linux-ext4 - Re: [PATCH v3 03/15] fanotify: Split fsid check from other fid mode checks

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Date:   Wed, 30 Jun 2021 06:14:11 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     "Darrick J. Wong" <djwong@...nel.org>,
        Theodore Tso <tytso@....edu>,
        Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
        David Howells <dhowells@...hat.com>,
        Khazhismel Kumykov <khazhy@...gle.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>, kernel@...labora.com
Subject: Re: [PATCH v3 03/15] fanotify: Split fsid check from other fid mode checks

On Tue, Jun 29, 2021 at 10:12 PM Gabriel Krisman Bertazi
<krisman@...labora.com> wrote:
>
> FAN_FS_ERROR will require fsid, but not necessarily require the
> filesystem to expose a file handle.  Split those checks into different
> functions, so they can be used separately when setting up an event.
>
> While there, update a comment about tmpfs having 0 fsid, which is no
> longer true.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
>
Reviewed-by: Amir Goldstein <amir73il@...il.com>

> ---
> Changes since v2:
>   - FAN_ERROR -> FAN_FS_ERROR (Amir)
>   - Update comment (Amir)
>
> Changes since v1:
>   (Amir)
>   - Sort hunks to simplify diff.
> Changes since RFC:
>   (Amir)
>   - Rename fanotify_check_path_fsid -> fanotify_test_fsid.
>   - Use dentry directly instead of path.
> ---
>  fs/notify/fanotify/fanotify_user.c | 27 ++++++++++++++++++---------
>  1 file changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index 68a53d3534f8..67b18dfe0025 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -1192,16 +1192,15 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
>         return fd;
>  }
>
> -/* Check if filesystem can encode a unique fid */
> -static int fanotify_test_fid(struct path *path, __kernel_fsid_t *fsid)
> +static int fanotify_test_fsid(struct dentry *dentry, __kernel_fsid_t *fsid)
>  {
>         __kernel_fsid_t root_fsid;
>         int err;
>
>         /*
> -        * Make sure path is not in filesystem with zero fsid (e.g. tmpfs).
> +        * Make sure dentry is not of a filesystem with zero fsid (e.g. fuse).
>          */
> -       err = vfs_get_fsid(path->dentry, fsid);
> +       err = vfs_get_fsid(dentry, fsid);
>         if (err)
>                 return err;
>
> @@ -1209,10 +1208,10 @@ static int fanotify_test_fid(struct path *path, __kernel_fsid_t *fsid)
>                 return -ENODEV;
>
>         /*
> -        * Make sure path is not inside a filesystem subvolume (e.g. btrfs)
> +        * Make sure dentry is not of a filesystem subvolume (e.g. btrfs)
>          * which uses a different fsid than sb root.
>          */
> -       err = vfs_get_fsid(path->dentry->d_sb->s_root, &root_fsid);
> +       err = vfs_get_fsid(dentry->d_sb->s_root, &root_fsid);
>         if (err)
>                 return err;
>
> @@ -1220,6 +1219,12 @@ static int fanotify_test_fid(struct path *path, __kernel_fsid_t *fsid)
>             root_fsid.val[1] != fsid->val[1])
>                 return -EXDEV;
>
> +       return 0;
> +}
> +
> +/* Check if filesystem can encode a unique fid */
> +static int fanotify_test_fid(struct dentry *dentry)
> +{
>         /*
>          * We need to make sure that the file system supports at least
>          * encoding a file handle so user can use name_to_handle_at() to
> @@ -1227,8 +1232,8 @@ static int fanotify_test_fid(struct path *path, __kernel_fsid_t *fsid)
>          * objects. However, name_to_handle_at() requires that the
>          * filesystem also supports decoding file handles.
>          */
> -       if (!path->dentry->d_sb->s_export_op ||
> -           !path->dentry->d_sb->s_export_op->fh_to_dentry)
> +       if (!dentry->d_sb->s_export_op ||
> +           !dentry->d_sb->s_export_op->fh_to_dentry)
>                 return -EOPNOTSUPP;
>
>         return 0;
> @@ -1379,7 +1384,11 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
>         }
>
>         if (fid_mode) {
> -               ret = fanotify_test_fid(&path, &__fsid);
> +               ret = fanotify_test_fsid(path.dentry, &__fsid);
> +               if (ret)
> +                       goto path_put_and_out;
> +
> +               ret = fanotify_test_fid(path.dentry);
>                 if (ret)
>                         goto path_put_and_out;
>
> --
> 2.32.0
>