cpython/Python/random.c

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#include "Python.h"
#ifdef MS_WINDOWS
#include <windows.h>
#else
#include <fcntl.h>
#ifdef HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif
#endif
#ifdef Py_DEBUG
int _Py_HashSecret_Initialized = 0;
#else
static int _Py_HashSecret_Initialized = 0;
#endif
#ifdef MS_WINDOWS
/* This handle is never explicitly released. Instead, the operating
system will release it when the process terminates. */
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);
else
Py_FatalError("Failed to initialize Windows random API (CryptoGen)");
return -1;
}
/* Fill buffer with size pseudo-random bytes generated by the Windows CryptoGen
API. Return 0 on success, or -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);
else
Py_FatalError("Failed to initialized the randomized hash "
"secret using CryptoGen)");
return -1;
}
buffer += chunk;
size -= chunk;
}
return 0;
}
#endif /* MS_WINDOWS */
#ifndef MS_WINDOWS
static struct {
int fd;
dev_t st_dev;
ino_t st_ino;
} urandom_cache = { -1 };
/* Read size bytes from /dev/urandom into buffer.
Call Py_FatalError() on error. */
static void
dev_urandom_noraise(unsigned char *buffer, Py_ssize_t size)
{
int fd;
Py_ssize_t n;
assert (0 < size);
fd = _Py_open("/dev/urandom", O_RDONLY);
if (fd < 0)
Py_FatalError("Failed to open /dev/urandom");
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 */
Py_FatalError("Failed to read bytes from /dev/urandom");
break;
}
buffer += n;
size -= (Py_ssize_t)n;
}
close(fd);
}
/* Read size bytes from /dev/urandom into buffer.
Return 0 on success, raise an exception and return -1 on error. */
static int
dev_urandom_python(char *buffer, Py_ssize_t size)
{
int fd;
Py_ssize_t n;
struct stat st;
if (size <= 0)
return 0;
if (urandom_cache.fd >= 0) {
/* Does the fd point to the same thing as before? (issue #21207) */
if (fstat(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 {
Py_BEGIN_ALLOW_THREADS
fd = _Py_open("/dev/urandom", O_RDONLY);
Py_END_ALLOW_THREADS
if (fd < 0)
{
if (errno == ENOENT || errno == ENXIO ||
errno == ENODEV || errno == EACCES)
PyErr_SetString(PyExc_NotImplementedError,
"/dev/urandom (or equivalent) not found");
else
PyErr_SetFromErrno(PyExc_OSError);
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 (fstat(fd, &st)) {
PyErr_SetFromErrno(PyExc_OSError);
close(fd);
return -1;
}
else {
urandom_cache.fd = fd;
urandom_cache.st_dev = st.st_dev;
urandom_cache.st_ino = st.st_ino;
}
}
}
Py_BEGIN_ALLOW_THREADS
do {
do {
n = read(fd, buffer, (size_t)size);
} while (n < 0 && errno == EINTR);
if (n <= 0)
break;
buffer += n;
size -= (Py_ssize_t)n;
} while (0 < size);
Py_END_ALLOW_THREADS
if (n <= 0)
{
/* stop on error or if read(size) returned 0 */
if (n < 0)
PyErr_SetFromErrno(PyExc_OSError);
else
PyErr_Format(PyExc_RuntimeError,
"Failed to read %zi bytes from /dev/urandom",
size);
return -1;
}
return 0;
}
static void
dev_urandom_close(void)
{
if (urandom_cache.fd >= 0) {
close(urandom_cache.fd);
urandom_cache.fd = -1;
}
}
#endif /* MS_WINDOWS */
/* 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;
}
}
/* Fill buffer with size pseudo-random bytes from the operating system random
number generator (RNG). It is suitable for for most cryptographic purposes
except long living private keys for asymmetric encryption.
Return 0 on success, raise an exception and return -1 on error. */
int
_PyOS_URandom(void *buffer, Py_ssize_t size)
{
if (size < 0) {
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, 1);
#else
return dev_urandom_python((char*)buffer, size);
#endif
}
void
_PyRandom_Init(void)
{
char *env;
unsigned char *secret = (unsigned char *)&_Py_HashSecret.uc;
Py_ssize_t secret_size = sizeof(_Py_HashSecret_t);
assert(secret_size == 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");
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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 {
#ifdef MS_WINDOWS
(void)win32_urandom(secret, secret_size, 0);
#else
dev_urandom_noraise(secret, secret_size);
#endif
}
}
void
_PyRandom_Fini(void)
{
#ifndef MS_WINDOWS
dev_urandom_close();
#endif
}