Re: [PATCH v2 17/36] fs: add ksys_chroot() helper; remove-in kernel calls to sys_chroot()

[Arnd Bergmann]

On Thu, Mar 15, 2018 at 8:05 PM, Dominik Brodowski
<linux@xxxxxxxxxxxxxxxxxxxx> wrote:
> Using this helper allows us to avoid the in-kernel calls to the sys_chroot()
> syscall.
>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/base/devtmpfs.c  | 2 +-
>  fs/open.c                | 7 ++++++-
>  include/linux/syscalls.h | 1 +
>  init/do_mounts.c         | 2 +-
>  init/do_mounts_initrd.c  | 4 ++--
>  5 files changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
> index 4afb04686c8e..5743f04014ca 100644
> --- a/drivers/base/devtmpfs.c
> +++ b/drivers/base/devtmpfs.c
> @@ -387,7 +387,7 @@ static int devtmpfsd(void *p)
>         if (*err)
>                 goto out;
>         sys_chdir("/.."); /* will traverse into overmounted root */
> -       sys_chroot(".");
> +       ksys_chroot(".");
>         complete(&setup_done);
>         while (1) {
>                 spin_lock(&req_lock);

Could this be done using kern_path()/set_fs_root() instead so we
avoid the __user pointer?

       Arnd