1 /* $OpenBSD: getentropy_osx.c,v 1.11 2016/09/03 15:24:09 bcook 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 <TargetConditionals.h> 24 #include <sys/types.h> 25 #include <sys/param.h> 26 #include <sys/ioctl.h> 27 #include <sys/resource.h> 28 #include <sys/syscall.h> 29 #include <sys/sysctl.h> 30 #include <sys/statvfs.h> 31 #include <sys/socket.h> 32 #include <sys/mount.h> 33 #include <sys/mman.h> 34 #include <sys/stat.h> 35 #include <sys/time.h> 36 #include <stdlib.h> 37 #include <stdint.h> 38 #include <stdio.h> 39 #include <termios.h> 40 #include <fcntl.h> 41 #include <signal.h> 42 #include <string.h> 43 #include <errno.h> 44 #include <unistd.h> 45 #include <time.h> 46 #include <mach/mach_time.h> 47 #include <mach/mach_host.h> 48 #include <mach/host_info.h> 49 #if TARGET_OS_OSX 50 #include <sys/socketvar.h> 51 #include <sys/vmmeter.h> 52 #endif 53 #include <netinet/in.h> 54 #include <netinet/tcp.h> 55 #if TARGET_OS_OSX 56 #include <netinet/udp.h> 57 #include <netinet/ip_var.h> 58 #include <netinet/tcp_var.h> 59 #include <netinet/udp_var.h> 60 #endif 61 #include <CommonCrypto/CommonDigest.h> 62 #define SHA512_Update(a, b, c) (CC_SHA512_Update((a), (b), (c))) 63 #define SHA512_Init(xxx) (CC_SHA512_Init((xxx))) 64 #define SHA512_Final(xxx, yyy) (CC_SHA512_Final((xxx), (yyy))) 65 #define SHA512_CTX CC_SHA512_CTX 66 #define SHA512_DIGEST_LENGTH CC_SHA512_DIGEST_LENGTH 67 68 #define REPEAT 5 69 #define min(a, b) (((a) < (b)) ? (a) : (b)) 70 71 #define HX(a, b) \ 72 do { \ 73 if ((a)) \ 74 HD(errno); \ 75 else \ 76 HD(b); \ 77 } while (0) 78 79 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l))) 80 #define HD(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (x))) 81 #define HF(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (void*))) 82 83 int getentropy(void *buf, size_t len); 84 85 static int gotdata(char *buf, size_t len); 86 static int getentropy_urandom(void *buf, size_t len); 87 static int getentropy_fallback(void *buf, size_t len); 88 89 int 90 getentropy(void *buf, size_t len) 91 { 92 int ret = -1; 93 94 if (len > 256) { 95 errno = EIO; 96 return (-1); 97 } 98 99 /* 100 * Try to get entropy with /dev/urandom 101 * 102 * This can fail if the process is inside a chroot or if file 103 * descriptors are exhausted. 104 */ 105 ret = getentropy_urandom(buf, len); 106 if (ret != -1) 107 return (ret); 108 109 /* 110 * Entropy collection via /dev/urandom and sysctl have failed. 111 * 112 * No other API exists for collecting entropy, and we have 113 * no failsafe way to get it on OSX that is not sensitive 114 * to resource exhaustion. 115 * 116 * We have very few options: 117 * - Even syslog_r is unsafe to call at this low level, so 118 * there is no way to alert the user or program. 119 * - Cannot call abort() because some systems have unsafe 120 * corefiles. 121 * - Could raise(SIGKILL) resulting in silent program termination. 122 * - Return EIO, to hint that arc4random's stir function 123 * should raise(SIGKILL) 124 * - Do the best under the circumstances.... 125 * 126 * This code path exists to bring light to the issue that OSX 127 * does not provide a failsafe API for entropy collection. 128 * 129 * We hope this demonstrates that OSX should consider 130 * providing a new failsafe API which works in a chroot or 131 * when file descriptors are exhausted. 132 */ 133 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK 134 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK 135 raise(SIGKILL); 136 #endif 137 ret = getentropy_fallback(buf, len); 138 if (ret != -1) 139 return (ret); 140 141 errno = EIO; 142 return (ret); 143 } 144 145 /* 146 * Basic sanity checking; wish we could do better. 147 */ 148 static int 149 gotdata(char *buf, size_t len) 150 { 151 char any_set = 0; 152 size_t i; 153 154 for (i = 0; i < len; ++i) 155 any_set |= buf[i]; 156 if (any_set == 0) 157 return (-1); 158 return (0); 159 } 160 161 static int 162 getentropy_urandom(void *buf, size_t len) 163 { 164 struct stat st; 165 size_t i; 166 int fd, flags; 167 int save_errno = errno; 168 169 start: 170 171 flags = O_RDONLY; 172 #ifdef O_NOFOLLOW 173 flags |= O_NOFOLLOW; 174 #endif 175 #ifdef O_CLOEXEC 176 flags |= O_CLOEXEC; 177 #endif 178 fd = open("/dev/urandom", flags, 0); 179 if (fd == -1) { 180 if (errno == EINTR) 181 goto start; 182 goto nodevrandom; 183 } 184 #ifndef O_CLOEXEC 185 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC); 186 #endif 187 188 /* Lightly verify that the device node looks sane */ 189 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) { 190 close(fd); 191 goto nodevrandom; 192 } 193 for (i = 0; i < len; ) { 194 size_t wanted = len - i; 195 ssize_t ret = read(fd, (char *)buf + i, wanted); 196 197 if (ret == -1) { 198 if (errno == EAGAIN || errno == EINTR) 199 continue; 200 close(fd); 201 goto nodevrandom; 202 } 203 i += ret; 204 } 205 close(fd); 206 if (gotdata(buf, len) == 0) { 207 errno = save_errno; 208 return (0); /* satisfied */ 209 } 210 nodevrandom: 211 errno = EIO; 212 return (-1); 213 } 214 215 #if TARGET_OS_OSX 216 static int tcpmib[] = { CTL_NET, AF_INET, IPPROTO_TCP, TCPCTL_STATS }; 217 static int udpmib[] = { CTL_NET, AF_INET, IPPROTO_UDP, UDPCTL_STATS }; 218 static int ipmib[] = { CTL_NET, AF_INET, IPPROTO_IP, IPCTL_STATS }; 219 #endif 220 static int kmib[] = { CTL_KERN, KERN_USRSTACK }; 221 static int hwmib[] = { CTL_HW, HW_USERMEM }; 222 223 static int 224 getentropy_fallback(void *buf, size_t len) 225 { 226 uint8_t results[SHA512_DIGEST_LENGTH]; 227 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat; 228 static int cnt; 229 struct timespec ts; 230 struct timeval tv; 231 struct rusage ru; 232 sigset_t sigset; 233 struct stat st; 234 SHA512_CTX ctx; 235 static pid_t lastpid; 236 pid_t pid; 237 size_t i, ii, m; 238 char *p; 239 #if TARGET_OS_OSX 240 struct tcpstat tcpstat; 241 struct udpstat udpstat; 242 struct ipstat ipstat; 243 #endif 244 u_int64_t mach_time; 245 unsigned int idata; 246 void *addr; 247 248 pid = getpid(); 249 if (lastpid == pid) { 250 faster = 1; 251 repeat = 2; 252 } else { 253 faster = 0; 254 lastpid = pid; 255 repeat = REPEAT; 256 } 257 for (i = 0; i < len; ) { 258 int j; 259 SHA512_Init(&ctx); 260 for (j = 0; j < repeat; j++) { 261 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 262 if (e != -1) { 263 cnt += (int)tv.tv_sec; 264 cnt += (int)tv.tv_usec; 265 } 266 267 mach_time = mach_absolute_time(); 268 HD(mach_time); 269 270 ii = sizeof(addr); 271 HX(sysctl(kmib, sizeof(kmib) / sizeof(kmib[0]), 272 &addr, &ii, NULL, 0) == -1, addr); 273 274 ii = sizeof(idata); 275 HX(sysctl(hwmib, sizeof(hwmib) / sizeof(hwmib[0]), 276 &idata, &ii, NULL, 0) == -1, idata); 277 278 #if TARGET_OS_OSX 279 ii = sizeof(tcpstat); 280 HX(sysctl(tcpmib, sizeof(tcpmib) / sizeof(tcpmib[0]), 281 &tcpstat, &ii, NULL, 0) == -1, tcpstat); 282 283 ii = sizeof(udpstat); 284 HX(sysctl(udpmib, sizeof(udpmib) / sizeof(udpmib[0]), 285 &udpstat, &ii, NULL, 0) == -1, udpstat); 286 287 ii = sizeof(ipstat); 288 HX(sysctl(ipmib, sizeof(ipmib) / sizeof(ipmib[0]), 289 &ipstat, &ii, NULL, 0) == -1, ipstat); 290 #endif 291 292 HX((pid = getpid()) == -1, pid); 293 HX((pid = getsid(pid)) == -1, pid); 294 HX((pid = getppid()) == -1, pid); 295 HX((pid = getpgid(0)) == -1, pid); 296 HX((e = getpriority(0, 0)) == -1, e); 297 298 if (!faster) { 299 ts.tv_sec = 0; 300 ts.tv_nsec = 1; 301 (void) nanosleep(&ts, NULL); 302 } 303 304 HX(sigpending(&sigset) == -1, sigset); 305 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1, 306 sigset); 307 308 HF(getentropy); /* an addr in this library */ 309 HF(printf); /* an addr in libc */ 310 p = (char *)&p; 311 HD(p); /* an addr on stack */ 312 p = (char *)&errno; 313 HD(p); /* the addr of errno */ 314 315 if (i == 0) { 316 struct sockaddr_storage ss; 317 struct statvfs stvfs; 318 struct termios tios; 319 struct statfs stfs; 320 socklen_t ssl; 321 off_t off; 322 323 /* 324 * Prime-sized mappings encourage fragmentation; 325 * thus exposing some address entropy. 326 */ 327 struct mm { 328 size_t npg; 329 void *p; 330 } mm[] = { 331 { 17, MAP_FAILED }, { 3, MAP_FAILED }, 332 { 11, MAP_FAILED }, { 2, MAP_FAILED }, 333 { 5, MAP_FAILED }, { 3, MAP_FAILED }, 334 { 7, MAP_FAILED }, { 1, MAP_FAILED }, 335 { 57, MAP_FAILED }, { 3, MAP_FAILED }, 336 { 131, MAP_FAILED }, { 1, MAP_FAILED }, 337 }; 338 339 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 340 HX(mm[m].p = mmap(NULL, 341 mm[m].npg * pgs, 342 PROT_READ|PROT_WRITE, 343 MAP_PRIVATE|MAP_ANON, -1, 344 (off_t)0), mm[m].p); 345 if (mm[m].p != MAP_FAILED) { 346 size_t mo; 347 348 /* Touch some memory... */ 349 p = mm[m].p; 350 mo = cnt % 351 (mm[m].npg * pgs - 1); 352 p[mo] = 1; 353 cnt += (int)((long)(mm[m].p) 354 / pgs); 355 } 356 357 /* Check cnts and times... */ 358 mach_time = mach_absolute_time(); 359 HD(mach_time); 360 cnt += (int)mach_time; 361 362 HX((e = getrusage(RUSAGE_SELF, 363 &ru)) == -1, ru); 364 if (e != -1) { 365 cnt += (int)ru.ru_utime.tv_sec; 366 cnt += (int)ru.ru_utime.tv_usec; 367 } 368 } 369 370 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 371 if (mm[m].p != MAP_FAILED) 372 munmap(mm[m].p, mm[m].npg * pgs); 373 mm[m].p = MAP_FAILED; 374 } 375 376 HX(stat(".", &st) == -1, st); 377 HX(statvfs(".", &stvfs) == -1, stvfs); 378 HX(statfs(".", &stfs) == -1, stfs); 379 380 HX(stat("/", &st) == -1, st); 381 HX(statvfs("/", &stvfs) == -1, stvfs); 382 HX(statfs("/", &stfs) == -1, stfs); 383 384 HX((e = fstat(0, &st)) == -1, st); 385 if (e == -1) { 386 if (S_ISREG(st.st_mode) || 387 S_ISFIFO(st.st_mode) || 388 S_ISSOCK(st.st_mode)) { 389 HX(fstatvfs(0, &stvfs) == -1, 390 stvfs); 391 HX(fstatfs(0, &stfs) == -1, 392 stfs); 393 HX((off = lseek(0, (off_t)0, 394 SEEK_CUR)) < 0, off); 395 } 396 if (S_ISCHR(st.st_mode)) { 397 HX(tcgetattr(0, &tios) == -1, 398 tios); 399 } else if (S_ISSOCK(st.st_mode)) { 400 memset(&ss, 0, sizeof ss); 401 ssl = sizeof(ss); 402 HX(getpeername(0, 403 (void *)&ss, &ssl) == -1, 404 ss); 405 } 406 } 407 408 HX((e = getrusage(RUSAGE_CHILDREN, 409 &ru)) == -1, ru); 410 if (e != -1) { 411 cnt += (int)ru.ru_utime.tv_sec; 412 cnt += (int)ru.ru_utime.tv_usec; 413 } 414 } else { 415 /* Subsequent hashes absorb previous result */ 416 HD(results); 417 } 418 419 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 420 if (e != -1) { 421 cnt += (int)tv.tv_sec; 422 cnt += (int)tv.tv_usec; 423 } 424 425 HD(cnt); 426 } 427 428 SHA512_Final(results, &ctx); 429 memcpy((char *)buf + i, results, min(sizeof(results), len - i)); 430 i += min(sizeof(results), len - i); 431 } 432 explicit_bzero(&ctx, sizeof ctx); 433 explicit_bzero(results, sizeof results); 434 if (gotdata(buf, len) == 0) { 435 errno = save_errno; 436 return (0); /* satisfied */ 437 } 438 errno = EIO; 439 return (-1); 440 } 441