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 <https://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 #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 int
 180 __try_tempname (char *tmpl, int suffixlen, void *args,
 181                 int (*tryfunc) (char *, void *))
 182 {
 183   int len;
 184   char *XXXXXX;
 185   static uint64_t value;
 186   uint64_t random_time_bits;
 187   unsigned int count;
 188   int fd = -1;
 189   int save_errno = errno;
 190
 191   /* A lower bound on the number of temporary files to attempt to
 192      generate.  The maximum total number of temporary file names that
 193      can exist for a given template is 62**6.  It should never be
 194      necessary to try all of these combinations.  Instead if a reasonable
 195      number of names is tried (we define reasonable as 62**3) fail to
 196      give the system administrator the chance to remove the problems.  */
 197 #define ATTEMPTS_MIN (62 * 62 * 62)
 198
 199   /* The number of times to attempt to generate a temporary file.  To
 200      conform to POSIX, this must be no smaller than TMP_MAX.  */
 201 #if ATTEMPTS_MIN < TMP_MAX
 202   unsigned int attempts = TMP_MAX;
 203 #else
 204   unsigned int attempts = ATTEMPTS_MIN;
 205 #endif
 206
 207   len = strlen (tmpl);
 208   if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
 209     {
 210       __set_errno (EINVAL);
 211       return -1;
 212     }
 213
 214   /* This is where the Xs start.  */
 215   XXXXXX = &tmpl[len - 6 - suffixlen];
 216
 217   /* Get some more or less random data.  */
 218 #ifdef RANDOM_BITS
 219   RANDOM_BITS (random_time_bits);
 220 #else
 221   {
 222     struct timeval tv;
 223     __gettimeofday (&tv, NULL);
 224     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 225   }
 226 #endif
 227   value += random_time_bits ^ __getpid ();
 228
 229   for (count = 0; count < attempts; value += 7777, ++count)
 230     {
 231       uint64_t v = value;
 232
 233       /* Fill in the random bits.  */
 234       XXXXXX[0] = letters[v % 62];
 235       v /= 62;
 236       XXXXXX[1] = letters[v % 62];
 237       v /= 62;
 238       XXXXXX[2] = letters[v % 62];
 239       v /= 62;
 240       XXXXXX[3] = letters[v % 62];
 241       v /= 62;
 242       XXXXXX[4] = letters[v % 62];
 243       v /= 62;
 244       XXXXXX[5] = letters[v % 62];
 245
 246       fd = tryfunc (tmpl, args);
 247       if (fd >= 0)
 248         {
 249           __set_errno (save_errno);
 250           return fd;
 251         }
 252       else if (errno != EEXIST)
 253         return -1;
 254     }
 255
 256   /* We got out of the loop because we ran out of combinations to try.  */
 257   __set_errno (EEXIST);
 258   return -1;
 259 }
 260
 261 static int
 262 try_file (char *tmpl, void *flags)
 263 {
 264   int *openflags = flags;
 265   return __open (tmpl,
 266                  (*openflags & ~O_ACCMODE)
 267                  | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 268 }
 269
 270 static int
 271 try_dir (char *tmpl, void *flags _GL_UNUSED)
 272 {
 273   return __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 274 }
 275
 276 static int
 277 try_nocreate (char *tmpl, void *flags _GL_UNUSED)
 278 {
 279   struct_stat64 st;
 280
 281   if (__lxstat64 (_STAT_VER, tmpl, &st) == 0 || errno == EOVERFLOW)
 282     __set_errno (EEXIST);
 283   return errno == ENOENT ? 0 : -1;
 284 }
 285
 286 /* Generate a temporary file name based on TMPL.  TMPL must match the
 287    rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix).
 288    The name constructed does not exist at the time of the call to
 289    __gen_tempname.  TMPL is overwritten with the result.
 290
 291    KIND may be one of:
 292    __GT_NOCREATE:       simply verify that the name does not exist
 293                         at the time of the call.
 294    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 295                         and return a read-write fd.  The file is mode 0600.
 296    __GT_DIR:            create a directory, which will be mode 0700.
 297
 298    We use a clever algorithm to get hard-to-predict names. */
 299 int
 300 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
 301 {
 302   int (*tryfunc) (char *, void *);
 303
 304   switch (kind)
 305     {
 306     case __GT_FILE:
 307       tryfunc = try_file;
 308       break;
 309
 310     case __GT_DIR:
 311       tryfunc = try_dir;
 312       break;
 313
 314     case __GT_NOCREATE:
 315       tryfunc = try_nocreate;
 316       break;
 317
 318     default:
 319       assert (! "invalid KIND in __gen_tempname");
 320       abort ();
 321     }
 322   return __try_tempname (tmpl, suffixlen, &flags, tryfunc);
 323 }