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

[Xiubo Li]

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@xxxxxxxxxx/xiubli@xxxxxxx
Slack: @Xiubo Li