Re: [PATCH 1/1][V3] Add reboot_pid_ns to handle the reboot syscall

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

On 12/04/2011 02:24 PM, Daniel Lezcano wrote:
> In the case of a child pid namespace, rebooting the system does not
> really makes sense. When the pid namespace is used in conjunction
> with the other namespaces in order to create a linux container, the
> reboot syscall leads to some problems.
>
> A container can reboot the host. That can be fixed by dropping
> the sys_reboot capability but we are unable to correctly to poweroff/
> halt/reboot a container and the container stays stuck at the shutdown
> time with the container's init process waiting indefinitively.
>
> After several attempts, no solution from userspace was found to reliabily
> handle the shutdown from a container.
>
> This patch propose to store the reboot value in the 16 upper bits of the
> exit code from the processes belonging to a pid namespace which has
> rebooted. When the reboot syscall is called and we are not in the initial
> pid namespace, we kill the pid namespace.
>
> By this way the parent process of the child pid namespace to know if
> it rebooted or not and take the right decision.
>
> Signed-off-by: Daniel Lezcano<daniel.lezcano@free.fr>

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

Tested it with reboot(2), worked as expected.

thanks,
-serge

> Acked-by: Serge Hallyn<serge.hallyn@canonical.com>
> ---
>   include/linux/pid_namespace.h |    8 +++++++-
>   kernel/pid_namespace.c        |   33 +++++++++++++++++++++++++++++++++
>   kernel/sys.c                  |    3 +++
>   3 files changed, 43 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index e7cf666..3279596 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -32,6 +32,7 @@ struct pid_namespace {
>   #endif
>   	gid_t pid_gid;
>   	int hide_pid;
> +	int reboot;
>   };
>
>   extern struct pid_namespace init_pid_ns;
> @@ -47,6 +48,7 @@ static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns)
>   extern struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *ns);
>   extern void free_pid_ns(struct kref *kref);
>   extern void zap_pid_ns_processes(struct pid_namespace *pid_ns);
> +extern int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd);
>
>   static inline void put_pid_ns(struct pid_namespace *ns)
>   {
> @@ -74,11 +76,15 @@ static inline void put_pid_ns(struct pid_namespace *ns)
>   {
>   }
>
> -
>   static inline void zap_pid_ns_processes(struct pid_namespace *ns)
>   {
>   	BUG();
>   }
> +
> +static inline int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
> +{
> +	BUG();
> +}
>   #endif /* CONFIG_PID_NS */
>
>   extern struct pid_namespace *task_active_pid_ns(struct task_struct *tsk);
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index a896839..c7a85ea 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -15,6 +15,7 @@
>   #include<linux/acct.h>
>   #include<linux/slab.h>
>   #include<linux/proc_fs.h>
> +#include<linux/reboot.h>
>
>   #define BITS_PER_PAGE		(PAGE_SIZE*8)
>
> @@ -187,6 +188,9 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
>   		rc = sys_wait4(-1, NULL, __WALL, NULL);
>   	} while (rc != -ECHILD);
>
> +	if (pid_ns->reboot)
> +		current->signal->group_exit_code = pid_ns->reboot;
> +
>   	acct_exit_ns(pid_ns);
>   	return;
>   }
> @@ -221,6 +225,35 @@ static struct ctl_table pid_ns_ctl_table[] = {
>
>   static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
>
> +int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
> +{
> +	switch(cmd) {
> +	case LINUX_REBOOT_CMD_RESTART2:
> +	case LINUX_REBOOT_CMD_RESTART:
> +		pid_ns->reboot = SYSTEM_RESTART<<  16;
> +		break;
> +
> +	case LINUX_REBOOT_CMD_HALT:
> +		pid_ns->reboot = SYSTEM_HALT<<  16;
> +		break;
> +
> +	case LINUX_REBOOT_CMD_POWER_OFF:
> +		pid_ns->reboot = SYSTEM_POWER_OFF<<  16;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	read_lock(&tasklist_lock);
> +	force_sig(SIGKILL, pid_ns->child_reaper);
> +	read_unlock(&tasklist_lock);
> +
> +	do_exit(0);
> +
> +	/* Not reached */
> +	return 0;
> +}
> +
>   static __init int pid_namespaces_init(void)
>   {
>   	pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
> diff --git a/kernel/sys.c b/kernel/sys.c
> index ddf8155..31acf63 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -444,6 +444,9 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
>   	                magic2 != LINUX_REBOOT_MAGIC2C))
>   		return -EINVAL;
>
> +	if (task_active_pid_ns(current) !=&init_pid_ns)
> +		return reboot_pid_ns(task_active_pid_ns(current), cmd);
> +
>   	/* Instead of trying to make the power_off code look like
>   	 * halt when pm_power_off is not set do it the easy way.
>   	 */