providers/implementations/rands/seeding/rand_unix.c

   1 /*
   2  * Copyright 1995-2023 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the Apache License 2.0 (the "License").  You may not use
   5  * this file except in compliance with the License.  You can obtain a copy
   6  * in the file LICENSE in the source distribution or at
   7  * https://www.openssl.org/source/license.html
   8  */
   9
  10 #ifndef _GNU_SOURCE
  11 # define _GNU_SOURCE
  12 #endif
  13 #include "internal/e_os.h"
  14 #include <stdio.h>
  15 #include "internal/cryptlib.h"
  16 #include <openssl/rand.h>
  17 #include <openssl/crypto.h>
  18 #include "crypto/rand_pool.h"
  19 #include "crypto/rand.h"
  20 #include "internal/dso.h"
  21 #include "internal/nelem.h"
  22 #include "prov/seeding.h"
  23
  24 #ifdef __linux
  25 # include <sys/syscall.h>
  26 # ifdef DEVRANDOM_WAIT
  27 #  include <sys/shm.h>
  28 #  include <sys/utsname.h>
  29 # endif
  30 #endif
  31 #if (defined(__FreeBSD__) || defined(__NetBSD__)) && !defined(OPENSSL_SYS_UEFI)
  32 # include <sys/types.h>
  33 # include <sys/sysctl.h>
  34 # include <sys/param.h>
  35 #endif
  36 #if defined(__OpenBSD__)
  37 # include <sys/param.h>
  38 #endif
  39 #if defined(__DragonFly__)
  40 # include <sys/param.h>
  41 # include <sys/random.h>
  42 #endif
  43
  44 #if (defined(OPENSSL_SYS_UNIX) && !defined(OPENSSL_SYS_VXWORKS)) \
  45      || defined(__DJGPP__)
  46 # include <sys/types.h>
  47 # include <sys/stat.h>
  48 # include <fcntl.h>
  49 # include <unistd.h>
  50 # include <sys/time.h>
  51
  52 static uint64_t get_time_stamp(void);
  53
  54 /* Macro to convert two thirty two bit values into a sixty four bit one */
  55 # define TWO32TO64(a, b) ((((uint64_t)(a)) << 32) + (b))
  56
  57 /*
  58  * Check for the existence and support of POSIX timers.  The standard
  59  * says that the _POSIX_TIMERS macro will have a positive value if they
  60  * are available.
  61  *
  62  * However, we want an additional constraint: that the timer support does
  63  * not require an extra library dependency.  Early versions of glibc
  64  * require -lrt to be specified on the link line to access the timers,
  65  * so this needs to be checked for.
  66  *
  67  * It is worse because some libraries define __GLIBC__ but don't
  68  * support the version testing macro (e.g. uClibc).  This means
  69  * an extra check is needed.
  70  *
  71  * The final condition is:
  72  *      "have posix timers and either not glibc or glibc without -lrt"
  73  *
  74  * The nested #if sequences are required to avoid using a parameterised
  75  * macro that might be undefined.
  76  */
  77 # undef OSSL_POSIX_TIMER_OKAY
  78 /* On some systems, _POSIX_TIMERS is defined but empty.
  79  * Subtracting by 0 when comparing avoids an error in this case. */
  80 # if defined(_POSIX_TIMERS) && _POSIX_TIMERS -0 > 0
  81 #  if defined(__GLIBC__)
  82 #   if defined(__GLIBC_PREREQ)
  83 #    if __GLIBC_PREREQ(2, 17)
  84 #     define OSSL_POSIX_TIMER_OKAY
  85 #    endif
  86 #   endif
  87 #  else
  88 #   define OSSL_POSIX_TIMER_OKAY
  89 #  endif
  90 # endif
  91 #endif /* (defined(OPENSSL_SYS_UNIX) && !defined(OPENSSL_SYS_VXWORKS))
  92           || defined(__DJGPP__) */
  93
  94 #if defined(OPENSSL_RAND_SEED_NONE)
  95 /* none means none. this simplifies the following logic */
  96 # undef OPENSSL_RAND_SEED_OS
  97 # undef OPENSSL_RAND_SEED_GETRANDOM
  98 # undef OPENSSL_RAND_SEED_LIBRANDOM
  99 # undef OPENSSL_RAND_SEED_DEVRANDOM
 100 # undef OPENSSL_RAND_SEED_RDTSC
 101 # undef OPENSSL_RAND_SEED_RDCPU
 102 # undef OPENSSL_RAND_SEED_EGD
 103 #endif
 104
 105 #if defined(OPENSSL_SYS_UEFI) && !defined(OPENSSL_RAND_SEED_NONE)
 106 # error "UEFI only supports seeding NONE"
 107 #endif
 108
 109 #if !(defined(OPENSSL_SYS_WINDOWS) || defined(OPENSSL_SYS_WIN32) \
 110     || defined(OPENSSL_SYS_VMS) || defined(OPENSSL_SYS_VXWORKS) \
 111     || defined(OPENSSL_SYS_UEFI))
 112
 113 # if defined(OPENSSL_SYS_VOS)
 114
 115 #  ifndef OPENSSL_RAND_SEED_OS
 116 #   error "Unsupported seeding method configured; must be os"
 117 #  endif
 118
 119 #  if defined(OPENSSL_SYS_VOS_HPPA) && defined(OPENSSL_SYS_VOS_IA32)
 120 #   error "Unsupported HP-PA and IA32 at the same time."
 121 #  endif
 122 #  if !defined(OPENSSL_SYS_VOS_HPPA) && !defined(OPENSSL_SYS_VOS_IA32)
 123 #   error "Must have one of HP-PA or IA32"
 124 #  endif
 125
 126 /*
 127  * The following algorithm repeatedly samples the real-time clock (RTC) to
 128  * generate a sequence of unpredictable data.  The algorithm relies upon the
 129  * uneven execution speed of the code (due to factors such as cache misses,
 130  * interrupts, bus activity, and scheduling) and upon the rather large
 131  * relative difference between the speed of the clock and the rate at which
 132  * it can be read.  If it is ported to an environment where execution speed
 133  * is more constant or where the RTC ticks at a much slower rate, or the
 134  * clock can be read with fewer instructions, it is likely that the results
 135  * would be far more predictable.  This should only be used for legacy
 136  * platforms.
 137  *
 138  * As a precaution, we assume only 2 bits of entropy per byte.
 139  */
 140 size_t ossl_pool_acquire_entropy(RAND_POOL *pool)
 141 {
 142     short int code;
 143     int i, k;
 144     size_t bytes_needed;
 145     struct timespec ts;
 146     unsigned char v;
 147 #  ifdef OPENSSL_SYS_VOS_HPPA
 148     long duration;
 149     extern void s$sleep(long *_duration, short int *_code);
 150 #  else
 151     long long duration;
 152     extern void s$sleep2(long long *_duration, short int *_code);
 153 #  endif
 154
 155     bytes_needed = ossl_rand_pool_bytes_needed(pool, 4 /*entropy_factor*/);
 156
 157     for (i = 0; i < bytes_needed; i++) {
 158         /*
 159          * burn some cpu; hope for interrupts, cache collisions, bus
 160          * interference, etc.
 161          */
 162         for (k = 0; k < 99; k++)
 163             ts.tv_nsec = random();
 164
 165 #  ifdef OPENSSL_SYS_VOS_HPPA
 166         /* sleep for 1/1024 of a second (976 us).  */
 167         duration = 1;
 168         s$sleep(&duration, &code);
 169 #  else
 170         /* sleep for 1/65536 of a second (15 us).  */
 171         duration = 1;
 172         s$sleep2(&duration, &code);
 173 #  endif
 174
 175         /* Get wall clock time, take 8 bits. */
 176         clock_gettime(CLOCK_REALTIME, &ts);
 177         v = (unsigned char)(ts.tv_nsec & 0xFF);
 178         ossl_rand_pool_add(pool, arg, &v, sizeof(v), 2);
 179     }
 180     return ossl_rand_pool_entropy_available(pool);
 181 }
 182
 183 void ossl_rand_pool_cleanup(void)
 184 {
 185 }
 186
 187 void ossl_rand_pool_keep_random_devices_open(int keep)
 188 {
 189 }
 190
 191 # else
 192
 193 #  if defined(OPENSSL_RAND_SEED_EGD) && \
 194         (defined(OPENSSL_NO_EGD) || !defined(DEVRANDOM_EGD))
 195 #   error "Seeding uses EGD but EGD is turned off or no device given"
 196 #  endif
 197
 198 #  if defined(OPENSSL_RAND_SEED_DEVRANDOM) && !defined(DEVRANDOM)
 199 #   error "Seeding uses urandom but DEVRANDOM is not configured"
 200 #  endif
 201
 202 #  if defined(OPENSSL_RAND_SEED_OS)
 203 #   if !defined(DEVRANDOM)
 204 #    error "OS seeding requires DEVRANDOM to be configured"
 205 #   endif
 206 #   define OPENSSL_RAND_SEED_GETRANDOM
 207 #   define OPENSSL_RAND_SEED_DEVRANDOM
 208 #  endif
 209
 210 #  if defined(OPENSSL_RAND_SEED_LIBRANDOM)
 211 #   error "librandom not (yet) supported"
 212 #  endif
 213
 214 #  if (defined(__FreeBSD__) || defined(__NetBSD__)) && defined(KERN_ARND)
 215 /*
 216  * sysctl_random(): Use sysctl() to read a random number from the kernel
 217  * Returns the number of bytes returned in buf on success, -1 on failure.
 218  */
 219 static ssize_t sysctl_random(char *buf, size_t buflen)
 220 {
 221     int mib[2];
 222     size_t done = 0;
 223     size_t len;
 224
 225     /*
 226      * Note: sign conversion between size_t and ssize_t is safe even
 227      * without a range check, see comment in syscall_random()
 228      */
 229
 230     /*
 231      * On FreeBSD old implementations returned longs, newer versions support
 232      * variable sizes up to 256 byte. The code below would not work properly
 233      * when the sysctl returns long and we want to request something not a
 234      * multiple of longs, which should never be the case.
 235      */
 236 #if   defined(__FreeBSD__)
 237     if (!ossl_assert(buflen % sizeof(long) == 0)) {
 238         errno = EINVAL;
 239         return -1;
 240     }
 241 #endif
 242
 243     /*
 244      * On NetBSD before 4.0 KERN_ARND was an alias for KERN_URND, and only
 245      * filled in an int, leaving the rest uninitialized. Since NetBSD 4.0
 246      * it returns a variable number of bytes with the current version supporting
 247      * up to 256 bytes.
 248      * Just return an error on older NetBSD versions.
 249      */
 250 #if   defined(__NetBSD__) && __NetBSD_Version__ < 400000000
 251     errno = ENOSYS;
 252     return -1;
 253 #endif
 254
 255     mib[0] = CTL_KERN;
 256     mib[1] = KERN_ARND;
 257
 258     do {
 259         len = buflen > 256 ? 256 : buflen;
 260         if (sysctl(mib, 2, buf, &len, NULL, 0) == -1)
 261             return done > 0 ? done : -1;
 262         done += len;
 263         buf += len;
 264         buflen -= len;
 265     } while (buflen > 0);
 266
 267     return done;
 268 }
 269 #  endif
 270
 271 #  if defined(OPENSSL_RAND_SEED_GETRANDOM)
 272
 273 #   if defined(__linux) && !defined(__NR_getrandom)
 274 #    if defined(__arm__)
 275 #     define __NR_getrandom    (__NR_SYSCALL_BASE+384)
 276 #    elif defined(__i386__)
 277 #     define __NR_getrandom    355
 278 #    elif defined(__x86_64__)
 279 #     if defined(__ILP32__)
 280 #      define __NR_getrandom   (__X32_SYSCALL_BIT + 318)
 281 #     else
 282 #      define __NR_getrandom   318
 283 #     endif
 284 #    elif defined(__xtensa__)
 285 #     define __NR_getrandom    338
 286 #    elif defined(__s390__) || defined(__s390x__)
 287 #     define __NR_getrandom    349
 288 #    elif defined(__bfin__)
 289 #     define __NR_getrandom    389
 290 #    elif defined(__powerpc__)
 291 #     define __NR_getrandom    359
 292 #    elif defined(__mips__) || defined(__mips64)
 293 #     if _MIPS_SIM == _MIPS_SIM_ABI32
 294 #      define __NR_getrandom   (__NR_Linux + 353)
 295 #     elif _MIPS_SIM == _MIPS_SIM_ABI64
 296 #      define __NR_getrandom   (__NR_Linux + 313)
 297 #     elif _MIPS_SIM == _MIPS_SIM_NABI32
 298 #      define __NR_getrandom   (__NR_Linux + 317)
 299 #     endif
 300 #    elif defined(__hppa__)
 301 #     define __NR_getrandom    (__NR_Linux + 339)
 302 #    elif defined(__sparc__)
 303 #     define __NR_getrandom    347
 304 #    elif defined(__ia64__)
 305 #     define __NR_getrandom    1339
 306 #    elif defined(__alpha__)
 307 #     define __NR_getrandom    511
 308 #    elif defined(__sh__)
 309 #     if defined(__SH5__)
 310 #      define __NR_getrandom   373
 311 #     else
 312 #      define __NR_getrandom   384
 313 #     endif
 314 #    elif defined(__avr32__)
 315 #     define __NR_getrandom    317
 316 #    elif defined(__microblaze__)
 317 #     define __NR_getrandom    385
 318 #    elif defined(__m68k__)
 319 #     define __NR_getrandom    352
 320 #    elif defined(__cris__)
 321 #     define __NR_getrandom    356
 322 #    else /* generic (f.e. aarch64, loongarch, loongarch64) */
 323 #     define __NR_getrandom    278
 324 #    endif
 325 #   endif
 326
 327 /*
 328  * syscall_random(): Try to get random data using a system call
 329  * returns the number of bytes returned in buf, or < 0 on error.
 330  */
 331 static ssize_t syscall_random(void *buf, size_t buflen)
 332 {
 333     /*
 334      * Note: 'buflen' equals the size of the buffer which is used by the
 335      * get_entropy() callback of the RAND_DRBG. It is roughly bounded by
 336      *
 337      *   2 * RAND_POOL_FACTOR * (RAND_DRBG_STRENGTH / 8) = 2^14
 338      *
 339      * which is way below the OSSL_SSIZE_MAX limit. Therefore sign conversion
 340      * between size_t and ssize_t is safe even without a range check.
 341      */
 342
 343     /*
 344      * Do runtime detection to find getentropy().
 345      *
 346      * Known OSs that should support this:
 347      * - Darwin since 16 (OSX 10.12, IOS 10.0).
 348      * - Solaris since 11.3
 349      * - OpenBSD since 5.6
 350      * - Linux since 3.17 with glibc 2.25
 351      * - FreeBSD since 12.0 (1200061)
 352      *
 353      * Note: Sometimes getentropy() can be provided but not implemented
 354      * internally. So we need to check errno for ENOSYS
 355      */
 356 #  if !defined(__DragonFly__) && !defined(__NetBSD__)
 357 #    if defined(__GNUC__) && __GNUC__>=2 && defined(__ELF__) && !defined(__hpux)
 358     extern int getentropy(void *buffer, size_t length) __attribute__((weak));
 359
 360     if (getentropy != NULL) {
 361         if (getentropy(buf, buflen) == 0)
 362             return (ssize_t)buflen;
 363         if (errno != ENOSYS)
 364             return -1;
 365     }
 366 #    elif defined(OPENSSL_APPLE_CRYPTO_RANDOM)
 367
 368     if (CCRandomGenerateBytes(buf, buflen) == kCCSuccess)
 369             return (ssize_t)buflen;
 370
 371     return -1;
 372 #    else
 373     union {
 374         void *p;
 375         int (*f)(void *buffer, size_t length);
 376     } p_getentropy;
 377
 378     /*
 379      * We could cache the result of the lookup, but we normally don't
 380      * call this function often.
 381      */
 382     ERR_set_mark();
 383     p_getentropy.p = DSO_global_lookup("getentropy");
 384     ERR_pop_to_mark();
 385     if (p_getentropy.p != NULL)
 386         return p_getentropy.f(buf, buflen) == 0 ? (ssize_t)buflen : -1;
 387 #    endif
 388 #  endif /* !__DragonFly__ */
 389
 390     /* Linux supports this since version 3.17 */
 391 #  if defined(__linux) && defined(__NR_getrandom)
 392     return syscall(__NR_getrandom, buf, buflen, 0);
 393 #  elif (defined(__FreeBSD__) || defined(__NetBSD__)) && defined(KERN_ARND)
 394     return sysctl_random(buf, buflen);
 395 #  elif (defined(__DragonFly__)  && __DragonFly_version >= 500700) \
 396      || (defined(__NetBSD__) && __NetBSD_Version >= 1000000000)
 397     return getrandom(buf, buflen, 0);
 398 #  elif defined(__wasi__)
 399     if (getentropy(buf, buflen) == 0)
 400       return (ssize_t)buflen;
 401     return -1;
 402 #  else
 403     errno = ENOSYS;
 404     return -1;
 405 #  endif
 406 }
 407 #  endif    /* defined(OPENSSL_RAND_SEED_GETRANDOM) */
 408
 409 #  if defined(OPENSSL_RAND_SEED_DEVRANDOM)
 410 static const char *random_device_paths[] = { DEVRANDOM };
 411 static struct random_device {
 412     int fd;
 413     dev_t dev;
 414     ino_t ino;
 415     mode_t mode;
 416     dev_t rdev;
 417 } random_devices[OSSL_NELEM(random_device_paths)];
 418 static int keep_random_devices_open = 1;
 419
 420 #   if defined(__linux) && defined(DEVRANDOM_WAIT) \
 421        && defined(OPENSSL_RAND_SEED_GETRANDOM)
 422 static void *shm_addr;
 423
 424 static void cleanup_shm(void)
 425 {
 426     shmdt(shm_addr);
 427 }
 428
 429 /*
 430  * Ensure that the system randomness source has been adequately seeded.
 431  * This is done by having the first start of libcrypto, wait until the device
 432  * /dev/random becomes able to supply a byte of entropy.  Subsequent starts
 433  * of the library and later reseedings do not need to do this.
 434  */
 435 static int wait_random_seeded(void)
 436 {
 437     static int seeded = OPENSSL_RAND_SEED_DEVRANDOM_SHM_ID < 0;
 438     static const int kernel_version[] = { DEVRANDOM_SAFE_KERNEL };
 439     int kernel[2];
 440     int shm_id, fd, r;
 441     char c, *p;
 442     struct utsname un;
 443     fd_set fds;
 444
 445     if (!seeded) {
 446         /* See if anything has created the global seeded indication */
 447         if ((shm_id = shmget(OPENSSL_RAND_SEED_DEVRANDOM_SHM_ID, 1, 0)) == -1) {
 448             /*
 449              * Check the kernel's version and fail if it is too recent.
 450              *
 451              * Linux kernels from 4.8 onwards do not guarantee that
 452              * /dev/urandom is properly seeded when /dev/random becomes
 453              * readable.  However, such kernels support the getentropy(2)
 454              * system call and this should always succeed which renders
 455              * this alternative but essentially identical source moot.
 456              */
 457             if (uname(&un) == 0) {
 458                 kernel[0] = atoi(un.release);
 459                 p = strchr(un.release, '.');
 460                 kernel[1] = p == NULL ? 0 : atoi(p + 1);
 461                 if (kernel[0] > kernel_version[0]
 462                     || (kernel[0] == kernel_version[0]
 463                         && kernel[1] >= kernel_version[1])) {
 464                     return 0;
 465                 }
 466             }
 467             /* Open /dev/random and wait for it to be readable */
 468             if ((fd = open(DEVRANDOM_WAIT, O_RDONLY)) != -1) {
 469                 if (DEVRANDM_WAIT_USE_SELECT && fd < FD_SETSIZE) {
 470                     FD_ZERO(&fds);
 471                     FD_SET(fd, &fds);
 472                     while ((r = select(fd + 1, &fds, NULL, NULL, NULL)) < 0
 473                            && errno == EINTR);
 474                 } else {
 475                     while ((r = read(fd, &c, 1)) < 0 && errno == EINTR);
 476                 }
 477                 close(fd);
 478                 if (r == 1) {
 479                     seeded = 1;
 480                     /* Create the shared memory indicator */
 481                     shm_id = shmget(OPENSSL_RAND_SEED_DEVRANDOM_SHM_ID, 1,
 482                                     IPC_CREAT | S_IRUSR | S_IRGRP | S_IROTH);
 483                 }
 484             }
 485         }
 486         if (shm_id != -1) {
 487             seeded = 1;
 488             /*
 489              * Map the shared memory to prevent its premature destruction.
 490              * If this call fails, it isn't a big problem.
 491              */
 492             shm_addr = shmat(shm_id, NULL, SHM_RDONLY);
 493             if (shm_addr != (void *)-1)
 494                 OPENSSL_atexit(&cleanup_shm);
 495         }
 496     }
 497     return seeded;
 498 }
 499 #   else /* defined __linux && DEVRANDOM_WAIT && OPENSSL_RAND_SEED_GETRANDOM */
 500 static int wait_random_seeded(void)
 501 {
 502     return 1;
 503 }
 504 #   endif
 505
 506 /*
 507  * Verify that the file descriptor associated with the random source is
 508  * still valid. The rationale for doing this is the fact that it is not
 509  * uncommon for daemons to close all open file handles when daemonizing.
 510  * So the handle might have been closed or even reused for opening
 511  * another file.
 512  */
 513 static int check_random_device(struct random_device *rd)
 514 {
 515     struct stat st;
 516
 517     return rd->fd != -1
 518            && fstat(rd->fd, &st) != -1
 519            && rd->dev == st.st_dev
 520            && rd->ino == st.st_ino
 521            && ((rd->mode ^ st.st_mode) & ~(S_IRWXU | S_IRWXG | S_IRWXO)) == 0
 522            && rd->rdev == st.st_rdev;
 523 }
 524
 525 /*
 526  * Open a random device if required and return its file descriptor or -1 on error
 527  */
 528 static int get_random_device(size_t n)
 529 {
 530     struct stat st;
 531     struct random_device *rd = &random_devices[n];
 532
 533     /* reuse existing file descriptor if it is (still) valid */
 534     if (check_random_device(rd))
 535         return rd->fd;
 536
 537     /* open the random device ... */
 538     if ((rd->fd = open(random_device_paths[n], O_RDONLY)) == -1)
 539         return rd->fd;
 540
 541     /* ... and cache its relevant stat(2) data */
 542     if (fstat(rd->fd, &st) != -1) {
 543         rd->dev = st.st_dev;
 544         rd->ino = st.st_ino;
 545         rd->mode = st.st_mode;
 546         rd->rdev = st.st_rdev;
 547     } else {
 548         close(rd->fd);
 549         rd->fd = -1;
 550     }
 551
 552     return rd->fd;
 553 }
 554
 555 /*
 556  * Close a random device making sure it is a random device
 557  */
 558 static void close_random_device(size_t n)
 559 {
 560     struct random_device *rd = &random_devices[n];
 561
 562     if (check_random_device(rd))
 563         close(rd->fd);
 564     rd->fd = -1;
 565 }
 566
 567 int ossl_rand_pool_init(void)
 568 {
 569     size_t i;
 570
 571     for (i = 0; i < OSSL_NELEM(random_devices); i++)
 572         random_devices[i].fd = -1;
 573
 574     return 1;
 575 }
 576
 577 void ossl_rand_pool_cleanup(void)
 578 {
 579     size_t i;
 580
 581     for (i = 0; i < OSSL_NELEM(random_devices); i++)
 582         close_random_device(i);
 583 }
 584
 585 void ossl_rand_pool_keep_random_devices_open(int keep)
 586 {
 587     if (!keep)
 588         ossl_rand_pool_cleanup();
 589
 590     keep_random_devices_open = keep;
 591 }
 592
 593 #  else     /* !defined(OPENSSL_RAND_SEED_DEVRANDOM) */
 594
 595 int ossl_rand_pool_init(void)
 596 {
 597     return 1;
 598 }
 599
 600 void ossl_rand_pool_cleanup(void)
 601 {
 602 }
 603
 604 void ossl_rand_pool_keep_random_devices_open(int keep)
 605 {
 606 }
 607
 608 #  endif    /* defined(OPENSSL_RAND_SEED_DEVRANDOM) */
 609
 610 /*
 611  * Try the various seeding methods in turn, exit when successful.
 612  *
 613  * If more than one entropy source is available, is it
 614  * preferable to stop as soon as enough entropy has been collected
 615  * (as favored by @rsalz) or should one rather be defensive and add
 616  * more entropy than requested and/or from different sources?
 617  *
 618  * Currently, the user can select multiple entropy sources in the
 619  * configure step, yet in practice only the first available source
 620  * will be used. A more flexible solution has been requested, but
 621  * currently it is not clear how this can be achieved without
 622  * overengineering the problem. There are many parameters which
 623  * could be taken into account when selecting the order and amount
 624  * of input from the different entropy sources (trust, quality,
 625  * possibility of blocking).
 626  */
 627 size_t ossl_pool_acquire_entropy(RAND_POOL *pool)
 628 {
 629 #  if defined(OPENSSL_RAND_SEED_NONE)
 630     return ossl_rand_pool_entropy_available(pool);
 631 #  else
 632     size_t entropy_available = 0;
 633
 634     (void)entropy_available;    /* avoid compiler warning */
 635
 636 #   if defined(OPENSSL_RAND_SEED_GETRANDOM)
 637     {
 638         size_t bytes_needed;
 639         unsigned char *buffer;
 640         ssize_t bytes;
 641         /* Maximum allowed number of consecutive unsuccessful attempts */
 642         int attempts = 3;
 643
 644         bytes_needed = ossl_rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
 645         while (bytes_needed != 0 && attempts-- > 0) {
 646             buffer = ossl_rand_pool_add_begin(pool, bytes_needed);
 647             bytes = syscall_random(buffer, bytes_needed);
 648             if (bytes > 0) {
 649                 ossl_rand_pool_add_end(pool, bytes, 8 * bytes);
 650                 bytes_needed -= bytes;
 651                 attempts = 3; /* reset counter after successful attempt */
 652             } else if (bytes < 0 && errno != EINTR) {
 653                 break;
 654             }
 655         }
 656     }
 657     entropy_available = ossl_rand_pool_entropy_available(pool);
 658     if (entropy_available > 0)
 659         return entropy_available;
 660 #   endif
 661
 662 #   if defined(OPENSSL_RAND_SEED_LIBRANDOM)
 663     {
 664         /* Not yet implemented. */
 665     }
 666 #   endif
 667
 668 #   if defined(OPENSSL_RAND_SEED_DEVRANDOM)
 669     if (wait_random_seeded()) {
 670         size_t bytes_needed;
 671         unsigned char *buffer;
 672         size_t i;
 673
 674         bytes_needed = ossl_rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
 675         for (i = 0; bytes_needed > 0 && i < OSSL_NELEM(random_device_paths);
 676              i++) {
 677             ssize_t bytes = 0;
 678             /* Maximum number of consecutive unsuccessful attempts */
 679             int attempts = 3;
 680             const int fd = get_random_device(i);
 681
 682             if (fd == -1)
 683                 continue;
 684
 685             while (bytes_needed != 0 && attempts-- > 0) {
 686                 buffer = ossl_rand_pool_add_begin(pool, bytes_needed);
 687                 bytes = read(fd, buffer, bytes_needed);
 688
 689                 if (bytes > 0) {
 690                     ossl_rand_pool_add_end(pool, bytes, 8 * bytes);
 691                     bytes_needed -= bytes;
 692                     attempts = 3; /* reset counter on successful attempt */
 693                 } else if (bytes < 0 && errno != EINTR) {
 694                     break;
 695                 }
 696             }
 697             if (bytes < 0 || !keep_random_devices_open)
 698                 close_random_device(i);
 699
 700             bytes_needed = ossl_rand_pool_bytes_needed(pool, 1);
 701         }
 702         entropy_available = ossl_rand_pool_entropy_available(pool);
 703         if (entropy_available > 0)
 704             return entropy_available;
 705     }
 706 #   endif
 707
 708 #   if defined(OPENSSL_RAND_SEED_RDTSC)
 709     entropy_available = ossl_prov_acquire_entropy_from_tsc(pool);
 710     if (entropy_available > 0)
 711         return entropy_available;
 712 #   endif
 713
 714 #   if defined(OPENSSL_RAND_SEED_RDCPU)
 715     entropy_available = ossl_prov_acquire_entropy_from_cpu(pool);
 716     if (entropy_available > 0)
 717         return entropy_available;
 718 #   endif
 719
 720 #   if defined(OPENSSL_RAND_SEED_EGD)
 721     {
 722         static const char *paths[] = { DEVRANDOM_EGD, NULL };
 723         size_t bytes_needed;
 724         unsigned char *buffer;
 725         int i;
 726
 727         bytes_needed = ossl_rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
 728         for (i = 0; bytes_needed > 0 && paths[i] != NULL; i++) {
 729             size_t bytes = 0;
 730             int num;
 731
 732             buffer = ossl_rand_pool_add_begin(pool, bytes_needed);
 733             num = RAND_query_egd_bytes(paths[i],
 734                                        buffer, (int)bytes_needed);
 735             if (num == (int)bytes_needed)
 736                 bytes = bytes_needed;
 737
 738             ossl_rand_pool_add_end(pool, bytes, 8 * bytes);
 739             bytes_needed = ossl_rand_pool_bytes_needed(pool, 1);
 740         }
 741         entropy_available = ossl_rand_pool_entropy_available(pool);
 742         if (entropy_available > 0)
 743             return entropy_available;
 744     }
 745 #   endif
 746
 747     return ossl_rand_pool_entropy_available(pool);
 748 #  endif
 749 }
 750 # endif
 751 #endif
 752
 753 #if (defined(OPENSSL_SYS_UNIX) && !defined(OPENSSL_SYS_VXWORKS)) \
 754      || defined(__DJGPP__)
 755 int ossl_pool_add_nonce_data(RAND_POOL *pool)
 756 {
 757     struct {
 758         pid_t pid;
 759         CRYPTO_THREAD_ID tid;
 760         uint64_t time;
 761     } data;
 762
 763     /* Erase the entire structure including any padding */
 764     memset(&data, 0, sizeof(data));
 765
 766     /*
 767      * Add process id, thread id, and a high resolution timestamp to
 768      * ensure that the nonce is unique with high probability for
 769      * different process instances.
 770      */
 771     data.pid = getpid();
 772     data.tid = CRYPTO_THREAD_get_current_id();
 773     data.time = get_time_stamp();
 774
 775     return ossl_rand_pool_add(pool, (unsigned char *)&data, sizeof(data), 0);
 776 }
 777
 778 /*
 779  * Get the current time with the highest possible resolution
 780  *
 781  * The time stamp is added to the nonce, so it is optimized for not repeating.
 782  * The current time is ideal for this purpose, provided the computer's clock
 783  * is synchronized.
 784  */
 785 static uint64_t get_time_stamp(void)
 786 {
 787 # if defined(OSSL_POSIX_TIMER_OKAY)
 788     {
 789         struct timespec ts;
 790
 791         if (clock_gettime(CLOCK_REALTIME, &ts) == 0)
 792             return TWO32TO64(ts.tv_sec, ts.tv_nsec);
 793     }
 794 # endif
 795 # if defined(__unix__) \
 796      || (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 200112L)
 797     {
 798         struct timeval tv;
 799
 800         if (gettimeofday(&tv, NULL) == 0)
 801             return TWO32TO64(tv.tv_sec, tv.tv_usec);
 802     }
 803 # endif
 804     return time(NULL);
 805 }
 806
 807 #endif /* (defined(OPENSSL_SYS_UNIX) && !defined(OPENSSL_SYS_VXWORKS))
 808           || defined(__DJGPP__) */