bpo-33871: Fix os.sendfile(), os.writev(), os.readv(), etc. (GH-7931)


* Fix integer overflow in os.readv(), os.writev(), os.preadv()
  and os.pwritev() and in os.sendfile() with headers or trailers
  arguments (on BSD-based OSes and MacOS).

* Fix sending the part of the file in os.sendfile() on MacOS.
  Using the trailers argument could cause sending more bytes from
  the input file than was specified.

Thanks Ned Deily for testing on 32-bit MacOS.
(cherry picked from commit 9d5727326af53ddd91016d98e16ae7cf829caa95)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index e509188..a140ae0 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -2532,12 +2532,14 @@
         def __init__(self, conn):
             asynchat.async_chat.__init__(self, conn)
             self.in_buffer = []
+            self.accumulate = True
             self.closed = False
             self.push(b"220 ready\r\n")
 
         def handle_read(self):
             data = self.recv(4096)
-            self.in_buffer.append(data)
+            if self.accumulate:
+                self.in_buffer.append(data)
 
         def get_data(self):
             return b''.join(self.in_buffer)
@@ -2618,6 +2620,8 @@
                                not sys.platform.startswith("sunos")
     requires_headers_trailers = unittest.skipUnless(SUPPORT_HEADERS_TRAILERS,
             'requires headers and trailers support')
+    requires_32b = unittest.skipUnless(sys.maxsize < 2**32,
+            'test is only meaningful on 32-bit builds')
 
     @classmethod
     def setUpClass(cls):
@@ -2648,17 +2652,13 @@
             self.server.stop()
         self.server = None
 
-    def sendfile_wrapper(self, sock, file, offset, nbytes, headers=[], trailers=[]):
+    def sendfile_wrapper(self, *args, **kwargs):
         """A higher level wrapper representing how an application is
         supposed to use sendfile().
         """
-        while 1:
+        while True:
             try:
-                if self.SUPPORT_HEADERS_TRAILERS:
-                    return os.sendfile(sock, file, offset, nbytes, headers,
-                                       trailers)
-                else:
-                    return os.sendfile(sock, file, offset, nbytes)
+                return os.sendfile(*args, **kwargs)
             except OSError as err:
                 if err.errno == errno.ECONNRESET:
                     # disconnected
@@ -2749,20 +2749,22 @@
     @requires_headers_trailers
     def test_headers(self):
         total_sent = 0
+        expected_data = b"x" * 512 + b"y" * 256 + self.DATA[:-1]
         sent = os.sendfile(self.sockno, self.fileno, 0, 4096,
-                            headers=[b"x" * 512])
+                            headers=[b"x" * 512, b"y" * 256])
+        self.assertLessEqual(sent, 512 + 256 + 4096)
         total_sent += sent
         offset = 4096
-        nbytes = 4096
-        while 1:
+        while total_sent < len(expected_data):
+            nbytes = min(len(expected_data) - total_sent, 4096)
             sent = self.sendfile_wrapper(self.sockno, self.fileno,
                                                     offset, nbytes)
             if sent == 0:
                 break
+            self.assertLessEqual(sent, nbytes)
             total_sent += sent
             offset += sent
 
-        expected_data = b"x" * 512 + self.DATA
         self.assertEqual(total_sent, len(expected_data))
         self.client.close()
         self.server.wait()
@@ -2778,12 +2780,30 @@
         create_file(TESTFN2, file_data)
 
         with open(TESTFN2, 'rb') as f:
-            os.sendfile(self.sockno, f.fileno(), 0, len(file_data),
-                        trailers=[b"1234"])
+            os.sendfile(self.sockno, f.fileno(), 0, 5,
+                        trailers=[b"123456", b"789"])
             self.client.close()
             self.server.wait()
             data = self.server.handler_instance.get_data()
-            self.assertEqual(data, b"abcdef1234")
+            self.assertEqual(data, b"abcde123456789")
+
+    @requires_headers_trailers
+    @requires_32b
+    def test_headers_overflow_32bits(self):
+        self.server.handler_instance.accumulate = False
+        with self.assertRaises(OSError) as cm:
+            os.sendfile(self.sockno, self.fileno, 0, 0,
+                        headers=[b"x" * 2**16] * 2**15)
+        self.assertEqual(cm.exception.errno, errno.EINVAL)
+
+    @requires_headers_trailers
+    @requires_32b
+    def test_trailers_overflow_32bits(self):
+        self.server.handler_instance.accumulate = False
+        with self.assertRaises(OSError) as cm:
+            os.sendfile(self.sockno, self.fileno, 0, 0,
+                        trailers=[b"x" * 2**16] * 2**15)
+        self.assertEqual(cm.exception.errno, errno.EINVAL)
 
     @requires_headers_trailers
     @unittest.skipUnless(hasattr(os, 'SF_NODISKIO'),