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 <http://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. */
96static int
97direxists (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 $TMPDIR,
105 P_tmpdir, /tmp that exists. Copies into TMPL a template suitable
106 for use with mk[s]temp. Will fail (-1) if DIR is non-null and
107 doesn't exist, none of the searched dirs exists, or there's not
108 enough space in TMPL. */
109int
110__path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
111 int try_tmpdir)
112{
113 const char *d;
114 size_t dlen, plen;
115
116 if (!pfx || !pfx[0])
117 {
118 pfx = "file";
119 plen = 4;
120 }
121 else
122 {
123 plen = strlen (pfx);
124 if (plen > 5)
125 plen = 5;
126 }
127
128 if (try_tmpdir)
129 {
130 d = __secure_getenv ("TMPDIR");
131 if (d != NULL && direxists (d))
132 dir = d;
133 else if (dir != NULL && direxists (dir))
134 /* nothing */ ;
135 else
136 dir = NULL;
137 }
138 if (dir == NULL)
139 {
140 if (direxists (P_tmpdir))
141 dir = P_tmpdir;
142 else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
143 dir = "/tmp";
144 else
145 {
146 __set_errno (ENOENT);
147 return -1;
148 }
149 }
150
151 dlen = strlen (dir);
152 while (dlen > 1 && dir[dlen - 1] == '/')
153 dlen--; /* remove trailing slashes */
154
155 /* check we have room for "${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. */
168static 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. */
184int
185__gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
186{
187 int len;
188 char *XXXXXX;
189 uint64_t value;
190 unsigned int count;
191 int fd = -1;
192 int save_errno = errno;
193 struct_stat64 st;
194
195 /* A lower bound on the number of temporary files to attempt to
196 generate. The maximum total number of temporary file names that
197 can exist for a given template is 62**6. It should never be
198 necessary to try all of these combinations. Instead if a reasonable
199 number of names is tried (we define reasonable as 62**3) fail to
200 give the system administrator the chance to remove the problems. */
201#define ATTEMPTS_MIN (62 * 62 * 62)
202
203 /* The number of times to attempt to generate a temporary file. To
204 conform to POSIX, this must be no smaller than TMP_MAX. */
205#if ATTEMPTS_MIN < TMP_MAX
206 unsigned int attempts = TMP_MAX;
207#else
208 unsigned int attempts = ATTEMPTS_MIN;
209#endif
210
211 len = strlen (tmpl);
212 if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
213 {
214 __set_errno (EINVAL);
215 return -1;
216 }
217
218 /* This is where the Xs start. */
219 XXXXXX = &tmpl[len - 6 - suffixlen];
220
221 /* Get some more or less random data. */
222 RANDOM_BITS (value);
223 value ^= (uint64_t)__getpid () << 32;
224
225 for (count = 0; count < attempts; value += 7777, ++count)
226 {
227 uint64_t v = value;
228
229 /* Fill in the random bits. */
230 XXXXXX[0] = letters[v % 62];
231 v /= 62;
232 XXXXXX[1] = letters[v % 62];
233 v /= 62;
234 XXXXXX[2] = letters[v % 62];
235 v /= 62;
236 XXXXXX[3] = letters[v % 62];
237 v /= 62;
238 XXXXXX[4] = letters[v % 62];
239 v /= 62;
240 XXXXXX[5] = letters[v % 62];
241
242 switch (kind)
243 {
244 case __GT_FILE:
245 fd = __open (tmpl,
246 (flags & ~O_ACCMODE)
247 | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
248 break;
249
250 case __GT_DIR:
251 fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
252 break;
253
254 case __GT_NOCREATE:
255 /* This case is backward from the other three. __gen_tempname
256 succeeds if __xstat fails because the name does not exist.
257 Note the continue to bypass the common logic at the bottom
258 of the loop. */
259 if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
260 {
261 if (errno == ENOENT)
262 {
263 __set_errno (save_errno);
264 return 0;
265 }
266 else
267 /* Give up now. */
268 return -1;
269 }
270 continue;
271
272 default:
273 assert (! "invalid KIND in __gen_tempname");
274 abort ();
275 }
276
277 if (fd >= 0)
278 {
279 __set_errno (save_errno);
280 return fd;
281 }
282 else if (errno != EEXIST)
283 return -1;
284 }
285
286 /* We got out of the loop because we ran out of combinations to try. */
287 __set_errno (EEXIST);
288 return -1;
289}
290