PYTHON-2061 bson: check for negative entry size in decode_file_iter (#429)

Raise InvalidBSON instead of ValueError when decode_file_iter reads an invalid
BSON object size.

Author: thetorpedodog

bson/__init__.py

@@ -1166,7 +1166,7 @@ def decode_file_iter(file_obj, codec_options=DEFAULT_CODEC_OPTIONS):
         elif len(size_data) != 4:
             raise InvalidBSON("cut off in middle of objsize")
         obj_size = _UNPACK_INT_FROM(size_data, 0)[0] - 4
-        elements = size_data + file_obj.read(obj_size)
+        elements = size_data + file_obj.read(max(0, obj_size))
         yield _bson_to_dict(elements, codec_options)
 
 

doc/contributors.rst

@@ -86,3 +86,4 @@ The following is a list of people who have contributed to
 - Shrey Batra(shreybatra)
 - Felipe Rodrigues(fbidu)
 - Terence Honles (terencehonles)
+- Paul Fisher (thetorpedodog)

test/test_bson.py

@@ -18,8 +18,10 @@
 
 import collections
 import datetime
+import os
 import re
 import sys
+import tempfile
 import uuid
 
 sys.path[0:0] = [""]
@@ -335,41 +337,41 @@ def test_invalid_decodes(self):
         self.assertRaises(InvalidBSON, list,
                           decode_file_iter(StringIO(b"\x1B")))
 
-        # An object size that's too small to even include the object size,
-        # but is correctly encoded, along with a correct EOO (and no data).
-        data = b"\x01\x00\x00\x00\x00"
-        self.assertRaises(InvalidBSON, decode_all, data)
-        self.assertRaises(InvalidBSON, list, decode_iter(data))
-        self.assertRaises(InvalidBSON, list, decode_file_iter(StringIO(data)))
-
-        # One object, but with object size listed smaller than it is in the
-        # data.
-        data = (b"\x1A\x00\x00\x00\x0E\x74\x65\x73\x74"
-                b"\x00\x0C\x00\x00\x00\x68\x65\x6C\x6C"
-                b"\x6f\x20\x77\x6F\x72\x6C\x64\x00\x00"
-                b"\x05\x00\x00\x00\x00")
-        self.assertRaises(InvalidBSON, decode_all, data)
-        self.assertRaises(InvalidBSON, list, decode_iter(data))
-        self.assertRaises(InvalidBSON, list, decode_file_iter(StringIO(data)))
-
-        # One object, missing the EOO at the end.
-        data = (b"\x1B\x00\x00\x00\x0E\x74\x65\x73\x74"
-                b"\x00\x0C\x00\x00\x00\x68\x65\x6C\x6C"
-                b"\x6f\x20\x77\x6F\x72\x6C\x64\x00\x00"
-                b"\x05\x00\x00\x00")
-        self.assertRaises(InvalidBSON, decode_all, data)
-        self.assertRaises(InvalidBSON, list, decode_iter(data))
-        self.assertRaises(InvalidBSON, list, decode_file_iter(StringIO(data)))
-
-        # One object, sized correctly, with a spot for an EOO, but the EOO
-        # isn't 0x00.
-        data = (b"\x1B\x00\x00\x00\x0E\x74\x65\x73\x74"
-                b"\x00\x0C\x00\x00\x00\x68\x65\x6C\x6C"
-                b"\x6f\x20\x77\x6F\x72\x6C\x64\x00\x00"
-                b"\x05\x00\x00\x00\xFF")
-        self.assertRaises(InvalidBSON, decode_all, data)
-        self.assertRaises(InvalidBSON, list, decode_iter(data))
-        self.assertRaises(InvalidBSON, list, decode_file_iter(StringIO(data)))
+        bad_bsons = [
+            # An object size that's too small to even include the object size,
+            # but is correctly encoded, along with a correct EOO (and no data).
+            b"\x01\x00\x00\x00\x00",
+            # One object, but with object size listed smaller than it is in the
+            # data.
+            (b"\x1A\x00\x00\x00\x0E\x74\x65\x73\x74"
+             b"\x00\x0C\x00\x00\x00\x68\x65\x6C\x6C"
+             b"\x6f\x20\x77\x6F\x72\x6C\x64\x00\x00"
+             b"\x05\x00\x00\x00\x00"),
+            # One object, missing the EOO at the end.
+            (b"\x1B\x00\x00\x00\x0E\x74\x65\x73\x74"
+             b"\x00\x0C\x00\x00\x00\x68\x65\x6C\x6C"
+             b"\x6f\x20\x77\x6F\x72\x6C\x64\x00\x00"
+             b"\x05\x00\x00\x00"),
+            # One object, sized correctly, with a spot for an EOO, but the EOO
+            # isn't 0x00.
+            (b"\x1B\x00\x00\x00\x0E\x74\x65\x73\x74"
+             b"\x00\x0C\x00\x00\x00\x68\x65\x6C\x6C"
+             b"\x6f\x20\x77\x6F\x72\x6C\x64\x00\x00"
+             b"\x05\x00\x00\x00\xFF"),
+        ]
+        for i, data in enumerate(bad_bsons):
+            msg = "bad_bson[{}]".format(i)
+            with self.assertRaises(InvalidBSON, msg=msg):
+                decode_all(data)
+            with self.assertRaises(InvalidBSON, msg=msg):
+                list(decode_iter(data))
+            with self.assertRaises(InvalidBSON, msg=msg):
+                list(decode_file_iter(StringIO(data)))
+            with tempfile.TemporaryFile() as scratch:
+                scratch.write(data)
+                scratch.seek(0, os.SEEK_SET)
+                with self.assertRaises(InvalidBSON, msg=msg):
+                    list(decode_file_iter(scratch))
 
     def test_data_timestamp(self):
         self.assertEqual({"test": Timestamp(4, 20)},