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Merge #9821: util: Specific GetOSRandom for Linux/FreeBSD/OpenBSD

7e6dcd9 random: Add fallback if getrandom syscall not available (Wladimir J. van der Laan)
7cad849 sanity: Move OS random to sanity check function (Wladimir J. van der Laan)
aa09ccb squashme: comment that NUM_OS_RANDOM_BYTES should not be changed lightly (Wladimir J. van der Laan)
224e6eb util: Specific GetOSRandom for Linux/FreeBSD/OpenBSD (Wladimir J. van der Laan)

Tree-SHA512: 9fd408b1316c69de86674f342339b2f89192fd317c8c036b5df4320f828fa263c7966146bfc1904c51137ee4a26e4cb0f560b2cd05e18cde4d808b9b92ad15c4
pull/1/head
Wladimir J. van der Laan 6 years ago
parent
commit
d19d45a1e6
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GPG Key ID: 74810B012346C9A6
  1. 27
      configure.ac
  2. 1
      src/Makefile.test.include
  3. 6
      src/init.cpp
  4. 115
      src/random.cpp
  5. 17
      src/random.h
  6. 19
      src/test/random_tests.cpp

27
configure.ac

@ -574,6 +574,33 @@ AC_LINK_IFELSE([AC_LANG_SOURCE([ @@ -574,6 +574,33 @@ AC_LINK_IFELSE([AC_LANG_SOURCE([
]
)
# Check for different ways of gathering OS randomness
AC_MSG_CHECKING(for Linux getrandom syscall)
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>
#include <sys/syscall.h>
#include <linux/random.h>]],
[[ syscall(SYS_getrandom, nullptr, 32, 0); ]])],
[ AC_MSG_RESULT(yes); AC_DEFINE(HAVE_SYS_GETRANDOM, 1,[Define this symbol if the Linux getrandom system call is available]) ],
[ AC_MSG_RESULT(no)]
)
AC_MSG_CHECKING(for getentropy)
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>]],
[[ getentropy(nullptr, 32) ]])],
[ AC_MSG_RESULT(yes); AC_DEFINE(HAVE_GETENTROPY, 1,[Define this symbol if the BSD getentropy system call is available]) ],
[ AC_MSG_RESULT(no)]
)
AC_MSG_CHECKING(for sysctl KERN_ARND)
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/types.h>
#include <sys/sysctl.h>]],
[[ static const int name[2] = {CTL_KERN, KERN_ARND};
sysctl(name, 2, nullptr, nullptr, nullptr, 0); ]])],
[ AC_MSG_RESULT(yes); AC_DEFINE(HAVE_SYSCTL_ARND, 1,[Define this symbol if the BSD sysctl(KERN_ARND) is available]) ],
[ AC_MSG_RESULT(no)]
)
# Check for reduced exports
if test x$use_reduce_exports = xyes; then
AX_CHECK_COMPILE_FLAG([-fvisibility=hidden],[RE_CXXFLAGS="-fvisibility=hidden"],
[AC_MSG_ERROR([Cannot set default symbol visibility. Use --disable-reduce-exports.])])

1
src/Makefile.test.include

@ -110,6 +110,7 @@ BITCOIN_TESTS =\ @@ -110,6 +110,7 @@ BITCOIN_TESTS =\
test/policyestimator_tests.cpp \
test/pow_tests.cpp \
test/prevector_tests.cpp \
test/random_tests.cpp \
test/raii_event_tests.cpp \
test/reverselock_tests.cpp \
test/rpc_tests.cpp \

6
src/init.cpp

@ -683,9 +683,15 @@ bool InitSanityCheck(void) @@ -683,9 +683,15 @@ bool InitSanityCheck(void)
InitError("Elliptic curve cryptography sanity check failure. Aborting.");
return false;
}
if (!glibc_sanity_test() || !glibcxx_sanity_test())
return false;
if (!Random_SanityCheck()) {
InitError("OS cryptographic RNG sanity check failure. Aborting.");
return false;
}
return true;
}

115
src/random.cpp

@ -21,6 +21,17 @@ @@ -21,6 +21,17 @@
#include <sys/time.h>
#endif
#ifdef HAVE_SYS_GETRANDOM
#include <sys/syscall.h>
#include <linux/random.h>
#endif
#ifdef HAVE_GETENTROPY
#include <unistd.h>
#endif
#ifdef HAVE_SYSCTL_ARND
#include <sys/sysctl.h>
#endif
#include <openssl/err.h>
#include <openssl/rand.h>
@ -91,34 +102,86 @@ static void RandAddSeedPerfmon() @@ -91,34 +102,86 @@ static void RandAddSeedPerfmon()
#endif
}
#ifndef WIN32
/** Fallback: get 32 bytes of system entropy from /dev/urandom. The most
* compatible way to get cryptographic randomness on UNIX-ish platforms.
*/
void GetDevURandom(unsigned char *ent32)
{
int f = open("/dev/urandom", O_RDONLY);
if (f == -1) {
RandFailure();
}
int have = 0;
do {
ssize_t n = read(f, ent32 + have, NUM_OS_RANDOM_BYTES - have);
if (n <= 0 || n + have > NUM_OS_RANDOM_BYTES) {
RandFailure();
}
have += n;
} while (have < NUM_OS_RANDOM_BYTES);
close(f);
}
#endif
/** Get 32 bytes of system entropy. */
static void GetOSRand(unsigned char *ent32)
void GetOSRand(unsigned char *ent32)
{
#ifdef WIN32
#if defined(WIN32)
HCRYPTPROV hProvider;
int ret = CryptAcquireContextW(&hProvider, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT);
if (!ret) {
RandFailure();
}
ret = CryptGenRandom(hProvider, 32, ent32);
ret = CryptGenRandom(hProvider, NUM_OS_RANDOM_BYTES, ent32);
if (!ret) {
RandFailure();
}
CryptReleaseContext(hProvider, 0);
#else
int f = open("/dev/urandom", O_RDONLY);
if (f == -1) {
#elif defined(HAVE_SYS_GETRANDOM)
/* Linux. From the getrandom(2) man page:
* "If the urandom source has been initialized, reads of up to 256 bytes
* will always return as many bytes as requested and will not be
* interrupted by signals."
*/
int rv = syscall(SYS_getrandom, ent32, NUM_OS_RANDOM_BYTES, 0);
if (rv != NUM_OS_RANDOM_BYTES) {
if (rv < 0 && errno == ENOSYS) {
/* Fallback for kernel <3.17: the return value will be -1 and errno
* ENOSYS if the syscall is not available, in that case fall back
* to /dev/urandom.
*/
GetDevURandom(ent32);
} else {
RandFailure();
}
}
#elif defined(HAVE_GETENTROPY)
/* On OpenBSD this can return up to 256 bytes of entropy, will return an
* error if more are requested.
* The call cannot return less than the requested number of bytes.
*/
if (getentropy(ent32, NUM_OS_RANDOM_BYTES) != 0) {
RandFailure();
}
#elif defined(HAVE_SYSCTL_ARND)
/* FreeBSD and similar. It is possible for the call to return less
* bytes than requested, so need to read in a loop.
*/
static const int name[2] = {CTL_KERN, KERN_ARND};
int have = 0;
do {
ssize_t n = read(f, ent32 + have, 32 - have);
if (n <= 0 || n + have > 32) {
size_t len = NUM_OS_RANDOM_BYTES - have;
if (sysctl(name, ARRAYLEN(name), ent32 + have, &len, NULL, 0) != 0) {
RandFailure();
}
have += n;
} while (have < 32);
close(f);
have += len;
} while (have < NUM_OS_RANDOM_BYTES);
#else
/* Fall back to /dev/urandom if there is no specific method implemented to
* get system entropy for this OS.
*/
GetDevURandom(ent32);
#endif
}
@ -195,3 +258,33 @@ FastRandomContext::FastRandomContext(bool fDeterministic) @@ -195,3 +258,33 @@ FastRandomContext::FastRandomContext(bool fDeterministic)
}
}
bool Random_SanityCheck()
{
/* This does not measure the quality of randomness, but it does test that
* OSRandom() overwrites all 32 bytes of the output given a maximum
* number of tries.
*/
static const ssize_t MAX_TRIES = 1024;
uint8_t data[NUM_OS_RANDOM_BYTES];
bool overwritten[NUM_OS_RANDOM_BYTES] = {}; /* Tracks which bytes have been overwritten at least once */
int num_overwritten;
int tries = 0;
/* Loop until all bytes have been overwritten at least once, or max number tries reached */
do {
memset(data, 0, NUM_OS_RANDOM_BYTES);
GetOSRand(data);
for (int x=0; x < NUM_OS_RANDOM_BYTES; ++x) {
overwritten[x] |= (data[x] != 0);
}
num_overwritten = 0;
for (int x=0; x < NUM_OS_RANDOM_BYTES; ++x) {
if (overwritten[x]) {
num_overwritten += 1;
}
}
tries += 1;
} while (num_overwritten < NUM_OS_RANDOM_BYTES && tries < MAX_TRIES);
return (num_overwritten == NUM_OS_RANDOM_BYTES); /* If this failed, bailed out after too many tries */
}

17
src/random.h

@ -46,4 +46,21 @@ public: @@ -46,4 +46,21 @@ public:
uint32_t Rw;
};
/* Number of random bytes returned by GetOSRand.
* When changing this constant make sure to change all call sites, and make
* sure that the underlying OS APIs for all platforms support the number.
* (many cap out at 256 bytes).
*/
static const ssize_t NUM_OS_RANDOM_BYTES = 32;
/** Get 32 bytes of system entropy. Do not use this in application code: use
* GetStrongRandBytes instead.
*/
void GetOSRand(unsigned char *ent32);
/** Check that OS randomness is available and returning the requested number
* of bytes.
*/
bool Random_SanityCheck();
#endif // BITCOIN_RANDOM_H

19
src/test/random_tests.cpp

@ -0,0 +1,19 @@ @@ -0,0 +1,19 @@
// Copyright (c) 2017 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include "random.h"
#include "test/test_bitcoin.h"
#include <boost/test/unit_test.hpp>
BOOST_FIXTURE_TEST_SUITE(random_tests, BasicTestingSetup)
BOOST_AUTO_TEST_CASE(osrandom_tests)
{
BOOST_CHECK(Random_SanityCheck());
}
BOOST_AUTO_TEST_SUITE_END()
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