linux-kernel - Re: [PATCH -mm 1/1] ptrace: PTRACE_GETFDPIC: fix the unsafe usage of child->mm

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Date:	Tue, 25 May 2010 14:30:27 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Roland McGrath <roland@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Frysinger <vapier@...too.org>, linux-sh@...r.kernel.org,
	Paul Mundt <lethal@...ux-sh.org>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 1/1] ptrace: PTRACE_GETFDPIC: fix the unsafe usage
	of child->mm

On 05/25, David Howells wrote:
>
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > > Like PEEKTEXT and POKETEXT?
> >
> > They use access_process_vm().
>
> Which needs to get the mm:
>
> 	int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
> 	{
> 		struct vm_area_struct *vma;
> 		struct mm_struct *mm;
>
> 		if (addr + len < addr)
> 			return 0;
>
> 		mm = get_task_mm(tsk);

Yes sure,

But I do not think it makes any sense to change the signature of
access_process_vm() as well, it has a lot of callers. And it is
complex, it does get_user_pages(). Compared to that get_task_mm()
inside of access_process_vm() is nothing.

Oleg.

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