1 /* $OpenBSD: getentropy_osx.c,v 1.8 2014/07/21 20:19:47 guenther 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://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/getentropy.2 21 */ 22 23 #include <sys/types.h> 24 #include <sys/param.h> 25 #include <sys/ioctl.h> 26 #include <sys/resource.h> 27 #include <sys/syscall.h> 28 #include <sys/sysctl.h> 29 #include <sys/statvfs.h> 30 #include <sys/socket.h> 31 #include <sys/mount.h> 32 #include <sys/mman.h> 33 #include <sys/stat.h> 34 #include <sys/time.h> 35 #include <stdlib.h> 36 #include <stdint.h> 37 #include <stdio.h> 38 #include <termios.h> 39 #include <fcntl.h> 40 #include <signal.h> 41 #include <string.h> 42 #include <errno.h> 43 #include <unistd.h> 44 #include <time.h> 45 #include <mach/mach_time.h> 46 #include <mach/mach_host.h> 47 #include <mach/host_info.h> 48 #include <sys/socketvar.h> 49 #include <sys/vmmeter.h> 50 #include <netinet/in.h> 51 #include <netinet/tcp.h> 52 #include <netinet/udp.h> 53 #include <netinet/ip_var.h> 54 #include <netinet/tcp_var.h> 55 #include <netinet/udp_var.h> 56 #include <CommonCrypto/CommonDigest.h> 57 #define SHA512_Update(a, b, c) (CC_SHA512_Update((a), (b), (c))) 58 #define SHA512_Init(xxx) (CC_SHA512_Init((xxx))) 59 #define SHA512_Final(xxx, yyy) (CC_SHA512_Final((xxx), (yyy))) 60 #define SHA512_CTX CC_SHA512_CTX 61 #define SHA512_DIGEST_LENGTH CC_SHA512_DIGEST_LENGTH 62 63 #define REPEAT 5 64 #define min(a, b) (((a) < (b)) ? (a) : (b)) 65 66 #define HX(a, b) \ 67 do { \ 68 if ((a)) \ 69 HD(errno); \ 70 else \ 71 HD(b); \ 72 } while (0) 73 74 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l))) 75 #define HD(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (x))) 76 #define HF(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (void*))) 77 78 int getentropy(void *buf, size_t len); 79 80 static int gotdata(char *buf, size_t len); 81 static int getentropy_urandom(void *buf, size_t len); 82 static int getentropy_fallback(void *buf, size_t len); 83 84 int 85 getentropy(void *buf, size_t len) 86 { 87 int ret = -1; 88 89 if (len > 256) { 90 errno = EIO; 91 return -1; 92 } 93 94 /* 95 * Try to get entropy with /dev/urandom 96 * 97 * This can fail if the process is inside a chroot or if file 98 * descriptors are exhausted. 99 */ 100 ret = getentropy_urandom(buf, len); 101 if (ret != -1) 102 return (ret); 103 104 /* 105 * Entropy collection via /dev/urandom and sysctl have failed. 106 * 107 * No other API exists for collecting entropy, and we have 108 * no failsafe way to get it on OSX that is not sensitive 109 * to resource exhaustion. 110 * 111 * We have very few options: 112 * - Even syslog_r is unsafe to call at this low level, so 113 * there is no way to alert the user or program. 114 * - Cannot call abort() because some systems have unsafe 115 * corefiles. 116 * - Could raise(SIGKILL) resulting in silent program termination. 117 * - Return EIO, to hint that arc4random's stir function 118 * should raise(SIGKILL) 119 * - Do the best under the circumstances.... 120 * 121 * This code path exists to bring light to the issue that OSX 122 * does not provide a failsafe API for entropy collection. 123 * 124 * We hope this demonstrates that OSX should consider 125 * providing a new failsafe API which works in a chroot or 126 * when file descriptors are exhausted. 127 */ 128 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK 129 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK 130 raise(SIGKILL); 131 #endif 132 ret = getentropy_fallback(buf, len); 133 if (ret != -1) 134 return (ret); 135 136 errno = EIO; 137 return (ret); 138 } 139 140 /* 141 * Basic sanity checking; wish we could do better. 142 */ 143 static int 144 gotdata(char *buf, size_t len) 145 { 146 char any_set = 0; 147 size_t i; 148 149 for (i = 0; i < len; ++i) 150 any_set |= buf[i]; 151 if (any_set == 0) 152 return -1; 153 return 0; 154 } 155 156 static int 157 getentropy_urandom(void *buf, size_t len) 158 { 159 struct stat st; 160 size_t i; 161 int fd, flags; 162 int save_errno = errno; 163 164 start: 165 166 flags = O_RDONLY; 167 #ifdef O_NOFOLLOW 168 flags |= O_NOFOLLOW; 169 #endif 170 #ifdef O_CLOEXEC 171 flags |= O_CLOEXEC; 172 #endif 173 fd = open("/dev/urandom", flags, 0); 174 if (fd == -1) { 175 if (errno == EINTR) 176 goto start; 177 goto nodevrandom; 178 } 179 #ifndef O_CLOEXEC 180 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC); 181 #endif 182 183 /* Lightly verify that the device node looks sane */ 184 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) { 185 close(fd); 186 goto nodevrandom; 187 } 188 for (i = 0; i < len; ) { 189 size_t wanted = len - i; 190 ssize_t ret = read(fd, (char *)buf + i, wanted); 191 192 if (ret == -1) { 193 if (errno == EAGAIN || errno == EINTR) 194 continue; 195 close(fd); 196 goto nodevrandom; 197 } 198 i += ret; 199 } 200 close(fd); 201 if (gotdata(buf, len) == 0) { 202 errno = save_errno; 203 return 0; /* satisfied */ 204 } 205 nodevrandom: 206 errno = EIO; 207 return -1; 208 } 209 210 static int tcpmib[] = { CTL_NET, AF_INET, IPPROTO_TCP, TCPCTL_STATS }; 211 static int udpmib[] = { CTL_NET, AF_INET, IPPROTO_UDP, UDPCTL_STATS }; 212 static int ipmib[] = { CTL_NET, AF_INET, IPPROTO_IP, IPCTL_STATS }; 213 static int kmib[] = { CTL_KERN, KERN_USRSTACK }; 214 static int hwmib[] = { CTL_HW, HW_USERMEM }; 215 216 static int 217 getentropy_fallback(void *buf, size_t len) 218 { 219 uint8_t results[SHA512_DIGEST_LENGTH]; 220 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat; 221 static int cnt; 222 struct timespec ts; 223 struct timeval tv; 224 struct rusage ru; 225 sigset_t sigset; 226 struct stat st; 227 SHA512_CTX ctx; 228 static pid_t lastpid; 229 pid_t pid; 230 size_t i, ii, m; 231 char *p; 232 struct tcpstat tcpstat; 233 struct udpstat udpstat; 234 struct ipstat ipstat; 235 u_int64_t mach_time; 236 unsigned int idata; 237 void *addr; 238 239 pid = getpid(); 240 if (lastpid == pid) { 241 faster = 1; 242 repeat = 2; 243 } else { 244 faster = 0; 245 lastpid = pid; 246 repeat = REPEAT; 247 } 248 for (i = 0; i < len; ) { 249 int j; 250 SHA512_Init(&ctx); 251 for (j = 0; j < repeat; j++) { 252 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 253 if (e != -1) { 254 cnt += (int)tv.tv_sec; 255 cnt += (int)tv.tv_usec; 256 } 257 258 mach_time = mach_absolute_time(); 259 HD(mach_time); 260 261 ii = sizeof(addr); 262 HX(sysctl(kmib, sizeof(kmib) / sizeof(kmib[0]), 263 &addr, &ii, NULL, 0) == -1, addr); 264 265 ii = sizeof(idata); 266 HX(sysctl(hwmib, sizeof(hwmib) / sizeof(hwmib[0]), 267 &idata, &ii, NULL, 0) == -1, idata); 268 269 ii = sizeof(tcpstat); 270 HX(sysctl(tcpmib, sizeof(tcpmib) / sizeof(tcpmib[0]), 271 &tcpstat, &ii, NULL, 0) == -1, tcpstat); 272 273 ii = sizeof(udpstat); 274 HX(sysctl(udpmib, sizeof(udpmib) / sizeof(udpmib[0]), 275 &udpstat, &ii, NULL, 0) == -1, udpstat); 276 277 ii = sizeof(ipstat); 278 HX(sysctl(ipmib, sizeof(ipmib) / sizeof(ipmib[0]), 279 &ipstat, &ii, NULL, 0) == -1, ipstat); 280 281 HX((pid = getpid()) == -1, pid); 282 HX((pid = getsid(pid)) == -1, pid); 283 HX((pid = getppid()) == -1, pid); 284 HX((pid = getpgid(0)) == -1, pid); 285 HX((e = getpriority(0, 0)) == -1, e); 286 287 if (!faster) { 288 ts.tv_sec = 0; 289 ts.tv_nsec = 1; 290 (void) nanosleep(&ts, NULL); 291 } 292 293 HX(sigpending(&sigset) == -1, sigset); 294 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1, 295 sigset); 296 297 HF(getentropy); /* an addr in this library */ 298 HF(printf); /* an addr in libc */ 299 p = (char *)&p; 300 HD(p); /* an addr on stack */ 301 p = (char *)&errno; 302 HD(p); /* the addr of errno */ 303 304 if (i == 0) { 305 struct sockaddr_storage ss; 306 struct statvfs stvfs; 307 struct termios tios; 308 struct statfs stfs; 309 socklen_t ssl; 310 off_t off; 311 312 /* 313 * Prime-sized mappings encourage fragmentation; 314 * thus exposing some address entropy. 315 */ 316 struct mm { 317 size_t npg; 318 void *p; 319 } mm[] = { 320 { 17, MAP_FAILED }, { 3, MAP_FAILED }, 321 { 11, MAP_FAILED }, { 2, MAP_FAILED }, 322 { 5, MAP_FAILED }, { 3, MAP_FAILED }, 323 { 7, MAP_FAILED }, { 1, MAP_FAILED }, 324 { 57, MAP_FAILED }, { 3, MAP_FAILED }, 325 { 131, MAP_FAILED }, { 1, MAP_FAILED }, 326 }; 327 328 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 329 HX(mm[m].p = mmap(NULL, 330 mm[m].npg * pgs, 331 PROT_READ|PROT_WRITE, 332 MAP_PRIVATE|MAP_ANON, -1, 333 (off_t)0), mm[m].p); 334 if (mm[m].p != MAP_FAILED) { 335 size_t mo; 336 337 /* Touch some memory... */ 338 p = mm[m].p; 339 mo = cnt % 340 (mm[m].npg * pgs - 1); 341 p[mo] = 1; 342 cnt += (int)((long)(mm[m].p) 343 / pgs); 344 } 345 346 /* Check cnts and times... */ 347 mach_time = mach_absolute_time(); 348 HD(mach_time); 349 cnt += (int)mach_time; 350 351 HX((e = getrusage(RUSAGE_SELF, 352 &ru)) == -1, ru); 353 if (e != -1) { 354 cnt += (int)ru.ru_utime.tv_sec; 355 cnt += (int)ru.ru_utime.tv_usec; 356 } 357 } 358 359 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 360 if (mm[m].p != MAP_FAILED) 361 munmap(mm[m].p, mm[m].npg * pgs); 362 mm[m].p = MAP_FAILED; 363 } 364 365 HX(stat(".", &st) == -1, st); 366 HX(statvfs(".", &stvfs) == -1, stvfs); 367 HX(statfs(".", &stfs) == -1, stfs); 368 369 HX(stat("/", &st) == -1, st); 370 HX(statvfs("/", &stvfs) == -1, stvfs); 371 HX(statfs("/", &stfs) == -1, stfs); 372 373 HX((e = fstat(0, &st)) == -1, st); 374 if (e == -1) { 375 if (S_ISREG(st.st_mode) || 376 S_ISFIFO(st.st_mode) || 377 S_ISSOCK(st.st_mode)) { 378 HX(fstatvfs(0, &stvfs) == -1, 379 stvfs); 380 HX(fstatfs(0, &stfs) == -1, 381 stfs); 382 HX((off = lseek(0, (off_t)0, 383 SEEK_CUR)) < 0, off); 384 } 385 if (S_ISCHR(st.st_mode)) { 386 HX(tcgetattr(0, &tios) == -1, 387 tios); 388 } else if (S_ISSOCK(st.st_mode)) { 389 memset(&ss, 0, sizeof ss); 390 ssl = sizeof(ss); 391 HX(getpeername(0, 392 (void *)&ss, &ssl) == -1, 393 ss); 394 } 395 } 396 397 HX((e = getrusage(RUSAGE_CHILDREN, 398 &ru)) == -1, ru); 399 if (e != -1) { 400 cnt += (int)ru.ru_utime.tv_sec; 401 cnt += (int)ru.ru_utime.tv_usec; 402 } 403 } else { 404 /* Subsequent hashes absorb previous result */ 405 HD(results); 406 } 407 408 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 409 if (e != -1) { 410 cnt += (int)tv.tv_sec; 411 cnt += (int)tv.tv_usec; 412 } 413 414 HD(cnt); 415 } 416 417 SHA512_Final(results, &ctx); 418 memcpy((char *)buf + i, results, min(sizeof(results), len - i)); 419 i += min(sizeof(results), len - i); 420 } 421 explicit_bzero(&ctx, sizeof ctx); 422 explicit_bzero(results, sizeof results); 423 if (gotdata(buf, len) == 0) { 424 errno = save_errno; 425 return 0; /* satisfied */ 426 } 427 errno = EIO; 428 return -1; 429 } 430