# Re: \[PATCH v7 14/28\] fanotify: Encode empty file handle when no inode is provided

- From: Jan Kara \<jack@suse.cz\>
- Date: 2021-10-15 09:32:50 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2021/10/216068
- Thread: https://ratatoskr.run/linux-fsdevel/2021/10/215996/t.md

```text
On Thu 14-10-21 18:36:32, Gabriel Krisman Bertazi wrote:
> Instead of failing, encode an invalid file handle in fanotify_encode_fh
> if no inode is provided.  This bogus file handle will be reported by
> FAN_FS_ERROR for non-inode errors.
> 
> Signed-off-by: Gabriel Krisman Bertazi <redacted>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza
 
> ---
> Changes since v6:
>   - Use FILEID_ROOT as the internal value (jan)
>   - Create an empty FH (jan)
> 
> Changes since v5:
>   - Preserve flags initialization (jan)
>   - Add BUILD_BUG_ON (amir)
>   - Require minimum of FANOTIFY_NULL_FH_LEN for fh_len(amir)
>   - Improve comment to explain the null FH length (jan)
>   - Simplify logic
> ---
>  fs/notify/fanotify/fanotify.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index ec84fee7ad01..c64d61b673ca 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -370,8 +370,14 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode,
>  	fh->type = FILEID_ROOT;
>  	fh->len = 0;
>  	fh->flags = 0;
> +
> +	/*
> +	 * Invalid FHs are used by FAN_FS_ERROR for errors not
> +	 * linked to any inode. The f_handle won't be reported
> +	 * back to userspace.
> +	 */
>  	if (!inode)
> -		return 0;
> +		goto out;
>  
>  	/*
>  	 * !gpf means preallocated variable size fh, but fh_len could
> @@ -403,6 +409,7 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode,
>  	fh->type = type;
>  	fh->len = fh_len;
>  
> +out:
>  	/*
>  	 * Mix fh into event merge key.  Hash might be NULL in case of
>  	 * unhashed FID events (i.e. FAN_FS_ERROR).
> -- 
> 2.33.0
> 
-- 
Jan Kara [ref]
SUSE Labs, CR
```