linux-ext4 - Re: [PATCH v7 14/28] fanotify: Encode empty file handle when no inode is provided

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Date:   Fri, 15 Oct 2021 09:02:47 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     Jan Kara <jack@...e.com>, "Darrick J. Wong" <djwong@...nel.org>,
        Theodore Tso <tytso@....edu>,
        David Howells <dhowells@...hat.com>,
        Khazhismel Kumykov <khazhy@...gle.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Matthew Bobrowski <repnop@...gle.com>, kernel@...labora.com
Subject: Re: [PATCH v7 14/28] fanotify: Encode empty file handle when no inode
 is provided

On Fri, Oct 15, 2021 at 12:38 AM Gabriel Krisman Bertazi
<krisman@...labora.com> 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 <krisman@...labora.com>
Reviewed-by: Amir Goldstein <amir73il@...il.com>

>
> ---
> 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
>