unbound/compat/getentropy_osx.c

   1 /*      $OpenBSD: getentropy_osx.c,v 1.3 2014/07/12 14:48:00 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 #include "config.h"
  20
  21 #include <sys/types.h>
  22 #include <sys/param.h>
  23 #include <sys/ioctl.h>
  24 #include <sys/resource.h>
  25 #include <sys/syscall.h>
  26 #include <sys/sysctl.h>
  27 #include <sys/statvfs.h>
  28 #include <sys/socket.h>
  29 #include <sys/mount.h>
  30 #include <sys/mman.h>
  31 #include <sys/stat.h>
  32 #include <sys/time.h>
  33 #include <stdlib.h>
  34 #include <stdint.h>
  35 #include <stdio.h>
  36 #include <termios.h>
  37 #include <fcntl.h>
  38 #include <signal.h>
  39 #include <string.h>
  40 #include <errno.h>
  41 #include <unistd.h>
  42 #include <time.h>
  43 #include <mach/mach_time.h>
  44 #include <mach/mach_host.h>
  45 #include <mach/host_info.h>
  46 #include <sys/socketvar.h>
  47 #include <sys/vmmeter.h>
  48 #include <netinet/in.h>
  49 #include <netinet/tcp.h>
  50 #include <netinet/udp.h>
  51 #include <netinet/ip_var.h>
  52 #include <netinet/tcp_var.h>
  53 #include <netinet/udp_var.h>
  54 #include <CommonCrypto/CommonDigest.h>
  55 #define SHA512_Update(a, b, c)  (CC_SHA512_Update((a), (b), (c)))
  56 #define SHA512_Init(xxx) (CC_SHA512_Init((xxx)))
  57 #define SHA512_Final(xxx, yyy) (CC_SHA512_Final((xxx), (yyy)))
  58 #define SHA512_CTX CC_SHA512_CTX
  59 #define SHA512_DIGEST_LENGTH CC_SHA512_DIGEST_LENGTH
  60
  61 #define REPEAT 5
  62 #define min(a, b) (((a) < (b)) ? (a) : (b))
  63
  64 #define HX(a, b) \
  65         do { \
  66                 if ((a)) \
  67                         HD(errno); \
  68                 else \
  69                         HD(b); \
  70         } while (0)
  71
  72 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
  73 #define HD(x)    (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
  74 #define HF(x)    (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))
  75
  76 int     getentropy(void *buf, size_t len);
  77
  78 #ifdef CAN_REFERENCE_MAIN
  79 extern int main(int, char *argv[]);
  80 #endif
  81 static int gotdata(char *buf, size_t len);
  82 static int getentropy_urandom(void *buf, size_t len);
  83 static int getentropy_fallback(void *buf, size_t len);
  84
  85 int
  86 getentropy(void *buf, size_t len)
  87 {
  88         int ret = -1;
  89
  90         if (len > 256) {
  91                 errno = EIO;
  92                 return -1;
  93         }
  94
  95         /*
  96          * Try to get entropy with /dev/urandom
  97          *
  98          * This can fail if the process is inside a chroot or if file
  99          * descriptors are exhausted.
 100          */
 101         ret = getentropy_urandom(buf, len);
 102         if (ret != -1)
 103                 return (ret);
 104
 105         /*
 106          * Entropy collection via /dev/urandom and sysctl have failed.
 107          *
 108          * No other API exists for collecting entropy, and we have
 109          * no failsafe way to get it on OSX that is not sensitive
 110          * to resource exhaustion.
 111          *
 112          * We have very few options:
 113          *     - Even syslog_r is unsafe to call at this low level, so
 114          *       there is no way to alert the user or program.
 115          *     - Cannot call abort() because some systems have unsafe
 116          *       corefiles.
 117          *     - Could raise(SIGKILL) resulting in silent program termination.
 118          *     - Return EIO, to hint that arc4random's stir function
 119          *       should raise(SIGKILL)
 120          *     - Do the best under the circumstances....
 121          *
 122          * This code path exists to bring light to the issue that OSX
 123          * does not provide a failsafe API for entropy collection.
 124          *
 125          * We hope this demonstrates that OSX should consider
 126          * providing a new failsafe API which works in a chroot or
 127          * when file descriptors are exhausted.
 128          */
 129 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
 130 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
 131         raise(SIGKILL);
 132 #endif
 133         ret = getentropy_fallback(buf, len);
 134         if (ret != -1)
 135                 return (ret);
 136
 137         errno = EIO;
 138         return (ret);
 139 }
 140
 141 /*
 142  * Basic sanity checking; wish we could do better.
 143  */
 144 static int
 145 gotdata(char *buf, size_t len)
 146 {
 147         char    any_set = 0;
 148         size_t  i;
 149
 150         for (i = 0; i < len; ++i)
 151                 any_set |= buf[i];
 152         if (any_set == 0)
 153                 return -1;
 154         return 0;
 155 }
 156
 157 static int
 158 getentropy_urandom(void *buf, size_t len)
 159 {
 160         struct stat st;
 161         size_t i;
 162         int fd, flags;
 163         int save_errno = errno;
 164
 165 start:
 166
 167         flags = O_RDONLY;
 168 #ifdef O_NOFOLLOW
 169         flags |= O_NOFOLLOW;
 170 #endif
 171 #ifdef O_CLOEXEC
 172         flags |= O_CLOEXEC;
 173 #endif
 174         fd = open("/dev/urandom", flags, 0);
 175         if (fd == -1) {
 176                 if (errno == EINTR)
 177                         goto start;
 178                 goto nodevrandom;
 179         }
 180 #ifndef O_CLOEXEC
 181         fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
 182 #endif
 183
 184         /* Lightly verify that the device node looks sane */
 185         if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
 186                 close(fd);
 187                 goto nodevrandom;
 188         }
 189         for (i = 0; i < len; ) {
 190                 size_t wanted = len - i;
 191                 ssize_t ret = read(fd, (char*)buf + i, wanted);
 192
 193                 if (ret == -1) {
 194                         if (errno == EAGAIN || errno == EINTR)
 195                                 continue;
 196                         close(fd);
 197                         goto nodevrandom;
 198                 }
 199                 i += ret;
 200         }
 201         close(fd);
 202         if (gotdata(buf, len) == 0) {
 203                 errno = save_errno;
 204                 return 0;               /* satisfied */
 205         }
 206 nodevrandom:
 207         errno = EIO;
 208         return -1;
 209 }
 210
 211 static int tcpmib[] = { CTL_NET, AF_INET, IPPROTO_TCP, TCPCTL_STATS };
 212 static int udpmib[] = { CTL_NET, AF_INET, IPPROTO_UDP, UDPCTL_STATS };
 213 static int ipmib[] = { CTL_NET, AF_INET, IPPROTO_IP, IPCTL_STATS };
 214 static int kmib[] = { CTL_KERN, KERN_USRSTACK };
 215 static int hwmib[] = { CTL_HW, HW_USERMEM };
 216
 217 static int
 218 getentropy_fallback(void *buf, size_t len)
 219 {
 220         uint8_t results[SHA512_DIGEST_LENGTH];
 221         int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
 222         static int cnt;
 223         struct timespec ts;
 224         struct timeval tv;
 225         struct rusage ru;
 226         sigset_t sigset;
 227         struct stat st;
 228         SHA512_CTX ctx;
 229         static pid_t lastpid;
 230         pid_t pid;
 231         size_t i, ii, m;
 232         char *p;
 233         struct tcpstat tcpstat;
 234         struct udpstat udpstat;
 235         struct ipstat ipstat;
 236         u_int64_t mach_time;
 237         unsigned int idata;
 238         void *addr;
 239
 240         pid = getpid();
 241         if (lastpid == pid) {
 242                 faster = 1;
 243                 repeat = 2;
 244         } else {
 245                 faster = 0;
 246                 lastpid = pid;
 247                 repeat = REPEAT;
 248         }
 249         for (i = 0; i < len; ) {
 250                 int j;
 251                 SHA512_Init(&ctx);
 252                 for (j = 0; j < repeat; j++) {
 253                         HX((e = gettimeofday(&tv, NULL)) == -1, tv);
 254                         if (e != -1) {
 255                                 cnt += (int)tv.tv_sec;
 256                                 cnt += (int)tv.tv_usec;
 257                         }
 258
 259                         mach_time = mach_absolute_time();
 260                         HD(mach_time);
 261
 262                         ii = sizeof(addr);
 263                         HX(sysctl(kmib, sizeof(kmib) / sizeof(kmib[0]),
 264                             &addr, &ii, NULL, 0) == -1, addr);
 265
 266                         ii = sizeof(idata);
 267                         HX(sysctl(hwmib, sizeof(hwmib) / sizeof(hwmib[0]),
 268                             &idata, &ii, NULL, 0) == -1, idata);
 269
 270                         ii = sizeof(tcpstat);
 271                         HX(sysctl(tcpmib, sizeof(tcpmib) / sizeof(tcpmib[0]),
 272                             &tcpstat, &ii, NULL, 0) == -1, tcpstat);
 273
 274                         ii = sizeof(udpstat);
 275                         HX(sysctl(udpmib, sizeof(udpmib) / sizeof(udpmib[0]),
 276                             &udpstat, &ii, NULL, 0) == -1, udpstat);
 277
 278                         ii = sizeof(ipstat);
 279                         HX(sysctl(ipmib, sizeof(ipmib) / sizeof(ipmib[0]),
 280                             &ipstat, &ii, NULL, 0) == -1, ipstat);
 281
 282                         HX((pid = getpid()) == -1, pid);
 283                         HX((pid = getsid(pid)) == -1, pid);
 284                         HX((pid = getppid()) == -1, pid);
 285                         HX((pid = getpgid(0)) == -1, pid);
 286                         HX((e = getpriority(0, 0)) == -1, e);
 287
 288                         if (!faster) {
 289                                 ts.tv_sec = 0;
 290                                 ts.tv_nsec = 1;
 291                                 (void) nanosleep(&ts, NULL);
 292                         }
 293
 294                         HX(sigpending(&sigset) == -1, sigset);
 295                         HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
 296                             sigset);
 297
 298 #ifdef CAN_REFERENCE_MAIN
 299                         HF(main);               /* an addr in program */
 300 #endif
 301                         HF(getentropy); /* an addr in this library */
 302                         HF(printf);             /* an addr in libc */
 303                         p = (char *)&p;
 304                         HD(p);          /* an addr on stack */
 305                         p = (char *)&errno;
 306                         HD(p);          /* the addr of errno */
 307
 308                         if (i == 0) {
 309                                 struct sockaddr_storage ss;
 310                                 struct statvfs stvfs;
 311                                 struct termios tios;
 312                                 struct statfs stfs;
 313                                 socklen_t ssl;
 314                                 off_t off;
 315
 316                                 /*
 317                                  * Prime-sized mappings encourage fragmentation;
 318                                  * thus exposing some address entropy.
 319                                  */
 320                                 struct mm {
 321                                         size_t  npg;
 322                                         void    *p;
 323                                 } mm[] =         {
 324                                         { 17, MAP_FAILED }, { 3, MAP_FAILED },
 325                                         { 11, MAP_FAILED }, { 2, MAP_FAILED },
 326                                         { 5, MAP_FAILED }, { 3, MAP_FAILED },
 327                                         { 7, MAP_FAILED }, { 1, MAP_FAILED },
 328                                         { 57, MAP_FAILED }, { 3, MAP_FAILED },
 329                                         { 131, MAP_FAILED }, { 1, MAP_FAILED },
 330                                 };
 331
 332                                 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
 333                                         HX(mm[m].p = mmap(NULL,
 334                                             mm[m].npg * pgs,
 335                                             PROT_READ|PROT_WRITE,
 336                                             MAP_PRIVATE|MAP_ANON, -1,
 337                                             (off_t)0), mm[m].p);
 338                                         if (mm[m].p != MAP_FAILED) {
 339                                                 size_t mo;
 340
 341                                                 /* Touch some memory... */
 342                                                 p = mm[m].p;
 343                                                 mo = cnt %
 344                                                     (mm[m].npg * pgs - 1);
 345                                                 p[mo] = 1;
 346                                                 cnt += (int)((long)(mm[m].p)
 347                                                     / pgs);
 348                                         }
 349
 350                                         /* Check cnts and times... */
 351                                         mach_time = mach_absolute_time();
 352                                         HD(mach_time);
 353                                         cnt += (int)mach_time;
 354
 355                                         HX((e = getrusage(RUSAGE_SELF,
 356                                             &ru)) == -1, ru);
 357                                         if (e != -1) {
 358                                                 cnt += (int)ru.ru_utime.tv_sec;
 359                                                 cnt += (int)ru.ru_utime.tv_usec;
 360                                         }
 361                                 }
 362
 363                                 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
 364                                         if (mm[m].p != MAP_FAILED)
 365                                                 munmap(mm[m].p, mm[m].npg * pgs);
 366                                         mm[m].p = MAP_FAILED;
 367                                 }
 368
 369                                 HX(stat(".", &st) == -1, st);
 370                                 HX(statvfs(".", &stvfs) == -1, stvfs);
 371                                 HX(statfs(".", &stfs) == -1, stfs);
 372
 373                                 HX(stat("/", &st) == -1, st);
 374                                 HX(statvfs("/", &stvfs) == -1, stvfs);
 375                                 HX(statfs("/", &stfs) == -1, stfs);
 376
 377                                 HX((e = fstat(0, &st)) == -1, st);
 378                                 if (e == -1) {
 379                                         if (S_ISREG(st.st_mode) ||
 380                                             S_ISFIFO(st.st_mode) ||
 381                                             S_ISSOCK(st.st_mode)) {
 382                                                 HX(fstatvfs(0, &stvfs) == -1,
 383                                                     stvfs);
 384                                                 HX(fstatfs(0, &stfs) == -1,
 385                                                     stfs);
 386                                                 HX((off = lseek(0, (off_t)0,
 387                                                     SEEK_CUR)) < 0, off);
 388                                         }
 389                                         if (S_ISCHR(st.st_mode)) {
 390                                                 HX(tcgetattr(0, &tios) == -1,
 391                                                     tios);
 392                                         } else if (S_ISSOCK(st.st_mode)) {
 393                                                 memset(&ss, 0, sizeof ss);
 394                                                 ssl = sizeof(ss);
 395                                                 HX(getpeername(0,
 396                                                     (void *)&ss, &ssl) == -1,
 397                                                     ss);
 398                                         }
 399                                 }
 400
 401                                 HX((e = getrusage(RUSAGE_CHILDREN,
 402                                     &ru)) == -1, ru);
 403                                 if (e != -1) {
 404                                         cnt += (int)ru.ru_utime.tv_sec;
 405                                         cnt += (int)ru.ru_utime.tv_usec;
 406                                 }
 407                         } else {
 408                                 /* Subsequent hashes absorb previous result */
 409                                 HD(results);
 410                         }
 411
 412                         HX((e = gettimeofday(&tv, NULL)) == -1, tv);
 413                         if (e != -1) {
 414                                 cnt += (int)tv.tv_sec;
 415                                 cnt += (int)tv.tv_usec;
 416                         }
 417
 418                         HD(cnt);
 419                 }
 420
 421                 SHA512_Final(results, &ctx);
 422                 memcpy((char*)buf + i, results, min(sizeof(results), len - i));
 423                 i += min(sizeof(results), len - i);
 424         }
 425         memset(results, 0, sizeof results);
 426         if (gotdata(buf, len) == 0) {
 427                 errno = save_errno;
 428                 return 0;               /* satisfied */
 429         }
 430         errno = EIO;
 431         return -1;
 432 }