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

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.

1 files changed, 10 insertions, 3 deletions

diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index e6b6465..785b080 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -3733,14 +3733,21 @@ Miscellaneous Functions
 
    This function returns random bytes from an OS-specific randomness source.  The
    returned data should be unpredictable enough for cryptographic applications,
-   though its exact quality depends on the OS implementation.  On a Unix-like
-   system this will query ``/dev/urandom``, and on Windows it will use
-   ``CryptGenRandom()``.  If a randomness source is not found,
+   though its exact quality depends on the OS implementation.
+
+   On Linux, ``getrandom()`` syscall is used if available and the urandom
+   entropy pool is initialized (``getrandom()`` does not block).
+   On a Unix-like system this will query ``/dev/urandom``. On Windows, it
+   will use ``CryptGenRandom()``.  If a randomness source is not found,
    :exc:`NotImplementedError` will be raised.
 
    For an easy-to-use interface to the random number generator
    provided by your platform, please see :class:`random.SystemRandom`.
 
+   .. versionchanged:: 3.5.2
+      On Linux, if ``getrandom()`` blocks (the urandom entropy pool is not
+      initialized yet), fall back on reading ``/dev/urandom``.
+
    .. versionchanged:: 3.5
       On Linux 3.17 and newer, the ``getrandom()`` syscall is now used
       when available.  On OpenBSD 5.6 and newer, the C ``getentropy()``