Hello, A few more questions about the new filesystem encryption code:
I found that a process without access to the master encryption key can read a file's full decrypted contents, provided that the file was opened recently by a process with access to the key. This is true even if the privileged process merely opened and closed the file, without reading any bytes. A similar story applies to filenames; a 'ls' by a process able to decrypt the names reveals them to all users/processes. Essentially, it seems that despite the use of the kernel keyrings mechanism where different users/processes can have different keys, this doesn't fully carry over into filesystem encryption. Is this a known and understood limitation of the design? The design document states that an encryption policy can be changed "if the directory is empty or the file is 0 bytes in length". However, the code doesn't allow an existing encryption policy to be changed. Which behavior was intended? I had brought up the question of the endianness of the XTS tweak value. I also realized that since the page index is used, the XTS tweak will be dependent on PAGE_SIZE. So the current behavior is that an encrypted filesystem can only be read on a device with the same endianness _and_ PAGE_SIZE. Is is the case that due to the early Android users, it is too late to start using the byte offset instead of the PAGE_SIZE? What about if the XTS tweak was fixed as the number of 4096-byte blocks from the start of the file as a le64 --- is that what the existing users are expected to be doing in practice? Are there any architectures with PAGE_SIZE < 4096 for which that value wouldn't work? Eric
