linux-kernel - Re: yama_ptrace_access_check(): possible recursive locking detected

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Message-ID: <20120815194426.52fd7936@pyramind.ukuu.org.uk>
Date:	Wed, 15 Aug 2012 19:44:26 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Kees Cook <keescook@...omium.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Fengguang Wu <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: yama_ptrace_access_check(): possible recursive locking detected

> It sounds like get_task_comm shouldn't have locking at all then? It
> should just do a length-limited copy and make sure there is a trailing
> 0-byte?

It has locking so that it has a consistent state and more importantly it
has an accessor function

Directly accessing it is asking for bugs in future. If you hold the
needed lock then just add an

__get_task_comm() 

method that asserts the lock is held. That way the rest of the behaviour
remains properly encapsulated for when someone changes it.

Alan
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