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From: Thomas Gleixner <tglx@linutronix.de>
To: Darren Hart <darren@dvhart.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Davidlohr Bueso <davidlohr@hp.com>, Kees Cook <kees@outflux.net>,
	wad@chromium.org
Subject: Re: [patch 1/5] futex: Make unlock_pi more robust
Date: Tue, 17 Jun 2014 00:28:00 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.10.1406170025510.5170@nanos> (raw)
In-Reply-To: <alpine.DEB.2.10.1406170002050.5170@nanos>

On Tue, 17 Jun 2014, Thomas Gleixner wrote:
> On Mon, 16 Jun 2014, Darren Hart wrote:
> > On Wed, 2014-06-11 at 20:45 +0000, Thomas Gleixner wrote:
> > In wake_futex_pi we verify ownership by matching pi_state->owner ==
> > current, but here the only test is the TID value, which is set by
> > userspace - which we don't trust...
> > 
> > I'm trying to determine if it matters in this case... if there are no
> > waiters, is the pi_state still around? If so, it does indeed matter, and
> > we should be verifying.
> 
> Erm. The whole point of this patch is to do:
> 
>      - Find existing state first and handle it.
> 
>      - If no state exists and TID == current, take it
> 
>      - Otherwise create state

Duh, that was the lock path. But here the point is:

      - Find existing state first and handle it.

      - If no state exists and TID == current, release it

The retry is obvious, right?

Thanks,

	tglx


  reply	other threads:[~2014-06-16 22:28 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-06-11 20:45 [patch 0/5] futex: More robustness tweaks Thomas Gleixner
2014-06-11 20:45 ` [patch 1/5] futex: Make unlock_pi more robust Thomas Gleixner
2014-06-16 16:18   ` Darren Hart
2014-06-16 22:15     ` Thomas Gleixner
2014-06-16 22:28       ` Thomas Gleixner [this message]
2014-06-16 22:49         ` Darren Hart
2014-06-16 22:39       ` Darren Hart
2014-06-21 20:33   ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 3/5] futex: Split out the waiter check from lookup_pi_state() Thomas Gleixner
2014-06-16 18:12   ` Darren Hart
2014-06-21 20:33   ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 2/5] futex: Use futex_top_waiter() in lookup_pi_state() Thomas Gleixner
2014-06-16 16:51   ` Darren Hart
2014-06-21 20:33   ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 4/5] futex: Split out the first waiter attachment from lookup_pi_state() Thomas Gleixner
2014-06-16 18:19   ` Darren Hart
2014-06-21 20:33   ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 5/5] futex: Simplify futex_lock_pi_atomic() and make it more robust Thomas Gleixner
2014-06-13  5:46   ` Darren Hart
2014-06-13  8:34     ` Thomas Gleixner
2014-06-13  9:36       ` Thomas Gleixner
2014-06-13  9:44         ` [patch V2 " Thomas Gleixner
2014-06-13 20:51           ` Davidlohr Bueso
2014-06-16 20:36           ` Darren Hart
2014-06-17  7:20             ` Thomas Gleixner
2014-06-21 20:34           ` [tip:locking/core] " tip-bot for Thomas Gleixner

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