Re: [PATCH] kernel: allow reboots from user_ns

[Daniel Lezcano <daniel.lezcano-GANU6spQydw@public.gmane.org>]

On 02/14/2013 12:56 PM, Glauber Costa wrote:
> Reboot support for pid namespaces is already implemented and it works
> well. However, in most containers the tasks will join all namespaces,
> including the now supported user namespace. In that situation, we will
> fail the "capable" test and won't be able to reboot.
>
> The proposed solution is to allow reboots for CAP_SYS_BOOT processes
> in the user namespace that owns the pid namespace.
>
> Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
> Cc: Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
> Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
> ---
Acked-by: Daniel Lezcano <daniel.lezcano-GANU6spQydw@public.gmane.org>

>  kernel/sys.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 265b376..3b0958e 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -435,9 +435,10 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
>  {
>  	char buffer[256];
>  	int ret = 0;
> +	struct pid_namespace *curr_pidns = task_active_pid_ns(current);
>  
>  	/* We only trust the superuser with rebooting the system. */
> -	if (!capable(CAP_SYS_BOOT))
> +	if (!ns_capable(curr_pidns->user_ns, CAP_SYS_BOOT))
>  		return -EPERM;
>  
>  	/* For safety, we require "magic" arguments. */
> @@ -453,7 +454,7 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
>  	 * pid_namespace, the command is handled by reboot_pid_ns() which will
>  	 * call do_exit().
>  	 */
> -	ret = reboot_pid_ns(task_active_pid_ns(current), cmd);
> +	ret = reboot_pid_ns(curr_pidns, cmd);
>  	if (ret)
>  		return ret;
>