Consider new position, not just offset

Tests/test_file_jpeg2k.py

@@ -234,7 +234,7 @@ def test_oversized_box_length() -> None:
     data = (
         b"\x00\x00\x00\x0cjP  \x0d\x0a\x87\x0a"  # JP2 signature box
         + struct.pack(">I4s", 1, b"")  # box with 64-bit length
-        + struct.pack(">Q", 16 + 2**63)  # length beyond the seek range
+        + struct.pack(">Q", 2**63 - 12)  # length beyond the seek range
     )
     with pytest.raises(SyntaxError, match="Box length too large"):
         Jpeg2KImagePlugin.Jpeg2KImageFile(BytesIO(data))

src/PIL/Jpeg2KImagePlugin.py

@@ -83,7 +83,7 @@ def has_next_box(self) -> bool:
     def next_box_type(self) -> bytes:
         # Skip the rest of the box if it has not been read
         if self.remaining_in_box > 0:
-            if self.remaining_in_box >= 2**63:
+            if self.fp.tell() + self.remaining_in_box >= 2**63:
                 msg = "Box length too large"
                 raise SyntaxError(msg)
             self.fp.seek(self.remaining_in_box, os.SEEK_CUR)