Opencv does not check for numpy writeable flags when writing on array.

[haixuanTao]

Expected behaviour

Numpy array has a flag indicating if the array is writeable or not.

In the case it is not writeable and the user is trying to write on the array, I would imagine opencv would raise an issue or would use a copy.

Actual behaviour

Opencv write on the array without checking the flag that can raise a segmentation fault.

Steps to reproduce

The following example is a simple example taken from https://github.com/dora-rs/dora , which use the latest pyarrow. You can probably make a numpy only example.

import pyarrow as pa
import numpy as np
import cv2

array = pa.array(np.zeros((100))).to_numpy().reshape((10,10))

assert array.flags.writeable == False, "Array should be not writable"

cv2.rectangle(array,(0,0),(5,5),(255),2)
print(array)

array([[255., 255., 255., 255., 255., 255., 255.,   0.,   0.,   0.],
       [255., 255., 255., 255., 255., 255., 255.,   0.,   0.,   0.],
       [255., 255.,   0.,   0., 255., 255., 255.,   0.,   0.,   0.],
       [255., 255.,   0.,   0., 255., 255., 255.,   0.,   0.,   0.],
       [255., 255., 255., 255., 255., 255., 255.,   0.,   0.,   0.],
       [255., 255., 255., 255., 255., 255., 255.,   0.,   0.,   0.],
       [255., 255., 255., 255., 255., 255.,   0.,   0.,   0.,   0.],
       [  0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.],
       [  0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.],
       [  0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.]])

Errors

This can lead to segmentation fault error if the data is not owned by the current process.

I wonder if #728 is linked to this issue.

[asmorkalov]

The fix will be released with 4.9.0.