Re: [PATCH] fscrypt: track master key presence separately from secret

From: Josef Bacik <josef@toxicpanda.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: linux-fscrypt@vger.kernel.org, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH] fscrypt: track master key presence separately from secret
Date: Mon, 16 Oct 2023 14:23:37 -0400	[thread overview]
Message-ID: <20231016182337.GA2339326@perftesting> (raw)
In-Reply-To: <20231015061055.62673-1-ebiggers@kernel.org>

On Sat, Oct 14, 2023 at 11:10:55PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> Master keys can be in one of three states: present, incompletely
> removed, and absent (as per FSCRYPT_KEY_STATUS_* used in the UAPI).
> Currently, the way that "present" is distinguished from "incompletely
> removed" internally is by whether ->mk_secret exists or not.
> 
> With extent-based encryption, it will be necessary to allow per-extent
> keys to be derived while the master key is incompletely removed, so that
> I/O on open files will reliably continue working after removal of the
> key has been initiated.  (We could allow I/O to sometimes fail in that
> case, but that seems problematic for reasons such as writes getting
> silently thrown away and diverging from the existing fscrypt semantics.)
> Therefore, when the filesystem is using extent-based encryption,
> ->mk_secret can't be wiped when the key becomes incompletely removed.
> 
> As a prerequisite for doing that, this patch makes the "present" state
> be tracked using a new field, ->mk_present.  No behavior is changed yet.
> 
> The basic idea here is borrowed from Josef Bacik's patch
> "fscrypt: use a flag to indicate that the master key is being evicted"
> (https://lore.kernel.org/r/e86c16dddc049ff065f877d793ad773e4c6bfad9.1696970227.git.josef@toxicpanda.com).
> I reimplemented it using a "present" bool instead of an "evicted" flag,
> fixed a couple bugs, and tried to update everything to be consistent.
> 
> Note: I considered adding a ->mk_status field instead, holding one of
> FSCRYPT_KEY_STATUS_*.  At first that seemed nice, but it ended up being
> more complex (despite simplifying FS_IOC_GET_ENCRYPTION_KEY_STATUS),
> since it would have introduced redundancy and had weird locking rules.
> 
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Based my fscrypt patches ontop of this one, ran tests with both btrfs and ext4
with it applied, in addition to my normal review stuff.  You can add

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef