[Python-checkins] cpython (merge 3.5 -> default): Merge 3.5 (os.urandom)

Tue Jun 7 05:27:27 EDT 2016

https://hg.python.org/cpython/rev/f477ce0d2345
changeset: 101776:f477ce0d2345
parent: 101774:b7a4c076ba40
parent: 101775:9de508dc4837
user: Victor Stinner <victor.stinner at gmail.com>
date: Tue Jun 07 11:25:43 2016 +0200
summary:
 Merge 3.5 (os.urandom)
files:
 Doc/library/os.rst | 13 ++++++++++---
 Misc/ACKS | 1 +
 Misc/NEWS | 4 ++++
 Python/random.c | 24 +++++++++++++++++++++---
 configure | 8 +++++---
 configure.ac | 7 ++++---
 pyconfig.h.in | 3 +++
 7 files changed, 48 insertions(+), 12 deletions(-)

diff --git a/Doc/library/os.rst b/Doc/library/os.rst
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -3768,14 +3768,21 @@
 
 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()``
diff --git a/Misc/ACKS b/Misc/ACKS
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -201,6 +201,7 @@
 Floris Bruynooghe
 Matt Bryant
 Stan Bubrouski
+Colm Buckley
 Erik de Bueger
 Jan-Hein Bührman
 Lars Buitinck
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -27,6 +27,10 @@
 Library
 -------
 
+- Issue #26839: On Linux, :func:`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.
+
 - Issue #23883: Added missing APIs to __all__ to match the documented APIs
 for the following modules: cgi, mailbox, mimetypes, plistlib and smtpd.
 Patches by Jacek Kołodziej.
diff --git a/Python/random.c b/Python/random.c
--- a/Python/random.c
+++ b/Python/random.c
@@ -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 @@
 /* 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 @@
 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()) {
diff --git a/configure b/configure
--- a/configure
+++ b/configure
@@ -2876,6 +2876,7 @@
 ac_config_headers="$ac_config_headers pyconfig.h"
 
 
+
 ac_aux_dir=
 for ac_dir in "$srcdir" "$srcdir/.." "$srcdir/../.."; do
 if test -f "$ac_dir/install-sh"; then
@@ -7568,7 +7569,7 @@
 sys/stat.h sys/syscall.h sys/sys_domain.h sys/termio.h sys/time.h \
 sys/times.h sys/types.h sys/uio.h sys/un.h sys/utsname.h sys/wait.h pty.h \
 libutil.h sys/resource.h netpacket/packet.h sysexits.h bluetooth.h \
-bluetooth/bluetooth.h linux/tipc.h spawn.h util.h alloca.h endian.h \
+bluetooth/bluetooth.h linux/tipc.h linux/random.h spawn.h util.h alloca.h endian.h \
 sys/endian.h
 do :
 as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
@@ -16431,12 +16432,13 @@
 
 #include <unistd.h>
 #include <sys/syscall.h>
+ #include <linux/random.h>
 
 int main() {
 char buffer[1];
 const size_t buflen = sizeof(buffer);
- const int flags = 0;
- /* ignore the result, Python checks for ENOSYS at runtime */
+ const int flags = GRND_NONBLOCK;
+ /* ignore the result, Python checks for ENOSYS and EAGAIN at runtime */
 (void)syscall(SYS_getrandom, buffer, buflen, flags);
 return 0;
 }
diff --git a/configure.ac b/configure.ac
--- a/configure.ac
+++ b/configure.ac
@@ -1881,7 +1881,7 @@
 sys/stat.h sys/syscall.h sys/sys_domain.h sys/termio.h sys/time.h \
 sys/times.h sys/types.h sys/uio.h sys/un.h sys/utsname.h sys/wait.h pty.h \
 libutil.h sys/resource.h netpacket/packet.h sysexits.h bluetooth.h \
-bluetooth/bluetooth.h linux/tipc.h spawn.h util.h alloca.h endian.h \
+bluetooth/bluetooth.h linux/tipc.h linux/random.h spawn.h util.h alloca.h endian.h \
 sys/endian.h)
 AC_HEADER_DIRENT
 AC_HEADER_MAJOR
@@ -5246,12 +5246,13 @@
 AC_LANG_SOURCE([[
 #include <unistd.h>
 #include <sys/syscall.h>
+ #include <linux/random.h>
 
 int main() {
 char buffer[1];
 const size_t buflen = sizeof(buffer);
- const int flags = 0;
- /* ignore the result, Python checks for ENOSYS at runtime */
+ const int flags = GRND_NONBLOCK;
+ /* ignore the result, Python checks for ENOSYS and EAGAIN at runtime */
 (void)syscall(SYS_getrandom, buffer, buflen, flags);
 return 0;
 }
diff --git a/pyconfig.h.in b/pyconfig.h.in
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -574,6 +574,9 @@
 /* Define to 1 if you have the <linux/tipc.h> header file. */
 #undef HAVE_LINUX_TIPC_H
 
+/* Define to 1 if you have the <linux/random.h> header file. */
+#undef HAVE_LINUX_RANDOM_H
+
 /* Define to 1 if you have the `lockf' function. */
 #undef HAVE_LOCKF
 
-- 
Repository URL: https://hg.python.org/cpython
