On Sat, 24 Apr 2021 at 16:04, Chengguang Xu <cgxu519@xxxxxxxxxxxx> wrote:
>
> Check upper file's write permission when open on writable mode.
This should already be done in ovl_open() -> ovl_open_realfile() ->
open_with_fake_path() -> do_dentry_open().
Do you have a test case indicating that the writecount test is not working?
Thanks,
Miklos
>
> NOTE: lower files may be shared between differnt overlayfs instances,
> so we skip the check of lower file to avoid introducing interferes.
>
> Signed-off-by: Chengguang Xu <cgxu519@xxxxxxxxxxxx>
> ---
> fs/overlayfs/file.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 6e454a294046..1c3c24d07d01 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -144,12 +144,18 @@ static int ovl_real_fdget(const struct file *file, struct fd *real)
> static int ovl_open(struct inode *inode, struct file *file)
> {
> struct file *realfile;
> + struct inode *upperinode;
> int err;
>
> err = ovl_maybe_copy_up(file_dentry(file), file->f_flags);
> if (err)
> return err;
>
> + upperinode = ovl_inode_upper(inode);
> + if (((file->f_mode & FMODE_WRITE) || file->f_flags & O_TRUNC) &&
> + (upperinode && atomic_read(&upperinode->i_writecount) < 0))
> + return -ETXTBSY;
> +
> /* No longer need these flags, so don't pass them on to underlying fs */
> file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
>
> --
> 2.27.0
>
>
