cpython/Python/random.c at 75024c6589539f72af69ce61cd6493b193989c2d · python/cpython · GitHub

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#include "Python.h"

#ifdef MS_WINDOWS

# include <windows.h>

/* All sample MSDN wincrypt programs include the header below. It is at least

* required with Min GW. */

# include <wincrypt.h>

#else

# include <fcntl.h>

# ifdef HAVE_SYS_STAT_H

# include <sys/stat.h>

# endif

# ifdef HAVE_LINUX_RANDOM_H

# include <linux/random.h>

# endif

# ifdef HAVE_GETRANDOM

# include <sys/random.h>

# elif defined(HAVE_GETRANDOM_SYSCALL)

# include <sys/syscall.h>

# endif

#endif

#ifdef Py_DEBUG

int _Py_HashSecret_Initialized = 0;

#else

static int _Py_HashSecret_Initialized = 0;

#endif

#ifdef MS_WINDOWS

static HCRYPTPROV hCryptProv = 0;

static int

win32_urandom_init(int raise)

{

/* Acquire context */

if (!CryptAcquireContext(&hCryptProv, NULL, NULL,

PROV_RSA_FULL, CRYPT_VERIFYCONTEXT))

goto error;

return 0;

error:

if (raise) {

PyErr_SetFromWindowsErr(0);

}

return -1;

}

/* Fill buffer with size pseudo-random bytes generated by the Windows CryptoGen

API. Return 0 on success, or raise an exception and return -1 on error. */

static int

win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise)

{

Py_ssize_t chunk;

if (hCryptProv == 0)

{

if (win32_urandom_init(raise) == -1) {

return -1;

}

while (size > 0)

{

chunk = size > INT_MAX ? INT_MAX : size;

if (!CryptGenRandom(hCryptProv, (DWORD)chunk, buffer))

{

/* CryptGenRandom() failed */

if (raise) {

PyErr_SetFromWindowsErr(0);

}

return -1;

}

buffer += chunk;

size -= chunk;

}

return 0;

}

/* Issue #25003: Don't use getentropy() on Solaris (available since

* Solaris 11.3), it is blocking whereas os.urandom() should not block. */

#elif defined(HAVE_GETENTROPY) && !defined(sun)

#define PY_GETENTROPY 1

/* Fill buffer with size pseudo-random bytes generated by getentropy().

Return 0 on success, or raise an exception and return -1 on error.

If raise is zero, don't raise an exception on error. */

static int

py_getentropy(char *buffer, Py_ssize_t size, int raise)

{

while (size > 0) {

Py_ssize_t len = Py_MIN(size, 256);

int res;

if (raise) {

Py_BEGIN_ALLOW_THREADS

res = getentropy(buffer, len);

Py_END_ALLOW_THREADS

}

else {

res = getentropy(buffer, len);

}

if (res < 0) {

if (raise) {

PyErr_SetFromErrno(PyExc_OSError);

}

return -1;

}

buffer += len;

size -= len;

}

return 0;

}

#else

#if defined(HAVE_GETRANDOM) || defined(HAVE_GETRANDOM_SYSCALL)

#define PY_GETRANDOM 1

/* Call getrandom()

- Return 1 on success

- Return 0 if getrandom() syscall is not available (failed with ENOSYS or

EPERM) or if getrandom(GRND_NONBLOCK) failed with EAGAIN (system urandom

not initialized yet) and raise=0.

- Raise an exception (if raise is non-zero) and return -1 on error:

getrandom() failed with EINTR and the Python signal handler raised an

exception, or getrandom() failed with a different error. */

static int

py_getrandom(void *buffer, Py_ssize_t size, int blocking, int raise)

{

/* Is getrandom() supported by the running kernel? Set to 0 if getrandom()

failed with ENOSYS or EPERM. Need Linux kernel 3.17 or newer, or Solaris

11.3 or newer */

static int getrandom_works = 1;

int flags;

char *dest;

long n;

if (!getrandom_works) {

return 0;

}

flags = blocking ? 0 : GRND_NONBLOCK;

dest = buffer;

while (0 < size) {

#ifdef sun

/* Issue #26735: On Solaris, getrandom() is limited to returning up

to 1024 bytes */

n = Py_MIN(size, 1024);

#else

n = Py_MIN(size, LONG_MAX);

#endif

errno = 0;

#ifdef HAVE_GETRANDOM

if (raise) {

Py_BEGIN_ALLOW_THREADS

n = getrandom(dest, n, flags);

Py_END_ALLOW_THREADS

}

else {

n = getrandom(dest, n, flags);

}

#else

/* On Linux, use the syscall() function because the GNU libc doesn't

expose the Linux getrandom() syscall yet. See:

https://sourceware.org/bugzilla/show_bug.cgi?id=17252 */

if (raise) {

Py_BEGIN_ALLOW_THREADS

n = syscall(SYS_getrandom, dest, n, flags);

Py_END_ALLOW_THREADS

}

else {

n = syscall(SYS_getrandom, dest, n, flags);

}

#endif

if (n < 0) {

/* ENOSYS: getrandom() syscall not supported by the kernel (but

* maybe supported by the host which built Python). EPERM:

* getrandom() syscall blocked by SECCOMP or something else. */

if (errno == ENOSYS || errno == EPERM) {

getrandom_works = 0;

return 0;

}

/* getrandom(GRND_NONBLOCK) fails with EAGAIN if the system urandom

is not initialiazed yet. For _PyRandom_Init(), we ignore their

error and fall back on reading /dev/urandom which never blocks,

even if the system urandom is not initialized yet. */

if (errno == EAGAIN && !raise && !blocking) {

return 0;

}

if (errno == EINTR) {

if (raise) {

if (PyErr_CheckSignals()) {

return -1;

}

/* retry getrandom() if it was interrupted by a signal */

continue;

}

if (raise) {

PyErr_SetFromErrno(PyExc_OSError);

}

return -1;

}

dest += n;

size -= n;

}

return 1;

}

#endif

static struct {

int fd;

dev_t st_dev;

ino_t st_ino;

} urandom_cache = { -1 };

/* Read 'size' random bytes from py_getrandom(). Fall back on reading from

/dev/urandom if getrandom() is not available.

Return 0 on success. Raise an exception (if raise is non-zero) and return -1

on error. */

static int

dev_urandom(char *buffer, Py_ssize_t size, int blocking, int raise)

{

int fd;

Py_ssize_t n;

#ifdef PY_GETRANDOM

int res;

#endif

assert(size > 0);

#ifdef PY_GETRANDOM

res = py_getrandom(buffer, size, blocking, raise);

if (res < 0) {

return -1;

}

if (res == 1) {

return 0;

}

/* getrandom() failed with ENOSYS or EPERM,

fall back on reading /dev/urandom */

#endif

if (raise) {

struct _Py_stat_struct st;

if (urandom_cache.fd >= 0) {

/* Does the fd point to the same thing as before? (issue #21207) */

if (_Py_fstat_noraise(urandom_cache.fd, &st)

|| st.st_dev != urandom_cache.st_dev

|| st.st_ino != urandom_cache.st_ino) {

/* Something changed: forget the cached fd (but don't close it,

since it probably points to something important for some

third-party code). */

urandom_cache.fd = -1;

}

if (urandom_cache.fd >= 0)

fd = urandom_cache.fd;

else {

fd = _Py_open("/dev/urandom", O_RDONLY);

if (fd < 0) {

if (errno == ENOENT || errno == ENXIO ||

errno == ENODEV || errno == EACCES)

PyErr_SetString(PyExc_NotImplementedError,

"/dev/urandom (or equivalent) not found");

/* otherwise, keep the OSError exception raised by _Py_open() */

return -1;

}

if (urandom_cache.fd >= 0) {

/* urandom_fd was initialized by another thread while we were

not holding the GIL, keep it. */

close(fd);

fd = urandom_cache.fd;

}

else {

if (_Py_fstat(fd, &st)) {

close(fd);

return -1;

}

else {

urandom_cache.fd = fd;

urandom_cache.st_dev = st.st_dev;

urandom_cache.st_ino = st.st_ino;

}

do {

n = _Py_read(fd, buffer, (size_t)size);

if (n == -1)

return -1;

if (n == 0) {

PyErr_Format(PyExc_RuntimeError,

"Failed to read %zi bytes from /dev/urandom",

size);

return -1;

}

buffer += n;

size -= n;

} while (0 < size);

}

else {

fd = _Py_open_noraise("/dev/urandom", O_RDONLY);

if (fd < 0) {

return -1;

}

while (0 < size)

{

do {

n = read(fd, buffer, (size_t)size);

} while (n < 0 && errno == EINTR);

if (n <= 0) {

/* stop on error or if read(size) returned 0 */

close(fd);

return -1;

}

buffer += n;

size -= n;

}

close(fd);

}

return 0;

}

static void

dev_urandom_close(void)

{

if (urandom_cache.fd >= 0) {

close(urandom_cache.fd);

urandom_cache.fd = -1;

}

#endif

/* Fill buffer with pseudo-random bytes generated by a linear congruent

generator (LCG):

x(n+1) = (x(n) * 214013 + 2531011) % 2^32

Use bits 23..16 of x(n) to generate a byte. */

static void

lcg_urandom(unsigned int x0, unsigned char *buffer, size_t size)

{

size_t index;

unsigned int x;

x = x0;

for (index=0; index < size; index++) {

x *= 214013;

x += 2531011;

/* modulo 2 ^ (8 * sizeof(int)) */

buffer[index] = (x >> 16) & 0xff;

}

/* If raise is zero:

- Don't raise exceptions on error

- Don't call PyErr_CheckSignals() on EINTR (retry directly the interrupted

syscall)

- Don't release the GIL to call syscalls. */

static int

pyurandom(void *buffer, Py_ssize_t size, int blocking, int raise)

{

if (size < 0) {

if (raise) {

PyErr_Format(PyExc_ValueError,

"negative argument not allowed");

}

return -1;

}

if (size == 0) {

return 0;

}

#ifdef MS_WINDOWS

return win32_urandom((unsigned char *)buffer, size, raise);

#elif defined(PY_GETENTROPY)

return py_getentropy(buffer, size, raise);

#else

return dev_urandom(buffer, size, blocking, raise);

#endif

}

/* Fill buffer with size pseudo-random bytes from the operating system random

number generator (RNG). It is suitable for most cryptographic purposes

except long living private keys for asymmetric encryption.

On Linux 3.17 and newer, the getrandom() syscall is used in blocking mode:

block until the system urandom entropy pool is initialized (128 bits are

collected by the kernel).

Return 0 on success. Raise an exception and return -1 on error. */

int

_PyOS_URandom(void *buffer, Py_ssize_t size)

{

return pyurandom(buffer, size, 1, 1);

}

/* Fill buffer with size pseudo-random bytes from the operating system random

number generator (RNG). It is not suitable for cryptographic purpose.

On Linux 3.17 and newer (when getrandom() syscall is used), if the system

urandom is not initialized yet, the function returns "weak" entropy read

from /dev/urandom.

Return 0 on success. Raise an exception and return -1 on error. */

int

_PyOS_URandomNonblock(void *buffer, Py_ssize_t size)

{

return pyurandom(buffer, size, 0, 1);

}

void

_PyRandom_Init(void)

{

char *env;

unsigned char *secret = (unsigned char *)&_Py_HashSecret.uc;

Py_ssize_t secret_size = sizeof(_Py_HashSecret_t);

Py_BUILD_ASSERT(sizeof(_Py_HashSecret_t) == sizeof(_Py_HashSecret.uc));

if (_Py_HashSecret_Initialized)

return;

_Py_HashSecret_Initialized = 1;

Hash randomization is enabled. Generate a per-process secret,

using PYTHONHASHSEED if provided.

env = Py_GETENV("PYTHONHASHSEED");

if (env && *env != '\0' && strcmp(env, "random") != 0) {

char *endptr = env;

unsigned long seed;

seed = strtoul(env, &endptr, 10);

if (*endptr != '\0'

|| seed > 4294967295UL

|| (errno == ERANGE && seed == ULONG_MAX))

{

Py_FatalError("PYTHONHASHSEED must be \"random\" or an integer "

"in range [0; 4294967295]");

}

if (seed == 0) {

/* disable the randomized hash */

memset(secret, 0, secret_size);

}

else {

lcg_urandom(seed, secret, secret_size);

}

else {

int res;

/* _PyRandom_Init() is called very early in the Python initialization

and so exceptions cannot be used (use raise=0).

_PyRandom_Init() must not block Python initialization: call

pyurandom() is non-blocking mode (blocking=0): see the PEP 524. */

res = pyurandom(secret, secret_size, 0, 0);

if (res < 0) {

Py_FatalError("failed to get random numbers to initialize Python");

}

void

_PyRandom_Fini(void)

{

#ifdef MS_WINDOWS

if (hCryptProv) {

CryptReleaseContext(hCryptProv, 0);

hCryptProv = 0;

}

#elif defined(PY_GETENTROPY)

/* nothing to clean */

#else

dev_urandom_close();

#endif

}

cpython/Python/random.c at 75024c6589539f72af69ce61cd6493b193989c2d · python/cpython · GitHub

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