linux-kernel - Re: [PATCH] Revert "ext4 crypto: fix to check feature status before get policy"

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Message-ID: <20191101043620.GA703@sol.localdomain>
Date:   Thu, 31 Oct 2019 21:36:20 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Gwendal Grignou <gwendal@...omium.org>, Chao Yu <chao@...nel.org>,
        Ryo Hashimoto <hashimoto@...omium.org>,
        Vadim Sukhomlinov <sukhomlinov@...gle.com>,
        Guenter Roeck <groeck@...omium.org>, apronin@...omium.org,
        linux-doc@...r.kernel.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Jonathan Corbet <corbet@....net>,
        LKML <linux-kernel@...r.kernel.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        linux-fscrypt@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH] Revert "ext4 crypto: fix to check feature status before
 get policy"

On Thu, Oct 31, 2019 at 10:52:19AM -0700, Doug Anderson wrote:
> Hi,
> 
> On Wed, Oct 30, 2019 at 2:59 PM Doug Anderson <dianders@...omium.org> wrote:
> >
> > Hi,
> >
> > On Wed, Oct 30, 2019 at 1:57 PM Eric Biggers <ebiggers@...nel.org> wrote:
> > >
> > > FWIW, from reading the Chrome OS code, I think the code you linked to isn't
> > > where the breakage actually is.  I think it's actually at
> > > https://chromium.googlesource.com/chromiumos/platform2/+/refs/heads/master/chromeos-common-script/share/chromeos-common.sh#375
> > > ... where an init script is using the error message printed by 'e4crypt
> > > get_policy' to decide whether to add -O encrypt to the filesystem or not.
> > >
> > > It really should check instead:
> > >
> > >         [ -e /sys/fs/ext4/features/encryption ]
> >
> > OK, I filed <https://crbug.com/1019939> and CCed all the people listed
> > in the cryptohome "OWNERS" file.  Hopefully one of them can pick this
> > up as a general cleanup.  Thanks!
> 
> Just to follow-up: I did a quick test here to see if I could fix
> "chromeos-common.sh" as you suggested.  Then I got rid of the Revert
> and tried to login.  No joy.
> 
> Digging a little deeper, the ext4_dir_encryption_supported() function
> is called in two places:
> * chromeos-install
> * chromeos_startup
> 
> In my test case I had a machine that I'd already logged into (on a
> previous kernel version) and I was trying to log into it a second
> time.  Thus there's no way that chromeos-install could be involved.
> Looking at chromeos_startup:
> 
> https://chromium.googlesource.com/chromiumos/platform2/+/refs/heads/master/init/chromeos_startup
> 
> ...the function is only used for setting up the "encrypted stateful"
> partition.  That wasn't where my failure was.  My failure was with
> logging in AKA with cryptohome.  Thus I think it's plausible that my
> original commit message pointing at cryptohome may have been correct.
> It's possible that there were _also_ problems with encrypted stateful
> that I wasn't noticing, but if so they were not the only problems.
> 
> It still may be wise to make Chrome OS use different tests, but it
> might not be quite as simple as hoped...
> 

Ah, I think I found it:

https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/2cbdedd5eca0a57d9596671a99da5fab8e60722b/sys-apps/upstart/files/upstart-1.2-dircrypto.patch

The init process does EXT4_IOC_GET_ENCRYPTION_POLICY on /, and if the error is
EOPNOTSUPP, it skips creating the "dircrypto" keyring.  So then cryptohome can't
add keys later.  (Note the error message you got, "Error adding dircrypto key".)

So it looks like the kernel patch broke both that and
ext4_dir_encryption_supported().

I don't see how it could have broken cryptohome by itself, since AFAICS
cryptohome only uses EXT4_IOC_GET_ENCRYPTION_POLICY on the partition which is
supposed to have the 'encrypt' feature set.

- Eric