Issue #22585: On OpenBSD 5.6 and newer, os.urandom() now calls getentropy(),

instead of reading /dev/urandom, to get pseudo-random bytes.

Lib/test/test_os.py

@@ -27,6 +27,7 @@ import codecs
 import decimal
 import fractions
 import pickle
+import sysconfig
 try:
     import threading
 except ImportError:
@@ -1103,6 +1104,12 @@ class URandomTests(unittest.TestCase):
         data2 = self.get_urandom_subprocess(16)
         self.assertNotEqual(data1, data2)
 
+
+HAVE_GETENTROPY = (sysconfig.get_config_var('HAVE_GETENTROPY') == 1)
+
+@unittest.skipIf(HAVE_GETENTROPY,
+                 "getentropy() does not use a file descriptor")
+class URandomFDTests(unittest.TestCase):
     @unittest.skipUnless(resource, "test requires the resource module")
     def test_urandom_failure(self):
         # Check urandom() failing when it is not able to open /dev/random.

Misc/NEWS

@@ -196,6 +196,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #22585: On OpenBSD 5.6 and newer, os.urandom() now calls getentropy(),
+  instead of reading /dev/urandom, to get pseudo-random bytes.
+
 - Issue #19104: pprint now produces evaluable output for wrapped strings.
 
 - Issue #23071: Added missing names to codecs.__all__.  Patch by Martin Panter.

Python/random.c

@@ -36,7 +36,7 @@ error:
 }
 
 /* Fill buffer with size pseudo-random bytes generated by the Windows CryptoGen
-   API. Return 0 on success, or -1 on error. */
+   API. Return 0 on success, or raise an exception and return -1 on error. */
 static int
 win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise)
 {
@@ -66,10 +66,35 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise)
     }
     return 0;
 }
-#endif /* MS_WINDOWS */
 
+#elif HAVE_GETENTROPY
+/* Fill buffer with size pseudo-random bytes generated by getentropy().
+   Return 0 on success, or raise an exception and return -1 on error.
 
-#ifndef MS_WINDOWS
+   If fatal is nonzero, call Py_FatalError() instead of raising an exception
+   on error. */
+static int
+py_getentropy(unsigned char *buffer, Py_ssize_t size, int fatal)
+{
+    while (size > 0) {
+        Py_ssize_t len = Py_MIN(size, 256);
+        int res = getentropy(buffer, len);
+        if (res < 0) {
+            if (fatal) {
+                Py_FatalError("getentropy() failed");
+            }
+            else {
+                PyErr_SetFromErrno(PyExc_OSError);
+                return -1;
+            }
+        }
+        buffer += len;
+        size -= len;
+    }
+    return 0;
+}
+
+#else
 static struct {
     int fd;
     dev_t st_dev;
@@ -201,7 +226,7 @@ dev_urandom_close(void)
     }
 }
 
-#endif /* MS_WINDOWS */
+#endif /* HAVE_GETENTROPY */
 
 /* Fill buffer with pseudo-random bytes generated by a linear congruent
    generator (LCG):
@@ -242,6 +267,8 @@ _PyOS_URandom(void *buffer, Py_ssize_t size)
 
 #ifdef MS_WINDOWS
     return win32_urandom((unsigned char *)buffer, size, 1);
+#elif HAVE_GETENTROPY
+    return py_getentropy(buffer, size, 0);
 #else
     return dev_urandom_python((char*)buffer, size);
 #endif
@@ -287,6 +314,8 @@ _PyRandom_Init(void)
     else {
 #ifdef MS_WINDOWS
         (void)win32_urandom(secret, secret_size, 0);
+#elif HAVE_GETENTROPY
+        (void)py_getentropy(secret, secret_size, 1);
 #else
         dev_urandom_noraise(secret, secret_size);
 #endif
@@ -301,6 +330,8 @@ _PyRandom_Fini(void)
         CryptReleaseContext(hCryptProv, 0);
         hCryptProv = 0;
     }
+#elif HAVE_GETENTROPY
+    /* nothing to clean */
 #else
     dev_urandom_close();
 #endif

configure

@@ -10697,7 +10697,7 @@ fi
 for ac_func in alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
  clock confstr ctermid dup3 execv faccessat fchmod fchmodat fchown fchownat \
  fexecve fdopendir fork fpathconf fstatat ftime ftruncate futimesat \
- futimens futimes gai_strerror \
+ futimens futimes gai_strerror getentropy \
  getgrouplist getgroups getlogin getloadavg getpeername getpgid getpid \
  getpriority getresuid getresgid getpwent getspnam getspent getsid getwd \
  if_nameindex \

configure.ac

@@ -3004,7 +3004,7 @@ fi
 AC_CHECK_FUNCS(alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
  clock confstr ctermid dup3 execv faccessat fchmod fchmodat fchown fchownat \
  fexecve fdopendir fork fpathconf fstatat ftime ftruncate futimesat \
- futimens futimes gai_strerror \
+ futimens futimes gai_strerror getentropy \
  getgrouplist getgroups getlogin getloadavg getpeername getpgid getpid \
  getpriority getresuid getresgid getpwent getspnam getspent getsid getwd \
  if_nameindex \

pyconfig.h.in

@@ -332,6 +332,9 @@
 /* Define this if you have flockfile(), getc_unlocked(), and funlockfile() */
 #undef HAVE_GETC_UNLOCKED
 
+/* Define to 1 if you have the `getentropy' function. */
+#undef HAVE_GETENTROPY
+
 /* Define to 1 if you have the `getgrouplist' function. */
 #undef HAVE_GETGROUPLIST