1 /* $OpenBSD: getentropy_osx.c,v 1.12 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 <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 getentropy_urandom(void *buf, size_t len); 86 static int getentropy_fallback(void *buf, size_t len); 87 88 int 89 getentropy(void *buf, size_t len) 90 { 91 int ret = -1; 92 93 if (len > 256) { 94 errno = EIO; 95 return (-1); 96 } 97 98 /* 99 * Try to get entropy with /dev/urandom 100 * 101 * This can fail if the process is inside a chroot or if file 102 * descriptors are exhausted. 103 */ 104 ret = getentropy_urandom(buf, len); 105 if (ret != -1) 106 return (ret); 107 108 /* 109 * Entropy collection via /dev/urandom and sysctl have failed. 110 * 111 * No other API exists for collecting entropy, and we have 112 * no failsafe way to get it on OSX that is not sensitive 113 * to resource exhaustion. 114 * 115 * We have very few options: 116 * - Even syslog_r is unsafe to call at this low level, so 117 * there is no way to alert the user or program. 118 * - Cannot call abort() because some systems have unsafe 119 * corefiles. 120 * - Could raise(SIGKILL) resulting in silent program termination. 121 * - Return EIO, to hint that arc4random's stir function 122 * should raise(SIGKILL) 123 * - Do the best under the circumstances.... 124 * 125 * This code path exists to bring light to the issue that OSX 126 * does not provide a failsafe API for entropy collection. 127 * 128 * We hope this demonstrates that OSX should consider 129 * providing a new failsafe API which works in a chroot or 130 * when file descriptors are exhausted. 131 */ 132 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK 133 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK 134 raise(SIGKILL); 135 #endif 136 ret = getentropy_fallback(buf, len); 137 if (ret != -1) 138 return (ret); 139 140 errno = EIO; 141 return (ret); 142 } 143 144 static int 145 getentropy_urandom(void *buf, size_t len) 146 { 147 struct stat st; 148 size_t i; 149 int fd, flags; 150 int save_errno = errno; 151 152 start: 153 154 flags = O_RDONLY; 155 #ifdef O_NOFOLLOW 156 flags |= O_NOFOLLOW; 157 #endif 158 #ifdef O_CLOEXEC 159 flags |= O_CLOEXEC; 160 #endif 161 fd = open("/dev/urandom", flags, 0); 162 if (fd == -1) { 163 if (errno == EINTR) 164 goto start; 165 goto nodevrandom; 166 } 167 #ifndef O_CLOEXEC 168 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC); 169 #endif 170 171 /* Lightly verify that the device node looks sane */ 172 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) { 173 close(fd); 174 goto nodevrandom; 175 } 176 for (i = 0; i < len; ) { 177 size_t wanted = len - i; 178 ssize_t ret = read(fd, (char *)buf + i, wanted); 179 180 if (ret == -1) { 181 if (errno == EAGAIN || errno == EINTR) 182 continue; 183 close(fd); 184 goto nodevrandom; 185 } 186 i += ret; 187 } 188 close(fd); 189 errno = save_errno; 190 return (0); /* satisfied */ 191 nodevrandom: 192 errno = EIO; 193 return (-1); 194 } 195 196 #if TARGET_OS_OSX 197 static int tcpmib[] = { CTL_NET, AF_INET, IPPROTO_TCP, TCPCTL_STATS }; 198 static int udpmib[] = { CTL_NET, AF_INET, IPPROTO_UDP, UDPCTL_STATS }; 199 static int ipmib[] = { CTL_NET, AF_INET, IPPROTO_IP, IPCTL_STATS }; 200 #endif 201 static int kmib[] = { CTL_KERN, KERN_USRSTACK }; 202 static int hwmib[] = { CTL_HW, HW_USERMEM }; 203 204 static int 205 getentropy_fallback(void *buf, size_t len) 206 { 207 uint8_t results[SHA512_DIGEST_LENGTH]; 208 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat; 209 static int cnt; 210 struct timespec ts; 211 struct timeval tv; 212 struct rusage ru; 213 sigset_t sigset; 214 struct stat st; 215 SHA512_CTX ctx; 216 static pid_t lastpid; 217 pid_t pid; 218 size_t i, ii, m; 219 char *p; 220 #if TARGET_OS_OSX 221 struct tcpstat tcpstat; 222 struct udpstat udpstat; 223 struct ipstat ipstat; 224 #endif 225 u_int64_t mach_time; 226 unsigned int idata; 227 void *addr; 228 229 pid = getpid(); 230 if (lastpid == pid) { 231 faster = 1; 232 repeat = 2; 233 } else { 234 faster = 0; 235 lastpid = pid; 236 repeat = REPEAT; 237 } 238 for (i = 0; i < len; ) { 239 int j; 240 SHA512_Init(&ctx); 241 for (j = 0; j < repeat; j++) { 242 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 243 if (e != -1) { 244 cnt += (int)tv.tv_sec; 245 cnt += (int)tv.tv_usec; 246 } 247 248 mach_time = mach_absolute_time(); 249 HD(mach_time); 250 251 ii = sizeof(addr); 252 HX(sysctl(kmib, sizeof(kmib) / sizeof(kmib[0]), 253 &addr, &ii, NULL, 0) == -1, addr); 254 255 ii = sizeof(idata); 256 HX(sysctl(hwmib, sizeof(hwmib) / sizeof(hwmib[0]), 257 &idata, &ii, NULL, 0) == -1, idata); 258 259 #if TARGET_OS_OSX 260 ii = sizeof(tcpstat); 261 HX(sysctl(tcpmib, sizeof(tcpmib) / sizeof(tcpmib[0]), 262 &tcpstat, &ii, NULL, 0) == -1, tcpstat); 263 264 ii = sizeof(udpstat); 265 HX(sysctl(udpmib, sizeof(udpmib) / sizeof(udpmib[0]), 266 &udpstat, &ii, NULL, 0) == -1, udpstat); 267 268 ii = sizeof(ipstat); 269 HX(sysctl(ipmib, sizeof(ipmib) / sizeof(ipmib[0]), 270 &ipstat, &ii, NULL, 0) == -1, ipstat); 271 #endif 272 273 HX((pid = getpid()) == -1, pid); 274 HX((pid = getsid(pid)) == -1, pid); 275 HX((pid = getppid()) == -1, pid); 276 HX((pid = getpgid(0)) == -1, pid); 277 HX((e = getpriority(0, 0)) == -1, e); 278 279 if (!faster) { 280 ts.tv_sec = 0; 281 ts.tv_nsec = 1; 282 (void) nanosleep(&ts, NULL); 283 } 284 285 HX(sigpending(&sigset) == -1, sigset); 286 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1, 287 sigset); 288 289 HF(getentropy); /* an addr in this library */ 290 HF(printf); /* an addr in libc */ 291 p = (char *)&p; 292 HD(p); /* an addr on stack */ 293 p = (char *)&errno; 294 HD(p); /* the addr of errno */ 295 296 if (i == 0) { 297 struct sockaddr_storage ss; 298 struct statvfs stvfs; 299 struct termios tios; 300 struct statfs stfs; 301 socklen_t ssl; 302 off_t off; 303 304 /* 305 * Prime-sized mappings encourage fragmentation; 306 * thus exposing some address entropy. 307 */ 308 struct mm { 309 size_t npg; 310 void *p; 311 } mm[] = { 312 { 17, MAP_FAILED }, { 3, MAP_FAILED }, 313 { 11, MAP_FAILED }, { 2, MAP_FAILED }, 314 { 5, MAP_FAILED }, { 3, MAP_FAILED }, 315 { 7, MAP_FAILED }, { 1, MAP_FAILED }, 316 { 57, MAP_FAILED }, { 3, MAP_FAILED }, 317 { 131, MAP_FAILED }, { 1, MAP_FAILED }, 318 }; 319 320 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 321 HX(mm[m].p = mmap(NULL, 322 mm[m].npg * pgs, 323 PROT_READ|PROT_WRITE, 324 MAP_PRIVATE|MAP_ANON, -1, 325 (off_t)0), mm[m].p); 326 if (mm[m].p != MAP_FAILED) { 327 size_t mo; 328 329 /* Touch some memory... */ 330 p = mm[m].p; 331 mo = cnt % 332 (mm[m].npg * pgs - 1); 333 p[mo] = 1; 334 cnt += (int)((long)(mm[m].p) 335 / pgs); 336 } 337 338 /* Check cnts and times... */ 339 mach_time = mach_absolute_time(); 340 HD(mach_time); 341 cnt += (int)mach_time; 342 343 HX((e = getrusage(RUSAGE_SELF, 344 &ru)) == -1, ru); 345 if (e != -1) { 346 cnt += (int)ru.ru_utime.tv_sec; 347 cnt += (int)ru.ru_utime.tv_usec; 348 } 349 } 350 351 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { 352 if (mm[m].p != MAP_FAILED) 353 munmap(mm[m].p, mm[m].npg * pgs); 354 mm[m].p = MAP_FAILED; 355 } 356 357 HX(stat(".", &st) == -1, st); 358 HX(statvfs(".", &stvfs) == -1, stvfs); 359 HX(statfs(".", &stfs) == -1, stfs); 360 361 HX(stat("/", &st) == -1, st); 362 HX(statvfs("/", &stvfs) == -1, stvfs); 363 HX(statfs("/", &stfs) == -1, stfs); 364 365 HX((e = fstat(0, &st)) == -1, st); 366 if (e == -1) { 367 if (S_ISREG(st.st_mode) || 368 S_ISFIFO(st.st_mode) || 369 S_ISSOCK(st.st_mode)) { 370 HX(fstatvfs(0, &stvfs) == -1, 371 stvfs); 372 HX(fstatfs(0, &stfs) == -1, 373 stfs); 374 HX((off = lseek(0, (off_t)0, 375 SEEK_CUR)) < 0, off); 376 } 377 if (S_ISCHR(st.st_mode)) { 378 HX(tcgetattr(0, &tios) == -1, 379 tios); 380 } else if (S_ISSOCK(st.st_mode)) { 381 memset(&ss, 0, sizeof ss); 382 ssl = sizeof(ss); 383 HX(getpeername(0, 384 (void *)&ss, &ssl) == -1, 385 ss); 386 } 387 } 388 389 HX((e = getrusage(RUSAGE_CHILDREN, 390 &ru)) == -1, ru); 391 if (e != -1) { 392 cnt += (int)ru.ru_utime.tv_sec; 393 cnt += (int)ru.ru_utime.tv_usec; 394 } 395 } else { 396 /* Subsequent hashes absorb previous result */ 397 HD(results); 398 } 399 400 HX((e = gettimeofday(&tv, NULL)) == -1, tv); 401 if (e != -1) { 402 cnt += (int)tv.tv_sec; 403 cnt += (int)tv.tv_usec; 404 } 405 406 HD(cnt); 407 } 408 409 SHA512_Final(results, &ctx); 410 memcpy((char *)buf + i, results, min(sizeof(results), len - i)); 411 i += min(sizeof(results), len - i); 412 } 413 explicit_bzero(&ctx, sizeof ctx); 414 explicit_bzero(results, sizeof results); 415 errno = save_errno; 416 return (0); /* satisfied */ 417 } 418