Received-SPF: pass (google.com: best guess record for domain of linux-ext4-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Andreas Dilger <adilger@dilger.ca>
Message-Id: <C0761869-5FCD-4CC7-9635-96C18744A0F8@dilger.ca>
Content-Type: multipart/signed;
 boundary="Apple-Mail=_3DA047BA-35EF-48C4-A8AB-ACB70041D364";
 protocol="application/pgp-signature"; micalg=pgp-sha256
Mime-Version: 1.0 (Mac OS X Mail 10.3 \(3273\))
Subject: Re: [PATCH 1/4] tune2fs: prevent changing UUID of fs with
 stable_inodes feature
Date:   Wed, 1 Apr 2020 20:19:38 -0600
In-Reply-To: <20200401203239.163679-2-ebiggers@kernel.org>
Cc:     linux-ext4 <linux-ext4@vger.kernel.org>,
        linux-fscrypt@vger.kernel.org
To:     Eric Biggers <ebiggers@kernel.org>
References: <20200401203239.163679-1-ebiggers@kernel.org>
 <20200401203239.163679-2-ebiggers@kernel.org>
Sender: linux-ext4-owner@vger.kernel.org
Precedence: bulk


--Apple-Mail=_3DA047BA-35EF-48C4-A8AB-ACB70041D364
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain;
	charset=us-ascii

On Apr 1, 2020, at 2:32 PM, Eric Biggers <ebiggers@kernel.org> wrote:
>=20
> From: Eric Biggers <ebiggers@google.com>
>=20
> The stable_inodes feature is intended to indicate that it's safe to =
use
> IV_INO_LBLK_64 encryption policies, where the encryption depends on =
the
> inode numbers and thus filesystem shrinking is not allowed.  However
> since inode numbers are not unique across filesystems, the encryption
> also depends on the filesystem UUID, and I missed that there is a
> supported way to change the filesystem UUID (tune2fs -U).
>=20
> So, make 'tune2fs -U' report an error if stable_inodes is set.
>=20
> We could add a separate stable_uuid feature flag, but it seems =
unlikely
> it would be useful enough on its own to warrant another flag.

What about having tune2fs walk the inode table checking for any inodes =
that
have this flag, and only refusing to clear the flag if it finds any?  =
That
takes some time on very large filesystems, but since inode table reading =
is
linear it is reasonable on most filesystems.

Cheers, Andreas

> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
> misc/tune2fs.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>=20
> diff --git a/misc/tune2fs.c b/misc/tune2fs.c
> index 314cc0d0..ca06c98b 100644
> --- a/misc/tune2fs.c
> +++ b/misc/tune2fs.c
> @@ -3236,6 +3236,13 @@ _("Warning: The journal is dirty. You may wish =
to replay the journal like:\n\n"
> 		char buf[SUPERBLOCK_SIZE] __attribute__ ((aligned(8)));
> 		__u8 old_uuid[UUID_SIZE];
>=20
> +		if (ext2fs_has_feature_stable_inodes(fs->super)) {
> +			fputs(_("Cannot change the UUID of this =
filesystem "
> +				"because it has the stable_inodes =
feature "
> +				"flag.\n"), stderr);
> +			exit(1);
> +		}
> +
> 		if (!ext2fs_has_feature_csum_seed(fs->super) &&
> 		    (ext2fs_has_feature_metadata_csum(fs->super) ||
> 		     ext2fs_has_feature_ea_inode(fs->super))) {
> --
> 2.26.0.rc2.310.g2932bb562d-goog
>=20


Cheers, Andreas


--Apple-Mail=_3DA047BA-35EF-48C4-A8AB-ACB70041D364
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
	filename=signature.asc
Content-Type: application/pgp-signature;
	name=signature.asc
Content-Description: Message signed with OpenPGP

-----BEGIN PGP SIGNATURE-----
Comment: GPGTools - http://gpgtools.org
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=oBpG
-----END PGP SIGNATURE-----

--Apple-Mail=_3DA047BA-35EF-48C4-A8AB-ACB70041D364--