linux-kernel - Re: [PATCH] ceph: make sure directories aren't complete after setting crypt context

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Date:   Thu, 17 Nov 2022 18:02:41 +0000
From:   Luís Henriques <lhenriques@...e.de>
To:     Xiubo Li <xiubli@...hat.com>
Cc:     Ilya Dryomov <idryomov@...il.com>,
        Jeff Layton <jlayton@...nel.org>, ceph-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ceph: make sure directories aren't complete after
 setting crypt context

Xiubo Li <xiubli@...hat.com> writes:

> On 17/11/2022 16:03, Xiubo Li wrote:
>>
>> On 16/11/2022 23:37, Luís Henriques wrote:
>>> When setting a directory's crypt context, __ceph_dir_clear_complete() needs
>>> to be used otherwise, if it was complete before, any old dentry that's still
>>> around will be valid.
>>>
>>> Signed-off-by: Luís Henriques <lhenriques@...e.de>
>>> ---
>>> Hi!
>>>
>>> Here's a simple way to trigger the bug this patch is fixing:
>>>
>>> # cd /cephfs
>>> # ls mydir
>>> nKRhofOAVNsAwVLvDw7a0c9ypsjbZfK3n0Npnmni6j0
>>> # ls mydir/nKRhofOAVNsAwVLvDw7a0c9ypsjbZfK3n0Npnmni6j0/
>>> Cyuer5xT+kBlEPgtwAqSj0WK2taEljP5vHZ,D8VXCJ8
>>> u+46b2XVCt7Obpz0gznZyNLRj79Q2l4KmkwbKOzdQKw
>>> # fscrypt unlock mydir
>>> # touch /mnt/test/mydir/mysubdir/file
>>> touch: cannot touch '/mnt/test/mydir/mysubdir/file': No such file or
>>> directory
>>>
>>>   fs/ceph/crypto.c | 4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> diff --git a/fs/ceph/crypto.c b/fs/ceph/crypto.c
>>> index 35a2ccfe6899..dc1557967032 100644
>>> --- a/fs/ceph/crypto.c
>>> +++ b/fs/ceph/crypto.c
>>> @@ -87,6 +87,10 @@ static int ceph_crypt_get_context(struct inode *inode,
>>> void *ctx, size_t len)
>>>           return -ERANGE;
>>>         memcpy(ctx, cfa->cfa_blob, ctxlen);
>>> +
>>> +    /* Directory isn't complete anymore */
>>> +    if (S_ISDIR(inode->i_mode) && __ceph_dir_is_complete(ci))
>>> +        __ceph_dir_clear_complete(ci);
>>
>> Hi Luis,
>>
>> Good catch!
>>
>> BTW, why do this in the ceph_crypt_get_context() ? As my understanding is that
>> we should mark 'mydir' as incomplete when unlocking it. While as I remembered
>> the unlock operation will do:
>>
>>
>> Step1: get_encpolicy via 'mydir' as ctx
>> Step2: rm_enckey of ctx from the superblock
>>
> Sorry, it should be add_enckey.
>>
>> Since I am still running the test cases for the file lock patches, so I didn't
>> catch logs to confirm the above steps yet.
>>
>> If I am right IMO then we should mark the dir as incomplete in the Step2
>> instead, because for non-unlock operations they may also do the Step1.
>>
> Your patch will work. But probably we should do this just around
> __fscrypt_prepare_readdir() or fscrypt_prepare_readdir() instead ? We need to
> detect that once the 'inode->i_crypt_info' changed then mark the dir as
> incomplete.
>
> For now for the lock operation it will evict the inode, which will help do this
> for us already. But for unlock case, we need to handle it by ourself.

OK, that makes sense and to be honest I thought that there should be
another place for doing this. Unfortunately, I didn't found it: in the
test case I have the fscrypt_prepare_readdir() isn't called:

   # cd /cephfs
   # ls mydir
   nKRhofOAVNsAwVLvDw7a0c9ypsjbZfK3n0Npnmni6j0
   # ls mydir/nKRhofOAVNsAwVLvDw7a0c9ypsjbZfK3n0Npnmni6j0/
   Cyuer5xT+kBlEPgtwAqSj0WK2taEljP5vHZ,D8VXCJ8 u+46b2XVCt7Obpz0gznZyNLRj79Q2l4KmkwbKOzdQKw

At this point readdir was executed, of course.  And
__ceph_dir_set_complete() is also used to indicate that we have the full
contents.  However, executing the following commands won't result in any
new readdir():

   # fscrypt unlock mydir
   # touch /mnt/test/mydir/mysubdir/file

and since the encryption key is set at the sb level, I couldn't find a way
to detect changes in inode->i_crypt_info.  ceph_d_revalidate() is invoked
but at that point I don't thing we have a way to know what is changing.

Any ideas?

Cheers,
-- 
Luís

>
> Thanks!
>
> - Xiubo
>
>
>> Thanks!
>>
>> - Xiubo
>>
>>>       return ctxlen;
>>>   }
>>>
>