Eric, On 30.11.2016 01:04, Eric Biggers wrote: > On Tue, Nov 29, 2016 at 10:59:28PM +0100, Richard Weinberger wrote: >> >> Do you also plan to address d/page cache related issues? >> i.e. when two users are logged into the system user rw >> is able to see decrypted file names and contents in /home/dags/ >> if user dags installs a key and accessed a file. >> > > As far as I know, there are no plans to make it possible for one user to see > plaintext while another user sees ciphertext. Fundamentally, the dentry, > inode, > and page caches are shared systemwide. This cannot be changed by using > namespaces; it can only be changed by doing something like an ecryptfs-style > stacked mount where the plaintext and ciphertext are actually exposed by > different filesystems. And it was a fundamental design goal of ext4 > encryption > to not do a stacked mount.
Well, we could over-mount /home/rw with an empty directory for every user except rw. > So the expectation is that to restrict access by other users once a key has > been > provisioned, file permissions should be used. > >> Or files in /home/dags/ are still readable even after >> user dags purged the key. > > If you revoke the key (with 'keyctl revoke') rather than unlink the key (with > 'keyctl unlink') then it actually does appear to work currently. The > difference > is that revoking the key is a modification of the key, whereas unlinking the > key > is only removing a link to the key without affecting any links which the > kernel > may have internally or which userspace may have in other keyrings. Revocation > (but not unlinking) is detected by fscrypt_get_encryption_info() when someone > tries to open an encrypted file or directory. There's also a d_revalidate > dentry operation which cause a dentry to be invalidated if it's a plaintext > name > but the directory key is no longer valid, or if it's a ciphertext name but the > directory key is now valid. Ahh, in my quick and dirty tests I've always used purge. Let me try revoke. :) BTW: This limitations needs to be clearly documented somewhere. Usually an user thinks that only she can access encrypted files... Thanks, //richard