sysdeps/posix/tempname.c

   1 /* Copyright (C) 1991-2016 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 !_LIBC
  19 # include <config.h>
  20 # include "tempname.h"
  21 #endif
  22
  23 #include <sys/types.h>
  24 #include <assert.h>
  25
  26 #include <errno.h>
  27 #ifndef __set_errno
  28 # define __set_errno(Val) errno = (Val)
  29 #endif
  30
  31 #include <stdio.h>
  32 #ifndef P_tmpdir
  33 # define P_tmpdir "/tmp"
  34 #endif
  35 #ifndef TMP_MAX
  36 # define TMP_MAX 238328
  37 #endif
  38 #ifndef __GT_FILE
  39 # define __GT_FILE      0
  40 # define __GT_DIR       1
  41 # define __GT_NOCREATE  2
  42 #endif
  43 #if !_LIBC && (GT_FILE != __GT_FILE || GT_DIR != __GT_DIR       \
  44                || GT_NOCREATE != __GT_NOCREATE)
  45 # error report this to bug-gnulib@gnu.org
  46 #endif
  47
  48 #include <stddef.h>
  49 #include <stdlib.h>
  50 #include <string.h>
  51
  52 #include <fcntl.h>
  53 #include <sys/time.h>
  54 #include <stdint.h>
  55 #include <unistd.h>
  56
  57 #include <sys/stat.h>
  58
  59 #if _LIBC
  60 # define struct_stat64 struct stat64
  61 # define __secure_getenv __libc_secure_getenv
  62 #else
  63 # define struct_stat64 struct stat
  64 # define __gen_tempname gen_tempname
  65 # define __getpid getpid
  66 # define __gettimeofday gettimeofday
  67 # define __mkdir mkdir
  68 # define __open open
  69 # define __lxstat64(version, file, buf) lstat (file, buf)
  70 # define __secure_getenv secure_getenv
  71 #endif
  72
  73 #ifdef _LIBC
  74 # include <hp-timing.h>
  75 # if HP_TIMING_AVAIL
  76 #  define RANDOM_BITS(Var) \
  77   if (__glibc_unlikely (value == UINT64_C (0)))                               \
  78     {                                                                         \
  79       /* If this is the first time this function is used initialize           \
  80          the variable we accumulate the value in to some somewhat             \
  81          random value.  If we'd not do this programs at startup time          \
  82          might have a reduced set of possible names, at least on slow         \
  83          machines.  */                                                        \
  84       struct timeval tv;                                                      \
  85       __gettimeofday (&tv, NULL);                                             \
  86       value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
  87     }                                                                         \
  88   HP_TIMING_NOW (Var)
  89 # endif
  90 #endif
  91
  92 /* Use the widest available unsigned type if uint64_t is not
  93    available.  The algorithm below extracts a number less than 62**6
  94    (approximately 2**35.725) from uint64_t, so ancient hosts where
  95    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
  96    which is better than not having mkstemp at all.  */
  97 #if !defined UINT64_MAX && !defined uint64_t
  98 # define uint64_t uintmax_t
  99 #endif
 100
 101 #if _LIBC
 102 /* Return nonzero if DIR is an existent directory.  */
 103 static int
 104 direxists (const char *dir)
 105 {
 106   struct_stat64 buf;
 107   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 108 }
 109
 110 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 111    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 112    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 113    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 114    doesn't exist, none of the searched dirs exists, or there's not
 115    enough space in TMPL. */
 116 int
 117 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 118                int try_tmpdir)
 119 {
 120   const char *d;
 121   size_t dlen, plen;
 122
 123   if (!pfx || !pfx[0])
 124     {
 125       pfx = "file";
 126       plen = 4;
 127     }
 128   else
 129     {
 130       plen = strlen (pfx);
 131       if (plen > 5)
 132         plen = 5;
 133     }
 134
 135   if (try_tmpdir)
 136     {
 137       d = __secure_getenv ("TMPDIR");
 138       if (d != NULL && direxists (d))
 139         dir = d;
 140       else if (dir != NULL && direxists (dir))
 141         /* nothing */ ;
 142       else
 143         dir = NULL;
 144     }
 145   if (dir == NULL)
 146     {
 147       if (direxists (P_tmpdir))
 148         dir = P_tmpdir;
 149       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 150         dir = "/tmp";
 151       else
 152         {
 153           __set_errno (ENOENT);
 154           return -1;
 155         }
 156     }
 157
 158   dlen = strlen (dir);
 159   while (dlen > 1 && dir[dlen - 1] == '/')
 160     dlen--;                     /* remove trailing slashes */
 161
 162   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 163   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 164     {
 165       __set_errno (EINVAL);
 166       return -1;
 167     }
 168
 169   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 170   return 0;
 171 }
 172 #endif /* _LIBC */
 173
 174 /* These are the characters used in temporary file names.  */
 175 static const char letters[] =
 176 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 177
 178 /* Generate a temporary file name based on TMPL.  TMPL must match the
 179    rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix).
 180    The name constructed does not exist at the time of the call to
 181    __gen_tempname.  TMPL is overwritten with the result.
 182
 183    KIND may be one of:
 184    __GT_NOCREATE:       simply verify that the name does not exist
 185                         at the time of the call.
 186    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 187                         and return a read-write fd.  The file is mode 0600.
 188    __GT_DIR:            create a directory, which will be mode 0700.
 189
 190    We use a clever algorithm to get hard-to-predict names. */
 191 int
 192 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
 193 {
 194   int len;
 195   char *XXXXXX;
 196   static uint64_t value;
 197   uint64_t random_time_bits;
 198   unsigned int count;
 199   int fd = -1;
 200   int save_errno = errno;
 201   struct_stat64 st;
 202
 203   /* A lower bound on the number of temporary files to attempt to
 204      generate.  The maximum total number of temporary file names that
 205      can exist for a given template is 62**6.  It should never be
 206      necessary to try all of these combinations.  Instead if a reasonable
 207      number of names is tried (we define reasonable as 62**3) fail to
 208      give the system administrator the chance to remove the problems.  */
 209 #define ATTEMPTS_MIN (62 * 62 * 62)
 210
 211   /* The number of times to attempt to generate a temporary file.  To
 212      conform to POSIX, this must be no smaller than TMP_MAX.  */
 213 #if ATTEMPTS_MIN < TMP_MAX
 214   unsigned int attempts = TMP_MAX;
 215 #else
 216   unsigned int attempts = ATTEMPTS_MIN;
 217 #endif
 218
 219   len = strlen (tmpl);
 220   if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
 221     {
 222       __set_errno (EINVAL);
 223       return -1;
 224     }
 225
 226   /* This is where the Xs start.  */
 227   XXXXXX = &tmpl[len - 6 - suffixlen];
 228
 229   /* Get some more or less random data.  */
 230 #ifdef RANDOM_BITS
 231   RANDOM_BITS (random_time_bits);
 232 #else
 233   {
 234     struct timeval tv;
 235     __gettimeofday (&tv, NULL);
 236     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 237   }
 238 #endif
 239   value += random_time_bits ^ __getpid ();
 240
 241   for (count = 0; count < attempts; value += 7777, ++count)
 242     {
 243       uint64_t v = value;
 244
 245       /* Fill in the random bits.  */
 246       XXXXXX[0] = letters[v % 62];
 247       v /= 62;
 248       XXXXXX[1] = letters[v % 62];
 249       v /= 62;
 250       XXXXXX[2] = letters[v % 62];
 251       v /= 62;
 252       XXXXXX[3] = letters[v % 62];
 253       v /= 62;
 254       XXXXXX[4] = letters[v % 62];
 255       v /= 62;
 256       XXXXXX[5] = letters[v % 62];
 257
 258       switch (kind)
 259         {
 260         case __GT_FILE:
 261           fd = __open (tmpl,
 262                        (flags & ~O_ACCMODE)
 263                        | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 264           break;
 265
 266         case __GT_DIR:
 267           fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 268           break;
 269
 270         case __GT_NOCREATE:
 271           /* This case is backward from the other three.  __gen_tempname
 272              succeeds if __xstat fails because the name does not exist.
 273              Note the continue to bypass the common logic at the bottom
 274              of the loop.  */
 275           if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
 276             {
 277               if (errno == ENOENT)
 278                 {
 279                   __set_errno (save_errno);
 280                   return 0;
 281                 }
 282               else
 283                 /* Give up now. */
 284                 return -1;
 285             }
 286           continue;
 287
 288         default:
 289           assert (! "invalid KIND in __gen_tempname");
 290           abort ();
 291         }
 292
 293       if (fd >= 0)
 294         {
 295           __set_errno (save_errno);
 296           return fd;
 297         }
 298       else if (errno != EEXIST)
 299         return -1;
 300     }
 301
 302   /* We got out of the loop because we ran out of combinations to try.  */
 303   __set_errno (EEXIST);
 304   return -1;
 305 }