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cpython/Python/bootstrap_hash.c

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#include "Python.h"
#include "pycore_fileutils.h" // _Py_fstat_noraise()
#include "pycore_initconfig.h"
#include "pycore_pylifecycle.h" // _PyOS_URandomNonblock()
#include "pycore_runtime.h" // _PyRuntime
#ifdef HAVE_UNISTD_H
# include <unistd.h> // close()
#endif
#ifdef MS_WINDOWS
# include <windows.h>
# include <bcrypt.h>
#else
# include <fcntl.h> // O_RDONLY
# ifdef HAVE_SYS_STAT_H
# include <sys/stat.h>
# endif
# ifdef HAVE_LINUX_RANDOM_H
# include <linux/random.h> // GRND_NONBLOCK
# endif
# if defined(HAVE_SYS_RANDOM_H) && (defined(HAVE_GETRANDOM) || defined(HAVE_GETENTROPY))
# include <sys/random.h> // getrandom()
# endif
# if !defined(HAVE_GETRANDOM) && defined(HAVE_GETRANDOM_SYSCALL)
# include <sys/syscall.h> // SYS_getrandom
# endif
#endif
#ifdef _Py_MEMORY_SANITIZER
# include <sanitizer/msan_interface.h>
#endif
#if defined(__APPLE__) && defined(__has_builtin)
# if __has_builtin(__builtin_available)
# define HAVE_GETENTRYPY_GETRANDOM_RUNTIME __builtin_available(macOS 10.12, iOS 10.10, tvOS 10.0, watchOS 3.0, *)
# endif
#endif
#ifndef HAVE_GETENTRYPY_GETRANDOM_RUNTIME
# define HAVE_GETENTRYPY_GETRANDOM_RUNTIME 1
#endif
#ifdef Py_DEBUG
int _Py_HashSecret_Initialized = 0;
#else
static int _Py_HashSecret_Initialized = 0;
#endif
#ifdef MS_WINDOWS
/* 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)
{
while (size > 0)
{
DWORD chunk = (DWORD)Py_MIN(size, PY_DWORD_MAX);
NTSTATUS status = BCryptGenRandom(NULL, buffer, chunk, BCRYPT_USE_SYSTEM_PREFERRED_RNG);
if (!BCRYPT_SUCCESS(status)) {
/* BCryptGenRandom() failed */
if (raise) {
PyErr_SetFromWindowsErr(0);
}
return -1;
}
buffer += chunk;
size -= chunk;
}
return 0;
}
#else /* !MS_WINDOWS */
#if defined(HAVE_GETRANDOM) || defined(HAVE_GETRANDOM_SYSCALL)
#define PY_GETRANDOM 1
/* Call getrandom() to get random bytes:
- Return 1 on success
- Return 0 if getrandom() 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:
if getrandom() failed with EINTR, raise is non-zero and the Python signal
handler raised an exception, or if getrandom() failed with a different
error.
getrandom() is retried if it failed with EINTR: interrupted by a signal. */
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) {
#if defined(__sun) && defined(__SVR4)
/* Issue #26735: On Solaris, getrandom() is limited to returning up
to 1024 bytes. Call it multiple times if more bytes are
requested. */
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);
}
# ifdef _Py_MEMORY_SANITIZER
if (n > 0) {
__msan_unpoison(dest, n);
}
# endif
#endif
if (n < 0) {
/* ENOSYS: the syscall is not supported by the kernel.
EPERM: the syscall is blocked by a security policy (ex: 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 initialized yet. For _PyRandom_Init(), we ignore the
error and fall back on reading /dev/urandom which never blocks,
even if the system urandom is not initialized yet:
see the PEP 524. */
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;
}
#elif defined(HAVE_GETENTROPY)
#define PY_GETENTROPY 1
/* Fill buffer with size pseudo-random bytes generated by getentropy():
- Return 1 on success
- Return 0 if getentropy() syscall is not available (failed with ENOSYS or
EPERM).
- Raise an exception (if raise is non-zero) and return -1 on error:
if getentropy() failed with EINTR, raise is non-zero and the Python signal
handler raised an exception, or if getentropy() failed with a different
error.
getentropy() is retried if it failed with EINTR: interrupted by a signal. */
#if defined(__APPLE__) && defined(__has_attribute) && __has_attribute(availability)
static int
py_getentropy(char *buffer, Py_ssize_t size, int raise)
__attribute__((availability(macos,introduced=10.12)))
__attribute__((availability(ios,introduced=10.0)))
__attribute__((availability(tvos,introduced=10.0)))
__attribute__((availability(watchos,introduced=3.0)));
#endif
static int
py_getentropy(char *buffer, Py_ssize_t size, int raise)
{
/* Is getentropy() supported by the running kernel? Set to 0 if
getentropy() failed with ENOSYS or EPERM. */
static int getentropy_works = 1;
if (!getentropy_works) {
return 0;
}
while (size > 0) {
/* getentropy() is limited to returning up to 256 bytes. Call it
multiple times if more bytes are requested. */
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) {
/* ENOSYS: the syscall is not supported by the running kernel.
EPERM: the syscall is blocked by a security policy (ex: SECCOMP)
or something else. */
if (errno == ENOSYS || errno == EPERM) {
getentropy_works = 0;
return 0;
}
if (errno == EINTR) {
if (raise) {
if (PyErr_CheckSignals()) {
return -1;
}
}
/* retry getentropy() if it was interrupted by a signal */
continue;
}
if (raise) {
PyErr_SetFromErrno(PyExc_OSError);
}
return -1;
}
buffer += len;
size -= len;
}
return 1;
}
#endif /* defined(HAVE_GETENTROPY) && !(defined(__sun) && defined(__SVR4)) */
#define urandom_cache (_PyRuntime.pyhash_state.urandom_cache)
/* Read random bytes from the /dev/urandom device:
- Return 0 on success
- Raise an exception (if raise is non-zero) and return -1 on error
Possible causes of errors:
- open() failed with ENOENT, ENXIO, ENODEV, EACCES: the /dev/urandom device
was not found. For example, it was removed manually or not exposed in a
chroot or container.
- open() failed with a different error
- fstat() failed
- read() failed or returned 0
read() is retried if it failed with EINTR: interrupted by a signal.
The file descriptor of the device is kept open between calls to avoid using
many file descriptors when run in parallel from multiple threads:
see the issue #18756.
st_dev and st_ino fields of the file descriptor (from fstat()) are cached to
check if the file descriptor was replaced by a different file (which is
likely a bug in the application): see the issue #21207.
If the file descriptor was closed or replaced, open a new file descriptor
but don't close the old file descriptor: it probably points to something
important for some third-party code. */
static int
dev_urandom(char *buffer, Py_ssize_t size, int raise)
{
int fd;
Py_ssize_t n;
if (raise) {
struct _Py_stat_struct st;
int fstat_result;
if (urandom_cache.fd >= 0) {
Py_BEGIN_ALLOW_THREADS
fstat_result = _Py_fstat_noraise(urandom_cache.fd, &st);
Py_END_ALLOW_THREADS
/* Does the fd point to the same thing as before? (issue #21207) */
if (fstat_result
|| 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;
}
}
#undef urandom_cache
#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;
}
}
/* Read random bytes:
- Return 0 on success
- Raise an exception (if raise is non-zero) and return -1 on error
Used sources of entropy ordered by preference, preferred source first:
- BCryptGenRandom() on Windows
- getrandom() function (ex: Linux and Solaris): call py_getrandom()
- getentropy() function (ex: OpenBSD): call py_getentropy()
- /dev/urandom device
Read from the /dev/urandom device if getrandom() or getentropy() function
is not available or does not work.
Prefer getrandom() over getentropy() because getrandom() supports blocking
and non-blocking mode: see the PEP 524. Python requires non-blocking RNG at
startup to initialize its hash secret, but os.urandom() must block until the
system urandom is initialized (at least on Linux 3.17 and newer).
Prefer getrandom() and getentropy() over reading directly /dev/urandom
because these functions don't need file descriptors and so avoid ENFILE or
EMFILE errors (too many open files): see the issue #18756.
Only the getrandom() function supports non-blocking mode.
Only use RNG running in the kernel. They are more secure because it is
harder to get the internal state of a RNG running in the kernel land than a
RNG running in the user land. The kernel has a direct access to the hardware
and has access to hardware RNG, they are used as entropy sources.
Note: the OpenSSL RAND_pseudo_bytes() function does not automatically reseed
its RNG on fork(), two child processes (with the same pid) generate the same
random numbers: see issue #18747. Kernel RNGs don't have this issue,
they have access to good quality entropy sources.
If raise is zero:
- Don't raise an exception on error
- Don't call the Python signal handler (don't call PyErr_CheckSignals()) if
a function fails with EINTR: retry directly the interrupted function
- Don't release the GIL to call functions.
*/
static int
pyurandom(void *buffer, Py_ssize_t size, int blocking, int raise)
{
#if defined(PY_GETRANDOM) || defined(PY_GETENTROPY)
int res;
#endif
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);
#else
#if defined(PY_GETRANDOM) || defined(PY_GETENTROPY)
if (HAVE_GETENTRYPY_GETRANDOM_RUNTIME) {
#ifdef PY_GETRANDOM
res = py_getrandom(buffer, size, blocking, raise);
#else
res = py_getentropy(buffer, size, raise);
#endif
if (res < 0) {
return -1;
}
if (res == 1) {
return 0;
}
/* getrandom() or getentropy() function is not available: failed with
ENOSYS or EPERM. Fall back on reading from /dev/urandom. */
} /* end of availability block */
#endif
return dev_urandom(buffer, size, 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);
}
PyStatus
_Py_HashRandomization_Init(const PyConfig *config)
{
void *secret = &_Py_HashSecret;
Py_ssize_t secret_size = sizeof(_Py_HashSecret_t);
if (_Py_HashSecret_Initialized) {
return _PyStatus_OK();
}
_Py_HashSecret_Initialized = 1;
if (config->use_hash_seed) {
if (config->hash_seed == 0) {
/* disable the randomized hash */
memset(secret, 0, secret_size);
}
else {
/* use the specified hash seed */
lcg_urandom(config->hash_seed, secret, secret_size);
}
}
else {
/* use a random hash seed */
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) {
return _PyStatus_ERR("failed to get random numbers "
"to initialize Python");
}
}
return _PyStatus_OK();
}
void
_Py_HashRandomization_Fini(void)
{
#ifndef MS_WINDOWS
dev_urandom_close();
#endif
}
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