Unapproachable mythical entity turned into a recognized thesis

Hans Liljestrand received Tietoturva ry’s prize for the best Master’s thesis in the area of information security.

Hans Liljestrand has won the annual MSc thesis competition by Tietoturva ry. His thesis Linux Kernel Memory Safety looked at memory safety from two aspects: spatial and temporal, e.g. traditional stack buffer overflows and pointer use-after-free. He did his thesis for the Networking and Services study track of the Master’s Programme in Computer Science.

Hans Liljestrand has been interested in information security for a long time. He did his internship under the guidance of Dr. Elena Reshetova in the Secure Systems Group for his thesis supervisor professor N. Asokan and found a new world with Linux kernel.

“The Linux kernel was something of an unapproachable mythical entity to me. At the summer internship I had a chance to actually familiarize myself with some platform security and realized my preconceptions were not accurate. So when I heard about a potential thesis topic combining Linux kernel work with security, I was immediately interested.”

The thesis explored the memory safety for the Linux kernel. As part of his thesis work, Liljestrand took part in the design and deployment of a secure reference counter variant that can prevent many types of real security bugs in the Linux kernel. The reference counter work resulted in over 150 patches deployed to the mainline Linux kernel.

A paper based on Liljestrand’s work has been published in a leading journal Software: Practice and Experience but it has also resulted in a number of software patches that have been accepted into the mainline Linux kernel. 

“What makes Hans' thesis stand out from other excellent theses that top Finnish universities produce is that it has had both academic and real-world impact,” says the supervisor of the thesis, professor Asokan. “It is very rare for a master's thesis work to succeed in both fronts simultaneously. Also, working with Linux kernel developers and learning what needs to be done to get them to accept research results has been a profound learning experience for Hans.”

Liljestrand was not sure about pursuing an academic career. 

“However, I was lucky enough to do my thesis with an inspiring advisor, and after completion, find myself in a good research group. As such, I am quite happy to have been able to continue pursuing a PhD with prof. Asokan. I am also currently collaborating with, and doing a PhD internship at, Huawei Technologies.”

Text: Tiina Palomäki
Photo: Tietoturva ry

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