char *) combined;
 186       else
 187         {
 188           const size_t varlen = namelen + 1 + vallen;
 189 #ifdef USE_TSEARCH
 190           char *new_value;
 191           int use_alloca = __libc_use_alloca (varlen);
 192           if (__builtin_expect (use_alloca, 1))
 193             new_value = (char *) alloca (varlen);
 194           else
 195             {
 196               new_value = malloc (varlen);
 197               if (new_value == NULL)
 198                 {
 199                   UNLOCK;
 200                   return -1;
 201                 }
 202             }
 203 # ifdef _LIBC
 204           __mempcpy (__mempcpy (__mempcpy (new_value, name, namelen), "=", 1),
 205                      value, vallen);
 206 # else
 207           memcpy (new_value, name, namelen);
 208           new_value[namelen] = '=';
 209           memcpy (&new_value[namelen + 1], value, vallen);
 210 # endif
 211
 212           np = KNOWN_VALUE (new_value);
 213           if (__glibc_likely (np == NULL))
 214 #endif
 215             {
 216 #ifdef USE_TSEARCH
 217               if (__glibc_unlikely (! use_alloca))
 218                 np = new_value;
 219               else
 220 #endif
 221                 {
 222                   np = malloc (varlen);
 223                   if (__glibc_unlikely (np == NULL))
 224                     {
 225                       UNLOCK;
 226                       return -1;
 227                     }
 228
 229 #ifdef USE_TSEARCH
 230                   memcpy (np, new_value, varlen);
 231 #else
 232                   memcpy (np, name, namelen);
 233                   np[namelen] = '=';
 234                   memcpy (&np[namelen + 1], value, vallen);
 235 #endif
 236                 }
 237               /* And remember the value.  */
 238               STORE_VALUE (np);
 239             }
 240 #ifdef USE_TSEARCH
 241           else
 242             {
 243               if (__glibc_unlikely (! use_alloca))
 244                 free (new_value);
 245             }
 246 #endif
 247         }
 248
 249       *ep = np;
 250     }
 251
 252   UNLOCK;
 253
 254   return 0;
 255 }
 256
 257 int
 258 setenv (name, value, replace)
 259      const char *name;
 260      const char *value;
 261      int replace;
 262 {
 263   if (name == NULL || *name == '\0' || strchr (name, '=') != NULL)
 264     {
 265       __set_errno (EINVAL);
 266       return -1;
 267     }
 268
 269   return __add_to_environ (name, value, NULL, replace);
 270 }
 271
 272 int
 273 unsetenv (name)
 274      const char *name;
 275 {
 276   size_t len;
 277   char **ep;
 278
 279   if (name == NULL || *name == '\0' || strchr (name, '=') != NULL)
 280     {
 281       __set_errno (EINVAL);
 282       return -1;
 283     }
 284
 285   len = strlen (name);
 286
 287   LOCK;
 288
 289   ep = __environ;
 290   if (ep != NULL)
 291     while (*ep != NULL)
 292       if (!strncmp (*ep, name, len) && (*ep)[len] == '=')
 293         {
 294           /* Found it.  Remove this pointer by moving later ones back.  */
 295           char **dp = ep;
 296
 297           do
 298             dp[0] = dp[1];
 299           while (*dp++);
 300           /* Continue the loop in case NAME appears again.  */
 301         }
 302       else
 303         ++ep;
 304
 305   UNLOCK;
 306
 307   return 0;
 308 }
 309
 310 /* The `clearenv' was planned to be added to POSIX.1 but probably
 311    never made it.  Nevertheless the POSIX.9 standard (POSIX bindings
 312    for Fortran 77) requires this function.  */
 313 int
 314 clearenv (void)
 315 {
 316   LOCK;
 317
 318   if (__environ == last_environ && __environ != NULL)
 319     {
 320       /* We allocated this environment so we can free it.  */
 321       free (__environ);
 322       last_environ = NULL;
 323     }
 324
 325   /* Clear the environment pointer removes the whole environment.  */
 326   __environ = NULL;
 327
 328   UNLOCK;
 329
 330   return 0;
 331 }
 332 #ifdef _LIBC
 333 libc_freeres_fn (free_mem)
 334 {
 335   /* Remove all traces.  */
 336   clearenv ();
 337
 338   /* Now remove the search tree.  */
 339   __tdestroy (known_values, free);
 340   known_values = NULL;
 341 }
 342
 343 # undef setenv
 344 # undef unsetenv
 345 # undef clearenv
 346 weak_alias (__setenv, setenv)
 347 weak_alias (__unsetenv, unsetenv)
 348 weak_alias (__clearenv, clearenv)
 349 #endif