linux-kernel - [patch 0/5] futex: More robustness tweaks

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Date:	Wed, 11 Jun 2014 20:45:37 -0000
From:	Thomas Gleixner <tglx@...utronix.de>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Darren Hart <darren@...art.com>,
	Ingo Molnar <mingo@...nel.org>,
	Davidlohr Bueso <davidlohr@...com>,
	Kees Cook <kees@...flux.net>, wad@...omium.org
Subject: [patch 0/5] futex: More robustness tweaks

While looking for the minimal functional fix for the futex CVE, I
found a few things which can be done simpler and therefor make the
code more robust.

1) UNLOCK_PI

   Change the ordering:

   - Lookup waiters first. If waiters exist wake up the top priority
     waiter with all sanity checks applied. That allows us to catch
     manipulation of the user space value.

   - Only if there are no waiters, do the atomic release

2) futex_lock_pi_atomic()

   Its a maze of retry hoops and loops. Reduce it to simple and
   userstandable states.

   That requires to split out the lookup and validation functions from
   lookup_pi_state(), but that turns out to be an overall win on
   readabilty.

The overall cleanup results in less code and 488 bytes text size
reduction on x8664.

Thanks,

	tglx
---
 futex.c |  385 ++++++++++++++++++++++++++++------------------------------------
 1 file changed, 171 insertions(+), 214 deletions(-)

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