Fix out-of-bounds read when cropping JPEG2000 images (#1654).

Backported from 25d968fdcf1abada4bd7bbcb8c72eeebda73b134 in v2.15.x.

2 files changed, 16 insertions, 1 deletions

diff --git a/src/lib/j2k_image_proxy.cc b/src/lib/j2k_image_proxy.cc
index 9893d65a6..d4c7a8716 100644
--- a/src/lib/j2k_image_proxy.cc
+++ b/src/lib/j2k_image_proxy.cc
@@ -138,7 +138,13 @@ 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);
 
-	_image.reset (new Image (_pixel_format, decompressed->size(), true));
+	/* 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));
 
 	int const shift = 16 - decompressed->precision (0);
 
diff --git a/test/image_test.cc b/test/image_test.cc
index 8a7feb126..40abfda43 100644
--- a/test/image_test.cc
+++ b/test/image_test.cc
@@ -267,6 +267,15 @@ BOOST_AUTO_TEST_CASE (crop_scale_window_test)
 	check_image("test/data/crop_scale_window_test.png", "build/test/crop_scale_window_test.png");
 }
 
+/** Special cases of Image::crop_scale_window which triggered some valgrind warnings */
+BOOST_AUTO_TEST_CASE (crop_scale_window_test2)
+{
+	/* This 2048 does the same as J2KImageProxy does when it makes an image */
+	shared_ptr<Image> image (new Image(AV_PIX_FMT_XYZ12LE, dcp::Size(2048, 858), true, 2048));
+	image->crop_scale_window (Crop(279, 0, 0, 0), dcp::Size(1069, 448), dcp::Size(1069, 578), dcp::YUV_TO_RGB_REC709, VIDEO_RANGE_FULL, AV_PIX_FMT_RGB24, false, false);
+	image->crop_scale_window (Crop(2048, 0, 0, 0), dcp::Size(1069, 448), dcp::Size(1069, 578), dcp::YUV_TO_RGB_REC709, VIDEO_RANGE_FULL, AV_PIX_FMT_RGB24, false, false);
+}
+
 BOOST_AUTO_TEST_CASE (as_png_test)
 {
 	shared_ptr<FFmpegImageProxy> proxy(new FFmpegImageProxy("test/data/3d_test/000001.png"));