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Issue #22181: On Linux, os.urandom() now uses the new getrandom() syscall if

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available, syscall introduced in the Linux kernel 3.17. It is more reliable
and more secure, because it avoids the need of a file descriptor and waits
until the kernel has enough entropy.
This commit is contained in:
Victor Stinner 2015-03-18 14:39:33 +01:00
parent 072248ec63
commit 59f7fb29ec
2 changed files with 89 additions and 6 deletions
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90
Python/random.c
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@ -1,11 +1,17 @@
#include "Python.h"
#ifdef MS_WINDOWS
#include <windows.h>
# include <windows.h>
#else
#include <fcntl.h>
#ifdef HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif
# include <fcntl.h>
# ifdef HAVE_SYS_STAT_H
# include <sys/stat.h>
# endif
# ifdef HAVE_SYS_SYSCALL_H
# include <sys/syscall.h>
# if defined(__linux__) && defined(SYS_getrandom)
# define HAVE_GETRANDOM
# endif
# endif
#endif
#ifdef Py_DEBUG
@ -94,13 +100,65 @@ py_getentropy(unsigned char *buffer, Py_ssize_t size, int fatal)
return 0;
}
#else
#else /* !HAVE_GETENTROPY */
#ifdef HAVE_GETRANDOM
static int
py_getrandom(void *buffer, Py_ssize_t size, int raise)
{
/* is getrandom() supported by the running kernel?
* need Linux kernel 3.17 or later */
static int getrandom_works = 1;
/* Use /dev/urandom, block if the kernel has no entropy */
const int flags = 0;
int n;
if (!getrandom_works)
return 0;
while (0 < size) {
errno = 0;
/* the libc doesn't expose getrandom() yet, see:
* https://sourceware.org/bugzilla/show_bug.cgi?id=17252 */
n = syscall(SYS_getrandom, buffer, size, flags);
if (n < 0) {
if (errno == ENOSYS) {
getrandom_works = 0;
return 0;
}
if (errno == EINTR) {
/* Note: EINTR should not occur with flags=0 */
if (PyErr_CheckSignals()) {
if (!raise)
Py_FatalError("getrandom() interrupted by a signal");
return -1;
}
/* retry getrandom() */
continue;
}
if (raise)
PyErr_SetFromErrno(PyExc_OSError);
else
Py_FatalError("getrandom() failed");
return -1;
}
buffer += n;
size -= n;
}
return 1;
}
#endif
static struct {
int fd;
dev_t st_dev;
ino_t st_ino;
} urandom_cache = { -1 };
/* Read size bytes from /dev/urandom into buffer.
Call Py_FatalError() on error. */
static void
@ -115,6 +173,13 @@ dev_urandom_noraise(unsigned char *buffer, Py_ssize_t size)
if (fd < 0)
Py_FatalError("Failed to open /dev/urandom");
#ifdef HAVE_GETRANDOM
if (py_getrandom(buffer, size, 0) == 1)
return;
/* getrandom() is not supported by the running kernel, fall back
* on reading /dev/urandom */
#endif
while (0 < size)
{
do {
@ -140,10 +205,23 @@ dev_urandom_python(char *buffer, Py_ssize_t size)
int fd;
Py_ssize_t n;
struct _Py_stat_struct st;
#ifdef HAVE_GETRANDOM
int res;
#endif
if (size <= 0)
return 0;
#ifdef HAVE_GETRANDOM
res = py_getrandom(buffer, size, 1);
if (res < 0)
return -1;
if (res == 1)
return 0;
/* getrandom() is not supported by the running kernel, 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(urandom_cache.fd, &st)