1 /* Copyright (C) 1991-2022 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 <libc-config.h> 20 # include "tempname.h" 21 #endif 22 23 #include <sys/types.h> 24 #include <assert.h> 25 #include <stdbool.h> 26 27 #include <errno.h> 28 29 #include <stdio.h> 30 #ifndef P_tmpdir 31 # define P_tmpdir "/tmp" 32 #endif 33 #ifndef TMP_MAX 34 # define TMP_MAX 238328 35 #endif 36 #ifndef __GT_FILE 37 # define __GT_FILE 0 38 # define __GT_DIR 1 39 # define __GT_NOCREATE 2 40 #endif 41 #if !_LIBC && (GT_FILE != __GT_FILE || GT_DIR != __GT_DIR \ 42 || GT_NOCREATE != __GT_NOCREATE) 43 # error report this to bug-gnulib@gnu.org 44 #endif 45 46 #include <stddef.h> 47 #include <stdlib.h> 48 #include <string.h> 49 50 #include <fcntl.h> 51 #include <stdalign.h> 52 #include <stdint.h> 53 #include <sys/random.h> 54 #include <sys/stat.h> 55 #include <time.h> 56 57 #if _LIBC 58 # define struct_stat64 struct stat64 59 # define __secure_getenv __libc_secure_getenv 60 #else 61 # define struct_stat64 struct stat 62 # define __gen_tempname gen_tempname 63 # define __mkdir mkdir 64 # define __open open 65 # define __lstat64(file, buf) lstat (file, buf) 66 # define __stat64(file, buf) stat (file, buf) 67 # define __getrandom getrandom 68 # define __clock_gettime64 clock_gettime 69 # define __timespec64 timespec 70 #endif 71 72 /* Use getrandom if it works, falling back on a 64-bit linear 73 congruential generator that starts with Var's value 74 mixed in with a clock's low-order bits if available. */ 75 typedef uint_fast64_t random_value; 76 #define RANDOM_VALUE_MAX UINT_FAST64_MAX 77 #define BASE_62_DIGITS 10 /* 62**10 < UINT_FAST64_MAX */ 78 #define BASE_62_POWER (62LL * 62 * 62 * 62 * 62 * 62 * 62 * 62 * 62 * 62) 79 80 static random_value 81 random_bits (random_value var, bool use_getrandom) 82 { 83 random_value r; 84 /* Without GRND_NONBLOCK it can be blocked for minutes on some systems. */ 85 if (use_getrandom && __getrandom (&r, sizeof r, GRND_NONBLOCK) == sizeof r) 86 return r; 87 #if _LIBC || (defined CLOCK_MONOTONIC && HAVE_CLOCK_GETTIME) 88 /* Add entropy if getrandom did not work. */ 89 struct __timespec64 tv; 90 __clock_gettime64 (CLOCK_MONOTONIC, &tv); 91 var ^= tv.tv_nsec; 92 #endif 93 return 2862933555777941757 * var + 3037000493; 94 } 95 96 #if _LIBC 97 /* Return nonzero if DIR is an existent directory. */ 98 static int 99 direxists (const char *dir) 100 { 101 struct_stat64 buf; 102 return __stat64 (dir, &buf) == 0 && S_ISDIR (buf.st_mode); 103 } 104 105 /* Path search algorithm, for tmpnam, tmpfile, etc. If DIR is 106 non-null and exists, uses it; otherwise uses the first of $TMPDIR, 107 P_tmpdir, /tmp that exists. Copies into TMPL a template suitable 108 for use with mk[s]temp. Will fail (-1) if DIR is non-null and 109 doesn't exist, none of the searched dirs exists, or there's not 110 enough space in TMPL. */ 111 int 112 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx, 113 int try_tmpdir) 114 { 115 const char *d; 116 size_t dlen, plen; 117 118 if (!pfx || !pfx[0]) 119 { 120 pfx = "file"; 121 plen = 4; 122 } 123 else 124 { 125 plen = strlen (pfx); 126 if (plen > 5) 127 plen = 5; 128 } 129 130 if (try_tmpdir) 131 { 132 d = __secure_getenv ("TMPDIR"); 133 if (d != NULL && direxists (d)) 134 dir = d; 135 else if (dir != NULL && direxists (dir)) 136 /* nothing */ ; 137 else 138 dir = NULL; 139 } 140 if (dir == NULL) 141 { 142 if (direxists (P_tmpdir)) 143 dir = P_tmpdir; 144 else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp")) 145 dir = "/tmp"; 146 else 147 { 148 __set_errno (ENOENT); 149 return -1; 150 } 151 } 152 153 dlen = strlen (dir); 154 while (dlen > 1 && dir[dlen - 1] == '/') 155 dlen--; /* remove trailing slashes */ 156 157 /* check we have room for "${dir}/${pfx}XXXXXX\0" */ 158 if (tmpl_len < dlen + 1 + plen + 6 + 1) 159 { 160 __set_errno (EINVAL); 161 return -1; 162 } 163 164 sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx); 165 return 0; 166 } 167 #endif /* _LIBC */ 168 169 #if _LIBC 170 static int try_tempname_len (char *, int, void *, int (*) (char *, void *), 171 size_t); 172 #endif 173 174 static int 175 try_file (char *tmpl, void *flags) 176 { 177 int *openflags = flags; 178 return __open (tmpl, 179 (*openflags & ~O_ACCMODE) 180 | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR); 181 } 182 183 static int 184 try_dir (char *tmpl, _GL_UNUSED void *flags) 185 { 186 return __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR); 187 } 188 189 static int 190 try_nocreate (char *tmpl, _GL_UNUSED void *flags) 191 { 192 struct_stat64 st; 193 194 if (__lstat64 (tmpl, &st) == 0 || errno == EOVERFLOW) 195 __set_errno (EEXIST); 196 return errno == ENOENT ? 0 : -1; 197 } 198 199 /* These are the characters used in temporary file names. */ 200 static const char letters[] = 201 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; 202 203 /* Generate a temporary file name based on TMPL. TMPL must match the 204 rules for mk[s]temp (i.e., end in at least X_SUFFIX_LEN "X"s, 205 possibly with a suffix). 206 The name constructed does not exist at the time of the call to 207 this function. TMPL is overwritten with the result. 208 209 KIND may be one of: 210 __GT_NOCREATE: simply verify that the name does not exist 211 at the time of the call. 212 __GT_FILE: create the file using open(O_CREAT|O_EXCL) 213 and return a read-write fd. The file is mode 0600. 214 __GT_DIR: create a directory, which will be mode 0700. 215 216 We use a clever algorithm to get hard-to-predict names. */ 217 #ifdef _LIBC 218 static 219 #endif 220 int 221 gen_tempname_len (char *tmpl, int suffixlen, int flags, int kind, 222 size_t x_suffix_len) 223 { 224 static int (*const tryfunc[]) (char *, void *) = 225 { 226 [__GT_FILE] = try_file, 227 [__GT_DIR] = try_dir, 228 [__GT_NOCREATE] = try_nocreate 229 }; 230 return try_tempname_len (tmpl, suffixlen, &flags, tryfunc[kind], 231 x_suffix_len); 232 } 233 234 #ifdef _LIBC 235 static 236 #endif 237 int 238 try_tempname_len (char *tmpl, int suffixlen, void *args, 239 int (*tryfunc) (char *, void *), size_t x_suffix_len) 240 { 241 size_t len; 242 char *XXXXXX; 243 unsigned int count; 244 int fd = -1; 245 int save_errno = errno; 246 247 /* A lower bound on the number of temporary files to attempt to 248 generate. The maximum total number of temporary file names that 249 can exist for a given template is 62**6. It should never be 250 necessary to try all of these combinations. Instead if a reasonable 251 number of names is tried (we define reasonable as 62**3) fail to 252 give the system administrator the chance to remove the problems. 253 This value requires that X_SUFFIX_LEN be at least 3. */ 254 #define ATTEMPTS_MIN (62 * 62 * 62) 255 256 /* The number of times to attempt to generate a temporary file. To 257 conform to POSIX, this must be no smaller than TMP_MAX. */ 258 #if ATTEMPTS_MIN < TMP_MAX 259 unsigned int attempts = TMP_MAX; 260 #else 261 unsigned int attempts = ATTEMPTS_MIN; 262 #endif 263 264 /* A random variable. The initial value is used only the for fallback path 265 on 'random_bits' on 'getrandom' failure. Its initial value tries to use 266 some entropy from the ASLR and ignore possible bits from the stack 267 alignment. */ 268 random_value v = ((uintptr_t) &v) / alignof (max_align_t); 269 270 /* How many random base-62 digits can currently be extracted from V. */ 271 int vdigits = 0; 272 273 /* Whether to consume entropy when acquiring random bits. On the 274 first try it's worth the entropy cost with __GT_NOCREATE, which 275 is inherently insecure and can use the entropy to make it a bit 276 less secure. On the (rare) second and later attempts it might 277 help against DoS attacks. */ 278 bool use_getrandom = tryfunc == try_nocreate; 279 280 /* Least unfair value for V. If V is less than this, V can generate 281 BASE_62_DIGITS digits fairly. Otherwise it might be biased. */ 282 random_value const unfair_min 283 = RANDOM_VALUE_MAX - RANDOM_VALUE_MAX % BASE_62_POWER; 284 285 len = strlen (tmpl); 286 if (len < x_suffix_len + suffixlen 287 || strspn (&tmpl[len - x_suffix_len - suffixlen], "X") < x_suffix_len) 288 { 289 __set_errno (EINVAL); 290 return -1; 291 } 292 293 /* This is where the Xs start. */ 294 XXXXXX = &tmpl[len - x_suffix_len - suffixlen]; 295 296 for (count = 0; count < attempts; ++count) 297 { 298 for (size_t i = 0; i < x_suffix_len; i++) 299 { 300 if (vdigits == 0) 301 { 302 do 303 { 304 v = random_bits (v, use_getrandom); 305 use_getrandom = true; 306 } 307 while (unfair_min <= v); 308 309 vdigits = BASE_62_DIGITS; 310 } 311 312 XXXXXX[i] = letters[v % 62]; 313 v /= 62; 314 vdigits--; 315 } 316 317 fd = tryfunc (tmpl, args); 318 if (fd >= 0) 319 { 320 __set_errno (save_errno); 321 return fd; 322 } 323 else if (errno != EEXIST) 324 return -1; 325 } 326 327 /* We got out of the loop because we ran out of combinations to try. */ 328 __set_errno (EEXIST); 329 return -1; 330 } 331 332 int 333 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind) 334 { 335 return gen_tempname_len (tmpl, suffixlen, flags, kind, 6); 336 } 337 338 #if !_LIBC 339 int 340 try_tempname (char *tmpl, int suffixlen, void *args, 341 int (*tryfunc) (char *, void *)) 342 { 343 return try_tempname_len (tmpl, suffixlen, args, tryfunc, 6); 344 } 345 #endif 346