Re: [PATCH] kernel: allow reboots from user_ns

[Serge Hallyn <serge.hallyn@ubuntu.com>]

Quoting Glauber Costa (glommer@parallels.com):
> 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@parallels.com>

Note Li Zefan sent this identical patch last year.  It's in my own
built userns kernel, and definately required :)

In any case,

Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>

> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Cc: Andrew Morton <akpm@linux-foundation.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;
>  
> -- 
> 1.8.1.2
> 
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