1/* Copyright (C) 1991-2020 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 <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 <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 __mkdir mkdir
67# define __open open
68# define __lxstat64(version, file, buf) lstat (file, buf)
69# define __secure_getenv secure_getenv
70#endif
71
72#ifdef _LIBC
73# include <random-bits.h>
74# define RANDOM_BITS(Var) ((Var) = random_bits ())
75# else
76# define RANDOM_BITS(Var) \
77 { \
78 struct timespec ts; \
79 clock_gettime (CLOCK_REALTIME, &ts); \
80 (Var) = ((uint64_t) tv.tv_nsec << 16) ^ tv.tv_sec; \
81 }
82#endif
83
84/* Use the widest available unsigned type if uint64_t is not
85 available. The algorithm below extracts a number less than 62**6
86 (approximately 2**35.725) from uint64_t, so ancient hosts where
87 uintmax_t is only 32 bits lose about 3.725 bits of randomness,
88 which is better than not having mkstemp at all. */
89#if !defined UINT64_MAX && !defined uint64_t
90# define uint64_t uintmax_t
91#endif
92
93#if _LIBC
94/* Return nonzero if DIR is an existent directory. */
95static int
96direxists (const char *dir)
97{
98 struct_stat64 buf;
99 return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
100}
101
102/* Path search algorithm, for tmpnam, tmpfile, etc. If DIR is
103 non-null and exists, uses it; otherwise uses the first of $TMPDIR,
104 P_tmpdir, /tmp that exists. Copies into TMPL a template suitable
105 for use with mk[s]temp. Will fail (-1) if DIR is non-null and
106 doesn't exist, none of the searched dirs exists, or there's not
107 enough space in TMPL. */
108int
109__path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
110 int try_tmpdir)
111{
112 const char *d;
113 size_t dlen, plen;
114
115 if (!pfx || !pfx[0])
116 {
117 pfx = "file";
118 plen = 4;
119 }
120 else
121 {
122 plen = strlen (pfx);
123 if (plen > 5)
124 plen = 5;
125 }
126
127 if (try_tmpdir)
128 {
129 d = __secure_getenv ("TMPDIR");
130 if (d != NULL && direxists (d))
131 dir = d;
132 else if (dir != NULL && direxists (dir))
133 /* nothing */ ;
134 else
135 dir = NULL;
136 }
137 if (dir == NULL)
138 {
139 if (direxists (P_tmpdir))
140 dir = P_tmpdir;
141 else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
142 dir = "/tmp";
143 else
144 {
145 __set_errno (ENOENT);
146 return -1;
147 }
148 }
149
150 dlen = strlen (dir);
151 while (dlen > 1 && dir[dlen - 1] == '/')
152 dlen--; /* remove trailing slashes */
153
154 /* check we have room for "${dir}/${pfx}XXXXXX\0" */
155 if (tmpl_len < dlen + 1 + plen + 6 + 1)
156 {
157 __set_errno (EINVAL);
158 return -1;
159 }
160
161 sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
162 return 0;
163}
164#endif /* _LIBC */
165
166/* These are the characters used in temporary file names. */
167static const char letters[] =
168"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
169
170/* Generate a temporary file name based on TMPL. TMPL must match the
171 rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix).
172 The name constructed does not exist at the time of the call to
173 __gen_tempname. TMPL is overwritten with the result.
174
175 KIND may be one of:
176 __GT_NOCREATE: simply verify that the name does not exist
177 at the time of the call.
178 __GT_FILE: create the file using open(O_CREAT|O_EXCL)
179 and return a read-write fd. The file is mode 0600.
180 __GT_DIR: create a directory, which will be mode 0700.
181
182 We use a clever algorithm to get hard-to-predict names. */
183int
184__gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
185{
186 int len;
187 char *XXXXXX;
188 unsigned int count;
189 int fd = -1;
190 int save_errno = errno;
191 struct_stat64 st;
192
193 /* A lower bound on the number of temporary files to attempt to
194 generate. The maximum total number of temporary file names that
195 can exist for a given template is 62**6. It should never be
196 necessary to try all of these combinations. Instead if a reasonable
197 number of names is tried (we define reasonable as 62**3) fail to
198 give the system administrator the chance to remove the problems. */
199#define ATTEMPTS_MIN (62 * 62 * 62)
200
201 /* The number of times to attempt to generate a temporary file. To
202 conform to POSIX, this must be no smaller than TMP_MAX. */
203#if ATTEMPTS_MIN < TMP_MAX
204 unsigned int attempts = TMP_MAX;
205#else
206 unsigned int attempts = ATTEMPTS_MIN;
207#endif
208
209 len = strlen (tmpl);
210 if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
211 {
212 __set_errno (EINVAL);
213 return -1;
214 }
215
216 /* This is where the Xs start. */
217 XXXXXX = &tmpl[len - 6 - suffixlen];
218
219 uint64_t pid = (uint64_t) __getpid () << 32;
220 for (count = 0; count < attempts; ++count)
221 {
222 uint64_t v;
223 /* Get some more or less random data. */
224 RANDOM_BITS (v);
225 v ^= pid;
226
227 /* Fill in the random bits. */
228 XXXXXX[0] = letters[v % 62];
229 v /= 62;
230 XXXXXX[1] = letters[v % 62];
231 v /= 62;
232 XXXXXX[2] = letters[v % 62];
233 v /= 62;
234 XXXXXX[3] = letters[v % 62];
235 v /= 62;
236 XXXXXX[4] = letters[v % 62];
237 v /= 62;
238 XXXXXX[5] = letters[v % 62];
239
240 switch (kind)
241 {
242 case __GT_FILE:
243 fd = __open (tmpl,
244 (flags & ~O_ACCMODE)
245 | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
246 break;
247
248 case __GT_DIR:
249 fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
250 break;
251
252 case __GT_NOCREATE:
253 /* This case is backward from the other three. __gen_tempname
254 succeeds if __xstat fails because the name does not exist.
255 Note the continue to bypass the common logic at the bottom
256 of the loop. */
257 if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
258 {
259 if (errno == ENOENT)
260 {
261 __set_errno (save_errno);
262 return 0;
263 }
264 else
265 /* Give up now. */
266 return -1;
267 }
268 continue;
269
270 default:
271 assert (! "invalid KIND in __gen_tempname");
272 abort ();
273 }
274
275 if (fd >= 0)
276 {
277 __set_errno (save_errno);
278 return fd;
279 }
280 else if (errno != EEXIST)
281 return -1;
282 }
283
284 /* We got out of the loop because we ran out of combinations to try. */
285 __set_errno (EEXIST);
286 return -1;
287}
288