unbound/compat/getentropy_linux.c

   1 /*      $OpenBSD: getentropy_linux.c,v 1.20 2014/07/12 15:43:49 beck 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 /*
  22 #define _POSIX_C_SOURCE 199309L
  23 #define _GNU_SOURCE     1
  24 */
  25 #include <sys/types.h>
  26 #include <sys/param.h>
  27 #include <sys/ioctl.h>
  28 #include <sys/resource.h>
  29 #include <sys/syscall.h>
  30 #ifdef HAVE_SYS_SYSCTL_H
  31 #include <sys/sysctl.h>
  32 #endif
  33 #include <sys/statvfs.h>
  34 #include <sys/socket.h>
  35 #include <sys/mount.h>
  36 #include <sys/mman.h>
  37 #include <sys/stat.h>
  38 #include <sys/time.h>
  39 #include <stdlib.h>
  40 #include <stdint.h>
  41 #include <stdio.h>
  42 #include <termios.h>
  43 #include <fcntl.h>
  44 #include <signal.h>
  45 #include <string.h>
  46 #include <errno.h>
  47 #include <unistd.h>
  48 #include <time.h>
  49 #include <openssl/sha.h>
  50
  51 #include <linux/types.h>
  52 #include <linux/random.h>
  53 #include <linux/sysctl.h>
  54 #ifdef HAVE_GETAUXVAL
  55 #include <sys/auxv.h>
  56 #endif
  57 #include <sys/vfs.h>
  58
  59 #define REPEAT 5
  60 #define min(a, b) (((a) < (b)) ? (a) : (b))
  61
  62 #define HX(a, b) \
  63         do { \
  64                 if ((a)) \
  65                         HD(errno); \
  66                 else \
  67                         HD(b); \
  68         } while (0)
  69
  70 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
  71 #define HD(x)    (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
  72 #define HF(x)    (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))
  73
  74 int     getentropy(void *buf, size_t len);
  75
  76 #ifdef CAN_REFERENCE_MAIN
  77 extern int main(int, char *argv[]);
  78 #endif
  79 static int gotdata(char *buf, size_t len);
  80 static int getentropy_urandom(void *buf, size_t len);
  81 #ifdef SYS__sysctl
  82 static int getentropy_sysctl(void *buf, size_t len);
  83 #endif
  84 static int getentropy_fallback(void *buf, size_t len);
  85
  86 int
  87 getentropy(void *buf, size_t len)
  88 {
  89         int ret = -1;
  90
  91         if (len > 256) {
  92                 errno = EIO;
  93                 return -1;
  94         }
  95
  96         /*
  97          * Try to get entropy with /dev/urandom
  98          *
  99          * This can fail if the process is inside a chroot or if file
 100          * descriptors are exhausted.
 101          */
 102         ret = getentropy_urandom(buf, len);
 103         if (ret != -1)
 104                 return (ret);
 105
 106 #ifdef SYS__sysctl
 107         /*
 108          * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID.
 109          * sysctl is a failsafe API, so it guarantees a result.  This
 110          * should work inside a chroot, or when file descriptors are
 111          * exhuasted.
 112          *
 113          * However this can fail if the Linux kernel removes support
 114          * for sysctl.  Starting in 2007, there have been efforts to
 115          * deprecate the sysctl API/ABI, and push callers towards use
 116          * of the chroot-unavailable fd-using /proc mechanism --
 117          * essentially the same problems as /dev/urandom.
 118          *
 119          * Numerous setbacks have been encountered in their deprecation
 120          * schedule, so as of June 2014 the kernel ABI still exists on
 121          * most Linux architectures. The sysctl() stub in libc is missing
 122          * on some systems.  There are also reports that some kernels
 123          * spew messages to the console.
 124          */
 125         ret = getentropy_sysctl(buf, len);
 126         if (ret != -1)
 127                 return (ret);
 128 #endif /* SYS__sysctl */
 129
 130         /*
 131          * Entropy collection via /dev/urandom and sysctl have failed.
 132          *
 133          * No other API exists for collecting entropy.  See the large
 134          * comment block above.
 135          *
 136          * We have very few options:
 137          *     - Even syslog_r is unsafe to call at this low level, so
 138          *       there is no way to alert the user or program.
 139          *     - Cannot call abort() because some systems have unsafe
 140          *       corefiles.
 141          *     - Could raise(SIGKILL) resulting in silent program termination.
 142          *     - Return EIO, to hint that arc4random's stir function
 143          *       should raise(SIGKILL)
 144          *     - Do the best under the circumstances....
 145          *
 146          * This code path exists to bring light to the issue that Linux
 147          * does not provide a failsafe API for entropy collection.
 148          *
 149          * We hope this demonstrates that Linux should either retain their
 150          * sysctl ABI, or consider providing a new failsafe API which
 151          * works in a chroot or when file descriptors are exhausted.
 152          */
 153 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
 154 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
 155         raise(SIGKILL);
 156 #endif
 157         ret = getentropy_fallback(buf, len);
 158         if (ret != -1)
 159                 return (ret);
 160
 161         errno = EIO;
 162         return (ret);
 163 }
 164
 165 /*
 166  * Basic sanity checking; wish we could do better.
 167  */
 168 static int
 169 gotdata(char *buf, size_t len)
 170 {
 171         char    any_set = 0;
 172         size_t  i;
 173
 174         for (i = 0; i < len; ++i)
 175                 any_set |= buf[i];
 176         if (any_set == 0)
 177                 return -1;
 178         return 0;
 179 }
 180
 181 static int
 182 getentropy_urandom(void *buf, size_t len)
 183 {
 184         struct stat st;
 185         size_t i;
 186         int fd, cnt, flags;
 187         int save_errno = errno;
 188
 189 start:
 190
 191         flags = O_RDONLY;
 192 #ifdef O_NOFOLLOW
 193         flags |= O_NOFOLLOW;
 194 #endif
 195 #ifdef O_CLOEXEC
 196         flags |= O_CLOEXEC;
 197 #endif
 198         fd = open("/dev/urandom", flags, 0);
 199         if (fd == -1) {
 200                 if (errno == EINTR)
 201                         goto start;
 202                 goto nodevrandom;
 203         }
 204 #ifndef O_CLOEXEC
 205         fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
 206 #endif
 207
 208         /* Lightly verify that the device node looks sane */
 209         if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
 210                 close(fd);
 211                 goto nodevrandom;
 212         }
 213         if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) {
 214                 close(fd);
 215                 goto nodevrandom;
 216         }
 217         for (i = 0; i < len; ) {
 218                 size_t wanted = len - i;
 219                 ssize_t ret = read(fd, (char*)buf + i, wanted);
 220
 221                 if (ret == -1) {
 222                         if (errno == EAGAIN || errno == EINTR)
 223                                 continue;
 224                         close(fd);
 225                         goto nodevrandom;
 226                 }
 227                 i += ret;
 228         }
 229         close(fd);
 230         if (gotdata(buf, len) == 0) {
 231                 errno = save_errno;
 232                 return 0;               /* satisfied */
 233         }
 234 nodevrandom:
 235         errno = EIO;
 236         return -1;
 237 }
 238
 239 #ifdef SYS__sysctl
 240 static int
 241 getentropy_sysctl(void *buf, size_t len)
 242 {
 243         static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
 244         size_t i;
 245         int save_errno = errno;
 246
 247         for (i = 0; i < len; ) {
 248                 size_t chunk = min(len - i, 16);
 249
 250                 /* SYS__sysctl because some systems already removed sysctl() */
 251                 struct __sysctl_args args = {
 252                         .name = mib,
 253                         .nlen = 3,
 254                         .oldval = buf + i,
 255                         .oldlenp = &chunk,
 256                 };
 257                 if (syscall(SYS__sysctl, &args) != 0)
 258                         goto sysctlfailed;
 259                 i += chunk;
 260         }
 261         if (gotdata(buf, len) == 0) {
 262                 errno = save_errno;
 263                 return (0);                     /* satisfied */
 264         }
 265 sysctlfailed:
 266         errno = EIO;
 267         return -1;
 268 }
 269 #endif /* SYS__sysctl */
 270
 271 static int cl[] = {
 272         CLOCK_REALTIME,
 273 #ifdef CLOCK_MONOTONIC
 274         CLOCK_MONOTONIC,
 275 #endif
 276 #ifdef CLOCK_MONOTONIC_RAW
 277         CLOCK_MONOTONIC_RAW,
 278 #endif
 279 #ifdef CLOCK_TAI
 280         CLOCK_TAI,
 281 #endif
 282 #ifdef CLOCK_VIRTUAL
 283         CLOCK_VIRTUAL,
 284 #endif
 285 #ifdef CLOCK_UPTIME
 286         CLOCK_UPTIME,
 287 #endif
 288 #ifdef CLOCK_PROCESS_CPUTIME_ID
 289         CLOCK_PROCESS_CPUTIME_ID,
 290 #endif
 291 #ifdef CLOCK_THREAD_CPUTIME_ID
 292         CLOCK_THREAD_CPUTIME_ID,
 293 #endif
 294 };
 295
 296 static int
 297 getentropy_fallback(void *buf, size_t len)
 298 {
 299         uint8_t results[SHA512_DIGEST_LENGTH];
 300         int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
 301         static int cnt;
 302         struct timespec ts;
 303         struct timeval tv;
 304         struct rusage ru;
 305         sigset_t sigset;
 306         struct stat st;
 307         SHA512_CTX ctx;
 308         static pid_t lastpid;
 309         pid_t pid;
 310         size_t i, ii, m;
 311         char *p;
 312
 313         pid = getpid();
 314         if (lastpid == pid) {
 315                 faster = 1;
 316                 repeat = 2;
 317         } else {
 318                 faster = 0;
 319                 lastpid = pid;
 320                 repeat = REPEAT;
 321         }
 322         for (i = 0; i < len; ) {
 323                 int j;
 324                 SHA512_Init(&ctx);
 325                 for (j = 0; j < repeat; j++) {
 326                         HX((e = gettimeofday(&tv, NULL)) == -1, tv);
 327                         if (e != -1) {
 328                                 cnt += (int)tv.tv_sec;
 329                                 cnt += (int)tv.tv_usec;
 330                         }
 331
 332                         for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
 333                                 HX(clock_gettime(cl[ii], &ts) == -1, ts);
 334
 335                         HX((pid = getpid()) == -1, pid);
 336                         HX((pid = getsid(pid)) == -1, pid);
 337                         HX((pid = getppid()) == -1, pid);
 338                         HX((pid = getpgid(0)) == -1, pid);
 339                         HX((e = getpriority(0, 0)) == -1, e);
 340
 341                         if (!faster) {
 342                                 ts.tv_sec = 0;
 343                                 ts.tv_nsec = 1;
 344                                 (void) nanosleep(&ts, NULL);
 345                         }
 346
 347                         HX(sigpending(&sigset) == -1, sigset);
 348                         HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
 349                             sigset);
 350
 351 #ifdef CAN_REFERENCE_MAIN
 352                         HF(main);               /* an addr in program */
 353 #endif
 354                         HF(getentropy); /* an addr in this library */
 355                         HF(printf);             /* an addr in libc */
 356                         p = (char *)&p;
 357                         HD(p);          /* an addr on stack */
 358                         p = (char *)&errno;
 359                         HD(p);          /* the addr of errno */
 360
 361                         if (i == 0) {
 362                                 struct sockaddr_storage ss;
 363                                 struct statvfs stvfs;
 364                                 struct termios tios;
 365                                 struct statfs stfs;
 366                                 socklen_t ssl;
 367                                 off_t off;
 368
 369                                 /*
 370                                  * Prime-sized mappings encourage fragmentation;
 371                                  * thus exposing some address entropy.
 372                                  */
 373                                 struct mm {
 374                                         size_t  npg;
 375                                         void    *p;
 376                                 } mm[] =         {
 377                                         { 17, MAP_FAILED }, { 3, MAP_FAILED },
 378                                         { 11, MAP_FAILED }, { 2, MAP_FAILED },
 379                                         { 5, MAP_FAILED }, { 3, MAP_FAILED },
 380                                         { 7, MAP_FAILED }, { 1, MAP_FAILED },
 381                                         { 57, MAP_FAILED }, { 3, MAP_FAILED },
 382                                         { 131, MAP_FAILED }, { 1, MAP_FAILED },
 383                                 };
 384
 385                                 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
 386                                         HX(mm[m].p = mmap(NULL,
 387                                             mm[m].npg * pgs,
 388                                             PROT_READ|PROT_WRITE,
 389                                             MAP_PRIVATE|MAP_ANON, -1,
 390                                             (off_t)0), mm[m].p);
 391                                         if (mm[m].p != MAP_FAILED) {
 392                                                 size_t mo;
 393
 394                                                 /* Touch some memory... */
 395                                                 p = mm[m].p;
 396                                                 mo = cnt %
 397                                                     (mm[m].npg * pgs - 1);
 398                                                 p[mo] = 1;
 399                                                 cnt += (int)((long)(mm[m].p)
 400                                                     / pgs);
 401                                         }
 402
 403                                         /* Check cnts and times... */
 404                                         for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
 405                                             ii++) {
 406                                                 HX((e = clock_gettime(cl[ii],
 407                                                     &ts)) == -1, ts);
 408                                                 if (e != -1)
 409                                                         cnt += (int)ts.tv_nsec;
 410                                         }
 411
 412                                         HX((e = getrusage(RUSAGE_SELF,
 413                                             &ru)) == -1, ru);
 414                                         if (e != -1) {
 415                                                 cnt += (int)ru.ru_utime.tv_sec;
 416                                                 cnt += (int)ru.ru_utime.tv_usec;
 417                                         }
 418                                 }
 419
 420                                 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
 421                                         if (mm[m].p != MAP_FAILED)
 422                                                 munmap(mm[m].p, mm[m].npg * pgs);
 423                                         mm[m].p = MAP_FAILED;
 424                                 }
 425
 426                                 HX(stat(".", &st) == -1, st);
 427                                 HX(statvfs(".", &stvfs) == -1, stvfs);
 428                                 HX(statfs(".", &stfs) == -1, stfs);
 429
 430                                 HX(stat("/", &st) == -1, st);
 431                                 HX(statvfs("/", &stvfs) == -1, stvfs);
 432                                 HX(statfs("/", &stfs) == -1, stfs);
 433
 434                                 HX((e = fstat(0, &st)) == -1, st);
 435                                 if (e == -1) {
 436                                         if (S_ISREG(st.st_mode) ||
 437                                             S_ISFIFO(st.st_mode) ||
 438                                             S_ISSOCK(st.st_mode)) {
 439                                                 HX(fstatvfs(0, &stvfs) == -1,
 440                                                     stvfs);
 441                                                 HX(fstatfs(0, &stfs) == -1,
 442                                                     stfs);
 443                                                 HX((off = lseek(0, (off_t)0,
 444                                                     SEEK_CUR)) < 0, off);
 445                                         }
 446                                         if (S_ISCHR(st.st_mode)) {
 447                                                 HX(tcgetattr(0, &tios) == -1,
 448                                                     tios);
 449                                         } else if (S_ISSOCK(st.st_mode)) {
 450                                                 memset(&ss, 0, sizeof ss);
 451                                                 ssl = sizeof(ss);
 452                                                 HX(getpeername(0,
 453                                                     (void *)&ss, &ssl) == -1,
 454                                                     ss);
 455                                         }
 456                                 }
 457
 458                                 HX((e = getrusage(RUSAGE_CHILDREN,
 459                                     &ru)) == -1, ru);
 460                                 if (e != -1) {
 461                                         cnt += (int)ru.ru_utime.tv_sec;
 462                                         cnt += (int)ru.ru_utime.tv_usec;
 463                                 }
 464                         } else {
 465                                 /* Subsequent hashes absorb previous result */
 466                                 HD(results);
 467                         }
 468
 469                         HX((e = gettimeofday(&tv, NULL)) == -1, tv);
 470                         if (e != -1) {
 471                                 cnt += (int)tv.tv_sec;
 472                                 cnt += (int)tv.tv_usec;
 473                         }
 474
 475                         HD(cnt);
 476                 }
 477 #ifdef AT_RANDOM
 478                 /* Not as random as you think but we take what we are given */
 479                 p = (char *) getauxval(AT_RANDOM);
 480                 if (p)
 481                         HR(p, 16);
 482 #endif
 483 #ifdef AT_SYSINFO_EHDR
 484                 p = (char *) getauxval(AT_SYSINFO_EHDR);
 485                 if (p)
 486                         HR(p, pgs);
 487 #endif
 488 #ifdef AT_BASE
 489                 p = (char *) getauxval(AT_BASE);
 490                 if (p)
 491                         HD(p);
 492 #endif
 493
 494                 SHA512_Final(results, &ctx);
 495                 memcpy((char*)buf + i, results, min(sizeof(results), len - i));
 496                 i += min(sizeof(results), len - i);
 497         }
 498         memset(results, 0, sizeof results);
 499         if (gotdata(buf, len) == 0) {
 500                 errno = save_errno;
 501                 return 0;               /* satisfied */
 502         }
 503         errno = EIO;
 504         return -1;
 505 }