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

From: Xiubo Li
Date: Tue Mar 14 2023 - 00:21:29 EST



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