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 20:47:18 +0800
From:   Xiubo Li <xiubli@...hat.com>
To:     Ilya Dryomov <idryomov@...il.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 20/03/2023 19:20, Ilya Dryomov wrote:
> 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.

Sure. This also LGTM.

Thanks

- Xiubo

> Thanks,
>
>                  Ilya
>