[PATCH 8/9] signal: Drop signals before sending them to init.

[Oleg Nesterov]

On 12/12, Eric W. Biederman wrote:
> 
> By making the rule (for init dropping signals):
> When sending a signal to init, the presence of a signal handler that
> is not SIG_DFL allows the signal to be sent to init.  If the signal
> is not sent it is silently dropped without becoming pending.

But isn't it better to modify sig_ignore() and handle_stop_signal()
instead? This way we seem to need less changes,

	http://marc.info/?l=linux-kernel&m=118753610515859

(the patch above itself is not complete and a bit obsolete)

> The only noticeable user space difference from todays init is that it
> no longer needs to worry about signals becoming pending when it has
> them marked as SIG_DFL and blocked.

Ugh. I have to apologize again. I got a fever, and it turns out I just
can't read English.

So, do you mean we can ignore the problems with the signals which are
currently blocked by /sbin/init?

I personally agree, but I'm not sure I understand this right.

> +static int sig_init_drop(struct task_struct *tsk, int sig)
> +{
> +	/* All signals for which init has a SIG_DFL handler are
> +	 * silently dropped without being sent.
> +	 */
> +	if (!is_sig_init(tsk))
> +		return 0;
> +
> +	return (tsk->sighand->action[sig-1].sa.sa_handler == SIG_DFL);
> +}

What if /sbin/init has a handler, but before this signal is delivered
/sbin/init does signal(SIG_DFL) ? We should modify so_sigaction() to
prevent this. Note again the patch above.

Oleg.