gh-140607: Validate returned byte count in RawIOBase.read (#140611)

While `RawIOBase.readinto` should return a count of bytes between 0 and
the length of the given buffer, it is not required to. Add validation
inside RawIOBase.read() that the returned byte count is valid.

Co-authored-by: Shamil <ashm.tech@proton.me>
Co-authored-by: Victor Stinner <vstinner@python.org>

Lib/test/test_io/test_general.py

@@ -592,6 +592,22 @@ def test_RawIOBase_read(self):
         self.assertEqual(rawio.read(2), None)
         self.assertEqual(rawio.read(2), b"")
 
+    def test_RawIOBase_read_bounds_checking(self):
+        # Make sure a `.readinto` call which returns a value outside
+        # (0, len(buffer)) raises.
+        class Misbehaved(self.io.RawIOBase):
+            def __init__(self, readinto_return) -> None:
+                self._readinto_return = readinto_return
+            def readinto(self, b):
+                return self._readinto_return
+
+        with self.assertRaises(ValueError) as cm:
+            Misbehaved(2).read(1)
+        self.assertEqual(str(cm.exception), "readinto returned 2 outside buffer size 1")
+        for bad_size in (2147483647, sys.maxsize, -1, -1000):
+            with self.assertRaises(ValueError):
+                Misbehaved(bad_size).read()
+
     def test_types_have_dict(self):
         test = (
             self.IOBase(),