lib/libcrypto/arc4random/getentropy_osx.c

   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 }