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

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Date:	Mon, 24 May 2010 15:36:57 +0100
From:	David Howells <dhowells@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	dhowells@...hat.com, 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

Oleg Nesterov <oleg@...hat.com> wrote:

> Now that Mike Frysinger unified the FDPIC ptrace code, we can fix
> the unsafe usage of child->mm in ptrace_request(PTRACE_GETFDPIC).
> 
> We have the reference to task_struct, and ptrace_check_attach()
> verified the tracee is stopped. But nothing can protect from
> SIGKILL after that, we must not assume child->mm != NULL.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-by: David Howells <dhowells@...hat.com>

Does it make sense to move the call to get_task_mm() up to sys_ptrace() since
several ptrace functions use it?  The mm pointer could then be handed down the
ptrace hierarchy.

David
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