linux-kernel - Re: [PATCH v3] security/keys: rewrite big

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Message-ID: <2858489.1589321003@warthog.procyon.org.uk>
Date:   Tue, 12 May 2020 23:03:23 +0100
From:   David Howells <dhowells@...hat.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     dhowells@...hat.com, keyrings@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        kernel-hardening@...ts.openwall.com,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH v3] security/keys: rewrite big_key crypto to use library interface

Jason A. Donenfeld <Jason@...c4.com> wrote:

> So long as that ->update function:
> 1. Deletes the old on-disk data.
> 2. Deletes the old key from the inode.
> 3. Generates a new key using get_random_bytes.
> 4. Stores that new key in the inode.
> 5. Encrypts the updated data afresh with the new key.
> 6. Puts the updated data onto disk,
> 
> then this is fine with me, and feel free to have my Acked-by if you
> want. But if it doesn't do that -- i.e. if it tries to reuse the old
> key or similar -- then this isn't fine. But it sounds like from what
> you've described that things are actually fine, in which case, I guess
> it makes sense to apply your patch ontop of mine and commit these.

Yep.  It calls big_key_destroy(), which clears away the old stuff just as when
a key is being destroyed, then generic_key_instantiate() just as when a key is
being set up.

The key ID and the key metadata (ownership, perms, expiry) are maintained, but
the payload is just completely replaced.

David