linux-ext4 - Re: [PATCH v7 08/16] fscrypt: add FS_IOC_GET_ENCRYPTION_KEY

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Message-ID: <20190728193012.GH6088@mit.edu>
Date:   Sun, 28 Jul 2019 15:30:12 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-mtd@...ts.infradead.org, linux-api@...r.kernel.org,
        linux-crypto@...r.kernel.org, keyrings@...r.kernel.org,
        Paul Crowley <paulcrowley@...gle.com>,
        Satya Tangirala <satyat@...gle.com>
Subject: Re: [PATCH v7 08/16] fscrypt: add FS_IOC_GET_ENCRYPTION_KEY_STATUS
 ioctl

On Fri, Jul 26, 2019 at 03:41:33PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> Add a new fscrypt ioctl, FS_IOC_GET_ENCRYPTION_KEY_STATUS.  Given a key
> specified by 'struct fscrypt_key_specifier' (the same way a key is
> specified for the other fscrypt key management ioctls), it returns
> status information in a 'struct fscrypt_get_key_status_arg'.
> 
> The main motivation for this is that applications need to be able to
> check whether an encrypted directory is "unlocked" or not, so that they
> can add the key if it is not, and avoid adding the key (which may
> involve prompting the user for a passphrase) if it already is.
> 
> It's possible to use some workarounds such as checking whether opening a
> regular file fails with ENOKEY, or checking whether the filenames "look
> like gibberish" or not.  However, no workaround is usable in all cases.
> 
> Like the other key management ioctls, the keyrings syscalls may seem at
> first to be a good fit for this.  Unfortunately, they are not.  Even if
> we exposed the keyring ID of the ->s_master_keys keyring and gave
> everyone Search permission on it (note: currently the keyrings
> permission system would also allow everyone to "invalidate" the keyring
> too), the fscrypt keys have an additional state that doesn't map cleanly
> to the keyrings API: the secret can be removed, but we can be still
> tracking the files that were using the key, and the removal can be
> re-attempted or the secret added again.
> 
> After later patches, some applications will also need a way to determine
> whether a key was added by the current user vs. by some other user.
> Reserved fields are included in fscrypt_get_key_status_arg for this and
> other future extensions.
> 
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Looks good, feel free to add:

Reviewed-by: Theodore Ts'o <tytso@....edu>