linux-kernel - Re: [PATCH] wait_for_helper: SIGCHLD from user-space can lead to use-after-free

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Message-Id: <20100310212710.D66A3A7C@magilla.sf.frob.com>
Date:	Wed, 10 Mar 2010 13:27:10 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	David Howells <dhowells@...hat.com>,
	Neil Horman <nhorman@...driver.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] wait_for_helper: SIGCHLD from user-space can lead to
	use-after-free

> Yes. kthreads run with all signal ignored, this is inherited from
> kthreadd() which does ignore_signal().

Ok.

> I don't think this can work. SIG_DFL for SIGCHLD is OK because it is
> sig_kernel_ignore(). But, say, SIGHUP and other signals still should
> be ignored, otherwise we have the same problems with the unwanted
> signal_pending() this patch tries to avoid.

Yes, I see.

> But even if we could do this,
> 
> > That should make it redundant in ____call_usermodehelper,
> > so it could be removed from there.
> 
> Please note that __call_usermodehelper() forks ____call_usermodehelper() too.

Ok.


Thanks,
Roland
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