Transcryptfs: A Dynamically Loadable Kernelspace Filesystem Architecture

Adarsh Jagannatha

Jun 2013 · Adarsh Jagannatha

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 TransCrypt is an encrypting filesystem, indigenously developed at IIT Kanpur. It has been under continuous development for the past 6 years, by various students of IIT Kanpur at Prabhu Goel Reasearch Centre for Computer and Internet Security. The codebase of Transcryptfs filesystem for Linux is spread across various sub systems of Linux kernel, viz. dm-layer, lsm, vfs, crypto, etc., making it difficult to keep Transcryptfs updated with changes in any of those subsystem in upstream kernel’s mainline code. One of the main features of Transcryptfs for Linux file server is the use of Linux security module (LSM) for providing access control mechanism; Due to changes in kernel architecture, since late 2007, LSM has to be statically linked with kernel during its compile time, thereby imposing a restriction that Transcryptfs supported kernel should be statically compiled with the Transcryptfs-lsm module.

This additionally imposed restriction has led to a complicated procedure for setting up of Transcryptfs filesystem and also has shifted the responsibility of patching kernel with new updates from the distribution managers to individual system administrators. These factors have resulted in non-adoption of Transcryptfs for real world usecase.

In this thesis, we re-engineer and come up with an architecture that aims to make Transcryptfs an easily deployable and dynamically loadable kernel module, in addition to decoupling codebase from the kernel source into a single manageable module, thereby easing maintenance and further development of Transcryptfs filesystem. The contribution of this thesis is in designing the kernelspace architecture and related implementation of Transcryptfs as an out-of-the-tree kernel module.

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Adarsh is a technology enthusiast, he wrote this thesis as part of his masters' thesis. He is a web developer, system admin and an entrepreneur.