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

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Date:   Tue, 14 Mar 2023 12:20:23 +0800
From:   Xiubo Li <xiubli@...hat.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Luís Henriques <lhenriques@...e.de>,
        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()


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.

- Xiubo
> - Eric
>
-- 
Best Regards,

Xiubo Li (李秀波)

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