1/* tempname.c - generate the name of a temporary file.
2
3   Copyright (C) 1991-2003, 2005-2007, 2009-2014 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 __gen_tempname gen_tempname
66# define __getpid getpid
67# define __gettimeofday gettimeofday
68# define __mkdir mkdir
69# define __open open
70# define __lxstat64(version, file, buf) lstat (file, buf)
71# define __secure_getenv secure_getenv
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.  */
104static int
105direxists (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 $TMPDIR,
113   P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
114   for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
115   doesn't exist, none of the searched dirs exists, or there's not
116   enough space in TMPL. */
117int
118__path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
119               int try_tmpdir)
120{
121  const char *d;
122  size_t dlen, plen;
123
124  if (!pfx || !pfx[0])
125    {
126      pfx = "file";
127      plen = 4;
128    }
129  else
130    {
131      plen = strlen (pfx);
132      if (plen > 5)
133        plen = 5;
134    }
135
136  if (try_tmpdir)
137    {
138      d = __secure_getenv ("TMPDIR");
139      if (d != NULL && direxists (d))
140        dir = d;
141      else if (dir != NULL && direxists (dir))
142        /* nothing */ ;
143      else
144        dir = NULL;
145    }
146  if (dir == NULL)
147    {
148      if (direxists (P_tmpdir))
149        dir = P_tmpdir;
150      else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
151        dir = "/tmp";
152      else
153        {
154          __set_errno (ENOENT);
155          return -1;
156        }
157    }
158
159  dlen = strlen (dir);
160  while (dlen > 1 && dir[dlen - 1] == '/')
161    dlen--;                     /* remove trailing slashes */
162
163  /* check we have room for "${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.  */
176static const char letters[] =
177"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
178
179/* Generate a temporary file name based on TMPL.  TMPL must match the
180   rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix).
181   The name constructed does not exist at the time of the call to
182   __gen_tempname.  TMPL is overwritten with the result.
183
184   KIND may be one of:
185   __GT_NOCREATE:       simply verify that the name does not exist
186                        at the time of the call.
187   __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
188                        and return a read-write fd.  The file is mode 0600.
189   __GT_DIR:            create a directory, which will be mode 0700.
190
191   We use a clever algorithm to get hard-to-predict names. */
192int
193__gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
194{
195  int len;
196  char *XXXXXX;
197  static uint64_t value;
198  uint64_t random_time_bits;
199  unsigned int count;
200  int fd = -1;
201  int save_errno = errno;
202  struct_stat64 st;
203
204  /* A lower bound on the number of temporary files to attempt to
205     generate.  The maximum total number of temporary file names that
206     can exist for a given template is 62**6.  It should never be
207     necessary to try all of these combinations.  Instead if a reasonable
208     number of names is tried (we define reasonable as 62**3) fail to
209     give the system administrator the chance to remove the problems.  */
210#define ATTEMPTS_MIN (62 * 62 * 62)
211
212  /* The number of times to attempt to generate a temporary file.  To
213     conform to POSIX, this must be no smaller than TMP_MAX.  */
214#if ATTEMPTS_MIN < TMP_MAX
215  unsigned int attempts = TMP_MAX;
216#else
217  unsigned int attempts = ATTEMPTS_MIN;
218#endif
219
220  len = strlen (tmpl);
221  if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
222    {
223      __set_errno (EINVAL);
224      return -1;
225    }
226
227  /* This is where the Xs start.  */
228  XXXXXX = &tmpl[len - 6 - suffixlen];
229
230  /* Get some more or less random data.  */
231#ifdef RANDOM_BITS
232  RANDOM_BITS (random_time_bits);
233#else
234  {
235    struct timeval tv;
236    __gettimeofday (&tv, NULL);
237    random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
238  }
239#endif
240  value += random_time_bits ^ __getpid ();
241
242  for (count = 0; count < attempts; value += 7777, ++count)
243    {
244      uint64_t v = value;
245
246      /* Fill in the random bits.  */
247      XXXXXX[0] = letters[v % 62];
248      v /= 62;
249      XXXXXX[1] = letters[v % 62];
250      v /= 62;
251      XXXXXX[2] = letters[v % 62];
252      v /= 62;
253      XXXXXX[3] = letters[v % 62];
254      v /= 62;
255      XXXXXX[4] = letters[v % 62];
256      v /= 62;
257      XXXXXX[5] = letters[v % 62];
258
259      switch (kind)
260        {
261        case __GT_FILE:
262          fd = __open (tmpl,
263                       (flags & ~O_ACCMODE)
264                       | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
265          break;
266
267        case __GT_DIR:
268          fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
269          break;
270
271        case __GT_NOCREATE:
272          /* This case is backward from the other three.  __gen_tempname
273             succeeds if __xstat fails because the name does not exist.
274             Note the continue to bypass the common logic at the bottom
275             of the loop.  */
276          if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
277            {
278              if (errno == ENOENT)
279                {
280                  __set_errno (save_errno);
281                  return 0;
282                }
283              else
284                /* Give up now. */
285                return -1;
286            }
287          continue;
288
289        default:
290          assert (! "invalid KIND in __gen_tempname");
291          abort ();
292        }
293
294      if (fd >= 0)
295        {
296          __set_errno (save_errno);
297          return fd;
298        }
299      else if (errno != EEXIST)
300        return -1;
301    }
302
303  /* We got out of the loop because we ran out of combinations to try.  */
304  __set_errno (EEXIST);
305  return -1;
306}
307