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os.urandom() doesn't block on Linux anymore

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Issue #26839: On Linux, os.urandom() now calls getrandom() with GRND_NONBLOCK
to fall back on reading /dev/urandom if the urandom entropy pool is not
initialized yet. Patch written by Colm Buckley.
This commit is contained in:
Victor Stinner 2016-06-07 11:21:42 +02:00
parent 6827fd867b
commit dddf4849ec
7 changed files with 48 additions and 12 deletions
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24
Python/random.c
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@ -6,6 +6,9 @@
# ifdef HAVE_SYS_STAT_H
# include <sys/stat.h>
# endif
# ifdef HAVE_LINUX_RANDOM_H
# include <linux/random.h>
# endif
# ifdef HAVE_GETRANDOM
# include <sys/random.h>
# elif defined(HAVE_GETRANDOM_SYSCALL)
@ -122,9 +125,13 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise)
/* Is getrandom() supported by the running kernel?
* Need Linux kernel 3.17 or newer, or Solaris 11.3 or newer */
static int getrandom_works = 1;
/* Use non-blocking /dev/urandom device. On Linux at boot, the getrandom()
* syscall blocks until /dev/urandom is initialized with enough entropy. */
const int flags = 0;
/* getrandom() on Linux will block if called before the kernel has
* initialized the urandom entropy pool. This will cause Python
* to hang on startup if called very early in the boot process -
* see https://bugs.python.org/issue26839. To avoid this, use the
* GRND_NONBLOCK flag. */
const int flags = GRND_NONBLOCK;
int n;
if (!getrandom_works)
@ -168,6 +175,17 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise)
getrandom_works = 0;
return 0;
}
if (errno == EAGAIN) {
/* If we failed with EAGAIN, the entropy pool was
* uninitialized. In this case, we return failure to fall
* back to reading from /dev/urandom.
*
* Note: In this case the data read will not be random so
* should not be used for cryptographic purposes. Retaining
* the existing semantics for practical purposes. */
getrandom_works = 0;
return 0;
}
if (errno == EINTR) {
if (PyErr_CheckSignals()) {