lib/tempname.c

   1 /* tempname.c - generate the name of a temporary file.
   2
   3    Copyright (C) 1991-2003, 2005-2007, 2009-2015 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  17
  18 /* Extracted from glibc sysdeps/posix/tempname.c.  See also tmpdir.c.  */
  19
  20 #if !_LIBC
  21 # include <config.h>
  22 # include "tempname.h"
  23 #endif
  24
  25 #include <sys/types.h>
  26 #include <assert.h>
  27
  28 #include <errno.h>
  29 #ifndef __set_errno
  30 # define __set_errno(Val) errno = (Val)
  31 #endif
  32
  33 #include <stdio.h>
  34 #ifndef P_tmpdir
  35 # define P_tmpdir "/tmp"
  36 #endif
  37 #ifndef TMP_MAX
  38 # define TMP_MAX 238328
  39 #endif
  40 #ifndef __GT_FILE
  41 # define __GT_FILE      0
  42 # define __GT_DIR       1
  43 # define __GT_NOCREATE  2
  44 #endif
  45 #if !_LIBC && (GT_FILE != __GT_FILE || GT_DIR != __GT_DIR       \
  46                || GT_NOCREATE != __GT_NOCREATE)
  47 # error report this to bug-gnulib@gnu.org
  48 #endif
  49
  50 #include <stddef.h>
  51 #include <stdlib.h>
  52 #include <string.h>
  53
  54 #include <fcntl.h>
  55 #include <sys/time.h>
  56 #include <stdint.h>
  57 #include <unistd.h>
  58
  59 #include <sys/stat.h>
  60
  61 #if _LIBC
  62 # define struct_stat64 struct stat64
  63 #else
  64 # define struct_stat64 struct stat
  65 # define __gen_tempname gen_tempname
  66 # define __getpid getpid
  67 # define __gettimeofday gettimeofday
  68 # define __mkdir mkdir
  69 # define __open open
  70 # define __lxstat64(version, file, buf) lstat (file, buf)
  71 # define __secure_getenv secure_getenv
  72 #endif
  73
  74 #ifdef _LIBC
  75 # include <hp-timing.h>
  76 # if HP_TIMING_AVAIL
  77 #  define RANDOM_BITS(Var) \
  78   if (__builtin_expect (value == UINT64_C (0), 0))                            \
  79     {                                                                         \
  80       /* If this is the first time this function is used initialize           \
  81          the variable we accumulate the value in to some somewhat             \
  82          random value.  If we'd not do this programs at startup time          \
  83          might have a reduced set of possible names, at least on slow         \
  84          machines.  */                                                        \
  85       struct timeval tv;                                                      \
  86       __gettimeofday (&tv, NULL);                                             \
  87       value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
  88     }                                                                         \
  89   HP_TIMING_NOW (Var)
  90 # endif
  91 #endif
  92
  93 /* Use the widest available unsigned type if uint64_t is not
  94    available.  The algorithm below extracts a number less than 62**6
  95    (approximately 2**35.725) from uint64_t, so ancient hosts where
  96    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
  97    which is better than not having mkstemp at all.  */
  98 #if !defined UINT64_MAX && !defined uint64_t
  99 # define uint64_t uintmax_t
 100 #endif
 101
 102 #if _LIBC
 103 /* Return nonzero if DIR is an existent directory.  */
 104 static int
 105 direxists (const char *dir)
 106 {
 107   struct_stat64 buf;
 108   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 109 }
 110
 111 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 112    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 113    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 114    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 115    doesn't exist, none of the searched dirs exists, or there's not
 116    enough space in TMPL. */
 117 int
 118 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 119                int try_tmpdir)
 120 {
 121   const char *d;
 122   size_t dlen, plen;
 123
 124   if (!pfx || !pfx[0])
 125     {
 126       pfx = "file";
 127       plen = 4;
 128     }
 129   else
 130     {
 131       plen = strlen (pfx);
 132       if (plen > 5)
 133         plen = 5;
 134     }
 135
 136   if (try_tmpdir)
 137     {
 138       d = __secure_getenv ("TMPDIR");
 139       if (d != NULL && direxists (d))
 140         dir = d;
 141       else if (dir != NULL && direxists (dir))
 142         /* nothing */ ;
 143       else
 144         dir = NULL;
 145     }
 146   if (dir == NULL)
 147     {
 148       if (direxists (P_tmpdir))
 149         dir = P_tmpdir;
 150       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 151         dir = "/tmp";
 152       else
 153         {
 154           __set_errno (ENOENT);
 155           return -1;
 156         }
 157     }
 158
 159   dlen = strlen (dir);
 160   while (dlen > 1 && dir[dlen - 1] == '/')
 161     dlen--;                     /* remove trailing slashes */
 162
 163   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 164   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 165     {
 166       __set_errno (EINVAL);
 167       return -1;
 168     }
 169
 170   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 171   return 0;
 172 }
 173 #endif /* _LIBC */
 174
 175 /* These are the characters used in temporary file names.  */
 176 static const char letters[] =
 177 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 178
 179 /* Generate a temporary file name based on TMPL.  TMPL must match the
 180    rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix).
 181    The name constructed does not exist at the time of the call to
 182    __gen_tempname.  TMPL is overwritten with the result.
 183
 184    KIND may be one of:
 185    __GT_NOCREATE:       simply verify that the name does not exist
 186                         at the time of the call.
 187    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 188                         and return a read-write fd.  The file is mode 0600.
 189    __GT_DIR:            create a directory, which will be mode 0700.
 190
 191    We use a clever algorithm to get hard-to-predict names. */
 192 int
 193 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
 194 {
 195   int len;
 196   char *XXXXXX;
 197   static uint64_t value;
 198   uint64_t random_time_bits;
 199   unsigned int count;
 200   int fd = -1;
 201   int save_errno = errno;
 202   struct_stat64 st;
 203
 204   /* A lower bound on the number of temporary files to attempt to
 205      generate.  The maximum total number of temporary file names that
 206      can exist for a given template is 62**6.  It should never be
 207      necessary to try all of these combinations.  Instead if a reasonable
 208      number of names is tried (we define reasonable as 62**3) fail to
 209      give the system administrator the chance to remove the problems.  */
 210 #define ATTEMPTS_MIN (62 * 62 * 62)
 211
 212   /* The number of times to attempt to generate a temporary file.  To
 213      conform to POSIX, this must be no smaller than TMP_MAX.  */
 214 #if ATTEMPTS_MIN < TMP_MAX
 215   unsigned int attempts = TMP_MAX;
 216 #else
 217   unsigned int attempts = ATTEMPTS_MIN;
 218 #endif
 219
 220   len = strlen (tmpl);
 221   if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
 222     {
 223       __set_errno (EINVAL);
 224       return -1;
 225     }
 226
 227   /* This is where the Xs start.  */
 228   XXXXXX = &tmpl[len - 6 - suffixlen];
 229
 230   /* Get some more or less random data.  */
 231 #ifdef RANDOM_BITS
 232   RANDOM_BITS (random_time_bits);
 233 #else
 234   {
 235     struct timeval tv;
 236     __gettimeofday (&tv, NULL);
 237     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 238   }
 239 #endif
 240   value += random_time_bits ^ __getpid ();
 241
 242   for (count = 0; count < attempts; value += 7777, ++count)
 243     {
 244       uint64_t v = value;
 245
 246       /* Fill in the random bits.  */
 247       XXXXXX[0] = letters[v % 62];
 248       v /= 62;
 249       XXXXXX[1] = letters[v % 62];
 250       v /= 62;
 251       XXXXXX[2] = letters[v % 62];
 252       v /= 62;
 253       XXXXXX[3] = letters[v % 62];
 254       v /= 62;
 255       XXXXXX[4] = letters[v % 62];
 256       v /= 62;
 257       XXXXXX[5] = letters[v % 62];
 258
 259       switch (kind)
 260         {
 261         case __GT_FILE:
 262           fd = __open (tmpl,
 263                        (flags & ~O_ACCMODE)
 264                        | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 265           break;
 266
 267         case __GT_DIR:
 268           fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 269           break;
 270
 271         case __GT_NOCREATE:
 272           /* This case is backward from the other three.  __gen_tempname
 273              succeeds if __xstat fails because the name does not exist.
 274              Note the continue to bypass the common logic at the bottom
 275              of the loop.  */
 276           if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
 277             {
 278               if (errno == ENOENT)
 279                 {
 280                   __set_errno (save_errno);
 281                   return 0;
 282                 }
 283               else
 284                 /* Give up now. */
 285                 return -1;
 286             }
 287           continue;
 288
 289         default:
 290           assert (! "invalid KIND in __gen_tempname");
 291           abort ();
 292         }
 293
 294       if (fd >= 0)
 295         {
 296           __set_errno (save_errno);
 297           return fd;
 298         }
 299       else if (errno != EEXIST)
 300         return -1;
 301     }
 302
 303   /* We got out of the loop because we ran out of combinations to try.  */
 304   __set_errno (EEXIST);
 305   return -1;
 306 }