1/* Copyright (C) 1991-2022 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 <libc-config.h>
20# include "tempname.h"
21#endif
22
23#include <sys/types.h>
24#include <assert.h>
25#include <stdbool.h>
26
27#include <errno.h>
28
29#include <stdio.h>
30#ifndef P_tmpdir
31# define P_tmpdir "/tmp"
32#endif
33#ifndef TMP_MAX
34# define TMP_MAX 238328
35#endif
36#ifndef __GT_FILE
37# define __GT_FILE      0
38# define __GT_DIR       1
39# define __GT_NOCREATE  2
40#endif
41#if !_LIBC && (GT_FILE != __GT_FILE || GT_DIR != __GT_DIR       \
42               || GT_NOCREATE != __GT_NOCREATE)
43# error report this to bug-gnulib@gnu.org
44#endif
45
46#include <stddef.h>
47#include <stdlib.h>
48#include <string.h>
49
50#include <fcntl.h>
51#include <stdalign.h>
52#include <stdint.h>
53#include <sys/random.h>
54#include <sys/stat.h>
55#include <time.h>
56
57#if _LIBC
58# define struct_stat64 struct stat64
59# define __secure_getenv __libc_secure_getenv
60#else
61# define struct_stat64 struct stat
62# define __gen_tempname gen_tempname
63# define __mkdir mkdir
64# define __open open
65# define __lstat64(file, buf) lstat (file, buf)
66# define __stat64(file, buf) stat (file, buf)
67# define __getrandom getrandom
68# define __clock_gettime64 clock_gettime
69# define __timespec64 timespec
70#endif
71
72/* Use getrandom if it works, falling back on a 64-bit linear
73   congruential generator that starts with Var's value
74   mixed in with a clock's low-order bits if available.  */
75typedef uint_fast64_t random_value;
76#define RANDOM_VALUE_MAX UINT_FAST64_MAX
77#define BASE_62_DIGITS 10 /* 62**10 < UINT_FAST64_MAX */
78#define BASE_62_POWER (62LL * 62 * 62 * 62 * 62 * 62 * 62 * 62 * 62 * 62)
79
80static random_value
81random_bits (random_value var, bool use_getrandom)
82{
83  random_value r;
84  /* Without GRND_NONBLOCK it can be blocked for minutes on some systems.  */
85  if (use_getrandom && __getrandom (&r, sizeof r, GRND_NONBLOCK) == sizeof r)
86    return r;
87#if _LIBC || (defined CLOCK_MONOTONIC && HAVE_CLOCK_GETTIME)
88  /* Add entropy if getrandom did not work.  */
89  struct __timespec64 tv;
90  __clock_gettime64 (CLOCK_MONOTONIC, &tv);
91  var ^= tv.tv_nsec;
92#endif
93  return 2862933555777941757 * var + 3037000493;
94}
95
96#if _LIBC
97/* Return nonzero if DIR is an existent directory.  */
98static int
99direxists (const char *dir)
100{
101  struct_stat64 buf;
102  return __stat64 (dir, &buf) == 0 && S_ISDIR (buf.st_mode);
103}
104
105/* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
106   non-null and exists, uses it; otherwise uses the first of $TMPDIR,
107   P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
108   for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
109   doesn't exist, none of the searched dirs exists, or there's not
110   enough space in TMPL. */
111int
112__path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
113               int try_tmpdir)
114{
115  const char *d;
116  size_t dlen, plen;
117
118  if (!pfx || !pfx[0])
119    {
120      pfx = "file";
121      plen = 4;
122    }
123  else
124    {
125      plen = strlen (pfx);
126      if (plen > 5)
127        plen = 5;
128    }
129
130  if (try_tmpdir)
131    {
132      d = __secure_getenv ("TMPDIR");
133      if (d != NULL && direxists (d))
134        dir = d;
135      else if (dir != NULL && direxists (dir))
136        /* nothing */ ;
137      else
138        dir = NULL;
139    }
140  if (dir == NULL)
141    {
142      if (direxists (P_tmpdir))
143        dir = P_tmpdir;
144      else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
145        dir = "/tmp";
146      else
147        {
148          __set_errno (ENOENT);
149          return -1;
150        }
151    }
152
153  dlen = strlen (dir);
154  while (dlen > 1 && dir[dlen - 1] == '/')
155    dlen--;                     /* remove trailing slashes */
156
157  /* check we have room for "${dir}/${pfx}XXXXXX\0" */
158  if (tmpl_len < dlen + 1 + plen + 6 + 1)
159    {
160      __set_errno (EINVAL);
161      return -1;
162    }
163
164  sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
165  return 0;
166}
167#endif /* _LIBC */
168
169#if _LIBC
170static int try_tempname_len (char *, int, void *, int (*) (char *, void *),
171                             size_t);
172#endif
173
174static int
175try_file (char *tmpl, void *flags)
176{
177  int *openflags = flags;
178  return __open (tmpl,
179                 (*openflags & ~O_ACCMODE)
180                 | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
181}
182
183static int
184try_dir (char *tmpl, _GL_UNUSED void *flags)
185{
186  return __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
187}
188
189static int
190try_nocreate (char *tmpl, _GL_UNUSED void *flags)
191{
192  struct_stat64 st;
193
194  if (__lstat64 (tmpl, &st) == 0 || errno == EOVERFLOW)
195    __set_errno (EEXIST);
196  return errno == ENOENT ? 0 : -1;
197}
198
199/* These are the characters used in temporary file names.  */
200static const char letters[] =
201"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
202
203/* Generate a temporary file name based on TMPL.  TMPL must match the
204   rules for mk[s]temp (i.e., end in at least X_SUFFIX_LEN "X"s,
205   possibly with a suffix).
206   The name constructed does not exist at the time of the call to
207   this function.  TMPL is overwritten with the result.
208
209   KIND may be one of:
210   __GT_NOCREATE:       simply verify that the name does not exist
211                        at the time of the call.
212   __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
213                        and return a read-write fd.  The file is mode 0600.
214   __GT_DIR:            create a directory, which will be mode 0700.
215
216   We use a clever algorithm to get hard-to-predict names. */
217#ifdef _LIBC
218static
219#endif
220int
221gen_tempname_len (char *tmpl, int suffixlen, int flags, int kind,
222                  size_t x_suffix_len)
223{
224  static int (*const tryfunc[]) (char *, void *) =
225    {
226      [__GT_FILE] = try_file,
227      [__GT_DIR] = try_dir,
228      [__GT_NOCREATE] = try_nocreate
229    };
230  return try_tempname_len (tmpl, suffixlen, &flags, tryfunc[kind],
231                           x_suffix_len);
232}
233
234#ifdef _LIBC
235static
236#endif
237int
238try_tempname_len (char *tmpl, int suffixlen, void *args,
239                  int (*tryfunc) (char *, void *), size_t x_suffix_len)
240{
241  size_t len;
242  char *XXXXXX;
243  unsigned int count;
244  int fd = -1;
245  int save_errno = errno;
246
247  /* A lower bound on the number of temporary files to attempt to
248     generate.  The maximum total number of temporary file names that
249     can exist for a given template is 62**6.  It should never be
250     necessary to try all of these combinations.  Instead if a reasonable
251     number of names is tried (we define reasonable as 62**3) fail to
252     give the system administrator the chance to remove the problems.
253     This value requires that X_SUFFIX_LEN be at least 3.  */
254#define ATTEMPTS_MIN (62 * 62 * 62)
255
256  /* The number of times to attempt to generate a temporary file.  To
257     conform to POSIX, this must be no smaller than TMP_MAX.  */
258#if ATTEMPTS_MIN < TMP_MAX
259  unsigned int attempts = TMP_MAX;
260#else
261  unsigned int attempts = ATTEMPTS_MIN;
262#endif
263
264  /* A random variable.  The initial value is used only the for fallback path
265     on 'random_bits' on 'getrandom' failure.  Its initial value tries to use
266     some entropy from the ASLR and ignore possible bits from the stack
267     alignment.  */
268  random_value v = ((uintptr_t) &v) / alignof (max_align_t);
269
270  /* How many random base-62 digits can currently be extracted from V.  */
271  int vdigits = 0;
272
273  /* Whether to consume entropy when acquiring random bits.  On the
274     first try it's worth the entropy cost with __GT_NOCREATE, which
275     is inherently insecure and can use the entropy to make it a bit
276     less secure.  On the (rare) second and later attempts it might
277     help against DoS attacks.  */
278  bool use_getrandom = tryfunc == try_nocreate;
279
280  /* Least unfair value for V.  If V is less than this, V can generate
281     BASE_62_DIGITS digits fairly.  Otherwise it might be biased.  */
282  random_value const unfair_min
283    = RANDOM_VALUE_MAX - RANDOM_VALUE_MAX % BASE_62_POWER;
284
285  len = strlen (tmpl);
286  if (len < x_suffix_len + suffixlen
287      || strspn (&tmpl[len - x_suffix_len - suffixlen], "X") < x_suffix_len)
288    {
289      __set_errno (EINVAL);
290      return -1;
291    }
292
293  /* This is where the Xs start.  */
294  XXXXXX = &tmpl[len - x_suffix_len - suffixlen];
295
296  for (count = 0; count < attempts; ++count)
297    {
298      for (size_t i = 0; i < x_suffix_len; i++)
299        {
300          if (vdigits == 0)
301            {
302              do
303                {
304                  v = random_bits (v, use_getrandom);
305                  use_getrandom = true;
306                }
307              while (unfair_min <= v);
308
309              vdigits = BASE_62_DIGITS;
310            }
311
312          XXXXXX[i] = letters[v % 62];
313          v /= 62;
314          vdigits--;
315        }
316
317      fd = tryfunc (tmpl, args);
318      if (fd >= 0)
319        {
320          __set_errno (save_errno);
321          return fd;
322        }
323      else if (errno != EEXIST)
324        return -1;
325    }
326
327  /* We got out of the loop because we ran out of combinations to try.  */
328  __set_errno (EEXIST);
329  return -1;
330}
331
332int
333__gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
334{
335  return gen_tempname_len (tmpl, suffixlen, flags, kind, 6);
336}
337
338#if !_LIBC
339int
340try_tempname (char *tmpl, int suffixlen, void *args,
341              int (*tryfunc) (char *, void *))
342{
343  return try_tempname_len (tmpl, suffixlen, args, tryfunc, 6);
344}
345#endif
346