Re: [PATCH 6/7]: Check for user-space mount of /dev/pts

[Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>]

sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org wrote:
> From: Sukadev Bhattiprolu <sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
> Subject: [PATCH 6/7]: Check for user-space mount of /dev/pts
> 
> When the pts namespace is cloned, the /dev/pts is not useful unless it
> is remounted from the user space.
> 
> If user-space clones pts namespace but does not remount /dev/pts, it
> would end up using the /dev/pts mount from parent-pts-ns but allocate
> the pts indices from current pts ns.
> 
> This patch (hack ?) prevents creation of PTYs in user space unless
> user-space mounts /dev/pts.
> 
> (While this patch can be folded into others, keeping this separate
> for now for easier review (and to highlight the hack :-)
> 
> Signed-off-by: Sukadev Bhattiprolu <sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
> ---
>  fs/devpts/inode.c         |   25 +++++++++++++++++++++++--
>  include/linux/devpts_fs.h |   20 +++++++++++++++++++-
>  2 files changed, 42 insertions(+), 3 deletions(-)
> 
> Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
> ===================================================================

[snip]

> ===================================================================
> --- 2.6.25-rc5-mm1.orig/fs/devpts/inode.c	2008-03-24 20:08:33.000000000 -0700
> +++ 2.6.25-rc5-mm1/fs/devpts/inode.c	2008-03-24 20:08:57.000000000 -0700
> @@ -201,8 +201,11 @@ static int devpts_get_sb(struct file_sys
>  	if (IS_ERR(sb))
>  		return PTR_ERR(sb);
>  
> -	if (sb->s_root)
> +	if (sb->s_root) {
> +		if (!(flags & MS_KERNMOUNT))
> +			ns->user_mounted = 1;

What if user space umounts this back? Won't this break?

Thanks,
Pavel