mirror of https://github.com/python/cpython
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.
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Victor Stinner
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commit
dddf4849ec
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@ -3733,14 +3733,21 @@ Miscellaneous Functions
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This function returns random bytes from an OS-specific randomness source. The
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returned data should be unpredictable enough for cryptographic applications,
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though its exact quality depends on the OS implementation. On a Unix-like
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system this will query ``/dev/urandom``, and on Windows it will use
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``CryptGenRandom()``. If a randomness source is not found,
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though its exact quality depends on the OS implementation.
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On Linux, ``getrandom()`` syscall is used if available and the urandom
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entropy pool is initialized (``getrandom()`` does not block).
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On a Unix-like system this will query ``/dev/urandom``. On Windows, it
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will use ``CryptGenRandom()``. If a randomness source is not found,
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:exc:`NotImplementedError` will be raised.
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For an easy-to-use interface to the random number generator
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provided by your platform, please see :class:`random.SystemRandom`.
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.. versionchanged:: 3.5.2
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On Linux, if ``getrandom()`` blocks (the urandom entropy pool is not
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initialized yet), fall back on reading ``/dev/urandom``.
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.. versionchanged:: 3.5
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On Linux 3.17 and newer, the ``getrandom()`` syscall is now used
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when available. On OpenBSD 5.6 and newer, the C ``getentropy()``
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@ -200,6 +200,7 @@ Ian Bruntlett
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Floris Bruynooghe
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Matt Bryant
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Stan Bubrouski
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Colm Buckley
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Erik de Bueger
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Jan-Hein Bührman
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Lars Buitinck
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@ -131,6 +131,10 @@ Core and Builtins
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Library
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-------
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- Issue #26839: On Linux, :func:`os.urandom` now calls ``getrandom()`` with
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``GRND_NONBLOCK`` to fall back on reading ``/dev/urandom`` if the urandom
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entropy pool is not initialized yet. Patch written by Colm Buckley.
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- Issue #27164: In the zlib module, allow decompressing raw Deflate streams
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with a predefined zdict. Based on patch by Xiang Zhang.
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@ -6,6 +6,9 @@
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# ifdef HAVE_SYS_STAT_H
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# include <sys/stat.h>
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# endif
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# ifdef HAVE_LINUX_RANDOM_H
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# include <linux/random.h>
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# endif
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# ifdef HAVE_GETRANDOM
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# include <sys/random.h>
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# elif defined(HAVE_GETRANDOM_SYSCALL)
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@ -122,9 +125,13 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise)
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/* Is getrandom() supported by the running kernel?
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* Need Linux kernel 3.17 or newer, or Solaris 11.3 or newer */
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static int getrandom_works = 1;
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/* Use non-blocking /dev/urandom device. On Linux at boot, the getrandom()
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* syscall blocks until /dev/urandom is initialized with enough entropy. */
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const int flags = 0;
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/* getrandom() on Linux will block if called before the kernel has
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* initialized the urandom entropy pool. This will cause Python
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* to hang on startup if called very early in the boot process -
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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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int n;
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if (!getrandom_works)
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@ -168,6 +175,17 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise)
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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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/* If we failed with EAGAIN, the entropy pool was
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* uninitialized. In this case, we return failure to fall
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* back to reading from /dev/urandom.
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*
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* Note: In this case the data read will not be random so
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* should not be used for cryptographic purposes. Retaining
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* the existing semantics for practical purposes. */
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getrandom_works = 0;
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return 0;
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}
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if (errno == EINTR) {
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if (PyErr_CheckSignals()) {
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@ -2876,6 +2876,7 @@ fi
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ac_config_headers="$ac_config_headers pyconfig.h"
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ac_aux_dir=
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for ac_dir in "$srcdir" "$srcdir/.." "$srcdir/../.."; do
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if test -f "$ac_dir/install-sh"; then
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@ -7568,7 +7569,7 @@ sys/param.h sys/select.h sys/sendfile.h sys/socket.h sys/statvfs.h \
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sys/stat.h sys/syscall.h sys/sys_domain.h sys/termio.h sys/time.h \
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sys/times.h sys/types.h sys/uio.h sys/un.h sys/utsname.h sys/wait.h pty.h \
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libutil.h sys/resource.h netpacket/packet.h sysexits.h bluetooth.h \
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bluetooth/bluetooth.h linux/tipc.h spawn.h util.h alloca.h endian.h \
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bluetooth/bluetooth.h linux/tipc.h linux/random.h spawn.h util.h alloca.h endian.h \
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sys/endian.h
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do :
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as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
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@ -16325,12 +16326,13 @@ cat confdefs.h - <<_ACEOF >conftest.$ac_ext
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#include <unistd.h>
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#include <sys/syscall.h>
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#include <linux/random.h>
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int main() {
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char buffer[1];
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const size_t buflen = sizeof(buffer);
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const int flags = 0;
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/* ignore the result, Python checks for ENOSYS at runtime */
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const int flags = GRND_NONBLOCK;
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/* ignore the result, Python checks for ENOSYS and EAGAIN at runtime */
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(void)syscall(SYS_getrandom, buffer, buflen, flags);
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return 0;
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}
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@ -1881,7 +1881,7 @@ sys/param.h sys/select.h sys/sendfile.h sys/socket.h sys/statvfs.h \
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sys/stat.h sys/syscall.h sys/sys_domain.h sys/termio.h sys/time.h \
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sys/times.h sys/types.h sys/uio.h sys/un.h sys/utsname.h sys/wait.h pty.h \
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libutil.h sys/resource.h netpacket/packet.h sysexits.h bluetooth.h \
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bluetooth/bluetooth.h linux/tipc.h spawn.h util.h alloca.h endian.h \
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bluetooth/bluetooth.h linux/tipc.h linux/random.h spawn.h util.h alloca.h endian.h \
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sys/endian.h)
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AC_HEADER_DIRENT
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AC_HEADER_MAJOR
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@ -5240,12 +5240,13 @@ AC_LINK_IFELSE(
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AC_LANG_SOURCE([[
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#include <unistd.h>
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#include <sys/syscall.h>
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#include <linux/random.h>
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int main() {
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char buffer[1];
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const size_t buflen = sizeof(buffer);
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const int flags = 0;
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/* ignore the result, Python checks for ENOSYS at runtime */
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const int flags = GRND_NONBLOCK;
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/* ignore the result, Python checks for ENOSYS and EAGAIN at runtime */
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(void)syscall(SYS_getrandom, buffer, buflen, flags);
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return 0;
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}
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@ -546,6 +546,9 @@
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/* Define to 1 if you have the <linux/tipc.h> header file. */
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#undef HAVE_LINUX_TIPC_H
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/* Define to 1 if you have the <linux/random.h> header file. */
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#undef HAVE_LINUX_RANDOM_H
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/* Define to 1 if you have the `lockf' function. */
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#undef HAVE_LOCKF
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