Issue #29157: Prefer getrandom() over getentropy()
* dev_urandom() now calls py_getentropy(). Prepare the fallback to support getentropy() failure and falls back on reading from /dev/urandom. * Simplify dev_urandom(). pyurandom() is now responsible to call getentropy() or getrandom(). Enhance also dev_urandom() and pyurandom() documentation. * getrandom() is now preferred over getentropy(). The glibc 2.24 now implements getentropy() on Linux using the getrandom() syscall. But getentropy() doesn't support non-blocking mode. Since getrandom() is tried first, it's not more needed to explicitly exclude getentropy() on Solaris. Replace: "if defined(HAVE_GETENTROPY) && !defined(sun)" with "if defined(HAVE_GETENTROPY)" * Enhance py_getrandom() documentation. py_getentropy() now supports ENOSYS, EPERM & EINTR
This commit is contained in:
Victor Stinner
parent
84b6fb0eea
commit
ff558f5aba
274
Python/random.c
274
Python/random.c
|
|
@ -77,57 +77,23 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise)
|
|||
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
|
||||
#else /* !MS_WINDOWS */
|
||||
|
||||
#if defined(HAVE_GETRANDOM) || defined(HAVE_GETRANDOM_SYSCALL)
|
||||
#define PY_GETRANDOM 1
|
||||
|
||||
/* Call getrandom()
|
||||
/* Call getrandom() to get random bytes:
|
||||
|
||||
- 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.
|
||||
- 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:
|
||||
getrandom() failed with EINTR and the Python signal handler raised an
|
||||
exception, or getrandom() failed with a different 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)
|
||||
{
|
||||
|
|
@ -148,7 +114,8 @@ py_getrandom(void *buffer, Py_ssize_t size, int blocking, int raise)
|
|||
while (0 < size) {
|
||||
#ifdef sun
|
||||
/* Issue #26735: On Solaris, getrandom() is limited to returning up
|
||||
to 1024 bytes */
|
||||
to 1024 bytes. Call it multiple times if more bytes are
|
||||
requested. */
|
||||
n = Py_MIN(size, 1024);
|
||||
#else
|
||||
n = Py_MIN(size, LONG_MAX);
|
||||
|
|
@ -179,18 +146,19 @@ py_getrandom(void *buffer, Py_ssize_t size, int blocking, int raise)
|
|||
#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. */
|
||||
/* 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 initialiazed yet. For _PyRandom_Init(), we ignore their
|
||||
is not initialiazed 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. */
|
||||
even if the system urandom is not initialized yet:
|
||||
see the PEP 524. */
|
||||
if (errno == EAGAIN && !raise && !blocking) {
|
||||
return 0;
|
||||
}
|
||||
|
|
@ -217,7 +185,80 @@ py_getrandom(void *buffer, Py_ssize_t size, int blocking, int raise)
|
|||
}
|
||||
return 1;
|
||||
}
|
||||
#endif
|
||||
|
||||
#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. */
|
||||
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) */
|
||||
|
||||
|
||||
static struct {
|
||||
int fd;
|
||||
|
|
@ -225,35 +266,38 @@ static struct {
|
|||
ino_t st_ino;
|
||||
} urandom_cache = { -1 };
|
||||
|
||||
/* Read random bytes from the /dev/urandom device:
|
||||
|
||||
/* 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
|
||||
|
||||
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 blocking, int raise)
|
||||
dev_urandom(char *buffer, Py_ssize_t size, 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;
|
||||
|
|
@ -275,9 +319,10 @@ dev_urandom(char *buffer, Py_ssize_t size, int blocking, int raise)
|
|||
fd = _Py_open("/dev/urandom", O_RDONLY);
|
||||
if (fd < 0) {
|
||||
if (errno == ENOENT || errno == ENXIO ||
|
||||
errno == ENODEV || errno == EACCES)
|
||||
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;
|
||||
}
|
||||
|
|
@ -349,8 +394,8 @@ dev_urandom_close(void)
|
|||
urandom_cache.fd = -1;
|
||||
}
|
||||
}
|
||||
#endif /* !MS_WINDOWS */
|
||||
|
||||
#endif
|
||||
|
||||
/* Fill buffer with pseudo-random bytes generated by a linear congruent
|
||||
generator (LCG):
|
||||
|
|
@ -373,14 +418,56 @@ lcg_urandom(unsigned int x0, unsigned char *buffer, size_t size)
|
|||
}
|
||||
}
|
||||
|
||||
/* 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. */
|
||||
/* 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:
|
||||
|
||||
- CryptGenRandom() 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,
|
||||
|
|
@ -395,10 +482,25 @@ pyurandom(void *buffer, Py_ssize_t size, int blocking, int raise)
|
|||
|
||||
#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);
|
||||
|
||||
#if defined(PY_GETRANDOM) || defined(PY_GETENTROPY)
|
||||
#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. */
|
||||
#endif
|
||||
|
||||
return dev_urandom(buffer, size, raise);
|
||||
#endif
|
||||
}
|
||||
|
||||
|
|
@ -491,8 +593,6 @@ _PyRandom_Fini(void)
|
|||
CryptReleaseContext(hCryptProv, 0);
|
||||
hCryptProv = 0;
|
||||
}
|
||||
#elif defined(PY_GETENTROPY)
|
||||
/* nothing to clean */
|
||||
#else
|
||||
dev_urandom_close();
|
||||
#endif
|
||||
|
|
|
|||
Loading…
Reference in New Issue