lib/libcrypto/arc4random/getentropy_osx.c

   1 /*      $OpenBSD: getentropy_osx.c,v 1.11.8.1 2018/12/15 15:10:12 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 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 }