1 /* $OpenBSD: getentropy_linux.c,v 1.44 2017/04/29 18:43:31 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 * Emulation of getentropy(2) as documented at: 20 * http://man.openbsd.org/getentropy.2 21 */ 22 23 #define _POSIX_C_SOURCE 199309L 24 #define _GNU_SOURCE 1 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 SYS__sysctl 31 #include <linux/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 <link.h> 43 #include <termios.h> 44 #include <fcntl.h> 45 #include <signal.h> 46 #include <string.h> 47 #include <errno.h> 48 #include <unistd.h> 49 #include <time.h> 50 #include <openssl/sha.h> 51 52 #include <linux/types.h> 53 #include <linux/random.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 static int gotdata(char *buf, size_t len); 77 #ifdef SYS_getrandom 78 static int getentropy_getrandom(void *buf, size_t len); 79 #endif 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 static int getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data); 86 87 int 88 getentropy(void *buf, size_t len) 89 { 90 int ret = -1; 91 92 if (len > 256) { 93 errno = EIO; 94 return (-1); 95 } 96 97 #ifdef SYS_getrandom 98 /* 99 * Try descriptor-less getrandom(), in non-blocking mode. 100 * 101 * The design of Linux getrandom is broken. It has an 102 * uninitialized phase coupled with blocking behaviour, which 103 * is unacceptable from within a library at boot time without 104 * possible recovery. See http://bugs.python.org/issue26839#msg267745 105 */ 106 ret = getentropy_getrandom(buf, len); 107 if (ret != -1) 108 return (ret); 109 #endif 110 111 /* 112 * Try to get entropy with /dev/urandom 113 * 114 * This can fail if the process is inside a chroot or if file 115 * descriptors are exhausted. 116 */ 117 ret = getentropy_urandom(buf, len); 118 if (ret != -1) 119 return (ret); 120 121 #ifdef SYS__sysctl 122 /* 123 * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID. 124 * sysctl is a failsafe API, so it guarantees a result. This 125 * should work inside a chroot, or when file descriptors are 126 * exhausted. 127 * 128 * However this can fail if the Linux kernel removes support 129 * for sysctl. Starting in 2007, there have been efforts to 130 * deprecate the sysctl API/ABI, and push callers towards use 131 * of the chroot-unavailable fd-using /proc mechanism -- 132 * essentially the same problems as /dev/urandom. 133 * 134 * Numerous setbacks have been encountered in their deprecation 135 * schedule, so as of June 2014 the kernel ABI still exists on 136 * most Linux architectures. The sysctl() stub in libc is missing 137 * on some systems. There are also reports that some kernels 138 * spew messages to the console. 139 */ 140 ret = getentropy_sysctl(buf, len); 141 if (ret != -1) 142 return (ret); 143 #endif /* SYS__sysctl */ 144 145 /* 146 * Entropy collection via /dev/urandom and sysctl have failed. 147 * 148 * No other API exists for collecting entropy. See the large 149 * comment block above. 150 * 151 * We have very few options: 152 * - Even syslog_r is unsafe to call at this low level, so 153 * there is no way to alert the user or program. 154 * - Cannot call abort() because some systems have unsafe 155 * corefiles. 156 * - Could raise(SIGKILL) resulting in silent program termination. 157 * - Return EIO, to hint that arc4random's stir function 158 * should raise(SIGKILL) 159 * - Do the best under the circumstances.... 160 * 161 * This code path exists to bring light to the issue that Linux 162 * still does not provide a failsafe API for entropy collection. 163 * 164 * We hope this demonstrates that Linux should either retain their 165 * sysctl ABI, or consider providing a new failsafe API which 166 * works in a chroot or when file descriptors are exhausted. 167 */ 168 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK 169 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK 170 raise(SIGKILL); 171 #endif 172 ret = getentropy_fallback(buf, len); 173 if (ret != -1) 174 return (ret); 175 176 errno = EIO; 177 return (ret); 178 } 179 180 /* 181 * Basic sanity checking; wish we could do better. 182 */ 183 static int 184 gotdata(char *buf, size_t len) 185 { 186 char any_set = 0; 187 size_t i; 188 189 for (i = 0; i < len; ++i) 190 any_set |= buf[i]; 191 if (any_set == 0) 192 return (-1); 193 return (0); 194 } 195 196 #ifdef SYS_getrandom 197 static int 198 getentropy_getrandom(void *buf, size_t len) 199 { 200 int pre_errno = errno; 201 int ret; 202 if (len > 256) 203 return (-1); 204 do { 205 ret = syscall(SYS_getrandom, buf, len, GRND_NONBLOCK); 206 } while (ret == -1 && errno == EINTR); 207 208 if (ret != len) 209 return (-1); 210 errno = pre_errno; 211 return (0); 212 } 213 #endif 214 215 static int 216 getentropy_urandom(void *buf, size_t len) 217 { 218 struct stat st; 219 size_t i; 220 int fd, cnt, flags; 221 int save_errno = errno; 222 223 start: 224 225 flags = O_RDONLY; 226 #ifdef O_NOFOLLOW 227 flags |= O_NOFOLLOW; 228 #endif 229 #ifdef O_CLOEXEC 230 flags |= O_CLOEXEC; 231 #endif 232 fd = open("/dev/urandom", flags, 0); 233 if (fd == -1) { 234 if (errno == EINTR) 235 goto start; 236 goto nodevrandom; 237 } 238 #ifndef O_CLOEXEC 239 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC); 240 #endif 241 242 /* Lightly verify that the device node looks sane */ 243 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) { 244 close(fd); 245 goto nodevrandom; 246 } 247 if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) { 248 close(fd); 249 goto nodevrandom; 250 } 251 for (i = 0; i < len; ) { 252 size_t wanted = len - i; 253 ssize_t ret = read(fd, (char *)buf + i, wanted); 254 255 if (ret == -1) { 256 if (errno == EAGAIN || errno == EINTR) 257 continue; 258 close(fd); 259 goto nodevrandom; 260 } 261 i += ret; 262 } 263 close(fd); 264 if (gotdata(buf, len) == 0) { 265 errno = save_errno; 266 return (0); /* satisfied */ 267 } 268 nodevrandom: 269 errno = EIO; 270 return (-1); 271 } 272 273 #ifdef SYS__sysctl 274 static int 275 getentropy_sysctl(void *buf, size_t len) 276 { 277 static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID }; 278 size_t i; 279 int save_errno = errno; 280 281 for (i = 0; i < len; ) { 282 size_t chunk = min(len - i, 16); 283 284 /* SYS__sysctl because some systems already removed sysctl() */ 285 struct __sysctl_args args = { 286 .name = mib, 287 .nlen = 3, 288 .oldval = (char *)buf + i, 289 .oldlenp = &chunk, 290 }; 291 if (syscall(SYS__sysctl, &args) != 0) 292 goto sysctlfailed; 293 i += chunk; 294 } 295 if (gotdata(buf, len) == 0) { 296 errno = save_errno; 297 return (0); /* satisfied */ 298 } 299 sysctlfailed: 300 errno = EIO; 301 return (-1); 302 } 303 #endif /* SYS__sysctl */ 304 305 static const int cl[] = { 306 CLOCK_REALTIME, 307 #ifdef CLOCK_MONOTONIC 308 CLOCK_MONOTONIC, 309 #endif 310 #ifdef CLOCK_MONOTONIC_RAW 311 CLOCK_MONOTONIC_RAW, 312 #endif 313 #ifdef CLOCK_TAI 314 CLOCK_TAI, 315 #endif 316 #ifdef CLOCK_VIRTUAL 317 CLOCK_VIRTUAL, 318 #endif 319 #ifdef CLOCK_UPTIME 320 CLOCK_UPTIME, 321 #endif 322 #ifdef CLOCK_PROCESS_CPUTIME_ID 323 CLOCK_PROCESS_CPUTIME_ID, 324 #endif 325 #ifdef CLOCK_THREAD_CPUTIME_ID 326 CLOCK_THREAD_CPUTIME_ID, 327 #endif 328 }; 329 330 static int 331 getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data) 332 { 333 SHA512_CTX *ctx = data; 334 335 SHA512_Update(ctx, &info->dlpi_addr, sizeof (info->dlpi_addr)); 336 return (0); 337 } 338 339 static int 340 getentropy_fallback(void *buf, size_t len) 341 { 342 uint8_t results[SHA512_DIGEST_LENGTH]; 343 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat; 344 static int cnt; 345 struct timespec ts; 346 struct timeval tv; 347 struct rusage ru; 348 sigset_t sigset; 349 struct stat st; 350 SHA512_CTX ctx; 351 static pid_t lastpid; 352 pid_t pid; 353 size_t i, ii, m; 354 char *p; 355 356 pid = getpid(); 357 if (lastpid == pid) { 358 faster = 1; 359 repeat = 2; 360 } else { 361 faster = 0; 362 lastpid = pid; 363 repeat = REPEAT; 364 } 365 for (i = 0; i < len; ) { 366 int j; 367 SHA512_Init(&ctx); 368 for (j = 0; j < repeat; j++) { 369 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 370 if (e != -1) { 371 cnt += (int)tv.tv_sec; 372 cnt += (int)tv.tv_usec; 373 } 374 375 dl_iterate_phdr(getentropy_phdr, &ctx); 376 377 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++) 378 HX(clock_gettime(cl[ii], &ts) == -1, ts); 379 380 HX((pid = getpid()) == -1, pid); 381 HX((pid = getsid(pid)) == -1, pid); 382 HX((pid = getppid()) == -1, pid); 383 HX((pid = getpgid(0)) == -1, pid); 384 HX((e = getpriority(0, 0)) == -1, e); 385 386 if (!faster) { 387 ts.tv_sec = 0; 388 ts.tv_nsec = 1; 389 (void) nanosleep(&ts, NULL); 390 } 391 392 HX(sigpending(&sigset) == -1, sigset); 393 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1, 394 sigset); 395 396 HF(getentropy); /* an addr in this library */ 397 HF(printf); /* an addr in libc */ 398 p = (char *)&p; 399 HD(p); /* an addr on stack */ 400 p = (char *)&errno; 401 HD(p); /* the addr of errno */ 402 403 if (i == 0) { 404 struct sockaddr_storage ss; 405 struct statvfs stvfs; 406 struct termios tios; 407 struct statfs stfs; 408 socklen_t ssl; 409 off_t off; 410 411 /* 412 * Prime-sized mappings encourage fragmentation; 413 * thus exposing some address entropy. 414 */ 415 struct mm { 416 size_t npg; 417 void *p; 418 } mm[] = { 419 { 17, MAP_FAILED }, { 3, MAP_FAILED }, 420 { 11, MAP_FAILED }, { 2, MAP_FAILED }, 421 { 5, MAP_FAILED }, { 3, MAP_FAILED }, 422 { 7, MAP_FAILED }, { 1, MAP_FAILED }, 423 { 57, MAP_FAILED }, { 3, MAP_FAILED }, 424 { 131, MAP_FAILED }, { 1, MAP_FAILED }, 425 }; 426 427 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 428 HX(mm[m].p = mmap(NULL, 429 mm[m].npg * pgs, 430 PROT_READ|PROT_WRITE, 431 MAP_PRIVATE|MAP_ANON, -1, 432 (off_t)0), mm[m].p); 433 if (mm[m].p != MAP_FAILED) { 434 size_t mo; 435 436 /* Touch some memory... */ 437 p = mm[m].p; 438 mo = cnt % 439 (mm[m].npg * pgs - 1); 440 p[mo] = 1; 441 cnt += (int)((long)(mm[m].p) 442 / pgs); 443 } 444 445 /* Check cnts and times... */ 446 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); 447 ii++) { 448 HX((e = clock_gettime(cl[ii], 449 &ts)) == -1, ts); 450 if (e != -1) 451 cnt += (int)ts.tv_nsec; 452 } 453 454 HX((e = getrusage(RUSAGE_SELF, 455 &ru)) == -1, ru); 456 if (e != -1) { 457 cnt += (int)ru.ru_utime.tv_sec; 458 cnt += (int)ru.ru_utime.tv_usec; 459 } 460 } 461 462 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 463 if (mm[m].p != MAP_FAILED) 464 munmap(mm[m].p, mm[m].npg * pgs); 465 mm[m].p = MAP_FAILED; 466 } 467 468 HX(stat(".", &st) == -1, st); 469 HX(statvfs(".", &stvfs) == -1, stvfs); 470 HX(statfs(".", &stfs) == -1, stfs); 471 472 HX(stat("/", &st) == -1, st); 473 HX(statvfs("/", &stvfs) == -1, stvfs); 474 HX(statfs("/", &stfs) == -1, stfs); 475 476 HX((e = fstat(0, &st)) == -1, st); 477 if (e == -1) { 478 if (S_ISREG(st.st_mode) || 479 S_ISFIFO(st.st_mode) || 480 S_ISSOCK(st.st_mode)) { 481 HX(fstatvfs(0, &stvfs) == -1, 482 stvfs); 483 HX(fstatfs(0, &stfs) == -1, 484 stfs); 485 HX((off = lseek(0, (off_t)0, 486 SEEK_CUR)) < 0, off); 487 } 488 if (S_ISCHR(st.st_mode)) { 489 HX(tcgetattr(0, &tios) == -1, 490 tios); 491 } else if (S_ISSOCK(st.st_mode)) { 492 memset(&ss, 0, sizeof ss); 493 ssl = sizeof(ss); 494 HX(getpeername(0, 495 (void *)&ss, &ssl) == -1, 496 ss); 497 } 498 } 499 500 HX((e = getrusage(RUSAGE_CHILDREN, 501 &ru)) == -1, ru); 502 if (e != -1) { 503 cnt += (int)ru.ru_utime.tv_sec; 504 cnt += (int)ru.ru_utime.tv_usec; 505 } 506 } else { 507 /* Subsequent hashes absorb previous result */ 508 HD(results); 509 } 510 511 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 512 if (e != -1) { 513 cnt += (int)tv.tv_sec; 514 cnt += (int)tv.tv_usec; 515 } 516 517 HD(cnt); 518 } 519 #ifdef HAVE_GETAUXVAL 520 #ifdef AT_RANDOM 521 /* Not as random as you think but we take what we are given */ 522 p = (char *) getauxval(AT_RANDOM); 523 if (p) 524 HR(p, 16); 525 #endif 526 #ifdef AT_SYSINFO_EHDR 527 p = (char *) getauxval(AT_SYSINFO_EHDR); 528 if (p) 529 HR(p, pgs); 530 #endif 531 #ifdef AT_BASE 532 p = (char *) getauxval(AT_BASE); 533 if (p) 534 HD(p); 535 #endif 536 #endif 537 538 SHA512_Final(results, &ctx); 539 memcpy((char *)buf + i, results, min(sizeof(results), len - i)); 540 i += min(sizeof(results), len - i); 541 } 542 explicit_bzero(&ctx, sizeof ctx); 543 explicit_bzero(results, sizeof results); 544 if (gotdata(buf, len) == 0) { 545 errno = save_errno; 546 return (0); /* satisfied */ 547 } 548 errno = EIO; 549 return (-1); 550 } 551