linux-kernel - Re: [PATCH 3/6][v5] Define siginfo_from_ancestor

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Date:	Mon, 5 Jan 2009 15:33:34 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	ebiederm@...ssion.com, roland@...hat.com, bastian@...di.eu.org,
	daniel@...ac.com, xemul@...nvz.org, containers@...ts.osdl.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6][v5] Define siginfo_from_ancestor_ns()

Really minor nit, just noticed...

On 12/27, Sukadev Bhattiprolu wrote:
>
> +static inline int siginfo_from_ancestor_ns(struct task_struct *t,
> +                       siginfo_t *info)
> +{
> +	struct pid_namespace *ns;
> +
> +	/*
> +	 * Ensure signal is from user-space before checking pid namespace.
> +	 * (We maybe called from interrupt context and dereferencing
> +	 * pid namespace would be safe).
> +	 */
> +	if (siginfo_from_user(info)) {

I can't parse the comment above, and imho it is confusing and
misleading. We can dereference pid namespace even in interrupt
context.

Also, the comment looks as if "when siginfo_from_user() is false,
it is not safe/possible to derive from_ancestor_ns". This is not
true, in that case we know that from_ancestor_ns must be false.

from_ancestor_ns == T means the signal was sent from the user
space, and it was sent to the task in the sub-namespace, so it
is clear why we check siginfo_from_user().

Oleg.

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