Reject mismatched frame size in libjpeg encoder - #249
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The extras JPEG encoder reads ppf.info.ysize rows and ppf.info.xsize columns from the frame's pixel buffer, but the shared VerifyImageSize check for frame size matching the image size is commented out. A PackedPixelFile whose info dimensions are larger than the frame buffer causes an out-of-bounds read in the encoder copy loops. Add an explicit frame size check in JPEGEncoder::Encode and a test that mirrors the existing jpegli encoder mismatch test.
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What
The extras JPEG encoder (
lib/extras/enc/jpg.cc) encodes frames with the loopfor (size_t y = 0; y < info.ysize; ++y)readingpixels + y * image.stride, and per-pixelfor (size_t x = 0; x < info.xsize; ++x)reads. The only gate before this isEncoder::VerifyPackedImage→Encoder::VerifyImageSize, whoseimage.xsize != info.xsize || image.ysize != info.ysizecheck is commented out (see the TODO atlib/extras/enc/encode.cc).When a
PackedPixelFilecarriesinfo.xsize/info.ysizelarger than the frame'scolor.xsize/color.ysize, the encoder reads past the pixel buffer — the same out-of-bounds read that PR #213 fixed for the jpegli encoder (lib/extras/enc/jpegli.cc), which this encoder path was missing.Why it matters
Encoder::FromExtension(".jpg")is the public route used bydjpegli(-o out.jpg) and by the extras encoder framework. An inconsistentPackedPixelFilecurrently leads to a heap-buffer-overflow read (crash under ASan/MSan) instead of a clean error.Fix
Add an explicit frame-size check in
JPEGEncoder::Encode, returningJPEGLI_FAILURE("Frame size does not match image size.")on mismatch, plus a regression testJpegliLibjpegEncodeRejectsMismatchedFrameSizethat mirrors the existingJpegliEncodeRejectsMismatchedFrameSizetest for the jpegli encoder.Verified against real code:
EncodeWithLibJpeg/EncodeWithSJpegiterateinfo.ysize/info.xsizeover the frame buffer, and no other guard rejects the mismatch.