gl/mkdtemp.c

   1 /* Copyright (C) 1999, 2001-2003, 2006 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3, or (at your option)
   7    any later version.
   8
   9    This program 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
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License along
  15    with this program; if not, see <http://www.gnu.org/licenses/>.  */
  16
  17 /* Extracted from misc/mkdtemp.c and sysdeps/posix/tempname.c.  */
  18
  19 #include <config.h>
  20
  21 /* Specification.  */
  22 #include "mkdtemp.h"
  23
  24 #include <errno.h>
  25 #ifndef __set_errno
  26 # define __set_errno(Val) errno = (Val)
  27 #endif
  28
  29 #include <stddef.h>
  30 #include <stdint.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33
  34 #include <stdio.h>
  35 #ifndef TMP_MAX
  36 # define TMP_MAX 238328
  37 #endif
  38
  39 #include <unistd.h>
  40
  41 #if HAVE_GETTIMEOFDAY || _LIBC
  42 # if HAVE_SYS_TIME_H || _LIBC
  43 #  include <sys/time.h>
  44 # endif
  45 #else
  46 # if HAVE_TIME_H || _LIBC
  47 #  include <time.h>
  48 # endif
  49 #endif
  50
  51 #include <sys/stat.h>
  52 #if !defined S_ISDIR && defined S_IFDIR
  53 # define S_ISDIR(mode) (((mode) & S_IFMT) == S_IFDIR)
  54 #endif
  55 #if !S_IRUSR && S_IREAD
  56 # define S_IRUSR S_IREAD
  57 #endif
  58 #if !S_IRUSR
  59 # define S_IRUSR 00400
  60 #endif
  61 #if !S_IWUSR && S_IWRITE
  62 # define S_IWUSR S_IWRITE
  63 #endif
  64 #if !S_IWUSR
  65 # define S_IWUSR 00200
  66 #endif
  67 #if !S_IXUSR && S_IEXEC
  68 # define S_IXUSR S_IEXEC
  69 #endif
  70 #if !S_IXUSR
  71 # define S_IXUSR 00100
  72 #endif
  73
  74 #ifdef __MINGW32__
  75 # include <io.h>
  76 #endif
  77
  78 #if !_LIBC
  79 # define __getpid getpid
  80 # define __gettimeofday gettimeofday
  81 # define __mkdir mkdir
  82 #endif
  83
  84 /* Use the widest available unsigned type if uint64_t is not
  85    available.  The algorithm below extracts a number less than 62**6
  86    (approximately 2**35.725) from uint64_t, so ancient hosts where
  87    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
  88    which is better than not having mkstemp at all.  */
  89 #if !defined UINT64_MAX && !defined uint64_t
  90 # define uint64_t uintmax_t
  91 #endif
  92
  93 /* These are the characters used in temporary filenames.  */
  94 static const char letters[] =
  95 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  96
  97 /* Generate a temporary file name based on TMPL.  TMPL must match the
  98    rules for mk[s]temp (i.e. end in "XXXXXX").  The name constructed
  99    does not exist at the time of the call to __gen_tempname.  TMPL is
 100    overwritten with the result.
 101
 102    KIND is:
 103    __GT_DIR:            create a directory, which will be mode 0700.
 104
 105    We use a clever algorithm to get hard-to-predict names. */
 106 static int
 107 gen_tempname (char *tmpl)
 108 {
 109   int len;
 110   char *XXXXXX;
 111   static uint64_t value;
 112   uint64_t random_time_bits;
 113   unsigned int count;
 114   int fd = -1;
 115   int save_errno = errno;
 116
 117   /* A lower bound on the number of temporary files to attempt to
 118      generate.  The maximum total number of temporary file names that
 119      can exist for a given template is 62**6.  It should never be
 120      necessary to try all these combinations.  Instead if a reasonable
 121      number of names is tried (we define reasonable as 62**3) fail to
 122      give the system administrator the chance to remove the problems.  */
 123 #define ATTEMPTS_MIN (62 * 62 * 62)
 124
 125   /* The number of times to attempt to generate a temporary file.  To
 126      conform to POSIX, this must be no smaller than TMP_MAX.  */
 127 #if ATTEMPTS_MIN < TMP_MAX
 128   unsigned int attempts = TMP_MAX;
 129 #else
 130   unsigned int attempts = ATTEMPTS_MIN;
 131 #endif
 132
 133   len = strlen (tmpl);
 134   if (len < 6 || strcmp (&tmpl[len - 6], "XXXXXX"))
 135     {
 136       __set_errno (EINVAL);
 137       return -1;
 138     }
 139
 140   /* This is where the Xs start.  */
 141   XXXXXX = &tmpl[len - 6];
 142
 143   /* Get some more or less random data.  */
 144 #ifdef RANDOM_BITS
 145   RANDOM_BITS (random_time_bits);
 146 #else
 147 # if HAVE_GETTIMEOFDAY || _LIBC
 148   {
 149     struct timeval tv;
 150     __gettimeofday (&tv, NULL);
 151     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 152   }
 153 # else
 154   random_time_bits = time (NULL);
 155 # endif
 156 #endif
 157   value += random_time_bits ^ __getpid ();
 158
 159   for (count = 0; count < attempts; value += 7777, ++count)
 160     {
 161       uint64_t v = value;
 162
 163       /* Fill in the random bits.  */
 164       XXXXXX[0] = letters[v % 62];
 165       v /= 62;
 166       XXXXXX[1] = letters[v % 62];
 167       v /= 62;
 168       XXXXXX[2] = letters[v % 62];
 169       v /= 62;
 170       XXXXXX[3] = letters[v % 62];
 171       v /= 62;
 172       XXXXXX[4] = letters[v % 62];
 173       v /= 62;
 174       XXXXXX[5] = letters[v % 62];
 175
 176 #ifdef MKDIR_TAKES_ONE_ARG
 177       fd = mkdir (tmpl);
 178 #else
 179       fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 180 #endif
 181
 182       if (fd >= 0)
 183         {
 184           __set_errno (save_errno);
 185           return fd;
 186         }
 187       else if (errno != EEXIST)
 188         return -1;
 189     }
 190
 191   /* We got out of the loop because we ran out of combinations to try.  */
 192   __set_errno (EEXIST);
 193   return -1;
 194 }
 195
 196 /* Generate a unique temporary directory from TEMPLATE.
 197    The last six characters of TEMPLATE must be "XXXXXX";
 198    they are replaced with a string that makes the filename unique.
 199    The directory is created, mode 700, and its name is returned.
 200    (This function comes from OpenBSD.) */
 201 char *
 202 mkdtemp (char *template)
 203 {
 204   if (gen_tempname (template))
 205     return NULL;
 206   else
 207     return template;
 208 }