[Python-checkins] cpython (3.6): Issue #29157: Prefer getrandom() over getentropy()
victor.stinner
python-checkins at python.org
Fri Jan 6 18:08:38 EST 2017
https://hg.python.org/cpython/rev/f8e24a0a1124
changeset: 106022:f8e24a0a1124
branch: 3.6
parent: 106020:50424a903593
user: Victor Stinner <victor.stinner at gmail.com>
date: Sat Jan 07 00:07:45 2017 +0100
summary:
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
files:
Python/random.c | 274 ++++++++++++++++++++++++-----------
1 files changed, 187 insertions(+), 87 deletions(-)
diff --git a/Python/random.c b/Python/random.c
--- a/Python/random.c
+++ b/Python/random.c
@@ -77,57 +77,23 @@
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 @@
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 @@
#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 @@
}
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 @@
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 @@
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 @@
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 @@
}
}
-/* 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 @@
#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 @@
CryptReleaseContext(hCryptProv, 0);
hCryptProv = 0;
}
-#elif defined(PY_GETENTROPY)
- /* nothing to clean */
#else
dev_urandom_close();
#endif
--
Repository URL: https://hg.python.org/cpython
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