Add kernelCTF CVE-2023-6931_mitigation

[Sechack06]

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[Sechack06]

Hello,

Thank you for reviewing my PR.

I've updated the write-up base on the comments.

I also tried my best to make the code fit the given format.

Please check it.

Thanks

[koczkatamas]

Thanks for the changes! Sorry for the delay processing the submission. You will get a separate email about the reward.