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