sysdeps/posix/tempname.c

   1 /* Copyright (C) 1991-2019 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    <https://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 <random-bits.h>
  75 # define RANDOM_BITS(Var) ((Var) = random_bits ())
  76 # else
  77 # define RANDOM_BITS(Var) \
  78     {                                                                         \
  79       struct timeval tv;                                                      \
  80       __gettimeofday (&tv, NULL);                                             \
  81       (Var) = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
  82     }
  83 #endif
  84
  85 /* Use the widest available unsigned type if uint64_t is not
  86    available.  The algorithm below extracts a number less than 62**6
  87    (approximately 2**35.725) from uint64_t, so ancient hosts where
  88    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
  89    which is better than not having mkstemp at all.  */
  90 #if !defined UINT64_MAX && !defined uint64_t
  91 # define uint64_t uintmax_t
  92 #endif
  93
  94 #if _LIBC
  95 /* Return nonzero if DIR is an existent directory.  */
  96 static int
  97 direxists (const char *dir)
  98 {
  99   struct_stat64 buf;
 100   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 101 }
 102
 103 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 104    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 105    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 106    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 107    doesn't exist, none of the searched dirs exists, or there's not
 108    enough space in TMPL. */
 109 int
 110 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 111                int try_tmpdir)
 112 {
 113   const char *d;
 114   size_t dlen, plen;
 115
 116   if (!pfx || !pfx[0])
 117     {
 118       pfx = "file";
 119       plen = 4;
 120     }
 121   else
 122     {
 123       plen = strlen (pfx);
 124       if (plen > 5)
 125         plen = 5;
 126     }
 127
 128   if (try_tmpdir)
 129     {
 130       d = __secure_getenv ("TMPDIR");
 131       if (d != NULL && direxists (d))
 132         dir = d;
 133       else if (dir != NULL && direxists (dir))
 134         /* nothing */ ;
 135       else
 136         dir = NULL;
 137     }
 138   if (dir == NULL)
 139     {
 140       if (direxists (P_tmpdir))
 141         dir = P_tmpdir;
 142       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 143         dir = "/tmp";
 144       else
 145         {
 146           __set_errno (ENOENT);
 147           return -1;
 148         }
 149     }
 150
 151   dlen = strlen (dir);
 152   while (dlen > 1 && dir[dlen - 1] == '/')
 153     dlen--;                     /* remove trailing slashes */
 154
 155   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 156   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 157     {
 158       __set_errno (EINVAL);
 159       return -1;
 160     }
 161
 162   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 163   return 0;
 164 }
 165 #endif /* _LIBC */
 166
 167 /* These are the characters used in temporary file names.  */
 168 static const char letters[] =
 169 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 170
 171 /* Generate a temporary file name based on TMPL.  TMPL must match the
 172    rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix).
 173    The name constructed does not exist at the time of the call to
 174    __gen_tempname.  TMPL is overwritten with the result.
 175
 176    KIND may be one of:
 177    __GT_NOCREATE:       simply verify that the name does not exist
 178                         at the time of the call.
 179    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 180                         and return a read-write fd.  The file is mode 0600.
 181    __GT_DIR:            create a directory, which will be mode 0700.
 182
 183    We use a clever algorithm to get hard-to-predict names. */
 184 int
 185 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
 186 {
 187   int len;
 188   char *XXXXXX;
 189   unsigned int count;
 190   int fd = -1;
 191   int save_errno = errno;
 192   struct_stat64 st;
 193
 194   /* A lower bound on the number of temporary files to attempt to
 195      generate.  The maximum total number of temporary file names that
 196      can exist for a given template is 62**6.  It should never be
 197      necessary to try all of these combinations.  Instead if a reasonable
 198      number of names is tried (we define reasonable as 62**3) fail to
 199      give the system administrator the chance to remove the problems.  */
 200 #define ATTEMPTS_MIN (62 * 62 * 62)
 201
 202   /* The number of times to attempt to generate a temporary file.  To
 203      conform to POSIX, this must be no smaller than TMP_MAX.  */
 204 #if ATTEMPTS_MIN < TMP_MAX
 205   unsigned int attempts = TMP_MAX;
 206 #else
 207   unsigned int attempts = ATTEMPTS_MIN;
 208 #endif
 209
 210   len = strlen (tmpl);
 211   if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
 212     {
 213       __set_errno (EINVAL);
 214       return -1;
 215     }
 216
 217   /* This is where the Xs start.  */
 218   XXXXXX = &tmpl[len - 6 - suffixlen];
 219
 220   uint64_t pid = (uint64_t) __getpid () << 32;
 221   for (count = 0; count < attempts; ++count)
 222     {
 223       uint64_t v;
 224       /* Get some more or less random data.  */
 225       RANDOM_BITS (v);
 226       v ^= pid;
 227
 228       /* Fill in the random bits.  */
 229       XXXXXX[0] = letters[v % 62];
 230       v /= 62;
 231       XXXXXX[1] = letters[v % 62];
 232       v /= 62;
 233       XXXXXX[2] = letters[v % 62];
 234       v /= 62;
 235       XXXXXX[3] = letters[v % 62];
 236       v /= 62;
 237       XXXXXX[4] = letters[v % 62];
 238       v /= 62;
 239       XXXXXX[5] = letters[v % 62];
 240
 241       switch (kind)
 242         {
 243         case __GT_FILE:
 244           fd = __open (tmpl,
 245                        (flags & ~O_ACCMODE)
 246                        | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 247           break;
 248
 249         case __GT_DIR:
 250           fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 251           break;
 252
 253         case __GT_NOCREATE:
 254           /* This case is backward from the other three.  __gen_tempname
 255              succeeds if __xstat fails because the name does not exist.
 256              Note the continue to bypass the common logic at the bottom
 257              of the loop.  */
 258           if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
 259             {
 260               if (errno == ENOENT)
 261                 {
 262                   __set_errno (save_errno);
 263                   return 0;
 264                 }
 265               else
 266                 /* Give up now. */
 267                 return -1;
 268             }
 269           continue;
 270
 271         default:
 272           assert (! "invalid KIND in __gen_tempname");
 273           abort ();
 274         }
 275
 276       if (fd >= 0)
 277         {
 278           __set_errno (save_errno);
 279           return fd;
 280         }
 281       else if (errno != EEXIST)
 282         return -1;
 283     }
 284
 285   /* We got out of the loop because we ran out of combinations to try.  */
 286   __set_errno (EEXIST);
 287   return -1;
 288 }