1 /* $OpenBSD: getentropy_linux.c,v 1.46 2018/11/20 08:04:28 deraadt 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 * Emulation of getentropy(2) as documented at: 20 * http://man.openbsd.org/getentropy.2 21 */ 22 23 #include "config.h" 24 /* 25 #define _POSIX_C_SOURCE 199309L 26 #define _GNU_SOURCE 1 27 */ 28 #include <sys/types.h> 29 #include <sys/param.h> 30 #include <sys/ioctl.h> 31 #include <sys/resource.h> 32 #include <sys/syscall.h> 33 #ifdef SYS__sysctl 34 #include <linux/sysctl.h> 35 #endif 36 #include <sys/statvfs.h> 37 #include <sys/socket.h> 38 #include <sys/mount.h> 39 #include <sys/mman.h> 40 #include <sys/stat.h> 41 #include <sys/time.h> 42 #include <stdlib.h> 43 #include <stdint.h> 44 #include <stdio.h> 45 #include <link.h> 46 #include <termios.h> 47 #include <fcntl.h> 48 #include <signal.h> 49 #include <string.h> 50 #include <errno.h> 51 #include <unistd.h> 52 #include <time.h> 53 #ifndef HAVE_NETTLE 54 #include <openssl/sha.h> 55 #else 56 #include <nettle/sha.h> 57 #define SHA512_CTX struct sha512_ctx 58 #define SHA512_Init(x) sha512_init(x) 59 #define SHA512_Update(x, b, s) sha512_update(x, s, b) 60 #define SHA512_Final(r, c) sha512_digest(c, SHA512_DIGEST_SIZE, r) 61 #endif 62 63 #include <linux/types.h> 64 #include <linux/random.h> 65 #ifdef HAVE_GETAUXVAL 66 #include <sys/auxv.h> 67 #endif 68 #include <sys/vfs.h> 69 #ifndef MAP_ANON 70 #define MAP_ANON MAP_ANONYMOUS 71 #endif 72 73 #define REPEAT 5 74 #define min(a, b) (((a) < (b)) ? (a) : (b)) 75 76 #define HX(a, b) \ 77 do { \ 78 if ((a)) \ 79 HD(errno); \ 80 else \ 81 HD(b); \ 82 } while (0) 83 84 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l))) 85 #define HD(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (x))) 86 #define HF(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (void*))) 87 88 int getentropy(void *buf, size_t len); 89 90 #if defined(SYS_getrandom) && defined(GRND_NONBLOCK) 91 static int getentropy_getrandom(void *buf, size_t len); 92 #endif 93 static int getentropy_urandom(void *buf, size_t len); 94 #ifdef SYS__sysctl 95 static int getentropy_sysctl(void *buf, size_t len); 96 #endif 97 static int getentropy_fallback(void *buf, size_t len); 98 static int getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data); 99 100 int 101 getentropy(void *buf, size_t len) 102 { 103 int ret = -1; 104 105 if (len > 256) { 106 errno = EIO; 107 return (-1); 108 } 109 110 #if defined(SYS_getrandom) && defined(GRND_NONBLOCK) 111 /* 112 * Try descriptor-less getrandom(), in non-blocking mode. 113 * 114 * The design of Linux getrandom is broken. It has an 115 * uninitialized phase coupled with blocking behaviour, which 116 * is unacceptable from within a library at boot time without 117 * possible recovery. See http://bugs.python.org/issue26839#msg267745 118 */ 119 ret = getentropy_getrandom(buf, len); 120 if (ret != -1) 121 return (ret); 122 #endif 123 124 /* 125 * Try to get entropy with /dev/urandom 126 * 127 * This can fail if the process is inside a chroot or if file 128 * descriptors are exhausted. 129 */ 130 ret = getentropy_urandom(buf, len); 131 if (ret != -1) 132 return (ret); 133 134 #ifdef SYS__sysctl 135 /* 136 * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID. 137 * sysctl is a failsafe API, so it guarantees a result. This 138 * should work inside a chroot, or when file descriptors are 139 * exhausted. 140 * 141 * However this can fail if the Linux kernel removes support 142 * for sysctl. Starting in 2007, there have been efforts to 143 * deprecate the sysctl API/ABI, and push callers towards use 144 * of the chroot-unavailable fd-using /proc mechanism -- 145 * essentially the same problems as /dev/urandom. 146 * 147 * Numerous setbacks have been encountered in their deprecation 148 * schedule, so as of June 2014 the kernel ABI still exists on 149 * most Linux architectures. The sysctl() stub in libc is missing 150 * on some systems. There are also reports that some kernels 151 * spew messages to the console. 152 */ 153 ret = getentropy_sysctl(buf, len); 154 if (ret != -1) 155 return (ret); 156 #endif /* SYS__sysctl */ 157 158 /* 159 * Entropy collection via /dev/urandom and sysctl have failed. 160 * 161 * No other API exists for collecting entropy. See the large 162 * comment block above. 163 * 164 * We have very few options: 165 * - Even syslog_r is unsafe to call at this low level, so 166 * there is no way to alert the user or program. 167 * - Cannot call abort() because some systems have unsafe 168 * corefiles. 169 * - Could raise(SIGKILL) resulting in silent program termination. 170 * - Return EIO, to hint that arc4random's stir function 171 * should raise(SIGKILL) 172 * - Do the best under the circumstances.... 173 * 174 * This code path exists to bring light to the issue that Linux 175 * still does not provide a failsafe API for entropy collection. 176 * 177 * We hope this demonstrates that Linux should either retain their 178 * sysctl ABI, or consider providing a new failsafe API which 179 * works in a chroot or when file descriptors are exhausted. 180 */ 181 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK 182 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK 183 raise(SIGKILL); 184 #endif 185 ret = getentropy_fallback(buf, len); 186 if (ret != -1) 187 return (ret); 188 189 errno = EIO; 190 return (ret); 191 } 192 193 #if defined(SYS_getrandom) && defined(GRND_NONBLOCK) 194 static int 195 getentropy_getrandom(void *buf, size_t len) 196 { 197 int pre_errno = errno; 198 int ret; 199 if (len > 256) 200 return (-1); 201 do { 202 ret = syscall(SYS_getrandom, buf, len, GRND_NONBLOCK); 203 } while (ret == -1 && errno == EINTR); 204 205 if (ret != (int)len) 206 return (-1); 207 errno = pre_errno; 208 return (0); 209 } 210 #endif 211 212 static int 213 getentropy_urandom(void *buf, size_t len) 214 { 215 struct stat st; 216 size_t i; 217 int fd, cnt, flags; 218 int save_errno = errno; 219 220 start: 221 222 flags = O_RDONLY; 223 #ifdef O_NOFOLLOW 224 flags |= O_NOFOLLOW; 225 #endif 226 #ifdef O_CLOEXEC 227 flags |= O_CLOEXEC; 228 #endif 229 fd = open("/dev/urandom", flags, 0); 230 if (fd == -1) { 231 if (errno == EINTR) 232 goto start; 233 goto nodevrandom; 234 } 235 #ifndef O_CLOEXEC 236 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC); 237 #endif 238 239 /* Lightly verify that the device node looks sane */ 240 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) { 241 close(fd); 242 goto nodevrandom; 243 } 244 if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) { 245 close(fd); 246 goto nodevrandom; 247 } 248 for (i = 0; i < len; ) { 249 size_t wanted = len - i; 250 ssize_t ret = read(fd, (char *)buf + i, wanted); 251 252 if (ret == -1) { 253 if (errno == EAGAIN || errno == EINTR) 254 continue; 255 close(fd); 256 goto nodevrandom; 257 } 258 i += ret; 259 } 260 close(fd); 261 errno = save_errno; 262 return (0); /* satisfied */ 263 nodevrandom: 264 errno = EIO; 265 return (-1); 266 } 267 268 #ifdef SYS__sysctl 269 static int 270 getentropy_sysctl(void *buf, size_t len) 271 { 272 static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID }; 273 size_t i; 274 int save_errno = errno; 275 276 for (i = 0; i < len; ) { 277 size_t chunk = min(len - i, 16); 278 279 /* SYS__sysctl because some systems already removed sysctl() */ 280 struct __sysctl_args args = { 281 .name = mib, 282 .nlen = 3, 283 .oldval = (char *)buf + i, 284 .oldlenp = &chunk, 285 }; 286 if (syscall(SYS__sysctl, &args) != 0) 287 goto sysctlfailed; 288 i += chunk; 289 } 290 errno = save_errno; 291 return (0); /* satisfied */ 292 sysctlfailed: 293 errno = EIO; 294 return (-1); 295 } 296 #endif /* SYS__sysctl */ 297 298 static const int cl[] = { 299 CLOCK_REALTIME, 300 #ifdef CLOCK_MONOTONIC 301 CLOCK_MONOTONIC, 302 #endif 303 #ifdef CLOCK_MONOTONIC_RAW 304 CLOCK_MONOTONIC_RAW, 305 #endif 306 #ifdef CLOCK_TAI 307 CLOCK_TAI, 308 #endif 309 #ifdef CLOCK_VIRTUAL 310 CLOCK_VIRTUAL, 311 #endif 312 #ifdef CLOCK_UPTIME 313 CLOCK_UPTIME, 314 #endif 315 #ifdef CLOCK_PROCESS_CPUTIME_ID 316 CLOCK_PROCESS_CPUTIME_ID, 317 #endif 318 #ifdef CLOCK_THREAD_CPUTIME_ID 319 CLOCK_THREAD_CPUTIME_ID, 320 #endif 321 }; 322 323 static int 324 getentropy_phdr(struct dl_phdr_info *info, size_t ATTR_UNUSED(size), void *data) 325 { 326 SHA512_CTX *ctx = data; 327 328 SHA512_Update(ctx, &info->dlpi_addr, sizeof (info->dlpi_addr)); 329 return (0); 330 } 331 332 static int 333 getentropy_fallback(void *buf, size_t len) 334 { 335 uint8_t results[SHA512_DIGEST_LENGTH]; 336 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat; 337 static int cnt; 338 struct timespec ts; 339 struct timeval tv; 340 struct rusage ru; 341 sigset_t sigset; 342 struct stat st; 343 SHA512_CTX ctx; 344 static pid_t lastpid; 345 pid_t pid; 346 size_t i, ii, m; 347 char *p; 348 349 pid = getpid(); 350 if (lastpid == pid) { 351 faster = 1; 352 repeat = 2; 353 } else { 354 faster = 0; 355 lastpid = pid; 356 repeat = REPEAT; 357 } 358 for (i = 0; i < len; ) { 359 int j; 360 SHA512_Init(&ctx); 361 for (j = 0; j < repeat; j++) { 362 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 363 if (e != -1) { 364 cnt += (int)tv.tv_sec; 365 cnt += (int)tv.tv_usec; 366 } 367 368 dl_iterate_phdr(getentropy_phdr, &ctx); 369 370 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++) 371 HX(clock_gettime(cl[ii], &ts) == -1, ts); 372 373 HX((pid = getpid()) == -1, pid); 374 HX((pid = getsid(pid)) == -1, pid); 375 HX((pid = getppid()) == -1, pid); 376 HX((pid = getpgid(0)) == -1, pid); 377 HX((e = getpriority(0, 0)) == -1, e); 378 379 if (!faster) { 380 ts.tv_sec = 0; 381 ts.tv_nsec = 1; 382 (void) nanosleep(&ts, NULL); 383 } 384 385 HX(sigpending(&sigset) == -1, sigset); 386 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1, 387 sigset); 388 389 HF(getentropy); /* an addr in this library */ 390 HF(printf); /* an addr in libc */ 391 p = (char *)&p; 392 HD(p); /* an addr on stack */ 393 p = (char *)&errno; 394 HD(p); /* the addr of errno */ 395 396 if (i == 0) { 397 struct sockaddr_storage ss; 398 struct statvfs stvfs; 399 struct termios tios; 400 struct statfs stfs; 401 socklen_t ssl; 402 off_t off; 403 404 /* 405 * Prime-sized mappings encourage fragmentation; 406 * thus exposing some address entropy. 407 */ 408 struct mm { 409 size_t npg; 410 void *p; 411 } mm[] = { 412 { 17, MAP_FAILED }, { 3, MAP_FAILED }, 413 { 11, MAP_FAILED }, { 2, MAP_FAILED }, 414 { 5, MAP_FAILED }, { 3, MAP_FAILED }, 415 { 7, MAP_FAILED }, { 1, MAP_FAILED }, 416 { 57, MAP_FAILED }, { 3, MAP_FAILED }, 417 { 131, MAP_FAILED }, { 1, MAP_FAILED }, 418 }; 419 420 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 421 HX(mm[m].p = mmap(NULL, 422 mm[m].npg * pgs, 423 PROT_READ|PROT_WRITE, 424 MAP_PRIVATE|MAP_ANON, -1, 425 (off_t)0), mm[m].p); 426 if (mm[m].p != MAP_FAILED) { 427 size_t mo; 428 429 /* Touch some memory... */ 430 p = mm[m].p; 431 mo = cnt % 432 (mm[m].npg * pgs - 1); 433 p[mo] = 1; 434 cnt += (int)((long)(mm[m].p) 435 / pgs); 436 } 437 438 /* Check cnts and times... */ 439 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); 440 ii++) { 441 HX((e = clock_gettime(cl[ii], 442 &ts)) == -1, ts); 443 if (e != -1) 444 cnt += (int)ts.tv_nsec; 445 } 446 447 HX((e = getrusage(RUSAGE_SELF, 448 &ru)) == -1, ru); 449 if (e != -1) { 450 cnt += (int)ru.ru_utime.tv_sec; 451 cnt += (int)ru.ru_utime.tv_usec; 452 } 453 } 454 455 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 456 if (mm[m].p != MAP_FAILED) 457 munmap(mm[m].p, mm[m].npg * pgs); 458 mm[m].p = MAP_FAILED; 459 } 460 461 HX(stat(".", &st) == -1, st); 462 HX(statvfs(".", &stvfs) == -1, stvfs); 463 HX(statfs(".", &stfs) == -1, stfs); 464 465 HX(stat("/", &st) == -1, st); 466 HX(statvfs("/", &stvfs) == -1, stvfs); 467 HX(statfs("/", &stfs) == -1, stfs); 468 469 HX((e = fstat(0, &st)) == -1, st); 470 if (e == -1) { 471 if (S_ISREG(st.st_mode) || 472 S_ISFIFO(st.st_mode) || 473 S_ISSOCK(st.st_mode)) { 474 HX(fstatvfs(0, &stvfs) == -1, 475 stvfs); 476 HX(fstatfs(0, &stfs) == -1, 477 stfs); 478 HX((off = lseek(0, (off_t)0, 479 SEEK_CUR)) < 0, off); 480 } 481 if (S_ISCHR(st.st_mode)) { 482 HX(tcgetattr(0, &tios) == -1, 483 tios); 484 } else if (S_ISSOCK(st.st_mode)) { 485 memset(&ss, 0, sizeof ss); 486 ssl = sizeof(ss); 487 HX(getpeername(0, 488 (void *)&ss, &ssl) == -1, 489 ss); 490 } 491 } 492 493 HX((e = getrusage(RUSAGE_CHILDREN, 494 &ru)) == -1, ru); 495 if (e != -1) { 496 cnt += (int)ru.ru_utime.tv_sec; 497 cnt += (int)ru.ru_utime.tv_usec; 498 } 499 } else { 500 /* Subsequent hashes absorb previous result */ 501 HD(results); 502 } 503 504 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 505 if (e != -1) { 506 cnt += (int)tv.tv_sec; 507 cnt += (int)tv.tv_usec; 508 } 509 510 HD(cnt); 511 } 512 #ifdef HAVE_GETAUXVAL 513 #ifdef AT_RANDOM 514 /* Not as random as you think but we take what we are given */ 515 p = (char *) getauxval(AT_RANDOM); 516 if (p) 517 HR(p, 16); 518 #endif 519 #ifdef AT_SYSINFO_EHDR 520 p = (char *) getauxval(AT_SYSINFO_EHDR); 521 if (p) 522 HR(p, pgs); 523 #endif 524 #ifdef AT_BASE 525 p = (char *) getauxval(AT_BASE); 526 if (p) 527 HD(p); 528 #endif 529 #endif 530 531 SHA512_Final(results, &ctx); 532 memcpy((char *)buf + i, results, min(sizeof(results), len - i)); 533 i += min(sizeof(results), len - i); 534 } 535 explicit_bzero(&ctx, sizeof ctx); 536 explicit_bzero(results, sizeof results); 537 errno = save_errno; 538 return (0); /* satisfied */ 539 } 540