1 /* tempname.c - generate the name of a temporary file. 2 3 Copyright (C) 1991-2003, 2005-2007, 2009-2018 Free Software Foundation, Inc. 4 5 This program is free software: you can redistribute it and/or modify 6 it under the terms of the GNU General Public License as published by 7 the Free Software Foundation; either version 3 of the License, or 8 (at your option) any later version. 9 10 This program is distributed in the hope that it will be useful, 11 but WITHOUT ANY WARRANTY; without even the implied warranty of 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13 GNU General Public License for more details. 14 15 You should have received a copy of the GNU General Public License 16 along with this program. If not, see <https://www.gnu.org/licenses/>. */ 17 18 /* Extracted from glibc sysdeps/posix/tempname.c. See also tmpdir.c. */ 19 20 #if !_LIBC 21 # include <config.h> 22 # include "tempname.h" 23 #endif 24 25 #include <sys/types.h> 26 #include <assert.h> 27 28 #include <errno.h> 29 #ifndef __set_errno 30 # define __set_errno(Val) errno = (Val) 31 #endif 32 33 #include <stdio.h> 34 #ifndef P_tmpdir 35 # define P_tmpdir "/tmp" 36 #endif 37 #ifndef TMP_MAX 38 # define TMP_MAX 238328 39 #endif 40 #ifndef __GT_FILE 41 # define __GT_FILE 0 42 # define __GT_DIR 1 43 # define __GT_NOCREATE 2 44 #endif 45 #if !_LIBC && (GT_FILE != __GT_FILE || GT_DIR != __GT_DIR \ 46 || GT_NOCREATE != __GT_NOCREATE) 47 # error report this to bug-gnulib@gnu.org 48 #endif 49 50 #include <stddef.h> 51 #include <stdlib.h> 52 #include <string.h> 53 54 #include <fcntl.h> 55 #include <sys/time.h> 56 #include <stdint.h> 57 #include <unistd.h> 58 59 #include <sys/stat.h> 60 61 #if _LIBC 62 # define struct_stat64 struct stat64 63 #else 64 # define struct_stat64 struct stat 65 # define __try_tempname try_tempname 66 # define __gen_tempname gen_tempname 67 # define __getpid getpid 68 # define __gettimeofday gettimeofday 69 # define __mkdir mkdir 70 # define __open open 71 # define __lxstat64(version, file, buf) lstat (file, buf) 72 #endif 73 74 #ifdef _LIBC 75 # include <hp-timing.h> 76 # if HP_TIMING_AVAIL 77 # define RANDOM_BITS(Var) \ 78 if (__builtin_expect (value == UINT64_C (0), 0)) \ 79 { \ 80 /* If this is the first time this function is used initialize \ 81 the variable we accumulate the value in to some somewhat \ 82 random value. If we'd not do this programs at startup time \ 83 might have a reduced set of possible names, at least on slow \ 84 machines. */ \ 85 struct timeval tv; \ 86 __gettimeofday (&tv, NULL); \ 87 value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec; \ 88 } \ 89 HP_TIMING_NOW (Var) 90 # endif 91 #endif 92 93 /* Use the widest available unsigned type if uint64_t is not 94 available. The algorithm below extracts a number less than 62**6 95 (approximately 2**35.725) from uint64_t, so ancient hosts where 96 uintmax_t is only 32 bits lose about 3.725 bits of randomness, 97 which is better than not having mkstemp at all. */ 98 #if !defined UINT64_MAX && !defined uint64_t 99 # define uint64_t uintmax_t 100 #endif 101 102 #if _LIBC 103 /* Return nonzero if DIR is an existent directory. */ 104 static int 105 direxists (const char *dir) 106 { 107 struct_stat64 buf; 108 return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode); 109 } 110 111 /* Path search algorithm, for tmpnam, tmpfile, etc. If DIR is 112 non-null and exists, uses it; otherwise uses the first of $TMPDIR, 113 P_tmpdir, /tmp that exists. Copies into TMPL a template suitable 114 for use with mk[s]temp. Will fail (-1) if DIR is non-null and 115 doesn't exist, none of the searched dirs exists, or there's not 116 enough space in TMPL. */ 117 int 118 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx, 119 int try_tmpdir) 120 { 121 const char *d; 122 size_t dlen, plen; 123 124 if (!pfx || !pfx[0]) 125 { 126 pfx = "file"; 127 plen = 4; 128 } 129 else 130 { 131 plen = strlen (pfx); 132 if (plen > 5) 133 plen = 5; 134 } 135 136 if (try_tmpdir) 137 { 138 d = __secure_getenv ("TMPDIR"); 139 if (d != NULL && direxists (d)) 140 dir = d; 141 else if (dir != NULL && direxists (dir)) 142 /* nothing */ ; 143 else 144 dir = NULL; 145 } 146 if (dir == NULL) 147 { 148 if (direxists (P_tmpdir)) 149 dir = P_tmpdir; 150 else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp")) 151 dir = "/tmp"; 152 else 153 { 154 __set_errno (ENOENT); 155 return -1; 156 } 157 } 158 159 dlen = strlen (dir); 160 while (dlen > 1 && dir[dlen - 1] == '/') 161 dlen--; /* remove trailing slashes */ 162 163 /* check we have room for "${dir}/${pfx}XXXXXX\0" */ 164 if (tmpl_len < dlen + 1 + plen + 6 + 1) 165 { 166 __set_errno (EINVAL); 167 return -1; 168 } 169 170 sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx); 171 return 0; 172 } 173 #endif /* _LIBC */ 174 175 /* These are the characters used in temporary file names. */ 176 static const char letters[] = 177 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; 178 179 int 180 __try_tempname (char *tmpl, int suffixlen, void *args, 181 int (*tryfunc) (char *, void *)) 182 { 183 int len; 184 char *XXXXXX; 185 static uint64_t value; 186 uint64_t random_time_bits; 187 unsigned int count; 188 int fd = -1; 189 int save_errno = errno; 190 191 /* A lower bound on the number of temporary files to attempt to 192 generate. The maximum total number of temporary file names that 193 can exist for a given template is 62**6. It should never be 194 necessary to try all of these combinations. Instead if a reasonable 195 number of names is tried (we define reasonable as 62**3) fail to 196 give the system administrator the chance to remove the problems. */ 197 #define ATTEMPTS_MIN (62 * 62 * 62) 198 199 /* The number of times to attempt to generate a temporary file. To 200 conform to POSIX, this must be no smaller than TMP_MAX. */ 201 #if ATTEMPTS_MIN < TMP_MAX 202 unsigned int attempts = TMP_MAX; 203 #else 204 unsigned int attempts = ATTEMPTS_MIN; 205 #endif 206 207 len = strlen (tmpl); 208 if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6)) 209 { 210 __set_errno (EINVAL); 211 return -1; 212 } 213 214 /* This is where the Xs start. */ 215 XXXXXX = &tmpl[len - 6 - suffixlen]; 216 217 /* Get some more or less random data. */ 218 #ifdef RANDOM_BITS 219 RANDOM_BITS (random_time_bits); 220 #else 221 { 222 struct timeval tv; 223 __gettimeofday (&tv, NULL); 224 random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec; 225 } 226 #endif 227 value += random_time_bits ^ __getpid (); 228 229 for (count = 0; count < attempts; value += 7777, ++count) 230 { 231 uint64_t v = value; 232 233 /* Fill in the random bits. */ 234 XXXXXX[0] = letters[v % 62]; 235 v /= 62; 236 XXXXXX[1] = letters[v % 62]; 237 v /= 62; 238 XXXXXX[2] = letters[v % 62]; 239 v /= 62; 240 XXXXXX[3] = letters[v % 62]; 241 v /= 62; 242 XXXXXX[4] = letters[v % 62]; 243 v /= 62; 244 XXXXXX[5] = letters[v % 62]; 245 246 fd = tryfunc (tmpl, args); 247 if (fd >= 0) 248 { 249 __set_errno (save_errno); 250 return fd; 251 } 252 else if (errno != EEXIST) 253 return -1; 254 } 255 256 /* We got out of the loop because we ran out of combinations to try. */ 257 __set_errno (EEXIST); 258 return -1; 259 } 260 261 static int 262 try_file (char *tmpl, void *flags) 263 { 264 int *openflags = flags; 265 return __open (tmpl, 266 (*openflags & ~O_ACCMODE) 267 | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR); 268 } 269 270 static int 271 try_dir (char *tmpl, void *flags _GL_UNUSED) 272 { 273 return __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR); 274 } 275 276 static int 277 try_nocreate (char *tmpl, void *flags _GL_UNUSED) 278 { 279 struct_stat64 st; 280 281 if (__lxstat64 (_STAT_VER, tmpl, &st) == 0 || errno == EOVERFLOW) 282 __set_errno (EEXIST); 283 return errno == ENOENT ? 0 : -1; 284 } 285 286 /* Generate a temporary file name based on TMPL. TMPL must match the 287 rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix). 288 The name constructed does not exist at the time of the call to 289 __gen_tempname. TMPL is overwritten with the result. 290 291 KIND may be one of: 292 __GT_NOCREATE: simply verify that the name does not exist 293 at the time of the call. 294 __GT_FILE: create the file using open(O_CREAT|O_EXCL) 295 and return a read-write fd. The file is mode 0600. 296 __GT_DIR: create a directory, which will be mode 0700. 297 298 We use a clever algorithm to get hard-to-predict names. */ 299 int 300 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind) 301 { 302 int (*tryfunc) (char *, void *); 303 304 switch (kind) 305 { 306 case __GT_FILE: 307 tryfunc = try_file; 308 break; 309 310 case __GT_DIR: 311 tryfunc = try_dir; 312 break; 313 314 case __GT_NOCREATE: 315 tryfunc = try_nocreate; 316 break; 317 318 default: 319 assert (! "invalid KIND in __gen_tempname"); 320 abort (); 321 } 322 return __try_tempname (tmpl, suffixlen, &flags, tryfunc); 323 } 324