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

[Eric Biggers <ebiggers@kernel.org>]

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().

- Eric