Fix incorrect images when cropping without stretch.

Always overallocate images so that Image::crop_scale_window is always
safe from over-reading buffers.  Relates to #1654 and probably #1653.

Backported from 7b0372776ac4da6a8e4ff29f41a4f08b9b4de506 in v2.15.x.

1 files changed, 1 insertions, 8 deletions

diff --git a/src/lib/j2k_image_proxy.cc b/src/lib/j2k_image_proxy.cc
index d4c7a8716..31fda2510 100644
--- a/src/lib/j2k_image_proxy.cc
+++ b/src/lib/j2k_image_proxy.cc
@@ -137,14 +137,7 @@ J2KImageProxy::prepare (optional<dcp::Size> target_size) const
 	}
 
 	shared_ptr<dcp::OpenJPEGImage> decompressed = dcp::decompress_j2k (const_cast<uint8_t*> (_data.data().get()), _data.size (), reduce);
-
-	/* When scaling JPEG2000 images (using AV_PIX_FMT_XYZ12LE) ffmpeg will call xyz12ToRgb48 which reads data
-	   from the whole of the image stride.  If we are cropping, Image::crop_scale_window munges the
-	   start addresses of each image row (to do the crop) but keeps the stride the same.  This means
-	   that under crop we will read over the end of the image by the amount of the crop.  To allow this
-	   to happen without invalid memory access we need to overallocate by one whole stride's worth of pixels.
-	*/
-	_image.reset (new Image (_pixel_format, decompressed->size(), true, decompressed->size().width));
+	_image.reset (new Image (_pixel_format, decompressed->size(), true));
 
 	int const shift = 16 - decompressed->precision (0);