From mboxrd@z Thu Jan 1 00:00:00 1970 From: Darren Hart Subject: [PATCH] futex: Fix handling of bad requeue syscall pairing Date: Fri, 07 Aug 2009 14:45:18 -0700 Message-ID: <4A7CA06E.1090904@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Thomas Gleixner , Peter Zijlstra , Steven Rostedt , Ingo Molnar , John Kacur , Eric Dumazet , Dinakar Guniguntala , John Stultz To: "lkml, " , linux-rt-users Return-path: Received: from e2.ny.us.ibm.com ([32.97.182.142]:51805 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752910AbZHGVpZ (ORCPT ); Fri, 7 Aug 2009 17:45:25 -0400 Sender: linux-rt-users-owner@vger.kernel.org List-ID: From: Darren Hart If futex_requeue(requeue_pi=1) finds a futex_q that was created by a call other than futex_wait_requeue_pi(), the q.rt_waiter will be null. If so, this will result in an oops from the following call graph: futex_requeue() rt_mutex_start_proxy_lock() task_blocks_on_rt_mutex() waiter->task dereference OOPS We currently WARN_ON() if this is detected, clearly this is inadequate. If we detect a mis-pairing in futex_requeue(), bail out, sending -EINVAL to user-space. Signed-off-by: Darren Hart Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Ingo Molnar CC: Eric Dumazet CC: John Kacur CC: Dinakar Guniguntala CC: John Stultz --- kernel/futex.c | 11 +++++++++-- 1 files changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 578c7b7..d806d6c 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1306,8 +1306,15 @@ retry_private: if (!match_futex(&this->key, &key1)) continue; - WARN_ON(!requeue_pi && this->rt_waiter); - WARN_ON(requeue_pi && !this->rt_waiter); + /* + * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always + * be paired with each other and no other futex ops. + */ + if (requeue_pi && !this->rt_waiter || + !requeue_pi && this->rt_waiter) { + ret = -EINVAL; + break; + } /* * Wake nr_wake waiters. For requeue_pi, if we acquired the -- Darren Hart IBM Linux Technology Center Real-Time Linux Team