Issue #18756: Improve error reporting in os.urandom() when the failure is due to something else than /dev/urandom not existing.

pitrou · pitrou · commit 95b21460ee7a · 2013-08-16T20:49:32.000+02:00
diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
@@ -30,6 +30,11 @@
     import threading
 except ImportError:
     threading = None
+try:
+    import resource
+except ImportError:
+    resource = None
+
 from test.script_helper import assert_python_ok
 
 with warnings.catch_warnings():
@@ -1010,6 +1015,21 @@ def test_urandom_subprocess(self):
         data2 = self.get_urandom_subprocess(16)
         self.assertNotEqual(data1, data2)
 
+    @unittest.skipUnless(resource, "test requires the resource module")
+    def test_urandom_failure(self):
+        soft_limit, hard_limit = resource.getrlimit(resource.RLIMIT_NOFILE)
+        resource.setrlimit(resource.RLIMIT_NOFILE, (1, hard_limit))
+        try:
+            with self.assertRaises(OSError) as cm:
+                os.urandom(16)
+            self.assertEqual(cm.exception.errno, errno.EMFILE)
+        finally:
+            # We restore the old limit as soon as possible.  If doing it
+            # using addCleanup(), code running in between would fail
+            # creating any file descriptor.
+            resource.setrlimit(resource.RLIMIT_NOFILE, (soft_limit, hard_limit))
+
+
 @contextlib.contextmanager
 def _execvpe_mockup(defpath=None):
     """
diff --git a/Misc/NEWS b/Misc/NEWS
@@ -28,6 +28,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #18756: Improve error reporting in os.urandom() when the failure
+  is due to something else than /dev/urandom not existing (for example,
+  exhausting the file descriptor limit).
+
 - Issue #18673: Add O_TMPFILE to os module. O_TMPFILE requires Linux kernel
   3.11 or newer. It's only defined on system with 3.11 uapi headers, too.
 
diff --git a/Python/random.c b/Python/random.c
@@ -138,8 +138,12 @@ dev_urandom_python(char *buffer, Py_ssize_t size)
     Py_END_ALLOW_THREADS
     if (fd < 0)
     {
-        PyErr_SetString(PyExc_NotImplementedError,
-                        "/dev/urandom (or equivalent) not found");
+        if (errno == ENOENT || errno == ENXIO ||
+            errno == ENODEV || errno == EACCES)
+            PyErr_SetString(PyExc_NotImplementedError,
+                            "/dev/urandom (or equivalent) not found");
+        else
+            PyErr_SetFromErrno(PyExc_OSError);
         return -1;
     }
 

Original file line number	Diff line number	Diff line change
`@@ -138,8 +138,12 @@ dev_urandom_python(char *buffer, Py_ssize_t size)`
`138`	`138`	`Py_END_ALLOW_THREADS`
`139`	`139`	`if (fd < 0)`
`140`	`140`	`{`
`141`		`- PyErr_SetString(PyExc_NotImplementedError,`
`142`		`- "/dev/urandom (or equivalent) not found");`
	`141`	`+ if (errno == ENOENT \|\| errno == ENXIO \|\|`
	`142`	`+ errno == ENODEV \|\| errno == EACCES)`
	`143`	`+ PyErr_SetString(PyExc_NotImplementedError,`
	`144`	`+ "/dev/urandom (or equivalent) not found");`
	`145`	`+ else`
	`146`	`+ PyErr_SetFromErrno(PyExc_OSError);`
`143`	`147`	`return -1;`
`144`	`148`	`}`
`145`	`149`