On Fri, 2018-08-24 at 09:16 -0700, Eric Biggers wrote: [...] > Since fs-verity provides the Merkle tree root hash in constant time and > verifies data blocks on-demand, it is useful for efficiently verifying > the authenticity of, or "appraising", large files of which only a small > portion may be accessed -- such as Android application (APK) files. It > can also be useful in "audit" use cases where file hashes are logged. > fs-verity also provides better protection against malicious disk > firmware than an ahead-of-time hash, since fs-verity re-verifies data > each time it's paged in. [...] > Feedback on the design and implementation is greatly appreciated. Hi, I've looked at the series and the slides linked form the recent lwn.net article, but I'm not sure how fs-verity intends to protect against malicious firmware (or offline modification). Similar to IMA/EVM, fs- verity doesn't seem to include the name/location of the file into it's verification. So the firmware/an attacker could replace one fs-verity- protected file with another (maybe a trusted system APK with another one for which a vulnerability was discovered, or /sbin/init with /bin/sh). Is the expected root hash of the file provided from somewhere else, so this is not a problem on Android? Or is this problem out-of-scope for fs-verity? For IMA/EVM, there were patches by Dmitry to address this class of attacks (they were not merged, though): https://lwn.net/Articles/574221/ Thanks, Jan [1] https://events.linuxfoundation.org/wp-content/uploads/2017/11/fs-ve rify_Mike-Halcrow_Eric-Biggers.pdf -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
