sysdeps/posix/tempname.c

   1 /* Copyright (C) 1991-2001, 2006, 2007, 2009 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 #include <sys/types.h>
  23 #include <assert.h>
  24
  25 #include <errno.h>
  26 #ifndef __set_errno
  27 # define __set_errno(Val) errno = (Val)
  28 #endif
  29
  30 #include <stdio.h>
  31 #ifndef P_tmpdir
  32 # define P_tmpdir "/tmp"
  33 #endif
  34 #ifndef TMP_MAX
  35 # define TMP_MAX 238328
  36 #endif
  37 #ifndef __GT_FILE
  38 # define __GT_FILE      0
  39 # define __GT_DIR       1
  40 # define __GT_NOCREATE  2
  41 #endif
  42
  43 #if STDC_HEADERS || _LIBC
  44 # include <stddef.h>
  45 # include <stdlib.h>
  46 # include <string.h>
  47 #endif
  48
  49 #if HAVE_FCNTL_H || _LIBC
  50 # include <fcntl.h>
  51 #endif
  52
  53 #if HAVE_SYS_TIME_H || _LIBC
  54 # include <sys/time.h>
  55 #endif
  56
  57 #if HAVE_STDINT_H || _LIBC
  58 # include <stdint.h>
  59 #endif
  60
  61 #if HAVE_UNISTD_H || _LIBC
  62 # include <unistd.h>
  63 #endif
  64
  65 #include <sys/stat.h>
  66 #if STAT_MACROS_BROKEN
  67 # undef S_ISDIR
  68 #endif
  69 #if !defined S_ISDIR && defined S_IFDIR
  70 # define S_ISDIR(mode) (((mode) & S_IFMT) == S_IFDIR)
  71 #endif
  72 #if !S_IRUSR && S_IREAD
  73 # define S_IRUSR S_IREAD
  74 #endif
  75 #if !S_IRUSR
  76 # define S_IRUSR 00400
  77 #endif
  78 #if !S_IWUSR && S_IWRITE
  79 # define S_IWUSR S_IWRITE
  80 #endif
  81 #if !S_IWUSR
  82 # define S_IWUSR 00200
  83 #endif
  84 #if !S_IXUSR && S_IEXEC
  85 # define S_IXUSR S_IEXEC
  86 #endif
  87 #if !S_IXUSR
  88 # define S_IXUSR 00100
  89 #endif
  90
  91 #if _LIBC
  92 # define struct_stat64 struct stat64
  93 #else
  94 # define struct_stat64 struct stat
  95 # define __getpid getpid
  96 # define __gettimeofday gettimeofday
  97 # define __mkdir mkdir
  98 # define __open open
  99 # define __open64 open
 100 # define __lxstat64(version, path, buf) lstat (path, buf)
 101 # define __xstat64(version, path, buf) stat (path, buf)
 102 #endif
 103
 104 #if ! (HAVE___SECURE_GETENV || _LIBC)
 105 # define __secure_getenv getenv
 106 #endif
 107
 108 #ifdef _LIBC
 109 # include <hp-timing.h>
 110 # if HP_TIMING_AVAIL
 111 #  define RANDOM_BITS(Var) \
 112   if (__builtin_expect (value == UINT64_C (0), 0))                            \
 113     {                                                                         \
 114       /* If this is the first time this function is used initialize           \
 115          the variable we accumulate the value in to some somewhat             \
 116          random value.  If we'd not do this programs at startup time          \
 117          might have a reduced set of possible names, at least on slow         \
 118          machines.  */                                                        \
 119       struct timeval tv;                                                      \
 120       __gettimeofday (&tv, NULL);                                             \
 121       value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
 122     }                                                                         \
 123   HP_TIMING_NOW (Var)
 124 # endif
 125 #endif
 126
 127 /* Use the widest available unsigned type if uint64_t is not
 128    available.  The algorithm below extracts a number less than 62**6
 129    (approximately 2**35.725) from uint64_t, so ancient hosts where
 130    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
 131    which is better than not having mkstemp at all.  */
 132 #if !defined UINT64_MAX && !defined uint64_t
 133 # define uint64_t uintmax_t
 134 #endif
 135
 136 /* Return nonzero if DIR is an existent directory.  */
 137 static int
 138 direxists (const char *dir)
 139 {
 140   struct_stat64 buf;
 141   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 142 }
 143
 144 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 145    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 146    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 147    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 148    doesn't exist, none of the searched dirs exists, or there's not
 149    enough space in TMPL. */
 150 int
 151 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 152                int try_tmpdir)
 153 {
 154   const char *d;
 155   size_t dlen, plen;
 156
 157   if (!pfx || !pfx[0])
 158     {
 159       pfx = "file";
 160       plen = 4;
 161     }
 162   else
 163     {
 164       plen = strlen (pfx);
 165       if (plen > 5)
 166         plen = 5;
 167     }
 168
 169   if (try_tmpdir)
 170     {
 171       d = __secure_getenv ("TMPDIR");
 172       if (d != NULL && direxists (d))
 173         dir = d;
 174       else if (dir != NULL && direxists (dir))
 175         /* nothing */ ;
 176       else
 177         dir = NULL;
 178     }
 179   if (dir == NULL)
 180     {
 181       if (direxists (P_tmpdir))
 182         dir = P_tmpdir;
 183       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 184         dir = "/tmp";
 185       else
 186         {
 187           __set_errno (ENOENT);
 188           return -1;
 189         }
 190     }
 191
 192   dlen = strlen (dir);
 193   while (dlen > 1 && dir[dlen - 1] == '/')
 194     dlen--;                     /* remove trailing slashes */
 195
 196   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 197   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 198     {
 199       __set_errno (EINVAL);
 200       return -1;
 201     }
 202
 203   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 204   return 0;
 205 }
 206
 207 /* These are the characters used in temporary filenames.  */
 208 static const char letters[] =
 209 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 210
 211 /* Generate a temporary file name based on TMPL.  TMPL must match the
 212    rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix).
 213    The name constructed does not exist at the time of the call to
 214    __gen_tempname.  TMPL is overwritten with the result.
 215
 216    KIND may be one of:
 217    __GT_NOCREATE:       simply verify that the name does not exist
 218                         at the time of the call.
 219    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 220                         and return a read-write fd.  The file is mode 0600.
 221    __GT_DIR:            create a directory, which will be mode 0700.
 222
 223    We use a clever algorithm to get hard-to-predict names. */
 224 int
 225 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
 226 {
 227   int len;
 228   char *XXXXXX;
 229   static uint64_t value;
 230   uint64_t random_time_bits;
 231   unsigned int count;
 232   int fd = -1;
 233   int save_errno = errno;
 234   struct_stat64 st;
 235
 236   /* A lower bound on the number of temporary files to attempt to
 237      generate.  The maximum total number of temporary file names that
 238      can exist for a given template is 62**6.  It should never be
 239      necessary to try all these combinations.  Instead if a reasonable
 240      number of names is tried (we define reasonable as 62**3) fail to
 241      give the system administrator the chance to remove the problems.  */
 242 #define ATTEMPTS_MIN (62 * 62 * 62)
 243
 244   /* The number of times to attempt to generate a temporary file.  To
 245      conform to POSIX, this must be no smaller than TMP_MAX.  */
 246 #if ATTEMPTS_MIN < TMP_MAX
 247   unsigned int attempts = TMP_MAX;
 248 #else
 249   unsigned int attempts = ATTEMPTS_MIN;
 250 #endif
 251
 252   len = strlen (tmpl);
 253   if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
 254     {
 255       __set_errno (EINVAL);
 256       return -1;
 257     }
 258
 259   /* This is where the Xs start.  */
 260   XXXXXX = &tmpl[len - 6 - suffixlen];
 261
 262   /* Get some more or less random data.  */
 263 #ifdef RANDOM_BITS
 264   RANDOM_BITS (random_time_bits);
 265 #else
 266 # if HAVE_GETTIMEOFDAY || _LIBC
 267   {
 268     struct timeval tv;
 269     __gettimeofday (&tv, NULL);
 270     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 271   }
 272 # else
 273   random_time_bits = time (NULL);
 274 # endif
 275 #endif
 276   value += random_time_bits ^ __getpid ();
 277
 278   for (count = 0; count < attempts; value += 7777, ++count)
 279     {
 280       uint64_t v = value;
 281
 282       /* Fill in the random bits.  */
 283       XXXXXX[0] = letters[v % 62];
 284       v /= 62;
 285       XXXXXX[1] = letters[v % 62];
 286       v /= 62;
 287       XXXXXX[2] = letters[v % 62];
 288       v /= 62;
 289       XXXXXX[3] = letters[v % 62];
 290       v /= 62;
 291       XXXXXX[4] = letters[v % 62];
 292       v /= 62;
 293       XXXXXX[5] = letters[v % 62];
 294
 295       switch (kind)
 296         {
 297         case __GT_FILE:
 298           fd = __open (tmpl,
 299                        (flags & ~O_ACCMODE)
 300                        | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 301           break;
 302
 303         case __GT_DIR:
 304           fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 305           break;
 306
 307         case __GT_NOCREATE:
 308           /* This case is backward from the other three.  __gen_tempname
 309              succeeds if __xstat fails because the name does not exist.
 310              Note the continue to bypass the common logic at the bottom
 311              of the loop.  */
 312           if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
 313             {
 314               if (errno == ENOENT)
 315                 {
 316                   __set_errno (save_errno);
 317                   return 0;
 318                 }
 319               else
 320                 /* Give up now. */
 321                 return -1;
 322             }
 323           continue;
 324
 325         default:
 326           assert (! "invalid KIND in __gen_tempname");
 327         }
 328
 329       if (fd >= 0)
 330         {
 331           __set_errno (save_errno);
 332           return fd;
 333         }
 334       else if (errno != EEXIST)
 335         return -1;
 336     }
 337
 338   /* We got out of the loop because we ran out of combinations to try.  */
 339   __set_errno (EEXIST);
 340   return -1;
 341 }