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 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 __try_tempname try_tempname
  66 # define __gen_tempname gen_tempname
  67 # define __getpid getpid
  68 # define __gettimeofday gettimeofday
  69 # define __mkdir mkdir
  70 # define __open open
  71 # define __lxstat64(version, file, buf) lstat (file, buf)
  72 # define __secure_getenv secure_getenv
  73 #endif
  74
  75 #ifdef _LIBC
  76 # include <hp-timing.h>
  77 # if HP_TIMING_AVAIL
  78 #  define RANDOM_BITS(Var) \
  79   if (__builtin_expect (value == UINT64_C (0), 0))                            \
  80     {                                                                         \
  81       /* If this is the first time this function is used initialize           \
  82          the variable we accumulate the value in to some somewhat             \
  83          random value.  If we'd not do this programs at startup time          \
  84          might have a reduced set of possible names, at least on slow         \
  85          machines.  */                                                        \
  86       struct timeval tv;                                                      \
  87       __gettimeofday (&tv, NULL);                                             \
  88       value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
  89     }                                                                         \
  90   HP_TIMING_NOW (Var)
  91 # endif
  92 #endif
  93
  94 /* Use the widest available unsigned type if uint64_t is not
  95    available.  The algorithm below extracts a number less than 62**6
  96    (approximately 2**35.725) from uint64_t, so ancient hosts where
  97    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
  98    which is better than not having mkstemp at all.  */
  99 #if !defined UINT64_MAX && !defined uint64_t
 100 # define uint64_t uintmax_t
 101 #endif
 102
 103 #if _LIBC
 104 /* Return nonzero if DIR is an existent directory.  */
 105 static int
 106 direxists (const char *dir)
 107 {
 108   struct_stat64 buf;
 109   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 110 }
 111
 112 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 113    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 114    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 115    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 116    doesn't exist, none of the searched dirs exists, or there's not
 117    enough space in TMPL. */
 118 int
 119 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 120                int try_tmpdir)
 121 {
 122   const char *d;
 123   size_t dlen, plen;
 124
 125   if (!pfx || !pfx[0])
 126     {
 127       pfx = "file";
 128       plen = 4;
 129     }
 130   else
 131     {
 132       plen = strlen (pfx);
 133       if (plen > 5)
 134         plen = 5;
 135     }
 136
 137   if (try_tmpdir)
 138     {
 139       d = __secure_getenv ("TMPDIR");
 140       if (d != NULL && direxists (d))
 141         dir = d;
 142       else if (dir != NULL && direxists (dir))
 143         /* nothing */ ;
 144       else
 145         dir = NULL;
 146     }
 147   if (dir == NULL)
 148     {
 149       if (direxists (P_tmpdir))
 150         dir = P_tmpdir;
 151       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 152         dir = "/tmp";
 153       else
 154         {
 155           __set_errno (ENOENT);
 156           return -1;
 157         }
 158     }
 159
 160   dlen = strlen (dir);
 161   while (dlen > 1 && dir[dlen - 1] == '/')
 162     dlen--;                     /* remove trailing slashes */
 163
 164   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 165   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 166     {
 167       __set_errno (EINVAL);
 168       return -1;
 169     }
 170
 171   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 172   return 0;
 173 }
 174 #endif /* _LIBC */
 175
 176 /* These are the characters used in temporary file names.  */
 177 static const char letters[] =
 178 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 179
 180 int
 181 __try_tempname (char *tmpl, int suffixlen, void *args,
 182                 int (*tryfunc) (char *, void *))
 183 {
 184   int len;
 185   char *XXXXXX;
 186   static uint64_t value;
 187   uint64_t random_time_bits;
 188   unsigned int count;
 189   int fd = -1;
 190   int save_errno = errno;
 191
 192   /* A lower bound on the number of temporary files to attempt to
 193      generate.  The maximum total number of temporary file names that
 194      can exist for a given template is 62**6.  It should never be
 195      necessary to try all of these combinations.  Instead if a reasonable
 196      number of names is tried (we define reasonable as 62**3) fail to
 197      give the system administrator the chance to remove the problems.  */
 198 #define ATTEMPTS_MIN (62 * 62 * 62)
 199
 200   /* The number of times to attempt to generate a temporary file.  To
 201      conform to POSIX, this must be no smaller than TMP_MAX.  */
 202 #if ATTEMPTS_MIN < TMP_MAX
 203   unsigned int attempts = TMP_MAX;
 204 #else
 205   unsigned int attempts = ATTEMPTS_MIN;
 206 #endif
 207
 208   len = strlen (tmpl);
 209   if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
 210     {
 211       __set_errno (EINVAL);
 212       return -1;
 213     }
 214
 215   /* This is where the Xs start.  */
 216   XXXXXX = &tmpl[len - 6 - suffixlen];
 217
 218   /* Get some more or less random data.  */
 219 #ifdef RANDOM_BITS
 220   RANDOM_BITS (random_time_bits);
 221 #else
 222   {
 223     struct timeval tv;
 224     __gettimeofday (&tv, NULL);
 225     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 226   }
 227 #endif
 228   value += random_time_bits ^ __getpid ();
 229
 230   for (count = 0; count < attempts; value += 7777, ++count)
 231     {
 232       uint64_t v = value;
 233
 234       /* Fill in the random bits.  */
 235       XXXXXX[0] = letters[v % 62];
 236       v /= 62;
 237       XXXXXX[1] = letters[v % 62];
 238       v /= 62;
 239       XXXXXX[2] = letters[v % 62];
 240       v /= 62;
 241       XXXXXX[3] = letters[v % 62];
 242       v /= 62;
 243       XXXXXX[4] = letters[v % 62];
 244       v /= 62;
 245       XXXXXX[5] = letters[v % 62];
 246
 247       fd = tryfunc (tmpl, args);
 248       if (fd >= 0)
 249         {
 250           __set_errno (save_errno);
 251           return fd;
 252         }
 253       else if (errno != EEXIST)
 254         return -1;
 255     }
 256
 257   /* We got out of the loop because we ran out of combinations to try.  */
 258   __set_errno (EEXIST);
 259   return -1;
 260 }
 261
 262 static int
 263 try_file (char *tmpl, void *flags)
 264 {
 265   int *openflags = flags;
 266   return __open (tmpl,
 267                  (*openflags & ~O_ACCMODE)
 268                  | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 269 }
 270
 271 static int
 272 try_dir (char *tmpl, void *flags _GL_UNUSED)
 273 {
 274   return __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 275 }
 276
 277 static int
 278 try_nocreate (char *tmpl, void *flags _GL_UNUSED)
 279 {
 280   struct_stat64 st;
 281
 282   if (__lxstat64 (_STAT_VER, tmpl, &st) == 0)
 283     __set_errno (EEXIST);
 284   return errno == ENOENT ? 0 : -1;
 285 }
 286
 287 /* Generate a temporary file name based on TMPL.  TMPL must match the
 288    rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix).
 289    The name constructed does not exist at the time of the call to
 290    __gen_tempname.  TMPL is overwritten with the result.
 291
 292    KIND may be one of:
 293    __GT_NOCREATE:       simply verify that the name does not exist
 294                         at the time of the call.
 295    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 296                         and return a read-write fd.  The file is mode 0600.
 297    __GT_DIR:            create a directory, which will be mode 0700.
 298
 299    We use a clever algorithm to get hard-to-predict names. */
 300 int
 301 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
 302 {
 303   int (*tryfunc) (char *, void *);
 304
 305   switch (kind)
 306     {
 307     case __GT_FILE:
 308       tryfunc = try_file;
 309       break;
 310
 311     case __GT_DIR:
 312       tryfunc = try_dir;
 313       break;
 314
 315     case __GT_NOCREATE:
 316       tryfunc = try_nocreate;
 317       break;
 318
 319     default:
 320       assert (! "invalid KIND in __gen_tempname");
 321       abort ();
 322     }
 323   return __try_tempname (tmpl, suffixlen, &flags, tryfunc);
 324 }