Raise ValueError if insufficient data is read from DDS RGB file (#9405)

Author: radarhere

Tests/images/timeout-041dd17dfde800360a47a172269df127af138c6b.dds

@@ -540,3 +540,18 @@ def test_save_large_file(tmp_path: Path, pixel_format: str, mode: str) -> None:
     im = hopper(mode).resize((440, 440))
     # should not error in valgrind
     im.save(tmp_path / "img.dds", pixel_format=pixel_format)
+
+
+@pytest.mark.parametrize(
+    "test_file",
+    [
+        "Tests/images/timeout-041dd17dfde800360a47a172269df127af138c6b.dds",
+        "Tests/images/timeout-755a4d204f4208e3597ac3391edebee196462bd0.dds",
+        "Tests/images/timeout-52d106579505547091ef69b58341351a37c23e31.dds",
+        "Tests/images/timeout-c60a3d7314213624607bfb3e38d551a8b24a7435.dds",
+    ],
+)
+def test_not_enough_image_data(test_file: str) -> None:
+    with Image.open(test_file) as im:
+        with pytest.raises(ValueError, match="not enough image data"):
+            im.load()

Tests/images/timeout-52d106579505547091ef69b58341351a37c23e31.dds

@@ -489,9 +489,14 @@ class DdsRgbDecoder(ImageFile.PyDecoder):
     _pulls_fd = True
 
     def decode(self, buffer: Image.DecoderInput) -> tuple[int, int]:
-        assert self.fd is not None
         bitcount, masks = self.args
 
+        data = bytearray()
+        bytecount = bitcount // 8
+        if not bytecount:
+            self.set_as_raw(data)
+            return -1, 0
+
         # Some masks will be padded with zeros, e.g. R 0b11 G 0b1100
         # Calculate how many zeros each mask is padded with
         mask_offsets = []
@@ -505,11 +510,13 @@ def decode(self, buffer: Image.DecoderInput) -> tuple[int, int]:
             mask_offsets.append(offset)
             mask_totals.append(mask >> offset)
 
-        data = bytearray()
-        bytecount = bitcount // 8
+        assert self.fd is not None
         dest_length = self.state.xsize * self.state.ysize * len(masks)
         while len(data) < dest_length:
-            value = int.from_bytes(self.fd.read(bytecount), "little")
+            bytes_read = self.fd.read(bytecount)
+            if len(bytes_read) < bytecount:
+                break
+            value = int.from_bytes(bytes_read, "little")
             for i, mask in enumerate(masks):
                 masked_value = value & mask
                 # Remove the zero padding, and scale it to 8 bits