Re: [PATCH 2/2] Notify container-init parent a 'reboot' occured

Oleg Nesterov
2011-08-14T16:04:12Z

On 08/11, Daniel Lezcano wrote:
>
> When the reboot syscall is called and the pid namespace where the calling
> process belongs to is not from the init pidns, we send a SIGCHLD with CLD_REBOOTED
> to the parent of this pid namespace.

OK, but why you can't simply send the signal?

Why do you need the strange do_notify_parent_cldreboot() which tries
to mimic do_notify_parent() for (afaics) no reason ?

> +void do_notify_parent_cldreboot(struct task_struct *tsk, int why, char *buffer)

buffer is not used. Why?

> + if (tsk->ptrace)
> + parent = tsk->parent;
> + else {
> + tsk = tsk->group_leader;
> + parent = tsk->real_parent;
> + }

For what? I simply can't understand this...

> + sighand = parent->sighand;
> + spin_lock_irqsave(&sighand->siglock, flags);

this is unsafe, we can't trust ->sighand and parent.

> + * Even if SIGCHLD is not generated, we must wake up wait4 calls.

but not in this case, afaics?

> + __wake_up_parent(tsk, parent);

Why do you need __wake_up_parent()?

> +static void pid_namespace_reboot(struct pid_namespace *pid_ns,
> + int cmd, char *buffer)
> +{
> + struct task_struct *tsk = pid_ns->child_reaper;
> + do_notify_parent_cldreboot(tsk, cmd, buffer);

nothing prevents ->child_reaper from exiting it it is multithreaded,
this can crash the kernel.

> @@ -426,10 +434,18 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
> {
> char buffer[256];

again, it is not used.

> int ret = 0;
> + struct pid_namespace *pid_ns = current->nsproxy->pid_ns;
> +
> + /* We only trust the superuser with rebooting the system. */
> + if (!capable(CAP_SYS_BOOT)) {
> + /* If we are not in the initial pid namespace, we send a signal
> + * to the parent of this init pid namespace, notifying a shutdown
> + * occured */
> + if (pid_ns != &init_pid_ns)
> + pid_namespace_reboot(pid_ns, cmd, buffer);

Hmm. Looks like pid_ns should be checked after CAP_SYS_BOOT?

Oleg.