Fw: [PATCH 2/2] Warn when container-init defaults fatal signals

[sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org]

Resend to the Eric's correct address...

Suka

----- Forwarded message from sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org -----

| Date: Sat, 27 Oct 2007 12:09:28 -0700
| From: sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org
| To: eric-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org, Pavel Emelianov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>,        Oleg Nesterov
|  <oleg-6lXkIZvqkOAvJsYlp49lxw@public.gmane.org>
| Cc: Containers <containers-qjLDD68F18O7TbgM5vRIOg@public.gmane.org>, clg-NmTC/0ZBporQT0dZR+AlfA@public.gmane.org
| Subject: [PATCH 2/2] Warn when container-init defaults fatal signals
| 
| 
| From: Sukadev Bhattiprolu <sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
| Subject: [PATCH 2/2] Warn when container-init defaults fatal signals
| 
| Print a warning the first time a container-init (other than global init)
| forks a child process without explicitly ignoring or handling a fatal signal.
| Comments in the patch below explain the gory background :-)
| 
| Signed-off-by: Sukadev Bhattiprolu <sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
| 
| ---
|  kernel/fork.c |   51 +++++++++++++++++++++++++++++++++++++++++++++++++++
|  1 file changed, 51 insertions(+)
| 
| Index: 2.6.23-mm1/kernel/fork.c
| ===================================================================
| --- 2.6.23-mm1.orig/kernel/fork.c	2007-10-27 11:46:38.000000000 -0700
| +++ 2.6.23-mm1/kernel/fork.c	2007-10-27 11:48:36.000000000 -0700
| @@ -966,6 +966,53 @@ static void rt_mutex_init_task(struct ta
|  }
| 
|  /*
| + * Container-init process must appear like a normal process to its sibling
| + * in the parent namespace and should be killable (or not) in the usual way.
| + *
| + * But it must be immune to any unwanted signals from within its own namespace.
| + *
| + * At the time of sending the signal, sig_init_ignore() checks and ignores
| + * if receiver is container-init and the signal is unwanted.
| + *
| + * A limitation with the check in sig_init_ignore() is that if the signal is
| + * blocked by the container-init at the time of the check, we cannot ignore
| + * the signal because the container-init may install a handler for the signal
| + * before unblocking it.
| + *
| + * But if the container-init unblocks the signal without installing the handler,
| + * the unwanted signal will still be delivered to the container-init. If the
| + * unwanted signal is fatal (i.e default action is to terminate), we end up
| + * terminating the container-init and hence the container.
| + *
| + * There does not seem to be an easy/clean way to address this blocked-signal
| + * issue in the kernel.  For now, it appears easier to let the container-init
| + * decide what it wants to do with signals i.e have it _explicitly_ ignore or
| + * handle all fatal signals.
| + *
| + * Following routine prints a warning if the container-init does not
| + * explicitly ignore or handle fatal signals.
| + *
| + * Return 1 if the warning is printed.  Return 0 otherwise.
| + */
| +static int check_fatal_signals(struct task_struct *task)
| +{
| +	int i;
| +
| +	if (!is_container_init(task))
| +		return 0;
| +
| +	for (i = 1; i < _NSIG; i++) {
| +		if (!sig_fatal(task, i))
| +			continue;
| +
| +		printk(KERN_WARNING "Container init %d does not handle/ignore "
| +				"all fatal signals\n", task_pid_nr(task));
| +		return 1;
| +	}
| +	return 0;
| +}
| +
| +/*
|   * This creates a new process as a copy of the old one,
|   * but does not actually start it yet.
|   *
| @@ -983,6 +1030,10 @@ static struct task_struct *copy_process(
|  	int retval;
|  	struct task_struct *p;
|  	int cgroup_callbacks_done = 0;
| +	static int fatal_signal_warned;
| +
| +	if (!is_global_init(current) && !fatal_signal_warned)
| +		fatal_signal_warned = check_fatal_signals(current);
| 
|  	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
|  		return ERR_PTR(-EINVAL);
| _______________________________________________
| Containers mailing list
| Containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
| https://lists.linux-foundation.org/mailman/listinfo/containers

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