linux-kernel - Re: safety of *mutex_unlock() (Was: [BUG] signal: sighand unprotected when accessed by /proc)

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Message-ID: <20140609142956.3d79e9d1@gandalf.local.home>
Date:	Mon, 9 Jun 2014 14:29:56 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Clark Williams <williams@...hat.com>
Subject: Re: safety of *mutex_unlock() (Was: [BUG] signal: sighand
 unprotected when accessed by /proc)

On Mon, 9 Jun 2014 20:15:53 +0200
Oleg Nesterov <oleg@...hat.com> wrote:


> > That would indeed be a bad thing, as it could potentially lead to
> > use-after-free bugs.  Though one could argue that any code that resulted
> > in use-after-free would be quite aggressive.  But still...
> 
> And once again, note that the normal mutex is already unsafe (unless I missed
> something).

Is it unsafe?

This thread was started because of a bug we triggered in -rt, which
ended up being a change specific to -rt that modified the way slub
handled SLAB_DESTROY_BY_RCU. What else was wrong with it?

-- Steve
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