Ted, Am Freitag, 15. März 2019, 14:51:28 CET schrieb Theodore Ts'o: > On Fri, Mar 15, 2019 at 08:48:10AM +0100, Richard Weinberger wrote: > > Ted, > > > > Am Freitag, 15. März 2019, 00:07:02 CET schrieb Theodore Ts'o: > > > Richard --- stepping back for a moment, in your use case, are you > > > assuming that the encryption key is always going to be present while > > > the system is running? > > > > it is not a hard requirement, it is something what is common on embedded > > systems that utilize UBIFS and fscrypt. > > > > Well, fscrypt was chosen as UBIFS encryption backend because per-file > > encryption > > with derived keys makes a lot of sense. > > Also the implementation was not super hard, David and I weren't keen to > > reinvent > > dm-crypt für UBI/MTD. > > > > That said, I'm happy with fscrypt, it works well in production. > > OK, but please note that fscrypt leaks i_size and timestamp > information; dm-crypt doesn't. An enterprising attacker could very > easily be able to do something interesting with that information, so > be sure you've thought through what the threat model for users of > ubifs is going to be.
No need to worry, I'm fully aware of all this. > If you need per-user keying, and you need to be able to mount the file > system and access some of the files without having any keys, and if > it's useful for an admin to be able to delete files without having the > key, then fscrypt is a great fit. > > You are proposing changes that (optionally) eliminate that last > advantage of fscrypt. So I just wanted to sanity check whether or not > the other advantages are useful to you, and worth the security > tradeoffs that are inherent in such a choice. If it's worth it, then > great. But if it isn't, I'd much rather that you appropriately > protect your users and your customers rather than be an additional > user of fscrypt. :-) Like I said, this patch series is an RFC, the mount option was suggested by Amir and Miklos, so I assumed showing some code is a good base for further discussion. For most of *my* use-cases it works but having general support for fscrypt+overlayfs would be the ultimate goal. Thanks, //richard
