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