Return the skipped byte count from the JPEG 2000 decoder skip callback

Tests/test_file_jpeg2k.py

@@ -255,6 +255,29 @@ def test_oversized_box_length(tbox: bytes) -> None:
         Jpeg2KImagePlugin.Jpeg2KImageFile(BytesIO(data))
 
 
+def test_large_skipped_box() -> None:
+    # A box larger than the stream buffer reaches the skip callback
+    xml = b" " * 2 * 1024 * 1024
+    box = _binary.o32be(8 + len(xml)) + b"xml " + xml
+    with open("Tests/images/test-card-lossless.jp2", "rb") as fp:
+        data = fp.read()
+    data = data[:326] + box + data[326:]
+
+    with Image.open(BytesIO(data)) as im:
+        assert_image_equal_tofile(im, "Tests/images/test-card-lossless.jp2")
+
+    class FailingSeek(BytesIO):
+        def seek(self, offset: int, whence: int = os.SEEK_SET) -> int:
+            if whence == os.SEEK_CUR and offset > 512 * 1024:
+                msg = "seek refused"
+                raise OSError(msg)
+            return super().seek(offset, whence)
+
+    with Image.open(FailingSeek(data)) as im:
+        with pytest.raises(OSError, match="seek refused"):
+            im.load()
+
+
 def test_layers_type(card: ImageFile.ImageFile, tmp_path: Path) -> None:
     outfile = tmp_path / "temp_layers.jp2"
     for quality_layers in [[100, 50, 10], (100, 50, 10), None]:

src/decode.c

@@ -140,6 +140,9 @@ _decode(ImagingDecoderObject *decoder, PyObject *args) {
     }
 
     PyBuffer_Release(&buffer);
+    if (PyErr_Occurred()) {
+        return NULL;
+    }
     return Py_BuildValue("ii", status, decoder->state.errcode);
 }
 

src/libImaging/Jpeg2KDecode.c

@@ -53,13 +53,13 @@ j2k_read(void *p_buffer, OPJ_SIZE_T p_nb_bytes, void *p_user_data) {
 
 static OPJ_OFF_T
 j2k_skip(OPJ_OFF_T p_nb_bytes, void *p_user_data) {
-    off_t pos;
     ImagingCodecState state = (ImagingCodecState)p_user_data;
 
-    _imaging_seek_pyFd(state->fd, p_nb_bytes, SEEK_CUR);
-    pos = _imaging_tell_pyFd(state->fd);
+    if (_imaging_seek_pyFd(state->fd, p_nb_bytes, SEEK_CUR) == -1) {
+        return (OPJ_OFF_T)-1;
+    }
 
-    return pos ? pos : (OPJ_OFF_T)-1;
+    return p_nb_bytes;
 }
 
 /* -------------------------------------------------------------------- */