linux-ext4 - Re: ext4 encryption trap

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Message-ID: <20160829124657.GA12024@amd>
Date:   Mon, 29 Aug 2016 14:46:57 +0200
From:   Pavel Machek <pavel@....cz>
To:     Bernd Schubert <bernd.schubert@...tmail.fm>
Cc:     tytso@....edu, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org
Subject: Re: ext4 encryption trap

On Mon 2016-08-29 13:36:55, Pavel Machek wrote:
> On Mon 2016-08-29 12:49:06, Pavel Machek wrote:
> > On Mon 2016-08-29 12:40:24, Bernd Schubert wrote:
> > > On Monday, August 29, 2016 12:08:16 PM CEST Pavel Machek wrote:
> > > > Hi!
> > > > 
> > > > You encrypt a directory -- sounds easy, right? Support is in 4.4
> > > > kernel, my machines run newer kernels than that. Encrypting root would
> > > > be hard, but encrypting parts of data partition should be easy.
> > > > 
> > > > Ok, lets follow howto... Need to do tune2fs. Right. Aha, still does
> > > > not work, looks like I'll need to reboot.
> > > > 
> > > > Hmm. Will not boot. Grub no longer recognizes my /data partition, and
> > > > that's where new kernels are. Old kernels are in /boot, but those are
> > > > now useless. Lets copy new kernel on machine using USB stick. Does not
> > > > boot. Fun.
> > > > 
> > > > tune2fs on root filesystem is useless, as it is too old. New one
> > > > is ... on the data partition. Right. Ok, lets bring newer version of
> > > > tune2fs in. "encryption" feature can not be cleared.
> > > > 
> > > > Argh! Come on, I did not even create single encrypted directory on the
> > > > partition. I want the damn bit to go off, so I can go back to working
> > > > configuration. "Old kernels can not read encrypted files" sounds ok,
> > > > but "old kernels can not mount filesystem at all" is not acceptable
> > > > here :-(.
> > > > 
> > > > Is there way to go back? Restoring 400GB from backups would not be fun
> > > 
> > > I have not tried it myself,  but this should work?
> > > 
> > > debugfs -w -R "feature -encrypt" /dev/device
> > > 
> > > 
> > > (assuming the feature flag is called "encrypt")
> > 
> > Yes, I figured out debugfs could be used to do this. (But thanks for
> > the command line). If all tunefs did was to set the bit, this is
> > safe. Is it?
> > 
> > [I guess I can do fsck -fn, debugfs, fsck -fn; if it passes I should
> > be safe, if it does not I can turn +encrypt back on, and would be no
> > worse than I'm now. Hmm?]
> 
> Ok, done, fsck passed, I'm back to previous configuration.
> 
> I guess I was too optimistic. Using ext4 encryption would require at
> least new e2fsprogs at the root filesystem, which was something I was
> hoping to avoid.

I'm trying to make some experiments on USB stick...

Hmm. I guess error handling in add_key should be improved?

pavel@duo:/mnt$ ~/g/e2fsprogs/misc/e4crypt add_key -S salt.txt
Invalid salt: salt.txt
pavel@duo:/mnt$ ~/g/e2fsprogs/misc/e4crypt add_key -S
/media/pavel/8EE9-E39F/salt.txt
EXT4_IOC_GET_ENCRYPTION_PWSALT: Inappropriate ioctl for device
pavel@duo:/mnt$

(The first one is probably ok, but why it accepts path instead of hex
value?)

Best regards,
								Pavel


-- 
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