Re: [PATCH] Forbid invocation of kexec_load() outside initial PID namespace

["Serge E. Hallyn" <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org>]

Quoting Daniel P. Berrange (berrange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org):
> From: "Daniel P. Berrange" <berrange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> 
> The following commit
> 
>     commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b
>     Author: Daniel Lezcano <daniel.lezcano-GANU6spQydw@public.gmane.org>
>     Date:   Wed Mar 28 14:42:51 2012 -0700
> 
>     pidns: add reboot_pid_ns() to handle the reboot syscall
> 
> introduced custom handling of the reboot() syscall when invoked
> from a non-initial PID namespace. The intent was that a process
> in a container can be allowed to keep CAP_SYS_BOOT and execute
> reboot() to shutdown/reboot just their private container, rather
> than the host.
> 
> Unfortunately the kexec_load() syscall also relies on the
> CAP_SYS_BOOT capability. So by allowing a container to keep
> this capability to safely invoke reboot(), they mistakenly
> also gain the ability to use kexec_load(). The solution is
> to make kexec_load() return -EPERM if invoked from a PID
> namespace that is not the initial namespace
> 
> Signed-off-by: Daniel P. Berrange <berrange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Cc: Serge Hallyn <serge.hallyn-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>

Acked-by: Serge Hallyn <serge.hallyn-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>

(Please see my previous email explaining why I believe the pidns
is an appropriate check)

> Cc: Daniel Lezcano <daniel.lezcano-GANU6spQydw@public.gmane.org>
> Cc: Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Cc: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
> Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> Cc: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
>  kernel/kexec.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index 0668d58..b152bde 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -947,6 +947,11 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
>  	if (!capable(CAP_SYS_BOOT))
>  		return -EPERM;
>  
> +	/* Processes in containers must not be allowed to load a new
> +	 * kernel, even if they have CAP_SYS_BOOT */
> +	if (task_active_pid_ns(current) != &init_pid_ns)
> +		return -EPERM;
> +
>  	/*
>  	 * Verify we have a legal set of flags
>  	 * This leaves us room for future extensions.
> -- 
> 1.7.11.2
> 
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