Re: [RFC PATCH 1/2] fscrypt: new helper function - __fscrypt_prepare_atomic_open()

[Luís Henriques]

Eric Biggers <ebiggers@xxxxxxxxxx> writes:

> On Thu, Mar 09, 2023 at 12:19:09PM +0000, Luís Henriques wrote:
>> This patch introduces a new helper function which prepares an atomic_open.
>> Because atomic open can act as a lookup if handed a dentry that is negative,
>> we need to set DCACHE_NOKEY_NAME if the key for the parent isn't available.
>> 
>> The reason for getting the encryption info before checking if the directory
>> has the encryption key is because we may have the key available but the
>> encryption info isn't yet set (maybe due to a drop_caches).  The regular
>> open path will use fscrypt_file_open for that but in the atomic open a
>> different approach is required.
>> 
>> Signed-off-by: Luís Henriques <lhenriques@xxxxxxx>
>> ---
>>  fs/crypto/hooks.c       | 14 ++++++++++++++
>>  include/linux/fscrypt.h |  6 ++++++
>>  2 files changed, 20 insertions(+)
>> 
>> diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
>> index 7b8c5a1104b5..cbb828ecc5eb 100644
>> --- a/fs/crypto/hooks.c
>> +++ b/fs/crypto/hooks.c
>> @@ -117,6 +117,20 @@ int __fscrypt_prepare_readdir(struct inode *dir)
>>  }
>>  EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir);
>>  
>> +int __fscrypt_prepare_atomic_open(struct inode *dir, struct dentry *dentry)
>
> Anything exported to filesystems should have a kerneldoc comment.  That would be
> a good place to put some of the explanation that you currently have only in the
> commit message.
>
> Also, double-underscored functions are not for use by filesystems directly.
> Normally the pattern would be to make fscrypt_prepare_atomic_open() an inline
> function that checks IS_ENCRYPTED() and calls an out-of-line function
> __fscrypt_prepare_atomic_open().  But if it happens to be simpler to make the
> caller handle the IS_ENCRYPTED() check in this case, then there should simply be
> one function: fscrypt_prepare_atomic_open() (no leading underscores).

Thank you, Eric.  I'll make sure that next rev will take these comments
into account.  It definitely makes sense to move (or duplicate) the
details as a kerneldoc comment.

>> +{
>> +	int err = fscrypt_get_encryption_info(dir, true);
>> +
>> +	if (err || (!err && !fscrypt_has_encryption_key(dir))) {
>> +		spin_lock(&dentry->d_lock);
>> +		dentry->d_flags |= DCACHE_NOKEY_NAME;
>> +		spin_unlock(&dentry->d_lock);
>> +	}
>
> Why does DCACHE_NOKEY_NAME need to be set on error?
> 
> Also note that the '!err &&' part has no effect.

To be honest, I wasn't really sure that if the d_flags should be set on
error either.  I'll drop that, and then the 'if' statement will make more
sense without the '||'.

Cheers
-- 
Luís