lib/tempname.c

   1 /* tempname.c - generate the name of a temporary file.
   2
   3    Copyright (C) 1991-2003, 2005-2007, 2009-2017 Free Software
   4    Foundation, Inc.
   5
   6    This program is free software: you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 /* Extracted from glibc sysdeps/posix/tempname.c.  See also tmpdir.c.  */
  20
  21 #if !_LIBC
  22 # include <config.h>
  23 # include "tempname.h"
  24 #endif
  25
  26 #include <sys/types.h>
  27 #include <assert.h>
  28
  29 #include <errno.h>
  30 #ifndef __set_errno
  31 # define __set_errno(Val) errno = (Val)
  32 #endif
  33
  34 #include <stdio.h>
  35 #ifndef P_tmpdir
  36 # define P_tmpdir "/tmp"
  37 #endif
  38 #ifndef TMP_MAX
  39 # define TMP_MAX 238328
  40 #endif
  41 #ifndef __GT_FILE
  42 # define __GT_FILE      0
  43 # define __GT_DIR       1
  44 # define __GT_NOCREATE  2
  45 #endif
  46 #if !_LIBC && (GT_FILE != __GT_FILE || GT_DIR != __GT_DIR       \
  47                || GT_NOCREATE != __GT_NOCREATE)
  48 # error report this to bug-gnulib@gnu.org
  49 #endif
  50
  51 #include <stddef.h>
  52 #include <stdlib.h>
  53 #include <string.h>
  54
  55 #include <fcntl.h>
  56 #include <sys/time.h>
  57 #include <stdint.h>
  58 #include <unistd.h>
  59
  60 #include <sys/stat.h>
  61
  62 #if _LIBC
  63 # define struct_stat64 struct stat64
  64 #else
  65 # define struct_stat64 struct stat
  66 # define __try_tempname try_tempname
  67 # define __gen_tempname gen_tempname
  68 # define __getpid getpid
  69 # define __gettimeofday gettimeofday
  70 # define __mkdir mkdir
  71 # define __open open
  72 # define __lxstat64(version, file, buf) lstat (file, buf)
  73 # define __secure_getenv secure_getenv
  74 #endif
  75
  76 #ifdef _LIBC
  77 # include <hp-timing.h>
  78 # if HP_TIMING_AVAIL
  79 #  define RANDOM_BITS(Var) \
  80   if (__builtin_expect (value == UINT64_C (0), 0))                            \
  81     {                                                                         \
  82       /* If this is the first time this function is used initialize           \
  83          the variable we accumulate the value in to some somewhat             \
  84          random value.  If we'd not do this programs at startup time          \
  85          might have a reduced set of possible names, at least on slow         \
  86          machines.  */                                                        \
  87       struct timeval tv;                                                      \
  88       __gettimeofday (&tv, NULL);                                             \
  89       value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
  90     }                                                                         \
  91   HP_TIMING_NOW (Var)
  92 # endif
  93 #endif
  94
  95 /* Use the widest available unsigned type if uint64_t is not
  96    available.  The algorithm below extracts a number less than 62**6
  97    (approximately 2**35.725) from uint64_t, so ancient hosts where
  98    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
  99    which is better than not having mkstemp at all.  */
 100 #if !defined UINT64_MAX && !defined uint64_t
 101 # define uint64_t uintmax_t
 102 #endif
 103
 104 #if _LIBC
 105 /* Return nonzero if DIR is an existent directory.  */
 106 static int
 107 direxists (const char *dir)
 108 {
 109   struct_stat64 buf;
 110   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 111 }
 112
 113 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 114    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 115    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 116    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 117    doesn't exist, none of the searched dirs exists, or there's not
 118    enough space in TMPL. */
 119 int
 120 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 121                int try_tmpdir)
 122 {
 123   const char *d;
 124   size_t dlen, plen;
 125
 126   if (!pfx || !pfx[0])
 127     {
 128       pfx = "file";
 129       plen = 4;
 130     }
 131   else
 132     {
 133       plen = strlen (pfx);
 134       if (plen > 5)
 135         plen = 5;
 136     }
 137
 138   if (try_tmpdir)
 139     {
 140       d = __secure_getenv ("TMPDIR");
 141       if (d != NULL && direxists (d))
 142         dir = d;
 143       else if (dir != NULL && direxists (dir))
 144         /* nothing */ ;
 145       else
 146         dir = NULL;
 147     }
 148   if (dir == NULL)
 149     {
 150       if (direxists (P_tmpdir))
 151         dir = P_tmpdir;
 152       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 153         dir = "/tmp";
 154       else
 155         {
 156           __set_errno (ENOENT);
 157           return -1;
 158         }
 159     }
 160
 161   dlen = strlen (dir);
 162   while (dlen > 1 && dir[dlen - 1] == '/')
 163     dlen--;                     /* remove trailing slashes */
 164
 165   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 166   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 167     {
 168       __set_errno (EINVAL);
 169       return -1;
 170     }
 171
 172   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 173   return 0;
 174 }
 175 #endif /* _LIBC */
 176
 177 /* These are the characters used in temporary file names.  */
 178 static const char letters[] =
 179 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 180
 181 int
 182 __try_tempname (char *tmpl, int suffixlen, void *args,
 183                 int (*tryfunc) (char *, void *))
 184 {
 185   int len;
 186   char *XXXXXX;
 187   static uint64_t value;
 188   uint64_t random_time_bits;
 189   unsigned int count;
 190   int fd = -1;
 191   int save_errno = errno;
 192
 193   /* A lower bound on the number of temporary files to attempt to
 194      generate.  The maximum total number of temporary file names that
 195      can exist for a given template is 62**6.  It should never be
 196      necessary to try all of these combinations.  Instead if a reasonable
 197      number of names is tried (we define reasonable as 62**3) fail to
 198      give the system administrator the chance to remove the problems.  */
 199 #define ATTEMPTS_MIN (62 * 62 * 62)
 200
 201   /* The number of times to attempt to generate a temporary file.  To
 202      conform to POSIX, this must be no smaller than TMP_MAX.  */
 203 #if ATTEMPTS_MIN < TMP_MAX
 204   unsigned int attempts = TMP_MAX;
 205 #else
 206   unsigned int attempts = ATTEMPTS_MIN;
 207 #endif
 208
 209   len = strlen (tmpl);
 210   if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
 211     {
 212       __set_errno (EINVAL);
 213       return -1;
 214     }
 215
 216   /* This is where the Xs start.  */
 217   XXXXXX = &tmpl[len - 6 - suffixlen];
 218
 219   /* Get some more or less random data.  */
 220 #ifdef RANDOM_BITS
 221   RANDOM_BITS (random_time_bits);
 222 #else
 223   {
 224     struct timeval tv;
 225     __gettimeofday (&tv, NULL);
 226     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 227   }
 228 #endif
 229   value += random_time_bits ^ __getpid ();
 230
 231   for (count = 0; count < attempts; value += 7777, ++count)
 232     {
 233       uint64_t v = value;
 234
 235       /* Fill in the random bits.  */
 236       XXXXXX[0] = letters[v % 62];
 237       v /= 62;
 238       XXXXXX[1] = letters[v % 62];
 239       v /= 62;
 240       XXXXXX[2] = letters[v % 62];
 241       v /= 62;
 242       XXXXXX[3] = letters[v % 62];
 243       v /= 62;
 244       XXXXXX[4] = letters[v % 62];
 245       v /= 62;
 246       XXXXXX[5] = letters[v % 62];
 247
 248       fd = tryfunc (tmpl, args);
 249       if (fd >= 0)
 250         {
 251           __set_errno (save_errno);
 252           return fd;
 253         }
 254       else if (errno != EEXIST)
 255         return -1;
 256     }
 257
 258   /* We got out of the loop because we ran out of combinations to try.  */
 259   __set_errno (EEXIST);
 260   return -1;
 261 }
 262
 263 static int
 264 try_file (char *tmpl, void *flags)
 265 {
 266   int *openflags = flags;
 267   return __open (tmpl,
 268                  (*openflags & ~O_ACCMODE)
 269                  | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 270 }
 271
 272 static int
 273 try_dir (char *tmpl, void *flags _GL_UNUSED)
 274 {
 275   return __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 276 }
 277
 278 static int
 279 try_nocreate (char *tmpl, void *flags _GL_UNUSED)
 280 {
 281   struct_stat64 st;
 282
 283   if (__lxstat64 (_STAT_VER, tmpl, &st) == 0)
 284     __set_errno (EEXIST);
 285   return errno == ENOENT ? 0 : -1;
 286 }
 287
 288 /* Generate a temporary file name based on TMPL.  TMPL must match the
 289    rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix).
 290    The name constructed does not exist at the time of the call to
 291    __gen_tempname.  TMPL is overwritten with the result.
 292
 293    KIND may be one of:
 294    __GT_NOCREATE:       simply verify that the name does not exist
 295                         at the time of the call.
 296    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 297                         and return a read-write fd.  The file is mode 0600.
 298    __GT_DIR:            create a directory, which will be mode 0700.
 299
 300    We use a clever algorithm to get hard-to-predict names. */
 301 int
 302 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
 303 {
 304   int (*tryfunc) (char *, void *);
 305
 306   switch (kind)
 307     {
 308     case __GT_FILE:
 309       tryfunc = try_file;
 310       break;
 311
 312     case __GT_DIR:
 313       tryfunc = try_dir;
 314       break;
 315
 316     case __GT_NOCREATE:
 317       tryfunc = try_nocreate;
 318       break;
 319
 320     default:
 321       assert (! "invalid KIND in __gen_tempname");
 322       abort ();
 323     }
 324   return __try_tempname (tmpl, suffixlen, &flags, tryfunc);
 325 }