Re: overlayfs vs. fscrypt
From: Richard Weinberger
Date: Wed Mar 13 2019 - 08:47:51 EST
Am Mittwoch, 13. März 2019, 13:36:02 CET schrieb Miklos Szeredi:
> I don't get it. Does fscrypt try to check permissions via
> ->d_revalidate? Why is it not doing that via ->permission()?
Please let me explain. Suppose we have a fscrypto directory /mnt and
I *don't* have the key.
When reading the directory contents of /mnt will return an encrypted filename.
e.g.
# ls /mnt
+mcQ46ne5Y8U6JMV9Wdq2C
As soon I load my key the real name is shown and I can read the file contents too.
That's why fscrypt has ->d_revalidate(). It checks for the key, if the key is
still not here -> stay with the old encrypted name. If the key is present
-> reveal the real name.
Same happens on the other direction if I unlink my key from the keyring.
> >
> > 2. Teach overlayfs to deal with a upper that has ->d_revalidate().
> > Given the complexity of overlayfs I'm not sure how feasible this is.
> > But I'm no overlayfs expert, maybe I miss something.
>
> I don't think it would be too complex. But first I'd like to
> understand exactly why fscrypt is (ab) using d_revalidate().
I hope my answer makes things more clear.
Thanks,
//richard