linux-kernel - Re: [BUGFIX] NULL pointer dereference in __vm_enough

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Date:	Sun, 12 Aug 2007 14:19:05 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	WU Fengguang <wfg@...l.ustc.edu.cn>
Cc:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [BUGFIX] NULL pointer dereference in __vm_enough_memory()

> > Great! So the problem might have existed for some time, but we never
> > saw it due to default over commit values? Were you using these values
> > for over commit even before?
> 
> No I changed it several weeks ago to stop my desktop from freezing.
> So yes, the bug may have been there for a while.

The bug is the new exec with lots of arguments code. It tries to insert a
vm struct without having a valid current->mm. That isn't permitted and
never had been (which is also why it broke the sparc mmu code etc).

You'll need to change the kernel security interface a little to make this
fly - I think the following should do it.

	- make __vm_enough_memory take a struct mm pointer and use it
	- make security_ops pass the extra current->mm
	- add a vm_enough_memory_mm security op
	- use security_vm_enough_memory_mm(mm, ...) in __insert_vm_struct

I'll knock up a quick patch and see what is needed (someone else can do
the selinux changes)
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