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SubjectRe: [PATCH] Forbid invocation of kexec_load() outside initial PID namespace
Quoting Daniel P. Berrange (berrange@redhat.com):
> From: "Daniel P. Berrange" <berrange@redhat.com>
>
> The following commit
>
> commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b
> Author: Daniel Lezcano <daniel.lezcano@free.fr>
> 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@redhat.com>
> Cc: Serge Hallyn <serge.hallyn@canonical.com>

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

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

> Cc: Daniel Lezcano <daniel.lezcano@free.fr>
> Cc: Michael Kerrisk <mtk.manpages@gmail.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> ---
> 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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