From:   =?utf-8?Q?Lu=C3=ADs_Henriques?= <lhenriques@suse.de>
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     Xiubo Li <xiubli@redhat.com>, Jeff Layton <jlayton@kernel.org>,
        "Theodore Y. Ts'o" <tytso@mit.edu>,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        Ilya Dryomov <idryomov@gmail.com>,
        linux-fscrypt@vger.kernel.org, ceph-devel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/2] fscrypt: new helper function -
 __fscrypt_prepare_atomic_open()
References: <20230309121910.18939-1-lhenriques@suse.de>
        <20230309121910.18939-2-lhenriques@suse.de>
        <ZAokFixlHwav4oio@sol.localdomain>
Date:   Fri, 10 Mar 2023 12:05:42 +0000
In-Reply-To: <ZAokFixlHwav4oio@sol.localdomain> (Eric Biggers's message of
        "Thu, 9 Mar 2023 10:23:18 -0800")
Message-ID: <87mt4k6cbt.fsf@suse.de>
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Precedence: bulk

Eric Biggers <ebiggers@kernel.org> writes:

> On Thu, Mar 09, 2023 at 12:19:09PM +0000, Lu=C3=ADs Henriques wrote:
>> This patch introduces a new helper function which prepares an atomic_ope=
n.
>> Because atomic open can act as a lookup if handed a dentry that is negat=
ive,
>> we need to set DCACHE_NOKEY_NAME if the key for the parent isn't availab=
le.
>>=20
>> The reason for getting the encryption info before checking if the direct=
ory
>> 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.
>>=20
>> Signed-off-by: Lu=C3=ADs Henriques <lhenriques@suse.de>
>> ---
>>  fs/crypto/hooks.c       | 14 ++++++++++++++
>>  include/linux/fscrypt.h |  6 ++++++
>>  2 files changed, 20 insertions(+)
>>=20
>> 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);
>>=20=20
>> +int __fscrypt_prepare_atomic_open(struct inode *dir, struct dentry *den=
try)
>
> Anything exported to filesystems should have a kerneldoc comment.  That w=
ould 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 directl=
y.
> Normally the pattern would be to make fscrypt_prepare_atomic_open() an in=
line
> 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 si=
mply 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 =3D fscrypt_get_encryption_info(dir, true);
>> +
>> +	if (err || (!err && !fscrypt_has_encryption_key(dir))) {
>> +		spin_lock(&dentry->d_lock);
>> +		dentry->d_flags |=3D DCACHE_NOKEY_NAME;
>> +		spin_unlock(&dentry->d_lock);
>> +	}
>
> Why does DCACHE_NOKEY_NAME need to be set on error?
>=20
> 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
--=20
Lu=C3=ADs