[Python-checkins] cpython (3.5): Issue #29157: Prefer getrandom() over getentropy()
victor.stinner
python-checkins at python.org
Mon Jan 9 05:22:20 EST 2017
https://hg.python.org/cpython/rev/8125d9a8152b
changeset: 106061:8125d9a8152b
branch: 3.5
parent: 106057:337461574c90
user: Victor Stinner <victor.stinner at gmail.com>
date: Mon Jan 09 11:18:53 2017 +0100
summary:
Issue #29157: Prefer getrandom() over getentropy()
Copy and then adapt Python/random.c from default branch. Difference between 3.5
and default branches:
* Python 3.5 only uses getrandom() in non-blocking mode: flags=GRND_NONBLOCK
* If getrandom() fails with EAGAIN: py_getrandom() immediately fails and
remembers that getrandom() doesn't work.
* Python 3.5 has no _PyOS_URandomNonblock() function: _PyOS_URandom()
works in non-blocking mode on Python 3.5
files:
Python/random.c | 520 +++++++++++++++++++++--------------
1 files changed, 307 insertions(+), 213 deletions(-)
diff --git a/Python/random.c b/Python/random.c
--- a/Python/random.c
+++ b/Python/random.c
@@ -1,6 +1,9 @@
#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
@@ -37,10 +40,9 @@
return 0;
error:
- if (raise)
+ if (raise) {
PyErr_SetFromWindowsErr(0);
- else
- Py_FatalError("Failed to initialize Windows random API (CryptoGen)");
+ }
return -1;
}
@@ -53,8 +55,9 @@
if (hCryptProv == 0)
{
- if (win32_urandom_init(raise) == -1)
+ if (win32_urandom_init(raise) == -1) {
return -1;
+ }
}
while (size > 0)
@@ -63,11 +66,9 @@
if (!CryptGenRandom(hCryptProv, (DWORD)chunk, buffer))
{
/* CryptGenRandom() failed */
- if (raise)
+ if (raise) {
PyErr_SetFromWindowsErr(0);
- else
- Py_FatalError("Failed to initialized the randomized hash "
- "secret using CryptoGen)");
+ }
return -1;
}
buffer += chunk;
@@ -76,58 +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 fatal is nonzero, call Py_FatalError() instead of raising an exception
- on error. */
-static int
-py_getentropy(unsigned char *buffer, Py_ssize_t size, int fatal)
-{
- while (size > 0) {
- Py_ssize_t len = Py_MIN(size, 256);
- int res;
-
- if (!fatal) {
- Py_BEGIN_ALLOW_THREADS
- res = getentropy(buffer, len);
- Py_END_ALLOW_THREADS
-
- if (res < 0) {
- PyErr_SetFromErrno(PyExc_OSError);
- return -1;
- }
- }
- else {
- res = getentropy(buffer, len);
- if (res < 0)
- Py_FatalError("getentropy() failed");
- }
-
- 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).
- 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 raise)
{
@@ -142,16 +108,19 @@
* see https://bugs.python.org/issue26839. To avoid this, use the
* GRND_NONBLOCK flag. */
const int flags = GRND_NONBLOCK;
+ char *dest;
long n;
if (!getrandom_works) {
return 0;
}
+ dest = buffer;
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);
@@ -161,34 +130,35 @@
#ifdef HAVE_GETRANDOM
if (raise) {
Py_BEGIN_ALLOW_THREADS
- n = getrandom(buffer, n, flags);
+ n = getrandom(dest, n, flags);
Py_END_ALLOW_THREADS
}
else {
- n = getrandom(buffer, n, flags);
+ 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 */
+ 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, buffer, n, flags);
+ n = syscall(SYS_getrandom, dest, n, flags);
Py_END_ALLOW_THREADS
}
else {
- n = syscall(SYS_getrandom, buffer, n, flags);
+ 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. */
+ /* 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;
}
+
if (errno == EAGAIN) {
/* getrandom(GRND_NONBLOCK) fails with EAGAIN if the system
urandom is not initialiazed yet. In this case, fall back on
@@ -202,32 +172,101 @@
}
if (errno == EINTR) {
- if (PyErr_CheckSignals()) {
- if (!raise) {
- Py_FatalError("getrandom() interrupted by a signal");
+ if (raise) {
+ if (PyErr_CheckSignals()) {
+ return -1;
}
- return -1;
}
- /* retry getrandom() */
+ /* retry getrandom() if it was interrupted by a signal */
continue;
}
if (raise) {
PyErr_SetFromErrno(PyExc_OSError);
}
- else {
- Py_FatalError("getrandom() failed");
+ 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. */
+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 += n;
- size -= n;
+ buffer += len;
+ size -= len;
}
return 1;
}
-#endif
+#endif /* defined(HAVE_GETENTROPY) && !defined(sun) */
+
static struct {
int fd;
@@ -235,136 +274,123 @@
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
- Call Py_FatalError() on error. */
-static void
-dev_urandom_noraise(unsigned char *buffer, Py_ssize_t size)
+ 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;
- assert (0 < size);
+ if (raise) {
+ struct _Py_stat_struct st;
-#ifdef PY_GETRANDOM
- if (py_getrandom(buffer, size, 0) == 1) {
- return;
+ 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);
}
- /* getrandom() failed with ENOSYS or EPERM,
- fall back on reading /dev/urandom */
-#endif
-
- fd = _Py_open_noraise("/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) {
- /* read() failed or returned 0 bytes */
- Py_FatalError("Failed to read bytes from /dev/urandom");
- break;
- }
- buffer += n;
- size -= n;
- }
- close(fd);
-}
-
-/* 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 and return -1 on error. */
-static int
-dev_urandom_python(char *buffer, Py_ssize_t size)
-{
- int fd;
- Py_ssize_t n;
- struct _Py_stat_struct st;
-#ifdef PY_GETRANDOM
- int res;
-#endif
-
- if (size <= 0)
- return 0;
-
-#ifdef PY_GETRANDOM
- res = py_getrandom(buffer, size, 1);
- if (res < 0) {
- return -1;
- }
- if (res == 1) {
- return 0;
- }
- /* getrandom() failed with ENOSYS or EPERM,
- fall back on reading /dev/urandom */
-#endif
-
- 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);
+ fd = _Py_open_noraise("/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)) {
+
+ 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;
}
- else {
- urandom_cache.fd = fd;
- urandom_cache.st_dev = st.st_dev;
- urandom_cache.st_ino = st.st_ino;
- }
+
+ buffer += n;
+ size -= n;
}
+ close(fd);
}
-
- 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);
-
return 0;
}
@@ -376,8 +402,8 @@
urandom_cache.fd = -1;
}
}
+#endif /* !MS_WINDOWS */
-#endif
/* Fill buffer with pseudo-random bytes generated by a linear congruent
generator (LCG):
@@ -400,29 +426,98 @@
}
}
+/* 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 and Python requires non-blocking RNG at startup to
+ initialize its hash secret: see the PEP 524.
+
+ 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 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 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)
+#ifdef PY_GETRANDOM
+ res = py_getrandom(buffer, size, 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, EPERM or EAGAIN. Fall back on reading from /dev/urandom. */
+#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.
- Return 0 on success, raise an exception and return -1 on error. */
+ 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);
-#elif defined(PY_GETENTROPY)
- return py_getentropy(buffer, size, 0);
-#else
- return dev_urandom_python((char*)buffer, size);
-#endif
+ return pyurandom(buffer, size, 1);
}
void
@@ -463,13 +558,14 @@
}
}
else {
-#ifdef MS_WINDOWS
- (void)win32_urandom(secret, secret_size, 0);
-#elif defined(PY_GETENTROPY)
- (void)py_getentropy(secret, secret_size, 1);
-#else
- dev_urandom_noraise(secret, secret_size);
-#endif
+ int res;
+
+ /* _PyRandom_Init() is called very early in the Python initialization
+ and so exceptions cannot be used (use raise=0). */
+ res = pyurandom(secret, secret_size, 0);
+ if (res < 0) {
+ Py_FatalError("failed to get random numbers to initialize Python");
+ }
}
}
@@ -481,8 +577,6 @@
CryptReleaseContext(hCryptProv, 0);
hCryptProv = 0;
}
-#elif defined(PY_GETENTROPY)
- /* nothing to clean */
#else
dev_urandom_close();
#endif
--
Repository URL: https://hg.python.org/cpython
More information about the Python-checkins
mailing list