linux-kernel - Re: [Patch] signal: let valid

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Message-ID: <20081225180054.GA24116@redhat.com>
Date:	Thu, 25 Dec 2008 19:00:54 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...l.org>
Subject: Re: [Patch] signal: let valid_signal() check more

On 12/26, Américo Wang wrote:
>
> Teach valid_signal() to check sig > 0 case.

Why?

> @@ -727,7 +727,7 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
>  	{
>  		if (!perm || !capable(CAP_KILL))
>  			goto eperm;
> -		if (!valid_signal(arg) || arg < 1 || arg == SIGKILL)
> +		if (!valid_signal((int)arg) || arg == SIGKILL)
                                  ^^^^^

The patch adds a lot of unnecessary typecasts like this.

> -static inline int valid_signal(unsigned long sig)
> +static inline int valid_signal(int sig)
>  {
> -	return sig <= _NSIG ? 1 : 0;
> +	return sig <= _NSIG ? (sig > 0) : 0;
>  }

This looks a bit strange, why not

	return sig > 0 && sig <= _NSIG;

?

But, more importantly, I don't think the patch is correct.

Unless I misread the patch, now kill(pid, 0) returns -EINVAL, no?

And we have other users of valid_signal() which assume that sig == 0
is OK, for example arch_ptrace().


Imho, the patch has a point, but perhaps it is better to add the
new helper and then convert the users which do something like

	if (valid_signal(sig) && sig)
		...

What do you think?

Oleg.

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