1 /* $OpenBSD: getentropy_linux.c,v 1.20 2014/07/12 15:43:49 beck Exp $ */ 2 3 /* 4 * Copyright (c) 2014 Theo de Raadt <deraadt@openbsd.org> 5 * Copyright (c) 2014 Bob Beck <beck@obtuse.com> 6 * 7 * Permission to use, copy, modify, and distribute this software for any 8 * purpose with or without fee is hereby granted, provided that the above 9 * copyright notice and this permission notice appear in all copies. 10 * 11 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 12 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 13 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 14 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 15 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 16 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 17 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 18 */ 19 #include "config.h" 20 21 /* 22 #define _POSIX_C_SOURCE 199309L 23 #define _GNU_SOURCE 1 24 */ 25 #include <sys/types.h> 26 #include <sys/param.h> 27 #include <sys/ioctl.h> 28 #include <sys/resource.h> 29 #include <sys/syscall.h> 30 #ifdef HAVE_SYS_SYSCTL_H 31 #include <sys/sysctl.h> 32 #endif 33 #include <sys/statvfs.h> 34 #include <sys/socket.h> 35 #include <sys/mount.h> 36 #include <sys/mman.h> 37 #include <sys/stat.h> 38 #include <sys/time.h> 39 #include <stdlib.h> 40 #include <stdint.h> 41 #include <stdio.h> 42 #include <termios.h> 43 #include <fcntl.h> 44 #include <signal.h> 45 #include <string.h> 46 #include <errno.h> 47 #include <unistd.h> 48 #include <time.h> 49 #include <openssl/sha.h> 50 51 #include <linux/types.h> 52 #include <linux/random.h> 53 #include <linux/sysctl.h> 54 #ifdef HAVE_GETAUXVAL 55 #include <sys/auxv.h> 56 #endif 57 #include <sys/vfs.h> 58 59 #define REPEAT 5 60 #define min(a, b) (((a) < (b)) ? (a) : (b)) 61 62 #define HX(a, b) \ 63 do { \ 64 if ((a)) \ 65 HD(errno); \ 66 else \ 67 HD(b); \ 68 } while (0) 69 70 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l))) 71 #define HD(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (x))) 72 #define HF(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (void*))) 73 74 int getentropy(void *buf, size_t len); 75 76 #ifdef CAN_REFERENCE_MAIN 77 extern int main(int, char *argv[]); 78 #endif 79 static int gotdata(char *buf, size_t len); 80 static int getentropy_urandom(void *buf, size_t len); 81 #ifdef SYS__sysctl 82 static int getentropy_sysctl(void *buf, size_t len); 83 #endif 84 static int getentropy_fallback(void *buf, size_t len); 85 86 int 87 getentropy(void *buf, size_t len) 88 { 89 int ret = -1; 90 91 if (len > 256) { 92 errno = EIO; 93 return -1; 94 } 95 96 #ifdef SYS_getrandom 97 /* try to use getrandom syscall introduced with kernel 3.17 */ 98 ret = syscall(SYS_getrandom, buf, len, 0); 99 if (ret != -1) 100 return (ret); 101 #endif /* SYS_getrandom */ 102 103 /* 104 * Try to get entropy with /dev/urandom 105 * 106 * This can fail if the process is inside a chroot or if file 107 * descriptors are exhausted. 108 */ 109 ret = getentropy_urandom(buf, len); 110 if (ret != -1) 111 return (ret); 112 113 #ifdef SYS__sysctl 114 /* 115 * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID. 116 * sysctl is a failsafe API, so it guarantees a result. This 117 * should work inside a chroot, or when file descriptors are 118 * exhuasted. 119 * 120 * However this can fail if the Linux kernel removes support 121 * for sysctl. Starting in 2007, there have been efforts to 122 * deprecate the sysctl API/ABI, and push callers towards use 123 * of the chroot-unavailable fd-using /proc mechanism -- 124 * essentially the same problems as /dev/urandom. 125 * 126 * Numerous setbacks have been encountered in their deprecation 127 * schedule, so as of June 2014 the kernel ABI still exists on 128 * most Linux architectures. The sysctl() stub in libc is missing 129 * on some systems. There are also reports that some kernels 130 * spew messages to the console. 131 */ 132 ret = getentropy_sysctl(buf, len); 133 if (ret != -1) 134 return (ret); 135 #endif /* SYS__sysctl */ 136 137 /* 138 * Entropy collection via /dev/urandom and sysctl have failed. 139 * 140 * No other API exists for collecting entropy. See the large 141 * comment block above. 142 * 143 * We have very few options: 144 * - Even syslog_r is unsafe to call at this low level, so 145 * there is no way to alert the user or program. 146 * - Cannot call abort() because some systems have unsafe 147 * corefiles. 148 * - Could raise(SIGKILL) resulting in silent program termination. 149 * - Return EIO, to hint that arc4random's stir function 150 * should raise(SIGKILL) 151 * - Do the best under the circumstances.... 152 * 153 * This code path exists to bring light to the issue that Linux 154 * does not provide a failsafe API for entropy collection. 155 * 156 * We hope this demonstrates that Linux should either retain their 157 * sysctl ABI, or consider providing a new failsafe API which 158 * works in a chroot or when file descriptors are exhausted. 159 */ 160 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK 161 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK 162 raise(SIGKILL); 163 #endif 164 ret = getentropy_fallback(buf, len); 165 if (ret != -1) 166 return (ret); 167 168 errno = EIO; 169 return (ret); 170 } 171 172 /* 173 * Basic sanity checking; wish we could do better. 174 */ 175 static int 176 gotdata(char *buf, size_t len) 177 { 178 char any_set = 0; 179 size_t i; 180 181 for (i = 0; i < len; ++i) 182 any_set |= buf[i]; 183 if (any_set == 0) 184 return -1; 185 return 0; 186 } 187 188 static int 189 getentropy_urandom(void *buf, size_t len) 190 { 191 struct stat st; 192 size_t i; 193 int fd, cnt, flags; 194 int save_errno = errno; 195 196 start: 197 198 flags = O_RDONLY; 199 #ifdef O_NOFOLLOW 200 flags |= O_NOFOLLOW; 201 #endif 202 #ifdef O_CLOEXEC 203 flags |= O_CLOEXEC; 204 #endif 205 fd = open("/dev/urandom", flags, 0); 206 if (fd == -1) { 207 if (errno == EINTR) 208 goto start; 209 goto nodevrandom; 210 } 211 #ifndef O_CLOEXEC 212 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC); 213 #endif 214 215 /* Lightly verify that the device node looks sane */ 216 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) { 217 close(fd); 218 goto nodevrandom; 219 } 220 if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) { 221 close(fd); 222 goto nodevrandom; 223 } 224 for (i = 0; i < len; ) { 225 size_t wanted = len - i; 226 ssize_t ret = read(fd, (char*)buf + i, wanted); 227 228 if (ret == -1) { 229 if (errno == EAGAIN || errno == EINTR) 230 continue; 231 close(fd); 232 goto nodevrandom; 233 } 234 i += ret; 235 } 236 close(fd); 237 if (gotdata(buf, len) == 0) { 238 errno = save_errno; 239 return 0; /* satisfied */ 240 } 241 nodevrandom: 242 errno = EIO; 243 return -1; 244 } 245 246 #ifdef SYS__sysctl 247 static int 248 getentropy_sysctl(void *buf, size_t len) 249 { 250 static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID }; 251 size_t i; 252 int save_errno = errno; 253 254 for (i = 0; i < len; ) { 255 size_t chunk = min(len - i, 16); 256 257 /* SYS__sysctl because some systems already removed sysctl() */ 258 struct __sysctl_args args = { 259 .name = mib, 260 .nlen = 3, 261 .oldval = buf + i, 262 .oldlenp = &chunk, 263 }; 264 if (syscall(SYS__sysctl, &args) != 0) 265 goto sysctlfailed; 266 i += chunk; 267 } 268 if (gotdata(buf, len) == 0) { 269 errno = save_errno; 270 return (0); /* satisfied */ 271 } 272 sysctlfailed: 273 errno = EIO; 274 return -1; 275 } 276 #endif /* SYS__sysctl */ 277 278 static int cl[] = { 279 CLOCK_REALTIME, 280 #ifdef CLOCK_MONOTONIC 281 CLOCK_MONOTONIC, 282 #endif 283 #ifdef CLOCK_MONOTONIC_RAW 284 CLOCK_MONOTONIC_RAW, 285 #endif 286 #ifdef CLOCK_TAI 287 CLOCK_TAI, 288 #endif 289 #ifdef CLOCK_VIRTUAL 290 CLOCK_VIRTUAL, 291 #endif 292 #ifdef CLOCK_UPTIME 293 CLOCK_UPTIME, 294 #endif 295 #ifdef CLOCK_PROCESS_CPUTIME_ID 296 CLOCK_PROCESS_CPUTIME_ID, 297 #endif 298 #ifdef CLOCK_THREAD_CPUTIME_ID 299 CLOCK_THREAD_CPUTIME_ID, 300 #endif 301 }; 302 303 static int 304 getentropy_fallback(void *buf, size_t len) 305 { 306 uint8_t results[SHA512_DIGEST_LENGTH]; 307 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat; 308 static int cnt; 309 struct timespec ts; 310 struct timeval tv; 311 struct rusage ru; 312 sigset_t sigset; 313 struct stat st; 314 SHA512_CTX ctx; 315 static pid_t lastpid; 316 pid_t pid; 317 size_t i, ii, m; 318 char *p; 319 320 pid = getpid(); 321 if (lastpid == pid) { 322 faster = 1; 323 repeat = 2; 324 } else { 325 faster = 0; 326 lastpid = pid; 327 repeat = REPEAT; 328 } 329 for (i = 0; i < len; ) { 330 int j; 331 SHA512_Init(&ctx); 332 for (j = 0; j < repeat; j++) { 333 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 334 if (e != -1) { 335 cnt += (int)tv.tv_sec; 336 cnt += (int)tv.tv_usec; 337 } 338 339 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++) 340 HX(clock_gettime(cl[ii], &ts) == -1, ts); 341 342 HX((pid = getpid()) == -1, pid); 343 HX((pid = getsid(pid)) == -1, pid); 344 HX((pid = getppid()) == -1, pid); 345 HX((pid = getpgid(0)) == -1, pid); 346 HX((e = getpriority(0, 0)) == -1, e); 347 348 if (!faster) { 349 ts.tv_sec = 0; 350 ts.tv_nsec = 1; 351 (void) nanosleep(&ts, NULL); 352 } 353 354 HX(sigpending(&sigset) == -1, sigset); 355 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1, 356 sigset); 357 358 #ifdef CAN_REFERENCE_MAIN 359 HF(main); /* an addr in program */ 360 #endif 361 HF(getentropy); /* an addr in this library */ 362 HF(printf); /* an addr in libc */ 363 p = (char *)&p; 364 HD(p); /* an addr on stack */ 365 p = (char *)&errno; 366 HD(p); /* the addr of errno */ 367 368 if (i == 0) { 369 struct sockaddr_storage ss; 370 struct statvfs stvfs; 371 struct termios tios; 372 struct statfs stfs; 373 socklen_t ssl; 374 off_t off; 375 376 /* 377 * Prime-sized mappings encourage fragmentation; 378 * thus exposing some address entropy. 379 */ 380 struct mm { 381 size_t npg; 382 void *p; 383 } mm[] = { 384 { 17, MAP_FAILED }, { 3, MAP_FAILED }, 385 { 11, MAP_FAILED }, { 2, MAP_FAILED }, 386 { 5, MAP_FAILED }, { 3, MAP_FAILED }, 387 { 7, MAP_FAILED }, { 1, MAP_FAILED }, 388 { 57, MAP_FAILED }, { 3, MAP_FAILED }, 389 { 131, MAP_FAILED }, { 1, MAP_FAILED }, 390 }; 391 392 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 393 HX(mm[m].p = mmap(NULL, 394 mm[m].npg * pgs, 395 PROT_READ|PROT_WRITE, 396 MAP_PRIVATE|MAP_ANON, -1, 397 (off_t)0), mm[m].p); 398 if (mm[m].p != MAP_FAILED) { 399 size_t mo; 400 401 /* Touch some memory... */ 402 p = mm[m].p; 403 mo = cnt % 404 (mm[m].npg * pgs - 1); 405 p[mo] = 1; 406 cnt += (int)((long)(mm[m].p) 407 / pgs); 408 } 409 410 /* Check cnts and times... */ 411 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); 412 ii++) { 413 HX((e = clock_gettime(cl[ii], 414 &ts)) == -1, ts); 415 if (e != -1) 416 cnt += (int)ts.tv_nsec; 417 } 418 419 HX((e = getrusage(RUSAGE_SELF, 420 &ru)) == -1, ru); 421 if (e != -1) { 422 cnt += (int)ru.ru_utime.tv_sec; 423 cnt += (int)ru.ru_utime.tv_usec; 424 } 425 } 426 427 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 428 if (mm[m].p != MAP_FAILED) 429 munmap(mm[m].p, mm[m].npg * pgs); 430 mm[m].p = MAP_FAILED; 431 } 432 433 HX(stat(".", &st) == -1, st); 434 HX(statvfs(".", &stvfs) == -1, stvfs); 435 HX(statfs(".", &stfs) == -1, stfs); 436 437 HX(stat("/", &st) == -1, st); 438 HX(statvfs("/", &stvfs) == -1, stvfs); 439 HX(statfs("/", &stfs) == -1, stfs); 440 441 HX((e = fstat(0, &st)) == -1, st); 442 if (e == -1) { 443 if (S_ISREG(st.st_mode) || 444 S_ISFIFO(st.st_mode) || 445 S_ISSOCK(st.st_mode)) { 446 HX(fstatvfs(0, &stvfs) == -1, 447 stvfs); 448 HX(fstatfs(0, &stfs) == -1, 449 stfs); 450 HX((off = lseek(0, (off_t)0, 451 SEEK_CUR)) < 0, off); 452 } 453 if (S_ISCHR(st.st_mode)) { 454 HX(tcgetattr(0, &tios) == -1, 455 tios); 456 } else if (S_ISSOCK(st.st_mode)) { 457 memset(&ss, 0, sizeof ss); 458 ssl = sizeof(ss); 459 HX(getpeername(0, 460 (void *)&ss, &ssl) == -1, 461 ss); 462 } 463 } 464 465 HX((e = getrusage(RUSAGE_CHILDREN, 466 &ru)) == -1, ru); 467 if (e != -1) { 468 cnt += (int)ru.ru_utime.tv_sec; 469 cnt += (int)ru.ru_utime.tv_usec; 470 } 471 } else { 472 /* Subsequent hashes absorb previous result */ 473 HD(results); 474 } 475 476 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 477 if (e != -1) { 478 cnt += (int)tv.tv_sec; 479 cnt += (int)tv.tv_usec; 480 } 481 482 HD(cnt); 483 } 484 #ifdef HAVE_GETAUXVAL 485 # ifdef AT_RANDOM 486 /* Not as random as you think but we take what we are given */ 487 p = (char *) getauxval(AT_RANDOM); 488 if (p) 489 HR(p, 16); 490 # endif 491 # ifdef AT_SYSINFO_EHDR 492 p = (char *) getauxval(AT_SYSINFO_EHDR); 493 if (p) 494 HR(p, pgs); 495 # endif 496 # ifdef AT_BASE 497 p = (char *) getauxval(AT_BASE); 498 if (p) 499 HD(p); 500 # endif 501 #endif /* HAVE_GETAUXVAL */ 502 503 SHA512_Final(results, &ctx); 504 memcpy((char*)buf + i, results, min(sizeof(results), len - i)); 505 i += min(sizeof(results), len - i); 506 } 507 memset(results, 0, sizeof results); 508 if (gotdata(buf, len) == 0) { 509 errno = save_errno; 510 return 0; /* satisfied */ 511 } 512 errno = EIO; 513 return -1; 514 } 515