sysdeps/posix/tempname.c

   1 /* Copyright (C) 1991-2014 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 # ifdef HAVE___SECURE_GETENV
 106 #  define __libc_secure_getenv __secure_getenv
 107 # else
 108 #  define __libc_secure_getenv getenv
 109 # endif
 110 #endif
 111
 112 #ifdef _LIBC
 113 # include <hp-timing.h>
 114 # if HP_TIMING_AVAIL
 115 #  define RANDOM_BITS(Var) \
 116   if (__builtin_expect (value == UINT64_C (0), 0))                            \
 117     {                                                                         \
 118       /* If this is the first time this function is used initialize           \
 119          the variable we accumulate the value in to some somewhat             \
 120          random value.  If we'd not do this programs at startup time          \
 121          might have a reduced set of possible names, at least on slow         \
 122          machines.  */                                                        \
 123       struct timeval tv;                                                      \
 124       __gettimeofday (&tv, NULL);                                             \
 125       value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
 126     }                                                                         \
 127   HP_TIMING_NOW (Var)
 128 # endif
 129 #endif
 130
 131 /* Use the widest available unsigned type if uint64_t is not
 132    available.  The algorithm below extracts a number less than 62**6
 133    (approximately 2**35.725) from uint64_t, so ancient hosts where
 134    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
 135    which is better than not having mkstemp at all.  */
 136 #if !defined UINT64_MAX && !defined uint64_t
 137 # define uint64_t uintmax_t
 138 #endif
 139
 140 /* Return nonzero if DIR is an existent directory.  */
 141 static int
 142 direxists (const char *dir)
 143 {
 144   struct_stat64 buf;
 145   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 146 }
 147
 148 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 149    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 150    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 151    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 152    doesn't exist, none of the searched dirs exists, or there's not
 153    enough space in TMPL. */
 154 int
 155 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 156                int try_tmpdir)
 157 {
 158   const char *d;
 159   size_t dlen, plen;
 160
 161   if (!pfx || !pfx[0])
 162     {
 163       pfx = "file";
 164       plen = 4;
 165     }
 166   else
 167     {
 168       plen = strlen (pfx);
 169       if (plen > 5)
 170         plen = 5;
 171     }
 172
 173   if (try_tmpdir)
 174     {
 175       d = __libc_secure_getenv ("TMPDIR");
 176       if (d != NULL && direxists (d))
 177         dir = d;
 178       else if (dir != NULL && direxists (dir))
 179         /* nothing */ ;
 180       else
 181         dir = NULL;
 182     }
 183   if (dir == NULL)
 184     {
 185       if (direxists (P_tmpdir))
 186         dir = P_tmpdir;
 187       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 188         dir = "/tmp";
 189       else
 190         {
 191           __set_errno (ENOENT);
 192           return -1;
 193         }
 194     }
 195
 196   dlen = strlen (dir);
 197   while (dlen > 1 && dir[dlen - 1] == '/')
 198     dlen--;                     /* remove trailing slashes */
 199
 200   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 201   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 202     {
 203       __set_errno (EINVAL);
 204       return -1;
 205     }
 206
 207   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 208   return 0;
 209 }
 210
 211 /* These are the characters used in temporary filenames.  */
 212 static const char letters[] =
 213 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 214
 215 /* Generate a temporary file name based on TMPL.  TMPL must match the
 216    rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix).
 217    The name constructed does not exist at the time of the call to
 218    __gen_tempname.  TMPL is overwritten with the result.
 219
 220    KIND may be one of:
 221    __GT_NOCREATE:       simply verify that the name does not exist
 222                         at the time of the call.
 223    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 224                         and return a read-write fd.  The file is mode 0600.
 225    __GT_DIR:            create a directory, which will be mode 0700.
 226
 227    We use a clever algorithm to get hard-to-predict names. */
 228 int
 229 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
 230 {
 231   int len;
 232   char *XXXXXX;
 233   static uint64_t value;
 234   uint64_t random_time_bits;
 235   unsigned int count;
 236   int fd = -1;
 237   int save_errno = errno;
 238   struct_stat64 st;
 239
 240   /* A lower bound on the number of temporary files to attempt to
 241      generate.  The maximum total number of temporary file names that
 242      can exist for a given template is 62**6.  It should never be
 243      necessary to try all these combinations.  Instead if a reasonable
 244      number of names is tried (we define reasonable as 62**3) fail to
 245      give the system administrator the chance to remove the problems.  */
 246 #define ATTEMPTS_MIN (62 * 62 * 62)
 247
 248   /* The number of times to attempt to generate a temporary file.  To
 249      conform to POSIX, this must be no smaller than TMP_MAX.  */
 250 #if ATTEMPTS_MIN < TMP_MAX
 251   unsigned int attempts = TMP_MAX;
 252 #else
 253   unsigned int attempts = ATTEMPTS_MIN;
 254 #endif
 255
 256   len = strlen (tmpl);
 257   if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
 258     {
 259       __set_errno (EINVAL);
 260       return -1;
 261     }
 262
 263   /* This is where the Xs start.  */
 264   XXXXXX = &tmpl[len - 6 - suffixlen];
 265
 266   /* Get some more or less random data.  */
 267 #ifdef RANDOM_BITS
 268   RANDOM_BITS (random_time_bits);
 269 #else
 270 # if HAVE_GETTIMEOFDAY || _LIBC
 271   {
 272     struct timeval tv;
 273     __gettimeofday (&tv, NULL);
 274     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 275   }
 276 # else
 277   random_time_bits = time (NULL);
 278 # endif
 279 #endif
 280   value += random_time_bits ^ __getpid ();
 281
 282   for (count = 0; count < attempts; value += 7777, ++count)
 283     {
 284       uint64_t v = value;
 285
 286       /* Fill in the random bits.  */
 287       XXXXXX[0] = letters[v % 62];
 288       v /= 62;
 289       XXXXXX[1] = letters[v % 62];
 290       v /= 62;
 291       XXXXXX[2] = letters[v % 62];
 292       v /= 62;
 293       XXXXXX[3] = letters[v % 62];
 294       v /= 62;
 295       XXXXXX[4] = letters[v % 62];
 296       v /= 62;
 297       XXXXXX[5] = letters[v % 62];
 298
 299       switch (kind)
 300         {
 301         case __GT_FILE:
 302           fd = __open (tmpl,
 303                        (flags & ~O_ACCMODE)
 304                        | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 305           break;
 306
 307         case __GT_DIR:
 308           fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 309           break;
 310
 311         case __GT_NOCREATE:
 312           /* This case is backward from the other three.  __gen_tempname
 313              succeeds if __xstat fails because the name does not exist.
 314              Note the continue to bypass the common logic at the bottom
 315              of the loop.  */
 316           if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
 317             {
 318               if (errno == ENOENT)
 319                 {
 320                   __set_errno (save_errno);
 321                   return 0;
 322                 }
 323               else
 324                 /* Give up now. */
 325                 return -1;
 326             }
 327           continue;
 328
 329         default:
 330           assert (! "invalid KIND in __gen_tempname");
 331         }
 332
 333       if (fd >= 0)
 334         {
 335           __set_errno (save_errno);
 336           return fd;
 337         }
 338       else if (errno != EEXIST)
 339         return -1;
 340     }
 341
 342   /* We got out of the loop because we ran out of combinations to try.  */
 343   __set_errno (EEXIST);
 344   return -1;
 345 }