linux-kernel - Re: [PATCH 1/2] fscrypt: new helper function

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Message-ID: <878rfzvg5u.fsf@suse.de>
Date:   Tue, 14 Mar 2023 09:25:01 +0000
From:   Luís Henriques <lhenriques@...e.de>
To:     Xiubo Li <xiubli@...hat.com>
Cc:     Eric Biggers <ebiggers@...nel.org>,
        Jeff Layton <jlayton@...nel.org>,
        "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 1/2] fscrypt: new helper function -
 fscrypt_prepare_atomic_open()

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

> On 14/03/2023 10:25, Eric Biggers wrote:
>> On Tue, Mar 14, 2023 at 08:53:51AM +0800, Xiubo Li wrote:
>>> On 14/03/2023 02:09, Eric Biggers wrote:
>>>> On Mon, Mar 13, 2023 at 12:33:09PM +0000, Luís Henriques wrote:
>>>>> + * The regular open path will use fscrypt_file_open for that, but in the
>>>>> + * atomic open a different approach is required.
>>>> This should actually be fscrypt_prepare_lookup, not fscrypt_file_open, right?
>>>>
>>>>> +int fscrypt_prepare_atomic_open(struct inode *dir, struct dentry *dentry)
>>>>> +{
>>>>> +	int err;
>>>>> +
>>>>> +	if (!IS_ENCRYPTED(dir))
>>>>> +		return 0;
>>>>> +
>>>>> +	err = fscrypt_get_encryption_info(dir, true);
>>>>> +	if (!err && !fscrypt_has_encryption_key(dir)) {
>>>>> +		spin_lock(&dentry->d_lock);
>>>>> +		dentry->d_flags |= DCACHE_NOKEY_NAME;
>>>>> +		spin_unlock(&dentry->d_lock);
>>>>> +	}
>>>>> +
>>>>> +	return err;
>>>>> +}
>>>>> +EXPORT_SYMBOL_GPL(fscrypt_prepare_atomic_open);
>>>> [...]
>>>>> +static inline int fscrypt_prepare_atomic_open(struct inode *dir,
>>>>> +					      struct dentry *dentry)
>>>>> +{
>>>>> +	return -EOPNOTSUPP;
>>>>> +}
>>>> This has different behavior on unencrypted directories depending on whether
>>>> CONFIG_FS_ENCRYPTION is enabled or not.  That's bad.
>>>>
>>>> In patch 2, the caller you are introducing has already checked IS_ENCRYPTED().
>>>>
>>>> Also, your kerneldoc comment for fscrypt_prepare_atomic_open() says it is for
>>>> *encrypted* directories.
>>>>
>>>> So IMO, just remove the IS_ENCRYPTED() check from the CONFIG_FS_ENCRYPTION
>>>> version of fscrypt_prepare_atomic_open().
>>> IMO we should keep this check in fscrypt_prepare_atomic_open() to make it
>>> consistent with the existing fscrypt_prepare_open(). And we can just remove
>>> the check from ceph instead.
>>>
>> Well, then the !CONFIG_FS_ENCRYPTION version would need to return 0 if
>> IS_ENCRYPTED() too.
>
> For the !CONFIG_FS_ENCRYPTION version I think you mean:
>
>  static inline int fscrypt_prepare_atomic_open(struct inode *dir, struct dentry
> *dentry)
>
>  {
>          if (IS_ENCRYPTED(dir))
>                  return -EOPNOTSUPP;
>          return 0;
>  }
>
>
>> Either way would be okay, but please don't do a mix of both approaches within a
>> single function, as this patch currently does.
>>
>> Note that there are other fscrypt_* functions, such as fscrypt_get_symlink(),
>> that require an IS_ENCRYPTED() inode, so that pattern is not new.
>
> Yeah, correct, I didn't notice that.

OK, thank you both for the feedback.  I'll send out v2 in a few hours.
But my preference will be to drop the IS_ENCRYPTED() from
fscrypt_prepare_atomic_open().  The reason is that we still need to keep
it in the caller function anyway, because we need to set the MDS flags
accordingly (see patch 2):

	if (IS_ENCRYPTED(dir)) {
		set_bit(CEPH_MDS_R_FSCRYPT_FILE, &req->r_req_flags);
		err = fscrypt_prepare_atomic_open(dir, dentry);
		if (err)
			goto out_req;
	}

Cheers,
-- 
Luís