Usage of uninitialized memory in module alphamat leads to unexpected behavior.

[Sintun]

System information (version)

• OpenCV => 4.4
• Operating System / Platform => Linux (Kubuntu 18.04.5) 64 Bit
• Compiler => g++ 8.4.0

Detailed description

In module alphamat: Usage of uninitialized Mat object leads to undefined behavior (segfault) in cm.cpp function lle

Memory allocation without initialization:

opencv_contrib/modules/alphamat/src/cm.cpp

Line 91 in e320d6a

Mat Cones(20, 1, DataType<float>::type), Cinv(20, 1, DataType<float>::type);

First usage after declaration and allocation:

opencv_contrib/modules/alphamat/src/cm.cpp

Line 93 in e320d6a

Cones += 1;

Next usage of uninitialized Mat object:

opencv_contrib/modules/alphamat/src/cm.cpp

Line 126 in e320d6a

solve(C, Cones, Cinv);

Probable solution

Change

opencv_contrib/modules/alphamat/src/cm.cpp

Line 93 in e320d6a

Cones += 1;

to

Cones = 1;

Remark

I've tested the fix on 23 images and it works for me.

Steps to reproduce

A look at the source code or a run of the example code in valgrind --track-origins=yes.

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  answers.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc

[alalek]

/cc @sunitanyk