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
This commit is contained in:
parent
9937d90ee8
commit
035ba5da3e
506
Python/random.c
506
Python/random.c
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@ -1,6 +1,9 @@
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#include "Python.h"
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#ifdef MS_WINDOWS
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# include <windows.h>
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/* All sample MSDN wincrypt programs include the header below. It is at least
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* required with Min GW. */
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# include <wincrypt.h>
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#else
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# include <fcntl.h>
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# ifdef HAVE_SYS_STAT_H
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@ -37,10 +40,9 @@ win32_urandom_init(int raise)
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return 0;
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error:
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if (raise)
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if (raise) {
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PyErr_SetFromWindowsErr(0);
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else
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Py_FatalError("Failed to initialize Windows random API (CryptoGen)");
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}
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return -1;
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}
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@ -53,8 +55,9 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise)
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if (hCryptProv == 0)
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{
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if (win32_urandom_init(raise) == -1)
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if (win32_urandom_init(raise) == -1) {
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return -1;
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}
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}
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while (size > 0)
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@ -63,11 +66,9 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise)
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if (!CryptGenRandom(hCryptProv, (DWORD)chunk, buffer))
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{
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/* CryptGenRandom() failed */
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if (raise)
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if (raise) {
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PyErr_SetFromWindowsErr(0);
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else
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Py_FatalError("Failed to initialized the randomized hash "
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"secret using CryptoGen)");
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}
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return -1;
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}
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buffer += chunk;
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@ -76,58 +77,23 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise)
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return 0;
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}
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/* Issue #25003: Don't use getentropy() on Solaris (available since
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* Solaris 11.3), it is blocking whereas os.urandom() should not block. */
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#elif defined(HAVE_GETENTROPY) && !defined(sun)
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#define PY_GETENTROPY 1
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/* Fill buffer with size pseudo-random bytes generated by getentropy().
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Return 0 on success, or raise an exception and return -1 on error.
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If fatal is nonzero, call Py_FatalError() instead of raising an exception
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on error. */
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static int
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py_getentropy(unsigned char *buffer, Py_ssize_t size, int fatal)
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{
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while (size > 0) {
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Py_ssize_t len = Py_MIN(size, 256);
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int res;
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if (!fatal) {
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Py_BEGIN_ALLOW_THREADS
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res = getentropy(buffer, len);
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Py_END_ALLOW_THREADS
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if (res < 0) {
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PyErr_SetFromErrno(PyExc_OSError);
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return -1;
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}
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}
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else {
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res = getentropy(buffer, len);
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if (res < 0)
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Py_FatalError("getentropy() failed");
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}
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buffer += len;
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size -= len;
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}
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return 0;
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}
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#else
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#else /* !MS_WINDOWS */
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#if defined(HAVE_GETRANDOM) || defined(HAVE_GETRANDOM_SYSCALL)
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#define PY_GETRANDOM 1
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/* Call getrandom()
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/* Call getrandom() to get random bytes:
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- Return 1 on success
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- Return 0 if getrandom() syscall is not available (failed with ENOSYS or
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EPERM) or if getrandom(GRND_NONBLOCK) failed with EAGAIN (system urandom
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not initialized yet) and raise=0.
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- Return 0 if getrandom() is not available (failed with ENOSYS or EPERM),
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or if getrandom(GRND_NONBLOCK) failed with EAGAIN (system urandom not
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initialized yet).
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- Raise an exception (if raise is non-zero) and return -1 on error:
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getrandom() failed with EINTR and the Python signal handler raised an
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exception, or getrandom() failed with a different error. */
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if getrandom() failed with EINTR, raise is non-zero and the Python signal
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handler raised an exception, or if getrandom() failed with a different
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error.
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getrandom() is retried if it failed with EINTR: interrupted by a signal. */
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static int
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py_getrandom(void *buffer, Py_ssize_t size, int raise)
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{
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@ -142,16 +108,19 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise)
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* see https://bugs.python.org/issue26839. To avoid this, use the
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* GRND_NONBLOCK flag. */
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const int flags = GRND_NONBLOCK;
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char *dest;
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long n;
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if (!getrandom_works) {
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return 0;
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}
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dest = buffer;
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while (0 < size) {
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#ifdef sun
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/* Issue #26735: On Solaris, getrandom() is limited to returning up
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to 1024 bytes */
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to 1024 bytes. Call it multiple times if more bytes are
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requested. */
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n = Py_MIN(size, 1024);
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#else
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n = Py_MIN(size, LONG_MAX);
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@ -161,34 +130,35 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise)
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#ifdef HAVE_GETRANDOM
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if (raise) {
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Py_BEGIN_ALLOW_THREADS
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n = getrandom(buffer, n, flags);
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n = getrandom(dest, n, flags);
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Py_END_ALLOW_THREADS
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}
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else {
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n = getrandom(buffer, n, flags);
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n = getrandom(dest, n, flags);
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}
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#else
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/* On Linux, use the syscall() function because the GNU libc doesn't
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* expose the Linux getrandom() syscall yet. See:
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* https://sourceware.org/bugzilla/show_bug.cgi?id=17252 */
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expose the Linux getrandom() syscall yet. See:
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https://sourceware.org/bugzilla/show_bug.cgi?id=17252 */
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if (raise) {
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Py_BEGIN_ALLOW_THREADS
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n = syscall(SYS_getrandom, buffer, n, flags);
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n = syscall(SYS_getrandom, dest, n, flags);
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Py_END_ALLOW_THREADS
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}
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else {
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n = syscall(SYS_getrandom, buffer, n, flags);
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n = syscall(SYS_getrandom, dest, n, flags);
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}
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#endif
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if (n < 0) {
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/* ENOSYS: getrandom() syscall not supported by the kernel (but
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* maybe supported by the host which built Python). EPERM:
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* getrandom() syscall blocked by SECCOMP or something else. */
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/* ENOSYS: the syscall is not supported by the kernel.
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EPERM: the syscall is blocked by a security policy (ex: SECCOMP)
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or something else. */
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if (errno == ENOSYS || errno == EPERM) {
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getrandom_works = 0;
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return 0;
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}
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if (errno == EAGAIN) {
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/* getrandom(GRND_NONBLOCK) fails with EAGAIN if the system
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urandom is not initialiazed yet. In this case, fall back on
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}
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if (errno == EINTR) {
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if (PyErr_CheckSignals()) {
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if (!raise) {
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Py_FatalError("getrandom() interrupted by a signal");
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if (raise) {
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if (PyErr_CheckSignals()) {
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return -1;
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}
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return -1;
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}
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/* retry getrandom() */
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/* retry getrandom() if it was interrupted by a signal */
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continue;
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}
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if (raise) {
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PyErr_SetFromErrno(PyExc_OSError);
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}
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else {
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Py_FatalError("getrandom() failed");
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}
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return -1;
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}
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buffer += n;
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dest += n;
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size -= n;
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}
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return 1;
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}
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#endif
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#elif defined(HAVE_GETENTROPY)
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#define PY_GETENTROPY 1
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/* Fill buffer with size pseudo-random bytes generated by getentropy():
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- Return 1 on success
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- Return 0 if getentropy() syscall is not available (failed with ENOSYS or
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EPERM).
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- Raise an exception (if raise is non-zero) and return -1 on error:
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if getentropy() failed with EINTR, raise is non-zero and the Python signal
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handler raised an exception, or if getentropy() failed with a different
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error.
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getentropy() is retried if it failed with EINTR: interrupted by a signal. */
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static int
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py_getentropy(char *buffer, Py_ssize_t size, int raise)
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{
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/* Is getentropy() supported by the running kernel? Set to 0 if
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getentropy() failed with ENOSYS or EPERM. */
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static int getentropy_works = 1;
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if (!getentropy_works) {
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return 0;
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}
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while (size > 0) {
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/* getentropy() is limited to returning up to 256 bytes. Call it
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multiple times if more bytes are requested. */
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Py_ssize_t len = Py_MIN(size, 256);
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int res;
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if (raise) {
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Py_BEGIN_ALLOW_THREADS
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res = getentropy(buffer, len);
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Py_END_ALLOW_THREADS
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}
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else {
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res = getentropy(buffer, len);
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}
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if (res < 0) {
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/* ENOSYS: the syscall is not supported by the running kernel.
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EPERM: the syscall is blocked by a security policy (ex: SECCOMP)
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or something else. */
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if (errno == ENOSYS || errno == EPERM) {
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getentropy_works = 0;
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return 0;
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}
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if (errno == EINTR) {
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if (raise) {
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if (PyErr_CheckSignals()) {
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return -1;
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}
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}
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/* retry getentropy() if it was interrupted by a signal */
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continue;
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}
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if (raise) {
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PyErr_SetFromErrno(PyExc_OSError);
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}
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return -1;
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}
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buffer += len;
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size -= len;
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}
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return 1;
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}
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#endif /* defined(HAVE_GETENTROPY) && !defined(sun) */
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static struct {
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int fd;
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ino_t st_ino;
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} urandom_cache = { -1 };
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/* Read random bytes from the /dev/urandom device:
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/* Read 'size' random bytes from py_getrandom(). Fall back on reading from
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/dev/urandom if getrandom() is not available.
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- Return 0 on success
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- Raise an exception (if raise is non-zero) and return -1 on error
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Call Py_FatalError() on error. */
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static void
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dev_urandom_noraise(unsigned char *buffer, Py_ssize_t size)
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{
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int fd;
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Py_ssize_t n;
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Possible causes of errors:
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assert (0 < size);
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- open() failed with ENOENT, ENXIO, ENODEV, EACCES: the /dev/urandom device
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was not found. For example, it was removed manually or not exposed in a
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chroot or container.
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- open() failed with a different error
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- fstat() failed
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- read() failed or returned 0
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#ifdef PY_GETRANDOM
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if (py_getrandom(buffer, size, 0) == 1) {
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return;
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}
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/* getrandom() failed with ENOSYS or EPERM,
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fall back on reading /dev/urandom */
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#endif
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read() is retried if it failed with EINTR: interrupted by a signal.
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fd = _Py_open_noraise("/dev/urandom", O_RDONLY);
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if (fd < 0) {
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Py_FatalError("Failed to open /dev/urandom");
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}
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The file descriptor of the device is kept open between calls to avoid using
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many file descriptors when run in parallel from multiple threads:
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see the issue #18756.
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while (0 < size)
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{
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do {
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n = read(fd, buffer, (size_t)size);
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} while (n < 0 && errno == EINTR);
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st_dev and st_ino fields of the file descriptor (from fstat()) are cached to
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check if the file descriptor was replaced by a different file (which is
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likely a bug in the application): see the issue #21207.
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if (n <= 0) {
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/* read() failed or returned 0 bytes */
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Py_FatalError("Failed to read bytes from /dev/urandom");
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break;
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}
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buffer += n;
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size -= n;
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}
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close(fd);
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}
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/* Read 'size' random bytes from py_getrandom(). Fall back on reading from
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/dev/urandom if getrandom() is not available.
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Return 0 on success. Raise an exception and return -1 on error. */
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If the file descriptor was closed or replaced, open a new file descriptor
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but don't close the old file descriptor: it probably points to something
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important for some third-party code. */
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static int
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dev_urandom_python(char *buffer, Py_ssize_t size)
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dev_urandom(char *buffer, Py_ssize_t size, int raise)
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{
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int fd;
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Py_ssize_t n;
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struct _Py_stat_struct st;
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#ifdef PY_GETRANDOM
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int res;
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#endif
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if (size <= 0)
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return 0;
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if (raise) {
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struct _Py_stat_struct st;
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#ifdef PY_GETRANDOM
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res = py_getrandom(buffer, size, 1);
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if (res < 0) {
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return -1;
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}
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if (res == 1) {
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return 0;
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}
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/* getrandom() failed with ENOSYS or EPERM,
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fall back on reading /dev/urandom */
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#endif
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if (urandom_cache.fd >= 0) {
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/* Does the fd point to the same thing as before? (issue #21207) */
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if (_Py_fstat_noraise(urandom_cache.fd, &st)
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|| st.st_dev != urandom_cache.st_dev
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|| st.st_ino != urandom_cache.st_ino) {
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/* Something changed: forget the cached fd (but don't close it,
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since it probably points to something important for some
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third-party code). */
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urandom_cache.fd = -1;
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if (urandom_cache.fd >= 0) {
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/* Does the fd point to the same thing as before? (issue #21207) */
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if (_Py_fstat_noraise(urandom_cache.fd, &st)
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|| st.st_dev != urandom_cache.st_dev
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|| st.st_ino != urandom_cache.st_ino) {
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/* Something changed: forget the cached fd (but don't close it,
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since it probably points to something important for some
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third-party code). */
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urandom_cache.fd = -1;
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}
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}
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if (urandom_cache.fd >= 0)
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fd = urandom_cache.fd;
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else {
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fd = _Py_open("/dev/urandom", O_RDONLY);
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if (fd < 0) {
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if (errno == ENOENT || errno == ENXIO ||
|
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errno == ENODEV || errno == EACCES) {
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PyErr_SetString(PyExc_NotImplementedError,
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"/dev/urandom (or equivalent) not found");
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}
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/* otherwise, keep the OSError exception raised by _Py_open() */
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return -1;
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}
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if (urandom_cache.fd >= 0) {
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/* urandom_fd was initialized by another thread while we were
|
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not holding the GIL, keep it. */
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close(fd);
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fd = urandom_cache.fd;
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}
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else {
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if (_Py_fstat(fd, &st)) {
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close(fd);
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return -1;
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}
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else {
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urandom_cache.fd = fd;
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urandom_cache.st_dev = st.st_dev;
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urandom_cache.st_ino = st.st_ino;
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}
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}
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}
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do {
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n = _Py_read(fd, buffer, (size_t)size);
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if (n == -1)
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return -1;
|
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if (n == 0) {
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PyErr_Format(PyExc_RuntimeError,
|
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"Failed to read %zi bytes from /dev/urandom",
|
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size);
|
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return -1;
|
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}
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|
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buffer += n;
|
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size -= n;
|
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} while (0 < size);
|
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}
|
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if (urandom_cache.fd >= 0)
|
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fd = urandom_cache.fd;
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else {
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fd = _Py_open("/dev/urandom", O_RDONLY);
|
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fd = _Py_open_noraise("/dev/urandom", O_RDONLY);
|
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if (fd < 0) {
|
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if (errno == ENOENT || errno == ENXIO ||
|
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errno == ENODEV || errno == EACCES)
|
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PyErr_SetString(PyExc_NotImplementedError,
|
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"/dev/urandom (or equivalent) not found");
|
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/* otherwise, keep the OSError exception raised by _Py_open() */
|
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return -1;
|
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}
|
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if (urandom_cache.fd >= 0) {
|
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/* urandom_fd was initialized by another thread while we were
|
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not holding the GIL, keep it. */
|
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close(fd);
|
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fd = urandom_cache.fd;
|
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}
|
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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 @@ 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):
|
||||
|
@ -400,29 +426,98 @@ lcg_urandom(unsigned int x0, unsigned char *buffer, size_t size)
|
|||
}
|
||||
}
|
||||
|
||||
/* 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 @@ _PyRandom_Init(void)
|
|||
}
|
||||
}
|
||||
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 @@ _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