linux-kernel - Re: [PATCH v3 0/3] ceph: fscrypt: fix atomic open bug for encrypted directories

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Date:   Mon, 20 Mar 2023 12:20:09 +0100
From:   Ilya Dryomov <idryomov@...il.com>
To:     Xiubo Li <xiubli@...hat.com>
Cc:     Luís Henriques <lhenriques@...e.de>,
        Eric Biggers <ebiggers@...nel.org>,
        Jeff Layton <jlayton@...nel.org>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        linux-fscrypt@...r.kernel.org, ceph-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/3] ceph: fscrypt: fix atomic open bug for encrypted directories

On Mon, Mar 20, 2023 at 2:07 AM Xiubo Li <xiubli@...hat.com> wrote:
>
>
> On 17/03/2023 02:14, Luís Henriques wrote:
> > Hi!
> >
> > I started seeing fstest generic/123 failing in ceph fscrypt, when running it
> > with 'test_dummy_encryption'.  This test is quite simple:
> >
> > 1. Creates a directory with write permissions for root only
> > 2. Writes into a file in that directory
> > 3. Uses 'su' to try to modify that file as a different user, and
> >     gets -EPERM
> >
> > All the test steps succeed, but the test fails to cleanup: 'rm -rf <dir>'
> > will fail with -ENOTEMPTY.  'strace' shows that calling unlinkat() to remove
> > the file got a -ENOENT and then -ENOTEMPTY for the directory.
> >
> > This is because 'su' does a drop_caches ('su (874): drop_caches: 2' in
> > dmesg), and ceph's atomic open will do:
> >
> >       if (IS_ENCRYPTED(dir)) {
> >               set_bit(CEPH_MDS_R_FSCRYPT_FILE, &req->r_req_flags);
> >               if (!fscrypt_has_encryption_key(dir)) {
> >                       spin_lock(&dentry->d_lock);
> >                       dentry->d_flags |= DCACHE_NOKEY_NAME;
> >                       spin_unlock(&dentry->d_lock);
> >               }
> >       }
> >
> > Although 'dir' has the encryption key available, fscrypt_has_encryption_key()
> > will return 'false' because fscrypt info isn't yet set after the cache
> > cleanup.
> >
> > The first patch will add a new helper for the atomic_open that will force
> > the fscrypt info to be loaded into an inode that has been evicted recently
> > but for which the key is still available.
> >
> > The second patch switches ceph atomic_open to use the new fscrypt helper.
> >
> > Cheers,
> > --
> > Luís
> >
> > Changes since v2:
> > - Make helper more generic and to be used both in lookup and atomic open
> >    operations
> > - Modify ceph_lookup (patch 0002) and ceph_atomic_open (patch 0003) to use
> >    the new helper
> >
> > Changes since v1:
> > - Dropped IS_ENCRYPTED() from helper function because kerneldoc says
> >    already that it applies to encrypted directories and, most importantly,
> >    because it would introduce a different behaviour for
> >    CONFIG_FS_ENCRYPTION and !CONFIG_FS_ENCRYPTION.
> > - Rephrased helper kerneldoc
> >
> > Changes since initial RFC (after Eric's review):
> > - Added kerneldoc comments to the new fscrypt helper
> > - Dropped '__' from helper name (now fscrypt_prepare_atomic_open())
> > - Added IS_ENCRYPTED() check in helper
> > - DCACHE_NOKEY_NAME is not set if fscrypt_get_encryption_info() returns an
> >    error
> > - Fixed helper for !CONFIG_FS_ENCRYPTION (now defined 'static inline')
>
> This series looks good to me.
>
> And I have run the test locally and worked well.
>
>
> > Luís Henriques (3):
> >    fscrypt: new helper function - fscrypt_prepare_lookup_partial()
>
> Eric,
>
> If possible I we can pick this together to ceph repo and need your ack
> about this. Or you can pick it to the crypto repo then please feel free
> to add:
>
> Tested-by: Xiubo Li <xiubli@...hat.com> and Reviewed-by: Xiubo Li
> <xiubli@...hat.com>

I would prefer the fscrypt helper to go through the fscrypt tree.

Thanks,

                Ilya