ref: 94f2907dc40a6415a10c252cb9ba3971f1f7e838
dir: /third_party/boringssl/src/crypto/rand_extra/urandom.c/
/* Copyright (c) 2014, Google Inc.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
#if !defined(_GNU_SOURCE)
#define _GNU_SOURCE // needed for syscall() on Linux.
#endif
#include <openssl/rand.h>
#include "../bcm_support.h"
#include "sysrand_internal.h"
#if defined(OPENSSL_RAND_URANDOM)
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#if defined(OPENSSL_LINUX)
#if defined(BORINGSSL_FIPS)
#include <linux/random.h>
#include <sys/ioctl.h>
#endif
#include <sys/syscall.h>
#if defined(OPENSSL_ANDROID)
#include <sys/system_properties.h>
#endif
#if !defined(OPENSSL_ANDROID)
#define OPENSSL_HAS_GETAUXVAL
#endif
// glibc prior to 2.16 does not have getauxval and sys/auxv.h. Android has some
// host builds (i.e. not building for Android itself, so |OPENSSL_ANDROID| is
// unset) which are still using a 2.15 sysroot.
//
// TODO(davidben): Remove this once Android updates their sysroot.
#if defined(__GLIBC_PREREQ)
#if !__GLIBC_PREREQ(2, 16)
#undef OPENSSL_HAS_GETAUXVAL
#endif
#endif
#if defined(OPENSSL_HAS_GETAUXVAL)
#include <sys/auxv.h>
#endif
#endif // OPENSSL_LINUX
#include <openssl/thread.h>
#include <openssl/mem.h>
#include "getrandom_fillin.h"
#include "../internal.h"
#if defined(USE_NR_getrandom)
#if defined(OPENSSL_MSAN)
void __msan_unpoison(void *, size_t);
#endif
static ssize_t boringssl_getrandom(void *buf, size_t buf_len, unsigned flags) {
ssize_t ret;
do {
ret = syscall(__NR_getrandom, buf, buf_len, flags);
} while (ret == -1 && errno == EINTR);
#if defined(OPENSSL_MSAN)
if (ret > 0) {
// MSAN doesn't recognise |syscall| and thus doesn't notice that we have
// initialised the output buffer.
__msan_unpoison(buf, ret);
}
#endif // OPENSSL_MSAN
return ret;
}
#endif // USE_NR_getrandom
// kHaveGetrandom in |urandom_fd| signals that |getrandom| or |getentropy| is
// available and should be used instead.
static const int kHaveGetrandom = -3;
// urandom_fd is a file descriptor to /dev/urandom. It's protected by |once|.
static int urandom_fd;
#if defined(USE_NR_getrandom)
// getrandom_ready is one if |getrandom| had been initialized by the time
// |init_once| was called and zero otherwise.
static int getrandom_ready;
// extra_getrandom_flags_for_seed contains a value that is ORed into the flags
// for getrandom() when reading entropy for a seed.
static int extra_getrandom_flags_for_seed;
// On Android, check a system property to decide whether to set
// |extra_getrandom_flags_for_seed| otherwise they will default to zero. If
// ro.oem_boringcrypto_hwrand is true then |extra_getrandom_flags_for_seed| will
// be set to GRND_RANDOM, causing all random data to be drawn from the same
// source as /dev/random.
static void maybe_set_extra_getrandom_flags(void) {
#if defined(BORINGSSL_FIPS) && defined(OPENSSL_ANDROID)
char value[PROP_VALUE_MAX + 1];
int length = __system_property_get("ro.boringcrypto.hwrand", value);
if (length < 0 || length > PROP_VALUE_MAX) {
return;
}
value[length] = 0;
if (OPENSSL_strcasecmp(value, "true") == 0) {
extra_getrandom_flags_for_seed = GRND_RANDOM;
}
#endif
}
#endif // USE_NR_getrandom
static CRYPTO_once_t rand_once = CRYPTO_ONCE_INIT;
// init_once initializes the state of this module to values previously
// requested. This is the only function that modifies |urandom_fd|, which may be
// read safely after calling the once.
static void init_once(void) {
#if defined(USE_NR_getrandom)
int have_getrandom;
uint8_t dummy;
ssize_t getrandom_ret =
boringssl_getrandom(&dummy, sizeof(dummy), GRND_NONBLOCK);
if (getrandom_ret == 1) {
getrandom_ready = 1;
have_getrandom = 1;
} else if (getrandom_ret == -1 && errno == EAGAIN) {
// We have getrandom, but the entropy pool has not been initialized yet.
have_getrandom = 1;
} else if (getrandom_ret == -1 && errno == ENOSYS) {
// Fallthrough to using /dev/urandom, below.
have_getrandom = 0;
} else {
// Other errors are fatal.
perror("getrandom");
abort();
}
if (have_getrandom) {
urandom_fd = kHaveGetrandom;
maybe_set_extra_getrandom_flags();
return;
}
#endif // USE_NR_getrandom
// FIPS builds must support getrandom.
//
// Historically, only Android FIPS builds required getrandom, while Linux FIPS
// builds had a /dev/urandom fallback which used RNDGETENTCNT as a poor
// approximation for getrandom's blocking behavior. This is now removed, but
// avoid making assumptions on this removal until March 2023, in case it needs
// to be restored. This comment can be deleted after March 2023.
#if defined(BORINGSSL_FIPS)
perror("getrandom not found");
abort();
#endif
int fd;
do {
fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC);
} while (fd == -1 && errno == EINTR);
if (fd < 0) {
perror("failed to open /dev/urandom");
abort();
}
urandom_fd = fd;
}
static CRYPTO_once_t wait_for_entropy_once = CRYPTO_ONCE_INIT;
static void wait_for_entropy(void) {
int fd = urandom_fd;
if (fd == kHaveGetrandom) {
// |getrandom| and |getentropy| support blocking in |fill_with_entropy|
// directly. For |getrandom|, we first probe with a non-blocking call to aid
// debugging.
#if defined(USE_NR_getrandom)
if (getrandom_ready) {
// The entropy pool was already initialized in |init_once|.
return;
}
uint8_t dummy;
ssize_t getrandom_ret =
boringssl_getrandom(&dummy, sizeof(dummy), GRND_NONBLOCK);
if (getrandom_ret == -1 && errno == EAGAIN) {
// Attempt to get the path of the current process to aid in debugging when
// something blocks.
const char *current_process = "<unknown>";
#if defined(OPENSSL_HAS_GETAUXVAL)
const unsigned long getauxval_ret = getauxval(AT_EXECFN);
if (getauxval_ret != 0) {
current_process = (const char *)getauxval_ret;
}
#endif
fprintf(
stderr,
"%s: getrandom indicates that the entropy pool has not been "
"initialized. Rather than continue with poor entropy, this process "
"will block until entropy is available.\n",
current_process);
getrandom_ret =
boringssl_getrandom(&dummy, sizeof(dummy), 0 /* no flags */);
}
if (getrandom_ret != 1) {
perror("getrandom");
abort();
}
#endif // USE_NR_getrandom
return;
}
}
// fill_with_entropy writes |len| bytes of entropy into |out|. It returns one
// on success and zero on error. If |block| is one, this function will block
// until the entropy pool is initialized. Otherwise, this function may fail,
// setting |errno| to |EAGAIN| if the entropy pool has not yet been initialized.
// If |seed| is one, this function will OR in the value of
// |*extra_getrandom_flags_for_seed()| when using |getrandom|.
static int fill_with_entropy(uint8_t *out, size_t len, int block, int seed) {
if (len == 0) {
return 1;
}
#if defined(USE_NR_getrandom) || defined(FREEBSD_GETRANDOM)
int getrandom_flags = 0;
if (!block) {
getrandom_flags |= GRND_NONBLOCK;
}
#endif
#if defined (USE_NR_getrandom)
if (seed) {
getrandom_flags |= extra_getrandom_flags_for_seed;
}
#endif
CRYPTO_init_sysrand();
if (block) {
CRYPTO_once(&wait_for_entropy_once, wait_for_entropy);
}
// Clear |errno| so it has defined value if |read| or |getrandom|
// "successfully" returns zero.
errno = 0;
while (len > 0) {
ssize_t r;
if (urandom_fd == kHaveGetrandom) {
#if defined(USE_NR_getrandom)
r = boringssl_getrandom(out, len, getrandom_flags);
#else // USE_NR_getrandom
fprintf(stderr, "urandom fd corrupt.\n");
abort();
#endif
} else {
do {
r = read(urandom_fd, out, len);
} while (r == -1 && errno == EINTR);
}
if (r <= 0) {
return 0;
}
out += r;
len -= r;
}
return 1;
}
void CRYPTO_init_sysrand(void) {
CRYPTO_once(&rand_once, init_once);
}
// CRYPTO_sysrand puts |requested| random bytes into |out|.
void CRYPTO_sysrand(uint8_t *out, size_t requested) {
if (!fill_with_entropy(out, requested, /*block=*/1, /*seed=*/0)) {
perror("entropy fill failed");
abort();
}
}
void CRYPTO_sysrand_for_seed(uint8_t *out, size_t requested) {
if (!fill_with_entropy(out, requested, /*block=*/1, /*seed=*/1)) {
perror("entropy fill failed");
abort();
}
}
int CRYPTO_sysrand_if_available(uint8_t *out, size_t requested) {
if (fill_with_entropy(out, requested, /*block=*/0, /*seed=*/0)) {
return 1;
} else if (errno == EAGAIN) {
OPENSSL_memset(out, 0, requested);
return 0;
} else {
perror("opportunistic entropy fill failed");
abort();
}
}
#endif // OPENSSL_RAND_URANDOM