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 General Public
6 License as published by the Free Software Foundation; either
7 version 3 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 General Public License for more details.
13
14 You should have received a copy of the GNU 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
26 #include <errno.h>
27
28 #include <stdio.h>
29 #ifndef P_tmpdir
30 # define P_tmpdir "/tmp"
31 #endif
32 #ifndef TMP_MAX
33 # define TMP_MAX 238328
34 #endif
35 #ifndef __GT_FILE
36 # define __GT_FILE 0
37 # define __GT_DIR 1
38 # define __GT_NOCREATE 2
39 #endif
40 #if !_LIBC && (GT_FILE != __GT_FILE || GT_DIR != __GT_DIR \
41 || GT_NOCREATE != __GT_NOCREATE)
42 # error report this to bug-gnulib@gnu.org
43 #endif
44
45 #include <stddef.h>
46 #include <stdlib.h>
47 #include <string.h>
48
49 #include <fcntl.h>
50 #include <stdalign.h>
51 #include <stdint.h>
52 #include <sys/random.h>
53 #include <sys/stat.h>
54 #include <time.h>
55
56 #if _LIBC
57 # define struct_stat64 struct stat64
58 # define __secure_getenv __libc_secure_getenv
59 #else
60 # define struct_stat64 struct stat
61 # define __gen_tempname gen_tempname
62 # define __mkdir mkdir
63 # define __open open
64 # define __lxstat64(version, file, buf) lstat (file, buf)
65 # define __getrandom getrandom
66 # define __clock_gettime64 clock_gettime
67 # define __timespec64 timespec
68 #endif
69
70 /* Use getrandom if it works, falling back on a 64-bit linear
71 congruential generator that starts with Var's value
72 mixed in with a clock's low-order bits if available. */
73 typedef uint_fast64_t random_value;
74 #define RANDOM_VALUE_MAX UINT_FAST64_MAX
75 #define BASE_62_DIGITS 10 /* 62**10 < UINT_FAST64_MAX */
76 #define BASE_62_POWER (62LL * 62 * 62 * 62 * 62 * 62 * 62 * 62 * 62 * 62)
77
78 static random_value
random_bits(random_value var)79 random_bits (random_value var)
80 {
81 random_value r;
82 if (__getrandom (&r, sizeof r, 0) == sizeof r)
83 return r;
84 #if _LIBC || (defined CLOCK_MONOTONIC && HAVE_CLOCK_GETTIME)
85 /* Add entropy if getrandom is not supported. */
86 struct __timespec64 tv;
87 __clock_gettime64 (CLOCK_MONOTONIC, &tv);
88 var ^= tv.tv_nsec;
89 #endif
90 return 2862933555777941757 * var + 3037000493;
91 }
92
93 #if _LIBC
94 /* Return nonzero if DIR is an existent directory. */
95 static int
direxists(const char * dir)96 direxists (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 $TMPDIR,
104 P_tmpdir, /tmp that exists. Copies into TMPL a template suitable
105 for use with mk[s]temp. Will fail (-1) if DIR is non-null and
106 doesn't exist, none of the searched dirs exists, or there's not
107 enough space in TMPL. */
108 int
__path_search(char * tmpl,size_t tmpl_len,const char * dir,const char * pfx,int try_tmpdir)109 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
110 int try_tmpdir)
111 {
112 const char *d;
113 size_t dlen, plen;
114
115 if (!pfx || !pfx[0])
116 {
117 pfx = "file";
118 plen = 4;
119 }
120 else
121 {
122 plen = strlen (pfx);
123 if (plen > 5)
124 plen = 5;
125 }
126
127 if (try_tmpdir)
128 {
129 d = __secure_getenv ("TMPDIR");
130 if (d != NULL && direxists (d))
131 dir = d;
132 else if (dir != NULL && direxists (dir))
133 /* nothing */ ;
134 else
135 dir = NULL;
136 }
137 if (dir == NULL)
138 {
139 if (direxists (P_tmpdir))
140 dir = P_tmpdir;
141 else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
142 dir = "/tmp";
143 else
144 {
145 __set_errno (ENOENT);
146 return -1;
147 }
148 }
149
150 dlen = strlen (dir);
151 while (dlen > 1 && dir[dlen - 1] == '/')
152 dlen--; /* remove trailing slashes */
153
154 /* check we have room for "${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 #if _LIBC
167 static int try_tempname_len (char *, int, void *, int (*) (char *, void *),
168 size_t);
169 #endif
170
171 static int
try_file(char * tmpl,void * flags)172 try_file (char *tmpl, void *flags)
173 {
174 int *openflags = flags;
175 return __open (tmpl,
176 (*openflags & ~O_ACCMODE)
177 | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
178 }
179
180 static int
try_dir(char * tmpl,void * flags _GL_UNUSED)181 try_dir (char *tmpl, void *flags _GL_UNUSED)
182 {
183 return __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
184 }
185
186 static int
try_nocreate(char * tmpl,void * flags _GL_UNUSED)187 try_nocreate (char *tmpl, void *flags _GL_UNUSED)
188 {
189 struct_stat64 st;
190
191 if (__lxstat64 (_STAT_VER, tmpl, &st) == 0 || errno == EOVERFLOW)
192 __set_errno (EEXIST);
193 return errno == ENOENT ? 0 : -1;
194 }
195
196 /* These are the characters used in temporary file names. */
197 static const char letters[] =
198 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
199
200 /* Generate a temporary file name based on TMPL. TMPL must match the
201 rules for mk[s]temp (i.e., end in at least X_SUFFIX_LEN "X"s,
202 possibly with a suffix).
203 The name constructed does not exist at the time of the call to
204 this function. TMPL is overwritten with the result.
205
206 KIND may be one of:
207 __GT_NOCREATE: simply verify that the name does not exist
208 at the time of the call.
209 __GT_FILE: create the file using open(O_CREAT|O_EXCL)
210 and return a read-write fd. The file is mode 0600.
211 __GT_DIR: create a directory, which will be mode 0700.
212
213 We use a clever algorithm to get hard-to-predict names. */
214 #ifdef _LIBC
215 static
216 #endif
217 int
gen_tempname_len(char * tmpl,int suffixlen,int flags,int kind,size_t x_suffix_len)218 gen_tempname_len (char *tmpl, int suffixlen, int flags, int kind,
219 size_t x_suffix_len)
220 {
221 static int (*const tryfunc[]) (char *, void *) =
222 {
223 [__GT_FILE] = try_file,
224 [__GT_DIR] = try_dir,
225 [__GT_NOCREATE] = try_nocreate
226 };
227 return try_tempname_len (tmpl, suffixlen, &flags, tryfunc[kind],
228 x_suffix_len);
229 }
230
231 #ifdef _LIBC
232 static
233 #endif
234 int
try_tempname_len(char * tmpl,int suffixlen,void * args,int (* tryfunc)(char *,void *),size_t x_suffix_len)235 try_tempname_len (char *tmpl, int suffixlen, void *args,
236 int (*tryfunc) (char *, void *), size_t x_suffix_len)
237 {
238 size_t len;
239 char *XXXXXX;
240 unsigned int count;
241 int fd = -1;
242 int save_errno = errno;
243
244 /* A lower bound on the number of temporary files to attempt to
245 generate. The maximum total number of temporary file names that
246 can exist for a given template is 62**6. It should never be
247 necessary to try all of these combinations. Instead if a reasonable
248 number of names is tried (we define reasonable as 62**3) fail to
249 give the system administrator the chance to remove the problems.
250 This value requires that X_SUFFIX_LEN be at least 3. */
251 #define ATTEMPTS_MIN (62 * 62 * 62)
252
253 /* The number of times to attempt to generate a temporary file. To
254 conform to POSIX, this must be no smaller than TMP_MAX. */
255 #if ATTEMPTS_MIN < TMP_MAX
256 unsigned int attempts = TMP_MAX;
257 #else
258 unsigned int attempts = ATTEMPTS_MIN;
259 #endif
260
261 /* A random variable. The initial value is used only the for fallback path
262 on 'random_bits' on 'getrandom' failure. Its initial value tries to use
263 some entropy from the ASLR and ignore possible bits from the stack
264 alignment. */
265 random_value v = ((uintptr_t) &v) / alignof (max_align_t);
266
267 /* How many random base-62 digits can currently be extracted from V. */
268 int vdigits = 0;
269
270 /* Least unfair value for V. If V is less than this, V can generate
271 BASE_62_DIGITS digits fairly. Otherwise it might be biased. */
272 random_value const unfair_min
273 = RANDOM_VALUE_MAX - RANDOM_VALUE_MAX % BASE_62_POWER;
274
275 len = strlen (tmpl);
276 if (len < x_suffix_len + suffixlen
277 || strspn (&tmpl[len - x_suffix_len - suffixlen], "X") < x_suffix_len)
278 {
279 __set_errno (EINVAL);
280 return -1;
281 }
282
283 /* This is where the Xs start. */
284 XXXXXX = &tmpl[len - x_suffix_len - suffixlen];
285
286 for (count = 0; count < attempts; ++count)
287 {
288 for (size_t i = 0; i < x_suffix_len; i++)
289 {
290 if (vdigits == 0)
291 {
292 do
293 v = random_bits (v);
294 while (unfair_min <= v);
295
296 vdigits = BASE_62_DIGITS;
297 }
298
299 XXXXXX[i] = letters[v % 62];
300 v /= 62;
301 vdigits--;
302 }
303
304 fd = tryfunc (tmpl, args);
305 if (fd >= 0)
306 {
307 __set_errno (save_errno);
308 return fd;
309 }
310 else if (errno != EEXIST)
311 return -1;
312 }
313
314 /* We got out of the loop because we ran out of combinations to try. */
315 __set_errno (EEXIST);
316 return -1;
317 }
318
319 int
__gen_tempname(char * tmpl,int suffixlen,int flags,int kind)320 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
321 {
322 return gen_tempname_len (tmpl, suffixlen, flags, kind, 6);
323 }
324
325 #if !_LIBC
326 int
try_tempname(char * tmpl,int suffixlen,void * args,int (* tryfunc)(char *,void *))327 try_tempname (char *tmpl, int suffixlen, void *args,
328 int (*tryfunc) (char *, void *))
329 {
330 return try_tempname_len (tmpl, suffixlen, args, tryfunc, 6);
331 }
332 #endif
333