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

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Date:   Mon, 13 Mar 2023 19:25:43 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Xiubo Li <xiubli@...hat.com>
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 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.

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.

- Eric