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 09:06:50 +0800
From:   Xiubo Li <xiubli@...hat.com>
To:     Luís Henriques <lhenriques@...e.de>,
        Eric Biggers <ebiggers@...nel.org>,
        Jeff Layton <jlayton@...nel.org>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        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 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>

Thanks

- Xiubo

>    ceph: switch ceph_open() to use new fscrypt helper
>    ceph: switch ceph_open_atomic() to use the new fscrypt helper
>
>   fs/ceph/dir.c           | 13 +++++++------
>   fs/ceph/file.c          |  8 +++-----
>   fs/crypto/hooks.c       | 37 +++++++++++++++++++++++++++++++++++++
>   include/linux/fscrypt.h |  7 +++++++
>   4 files changed, 54 insertions(+), 11 deletions(-)
>
-- 
Best Regards,

Xiubo Li (李秀波)

Email: xiubli@...hat.com/xiubli@....com
Slack: @Xiubo Li