linux-kernel - Re: kernel: signal: NULL ptr deref when killing process

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Date:	Thu, 21 Aug 2014 19:11:26 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	David Howells <dhowells@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, richard@....at,
	Dave Jones <davej@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: kernel: signal: NULL ptr deref when killing process

On 08/21, Sasha Levin wrote:
>
> On 08/20/2014 10:12 AM, Oleg Nesterov wrote:
> > On 08/20, Sasha Levin wrote:
> >> >
> >> > Hi all,
> >> >
> >> > While fuzzing with trinity inside a KVM tools guest running the latest -next
> >> > kernel, I've stumbled on the following spew:
> > Thanks...
> >
> > looks like, kill_ok_by_cred()->__task_cred(t) returns NULL at first glance.
> > perhaps you can show the result of "make kernel/signal.s" to be sure? Or at
> > least the full "objdump -d kernel/signal.o".
>
> Attached.

Thanks.

Yes, t->real_cred == NULL (r14).

Interestingly, t->signal is NULL too (rcx). And ->signal must be never NULL.
So it looks like this task_struct was reallocated/reused. Or corrupted.

t == 0xffff880546803000 (r12), this doesn't look wrong.

Oleg.

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